- Email: [email protected]
Effect of Headache on the Pathologic Findings of Unruptured Cerebral Saccular Aneurysms
Accepted Manuscript Effect of headache on the pathological findings of unruptured cerebral saccular aneurysms Masaaki Hokari, MD, PhD, Naoki Nakayama, MD, PhD;, Yusuke Shimoda, MD, Kiyohiro Houkin, MD, PhD PII:
S1878-8750(17)30092-X
DOI:
10.1016/j.wneu.2017.01.069
Reference:
WNEU 5166
To appear in:
World Neurosurgery
Received Date: 17 November 2016 Revised Date:
15 January 2017
Accepted Date: 17 January 2017
Please cite this article as: Hokari M, Nakayama N, Shimoda Y, Kiyohiro Houkin Effect of headache on the pathological findings of unruptured cerebral saccular aneurysms, World Neurosurgery (2017), doi: 10.1016/j.wneu.2017.01.069. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Abbreviations and Acronyms 3D-CTA: 3-dimensional computed tomographic angiography ACA: anterior cerebral artery
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A-com: anterior communicating artery EM: Elastica–Masson (EM) HE: hematoxylin-eosin
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ICA: internal carotid artery IC-IC: intracranial-intracranial
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MCA: middle cerebral artery PTAH: phosphor-tungstic acid hematoxylin
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SAH: subarachnoid hemorrhage
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Effect of headache on the pathological findings of unruptured cerebral saccular aneurysms
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Masaaki Hokari, MD, PhD; Naoki Nakayama, MD, PhD; Yusuke Shimoda, MD; Kiyohiro Houkin, MD, PhD
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Department of Neurosurgery, Hokkaido University Graduate School of Medicine
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Running Title: Headache impact on unruptured aneurysms
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COI: There are no conflicts of interest to declare.
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Correspondence:
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Masaaki Hokari, MD, PhD,
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Department of Neurosurgery, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita-ku,
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Sapporo 060-8638, Japan
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TEL：+81-11-706-5987 FAX：+81-11-708-7737
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E-mail: [email protected]
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Abstract
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Background: Some patients with aneurysm exhibit warning headaches without minor bleeding, and this could
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be caused by stretching of the aneurysm wall. Recently, our pathological study observed subintimal fibrin
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deposition in a majority of the ruptured aneurysms. However, these findings were also observed in some
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unruptured aneurysms. In this report, two unruptured aneurysms exhibited subintimal fibrin, and interestingly,
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one of the patients experienced severe headache within 1 month before neuroimaging.
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Objective: We performed pathological analysis of unruptured aneurysms and collected their various clinical
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variables, including severe headache, to clarify the clinical characteristics of “dangerous” unruptured
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aneurysms.
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Methods: This study included unruptured saccular aneurysm samples (n = 17) that were resected after clipping.
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We compared the differences in clinical variables, including warning headache, between aneurysms with and
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without fibrin deposition.
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Results: Fibrin deposition was present in the subintimal layer in four patients and in the peri-outer membrane
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in four patients. Three of the four former patients experienced warning headaches, and one presented aneurysm
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growth. Of the latter four patients, one exhibited aneurysm growth, while the others presented with relatively
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large aneurysms. In the remaining nine aneurysms without fibrin deposition, monocyte infiltration was
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observed in one, all aneurysms were small, and no patients experienced warning headaches or aneurysm
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growth.
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Conclusion: Subintimal fibrin deposition is frequently observed in patients with aneurysm with warning
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headaches. These pathological findings are clinically inspiring and may suggest that these aneurysms exhibit
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rapid stretching by newly formed aneurysms, which can result in rupture at an early stage.
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Keywords: cerebral aneurysms; pathology; headache
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Highlights:
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We performed pathological analysis of 17 unruptured aneurysms.
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Our prior study observed subintimal fibrin deposition in most of ruptured aneurysms.
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This study demonstrated fibrin deposition in unruptured aneurysms with headaches.
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These may be newly formed aneurysms, which can result in rupture at an early stage.
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Introduction
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Recent advances in noninvasive imaging techniques have resulted in increased detection of unruptured
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aneurysms. Although various surgical interventions have been suggested for prevention of future ruptures,1, 2
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there are some recommendations against them because of the relatively low risk of rupture.3, 4 Moreover, there
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is some discrepancy between the low rupture rate of small unruptured aneurysms and the size of ruptured
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aneurysms.5 According to previous reports,4, 6 the rupture rate does not remain constant after formation and
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may be higher in the early stages. Therefore, ruptured aneurysms may be fundamentally different from stable
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aneurysms that have remained unruptured for several years. Although it is clear that we should only perform
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interventions for unruptured aneurysms that are at a high risk of rupture, prediction of aneurysmal ruptures has
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not been promising till date. To clarify the mechanisms leading to their rupture, several pathological studies
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examining human saccular aneurysms have been conducted and have proposed the notion that chronic
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inflammation plays a role in aneurysmal wall degeneration and potentially increases the subsequent risk of
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rupture.7-11 Frosen et al. reported that luminal thrombosis and chronic inflammation were observed more
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frequently in the ruptured aneurysm wall than in the unruptured wall.8, 9 In several clinical reports, the
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existence of a laminar thrombus and thrombus in the aneurysm has been regarded as a risk factor of rupture in
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the dissecting, fusiform, or giant saccular aneurysms12-16.In those reports, thrombosis in the aneurysm change
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in the time course between a few days and several months. However, the time course for formation of fibrin
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and the mechanism in the saccular non-giant aneurysms has not been recognized.
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Recently, our pathological study detected severe monocyte infiltration in the aneurysmal wall and subintimal
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fibrin deposition containing no erythrocytes in a majority of ruptured aneurysms resected within 24 h of
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onset.17 This suggests that the fibrin components in the subintimal layer and chronic inflammation in the
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aneurysmal wall were present prior to rupture. The existence of subintimal fibrin deposition and monocyte
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infiltration was also more frequently observed in 28 ruptured aneurysms compared with 12 unruptured
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aneurysms (92.9% and 100% in ruptured group versus 16.7% and 33.3% in unruptured group, respectively).
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However, pathological findings that were frequently observed in the ruptured aneurysm were also
occasionally observed in some unruptured aneurysms that were regarded as “dangerous” as they were at a high
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risk of rupture. In our previous report,17 we observed two unruptured aneurysms with subintimal fibrin and
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interestingly, one of the patients presented with severe headache within 1 month before neuroimaging. An
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exhaustive systematic review reported that 10%–43% of subarachnoid hemorrhage (SAH) patients frequently
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experience a sudden headache (termed “warning headache” or “sentinel headache”)18 that precedes an episode
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of aneurysmal SAH. A majority of these episodes occur within 1 month before rupture, and these headaches
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are considered to represent minor bleeding into the subarachnoid space. However, some patients exhibit
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sentinel headaches without minor bleeding,19-21 and these may be caused by stretching or dissection of the
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aneurysm wall. Thus, based on these reports, unruptured aneurysms with subintimal fibrin deposition in
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patients experiencing severe headaches may be at a higher risk of rupture.
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The present study is a pathological analysis of 17 unruptured aneurysms. It compares various clinical
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variables including severe headache between unruptured aneurysms with and without certain pathological
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findings to clarify the clinical characteristics of “dangerous” unruptured aneurysms.
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Patients and Methods
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Patients
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This study included unruptured saccular aneurysms (n = 17) that were resected after microsurgical clipping
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between 2010 and 2013 (Table 1). To retain the original state of saccular unruptured aneurysms as far as
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possible, the aneurysms were fully exposed before clip application. The aneurysm sacs were not resected when
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full exposure was considered to be too dangerous, and all such aneurysms including those that were small or
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had a very thick neck were excluded.
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Clinical information including age, gender, aneurysm size, location, aneurysm growth, multiple aneurysms,
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history of SAH, history of hypertension, smoking, history of hyperlipidemia, and symptoms for neuroimaging
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was collected from the patients’ medical records. The sizes of the aneurysms were measured using preoperative
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vascular imaging studies including either three-dimensional computed tomographic angiography (3D-CTA) or
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magnetic resonance angiography (MRA). Warning headache was defined as a sudden and unusually severe
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headache lasting at least 1 h followed by a symptom-free interval within 1 month prior to detection of
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aneurysm. Symptoms including warning headache, other chronic headaches, and vertigo were recorded using
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medical records that were based on a thorough interview of the patients and their relatives/accompanying
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persons. All quantitative clinical data have been expressed as mean ± SD. This study was approved by the
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ethics committee of Hokkaido University (IRB No.011-0321) and written informed consent was waived
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because of the retrospective design.
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Histology and Immunohistochemistry
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Histological examination was performed in a manner similar to the method described previously.17 Briefly,
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following aneurysm resection, the specimens were gently washed with saline to remove any blood and fixed in
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10% formalin. The specimens were sliced to a 3 µm thickness, and slides for classical histological staining
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were prepared every 90 µm. The number of slices varied from five to twenty and depended on the size of the
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aneurysm. For classical histological staining, hematoxylin-eosin (HE) and Elastica–Masson (EM) methods
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were used. We also performed phosphor-tungstic acid hematoxylin (PTAH) staining to detect and confirm
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fibrin components in the specimens. PTAH staining was originally introduced by Mallory for glial fiber
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staining but has also been used for the demonstration of fibrin.22-26 It stains collagen pink and glial fibers,
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muscle fibers, and fibrin blue, although the mechanism is still largely unknown.24-26 As for
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immunohistochemistry, CD68 was used as a marker for macrophage infiltration. The de-paraffinized sections
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were processed through antigen retrieve for 15 min and then incubated with primary mouse monoclonal
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antibody against human CD68 (Dako, 1:100). Thereafter, the immunoreactivity was visualized by treating with
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Dako Envision kit HRP (DAB) (Dako). Finally, the sections were counterstained with hematoxylin.
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Histological analysis
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Histological analysis was performed to confirm pathological variables such as myointimal hyperplasia (>200
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µm), existence of fibrin deposition in the aneurysmal wall, and severe monocyte infiltration, as described
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previously.17 Briefly, by observing HE and EM all sections through an optical microscope (Olympus BX50),
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the existence of fibrin deposition was evaluated using PTAH and HE stainings. A hyaline-like structure was
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observed under the intimal layer in HE sections, and this was also seen in PTAH sections as a deep blue-
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stained layer. The number of CD68 positive cells in an area (100 µm × 100 µm) of the aneurysmal wall where
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active invasion of inflammatory cells was observed on HE was counted under 40× magnification. Severe
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infiltration by chronic inflammatory cells is defined as the presence of more than 50 CD68-positive cells in the
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area, while mild infiltration is defined as the presence of more than 10 CD68-positive cells. Histological
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analysis was conducted by M.H and Y.S.
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Statistics
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Fisher's test was performed to estimate whether a warning headache is associated with “dangerous”
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pathological findings, such as subintimal fibrin deposition or monocyte infiltration. Differences with a P value
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of <0.05 were considered statistically significant.
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Results
Clinical Data and Radiological Findings
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The characteristics of the patients and the aneurysms included in this study are shown in Table 1.
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The participants included 7 men and 10 women, and the mean age of the patients was 60.7 ± 8.8 years. This
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was slightly younger than that of the participants of The Unruptured Cerebral Aneurysm Study of Japan
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(UCAS Japan; 62.5 ± 10.3 years old). Moreover, in comparison with UCAS Japan (43.4%), a larger number of
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patients reported history of hypertension (64.7%). The percentage of smoking (17.6%) and history of
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hyperlipidemia (17.6%) were almost the same as those seen in UCAS Japan27 (14.1% and 16.8%, respectively).
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Similar to UCAS Japan, headache (N = 7) and vertigo (N = 5) were the most common symptoms for imaging,
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and screening was also a typical reason for imaging. Other reasons for neuroimaging included dementia in one
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patient and visual disturbance in another patient. Four patients presented with a chronic headache, while three
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experienced a severe headache within 1 month before imaging (Cases 1–3). The mean size of aneurysms was
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6.4 ± 3.3 mm, and this was slightly bigger than those included in UCAS Japan, which is considered to be the
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largest cohort study examining unruptured cerebral aneurysms in Japan (5.7 ± 3.7 mm). With regard to location,
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eight aneurysms were anterior communicating artery (A-com), four were of middle cerebral artery (MCA),
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four were internal carotid artery (ICA), and one was of a distal anterior cerebral artery (ACA). The prevalence
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of characteristics such as location and size in this study may have been influenced by our decision to be safe
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with regard to full exposure and aneurysmal sac resection.
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Histology of cerebral saccular aneurysms and clinical course
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Deposition of fibrin was observed in 8 of 17 patients, all of whom (Cases 1–8) also exhibited chronic
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monocyte infiltration. Fibrin deposition was present in the subintimal layer in four of eight patients (Cases 1–
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4), and in the intramural layer (peri-outer membrane) in the remaining four patients (Cases 5–8). Among cases
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1–4, who presented with unruptured aneurysms with “dangerous” pathological findings, three patients
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experienced severe headache within 1 month before imaging (Cases 1–3) and one exhibited aneurysm growth
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(from 4 to 5 mm). Among cases 5–8, one patient (Case 5) exhibited aneurysm growth (from 3 to 8 mm), while
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the others (Cases 6–8) presented with relatively large aneurysms (≥7 mm) during initial neuroimaging. In
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these three cases, follow-up neuroimaging was not performed as the aneurysms were clipped within 6 months
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after diagnosis. Therefore, these aneurysms may be growing. In the remaining nine aneurysms without fibrin
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deposition (Cases 9–17), monocyte infiltration was observed in one case only, and all aneurysms were small
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(<6 mm). During 1 month before imaging, none of the nine patients (Cases 9–17) experienced warning
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headache or exhibited aneurysm growth. Fisher’s test revealed that a warning headache was associated with
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subintimal fibrin deposition (P = 0.006) but not with monocyte infiltration.
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Representative Cases
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Case 1: 10
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A 61-year-old man with hypertension presented at the hospital with severe frontal headache. Magnetic
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resonance image (MRI) and MRA revealed 4 mm A-com aneurysm with no subarachnoid hemorrhage. He
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underwent clipping and removal of the aneurysm 4 months later (Fig. 1A and B). No old subarachnoid
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hemorrhages were found during the surgery, and the pathological specimens revealed subintimal and
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intramural fibrin deposition (Fig. 1C–F) and monocyte infiltration (Fig. 1G).
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Case 2:
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A 44-year-old woman with hypertension presented at the hospital with a sudden, severe sudden headache. MRI
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and MRA examination revealed 5 mm distal ACA aneurysm with no subarachnoid hemorrhage, and this was
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confirmed by lumbar puncture. She underwent clipping and removal of the aneurysm 2 months later (Fig. 2A
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and B). No old subarachnoid hemorrhages were recognized during the surgery, and the pathological sections
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revealed subintimal and intramural fibrin deposition (Fig. 2C-–E) and monocyte infiltration (Fig. 2F).
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Case 4:
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MRI and MRA examination performed in a 56-year-old woman with hypertension for the purpose of screening
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revealed a 4 mm MCA aneurysm and a 3 mm basilar artery aneurysm (Fig. 3A). Eleven months later, she
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underwent a follow-up MRI and MRA, which demonstrated MCA aneurysm growth from 4 to 5 mm (Fig. 3B).
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Therefore, she underwent clipping surgery and removal of the aneurysm (Fig. 3C). No old subarachnoid
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hemorrhages were found during the surgery, and pathological sections revealed subintimal and intramural
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fibrin deposition (arrow heads in Fig. 3D–G) and monocyte infiltration (known as form cells; arrows in Fig.
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3H).
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Case 7:
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A 75-year-old man with hypertension and hyperlipidemia underwent MRI and MRA examination for dementia,
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which revealed an 11 mm A-com aneurysm. He then underwent clipping surgery and removal of the aneurysm
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(Fig. 4A and B). No old subarachnoid hemorrhages were recognized during the surgery, and the pathological
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sections revealed fibrin deposition in the intramural layer (peri-outer membrane; Fig. 4C–E) and monocyte
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infiltration (Fig. 4F).
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Case 8:
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A 64-year-old woman with hypertension underwent MRI and MRA examination for the purpose of screening,
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which revealed a 7 mm MCA aneurysm. She then underwent clipping and removal of the aneurysm (Fig. 5A
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and B). No old subarachnoid hemorrhages were recognized during the surgery, and the pathological sections
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revealed fibrin deposition in the intramural layer (peri-outer membrane; Fig. 5C–E) and monocyte infiltration
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(Fig. 5F).
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Case 12:
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A 54-year-old woman with hypertension, hyperlipidemia, and smoking habit underwent MRI and MRA
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examinations for a chronic headache, which revealed a 5 mm MCA aneurysm. She then underwent clipping
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surgery and removal of the aneurysm (Fig. 6A). No old subarachnoid hemorrhages were recognized during the
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surgery, and the pathological sections revealed typical findings of unruptured aneurysms, that is, partial thin
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walls with no fibrin deposition in the intramural layer (Fig. 6B).
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Discussion
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In this clinicopathological study, unruptured aneurysms with intramural fibrin deposition and monocyte
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infiltration,17 which are usually observed in ruptured aneurysm specimens, were frequently observed in
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patients experiencing severe headaches within 1 month before imaging. In addition to large aneurysms and
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aneurysm growth, severe headaches may also serve as a predictor for aneurysm rupture. Although no
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association between severe headache and the mechanism of aneurysm rupture was demonstrated, the
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pathological findings of the representative cases are clinically inspiring and arouse interest in the natural
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course of saccular aneurysms and the impact of aneurysm degeneration that may ultimately result in rupture.
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Risk Factors for Rupture of Unruptured Aneurysms and their Natural Course
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Previous studies have identified several factors including large size,27-32 location (A-com,6, 27 IC-PC,27 and
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posterior circulation27, 29-32), irregular protrusion of the aneurysm wall,27, 33 aneurysm growth,34 a history of
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SAH,29 smoking,30, 35 age,6, 32 race,32 and presence of multiple aneurysms6 as possible risk factors for rupture of
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an aneurysm. Furthermore, according to previous reports,4, 6 the rupture rate does not remain constant after
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formation and may be higher in the early stages. In other words, aneurysms may be at a higher risk of rupture
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shortly after formation. Sato et al. examined a mathematical model of the natural history of unruptured
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aneurysms and reported that some aneurysms bleed shortly after formation.4 With regard to the origin and
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growth of cerebral aneurysms, Yonekura et al. classified the natural course of unruptured aneurysms into the
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following four types: Type 1—aneurysm ruptures within a few days to a few months after formation; Type
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2—aneurysm builds up slowly for several months to several years after formation and ruptures during this
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process; Type 3—aneurysm keeps growing slowly for many years without rupturing; and Type 4—aneurysm
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grows to a certain size, probably under 5 mm in diameter, and thereafter remains unchanged.6 The difficulty in
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following Type 1 aneurysms clinically and radiologically from formation to rupture may explain the
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discrepancy between the low rupture rate of small unruptured aneurysms and the size of ruptured aneurysms.5
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Some other previous reports have also suggested that a certain portion of acute SAH is derived from a recently
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formed aneurysm.36, 37 Mitchell et al. proved this with a mathematical model utilizing data from previously
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published large studies and concluded that the duration of this high-risk period varies from 1 to 2 days to a
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maximum of approximately 8 weeks.36 After this initial period, the risk of rupture falls to a lower level.
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Natural Course of the Unruptured Aneurysm and its Pathology (Fig. 7)
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The aneurysms accompanied by severe headache (Cases 1–3) were small (≤7 mm) and their pathological
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findings including subintimal and intramural fibrin deposition that classified them as “dangerous.” Therefore,
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we speculate that the severe headaches in these cases (Cases 1–3) may be caused by rapid stretching or
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dissection of the wall caused by newly formed aneurysms which, in turn, can result in rupture at an early stage
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(just before rupture in Type 1 by Yonekura et al.). The enlarging aneurysm with subintimal fibrin deposition
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observed in Case 4 is also considered to be at a relatively high risk of rupture and may be classified as Type 2
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The aneurysms exhibiting fibrin deposition in the intramural layer (peri-outer membrane) in Cases 5–8 may be
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classified as Type 3. Of these aneurysms, one was undergoing enlargement (Case 5) and others were already
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relatively large and may be growing (Cases 6–8). Interestingly, two “humps” (black arrow heads and black
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arrows in Fig. 5A and C) were observed in Case 8, and fibrin deposition was seen in the peri-outer membrane
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of the “hump” (black arrow head in Fig. 5A and C). We speculate that the walls of these humps may have been
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thin, and the fibrin deposition may have actually been situated in the subintimal layer. To prevent rupture,
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aneurysmal wall remodeling may have then thickened the walls due to laminar thrombosis or myo-intimal
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hyperplasia.8, 9
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The aneurysms in Cases 9–17 were all small (<7 mm), had stable pathology, and were considered to be “not
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dangerous” as there was no fibrin deposition in the wall. These may be classified as Type 4.
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Impact of Headache on Unruptured Cerebral Saccular Aneurysms
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Sentinel headaches occur 1 month before rupture, as mentioned before, and a majority of these episodes are
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considered to represent minor bleeding into the subarachnoid space.18 Accurate diagnosis of previous
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headaches by interview is difficult because of the inability to obtain complete information from patients in
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poor clinical conditions. Therefore, Oda et al. conducted neuroradiologic diagnosis of minor leaks using
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T1-FLAIR mismatch and also found radiological minor leaks in patients without warning headaches.38 On the
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contrary, there are some patients with sentinel headaches not accompanied by minor bleeding,19-21 and these
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may be caused by stretching or dissection of the aneurysm wall. Therefore, de Falco suggested that MRA or
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3D-CTA should be performed to identify de novo small or enlarged aneurysms with high risk of rupture in
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patients with unusual, acute onset headaches, even if the CT and lumbar puncture examinations reveal negative
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findings.39 Interestingly, Ankeete et al. reported that both surgical clipping and endovascular embolization of
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unruptured aneurysms were associated with long-term improvement in self-reported quantitative headache
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scores. They then raised the question “When a patient presents to a neurosurgeon with headache and a
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diagnosis of unruptured saccular aneurysm, can we decide that the headaches are unrelated to the aneurysm
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and are defined as ‘incidental’?” Although there are a limited number of reports examining patients with
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unruptured saccular aneurysm with warning headaches,19-21 most of the patients with unruptured intracranial
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artery dissections complain of a headache, and it is well known that some of these rupture within a month.40-42
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Dissecting aneurysms are usually generated by sudden, widespread disruption of the internal elastic lamina and
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media, frequently accompanied by sudden, severe headaches.41, 42 However, previous pathological studies
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examining saccular aneurysms have also demonstrated that the absence or fragmentation of internal elastica
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lamina a generally observed in both ruptured and unruptured saccular aneurysms.7-10,
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saccular aneurysms may be generated with relatively rapid disruption of the internal elastic lamina and media
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at the bifurcation, resulting in severe headaches. Furthermore, it is interesting that three aneurysms with
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subintimal fibrin deposition (Cases 1–3) were aneurysms at A-com or distal ACA. Ruptured A-com or distal
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ACA aneurysms are found more frequently than unruptured. Thus, it is likely that they rapidly grow and
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rupture at an early stage, even when small in size.43-45
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Therefore, some
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Limitations
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(1) This is a small-sized study; (2) histological analysis was not conducted by independent investigators; (3)
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the presence of a severe recent headache (within 1 month before the aneurysm found) can only be determined
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by interviews and relies heavily on recall; and (4) there are no established neuro-radiological diagnostic
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procedures to prove aneurysm formation or acute expansion associated with headache.
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Conclusions
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This study demonstrated intramural fibrin deposition and monocyte infiltration in unruptured aneurysms, and
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these findings were frequently observed in patients who experienced severe headaches within 1 month before
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imaging. The pathological findings of aneurysms accompanied by severe headache are clinically inspiring and
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arouse interest in the natural course of saccular aneurysms. It may be suggested that these aneurysms may
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exhibit rapid stretching or dissection of the wall caused by newly formed aneurysms and can result in rupture
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at an early stage.
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Acknowledgments
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The authors thank Yumiko Shinohe and Rika Nagashima deeply for their technical assistance. This study was
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supported by grant-in-aid from the Ministry of Education, Science and Culture of Japan (15K10287 and
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15K10284). 17
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Akiyama Y, Houkin K, Nozaki K, Hashimoto N. Practical decision-making in the treatment of unruptured cerebral aneurysm in Japan: The u-care study. Cerebrovasc Dis.30:491-499
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Hokari M, Kuroda S, Nakayama N, Houkin K, Ishikawa T, Kamiyama H. Long-term prognosis in patients
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Frosen J, Piippo A, Paetau A, Kangasniemi M, Niemela M, Hernesniemi J, et al. Remodeling of saccular cerebral artery aneurysm wall is associated with rupture: Histological analysis of 24 unruptured and 42
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9.
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Frosen J, Tulamo R, Paetau A, Laaksamo E, Korja M, Laakso A, et al. Saccular intracranial aneurysm: Pathology and mechanisms. Acta Neuropathol. 2012;123:773-786
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aneurysms. Stroke. 1999;30:1396-1401 11.
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activated by the classical pathway in intracranial aneurysm walls. Lab Invest. 2010;90:168-179
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Mizutani T. A fatal, chronically growing basilar artery: A new type of dissecting aneurysm. J Neurosurg. 1996;84:962-971
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Martin AJ, Hetts SW, Dillon WP, Higashida RT, Halbach V, Dowd CF, et al. Mr imaging of partially
thrombosed cerebral aneurysms: Characteristics and evolution. AJNR Am J Neuroradiol. 2011;32:346-351
331 332
Lawton MT, Quinones-Hinojosa A, Chang EF, Yu T. Thrombotic intracranial aneurysms: Classification
scheme and management strategies in 68 patients. Neurosurgery. 2005;56:441-454; discussion 441-454
329 330
Tulamo R, Frosen J, Junnikkala S, Paetau A, Kangasniemi M, Pelaez J, et al. Complement system becomes
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Rayz VL, Boussel L, Ge L, Leach JR, Martin AJ, Lawton MT, et al. Flow residence time and regions of intraluminal thrombus deposition in intracranial aneurysms. Ann Biomed Eng. 2010;38:3058-3069
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Roccatagliata L, Guedin P, Condette-Auliac S, Gaillard S, Colas F, Boulin A, et al. Partially thrombosed
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intracranial aneurysms: Symptoms, evolution, and therapeutic management. Acta Neurochir (Wien).
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2010;152:2133-2142
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Hokari M, Nakayama N, Nishihara H, Houkin K. Pathological findings of saccular cerebral aneurysms-impact of subintimal fibrin deposition on aneurysm rupture. Neurosurg Rev. 2015;38:531-540;
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discussion 540
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Polmear A. Sentinel headaches in aneurysmal subarachnoid haemorrhage: What is the true incidence? A systematic review. Cephalalgia. 2003;23:935-941
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Cheng YC, Wong YK, Lai TH. Sentinel headache: A prospective case. Acta Neurol Taiwan. 2012;21:147-148
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Evans RW, Dilli E, Dodick DW. Sentinel headache. Headache. 2009;49:599-603
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Raps EC, Rogers JD, Galetta SL, Solomon RA, Lennihan L, Klebanoff LM, et al. The clinical spectrum of
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unruptured intracranial aneurysms. Arch Neurol. 1993;50:265-268
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stroke in the rat. Stroke. 1994;25:1632-1636 23.
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Huber A, Dorn A, Witzmann A, Cervos-Navarro J. Microthrombi formation after severe head trauma. Int J Legal Med. 1993;106:152-155
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Halvorsen AM, Futrell N, Wang LC. Fibrin content of carotid thrombi alters the production of embolic
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Moe N. The deposits of fibrin and fibrin-like materials in the basal plate of the normal human placenta. Acta Pathol Microbiol Scand. 1969;75:1-17
25.
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Moe N, Abildgaard U. Histological staining properties of in vitro formed fibrin clots and precipitated fibrinogen. Acta Pathol Microbiol Scand. 1969;76:61-73
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Pearse AG. Histochemistry, 3rd ed. J.A. Churchill, London. 1968:642
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Morita A, Kirino T, Hashi K, Aoki N, Fukuhara S, Hashimoto N, et al. The natural course of unruptured
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intervention. N Engl J Med.1998;339:1725-1733 29.
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2005;102:601-606 32.
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Morita A, Fujiwara S, Hashi K, Ohtsu H, Kirino T. Risk of rupture associated with intact cerebral
aneurysms in the Japanese population: A systematic review of the literature from Japan. J Neurosurg.
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Juvela S, Porras M, Poussa K. Natural history of unruptured intracranial aneurysms: Probability of and risk
factors for aneurysm rupture. J Neurosurg. 2000;93:379-387
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Ishibashi T, Murayama Y, Urashima M, Saguchi T, Ebara M, Arakawa H, et al. Unruptured intracranial aneurysms: Incidence of rupture and risk factors. Stroke. 2009;40:313-316
363 364
Investigators TISoUIA. Unruptured intracranial aneurysms — risk of rupture and risks of surgical
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cerebral aneurysms in a Japanese cohort. N Engl J Med. 2012;366:2474-2482
Wermer MJ, van der Schaaf IC, Algra A, Rinkel GJ. Risk of rupture of unruptured intracranial aneurysms in relation to patient and aneurysm characteristics: An updated meta-analysis. Stroke. 2007;38:1404-1410
33.
Ujiie H, Tachibana H, Hiramatsu O, Hazel AL, Matsumoto T, Ogasawara Y, et al. Effects of size and shape (aspect ratio) on the hemodynamics of saccular aneurysms: A possible index for surgical treatment of
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aneurysms detected by magnetic resonance angiography. J Neurosurg. 2012;117:20-25 35.
375 376
Inagawa T. Risk factors for the formation and rupture of intracranial saccular aneurysms in Shimane, Japan. World Neurosurg. 2010;73:155-164; discussion e123
36.
377 378
Inoue T, Shimizu H, Fujimura M, Saito A, Tominaga T. Annual rupture risk of growing unruptured cerebral
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intracranial aneurysms. Neurosurgery. 1999;45:119-129; discussion 129-130
Mitchell P, Jakubowski J. Estimate of the maximum time interval between formation of cerebral aneurysm and rupture. J Neurol Neurosurg Psychiatry. 2000;69:760-767
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Wiebers DO, Whisnant JP, Huston J, 3rd, Meissner I, Brown RD, Jr., Piepgras DG, et al. Unruptured intracranial aneurysms: Natural history, clinical outcome, and risks of surgical and endovascular treatment.
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Lancet. 2003;362:103-110
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38.
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Oda S, Shimoda M, Hirayama A, Imai M, Komatsu F, Shigematsu H, et al. Neuroradiologic diagnosis of minor leak prior to major sah: Diagnosis by T1-FLAIR mismatch. AJNR Am J Neuroradiol.
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2015;36:1616-1622
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de Falco FA. Sentinel headache. Neurol Sci. 2004;25 Suppl 3:S215-217
385
40.
Mizutani T. Natural course of intracranial arterial dissections. J Neurosurg. 2011;114:1037-1044
386
41.
Mizutani T, Kojima H, Asamoto S. Healing process for cerebral dissecting aneurysms presenting with
387 42.
389
cerebral dissecting aneurysms. J Neurosurg. 2001;94:712-717
391 392
Dis. 2010;30:72-84 44.
393 394 395 396
397
Inagawa T. Site of ruptured intracranial saccular aneurysms in patients in Izumo city, Japan. Cerebrovasc
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43.
Kashiwazaki D, Kuroda S, Sapporo SAHSG. Size ratio can highly predict rupture risk in intracranial small (<5 mm) aneurysms. Stroke. 2013;44:2169-2173
45.
Ohashi Y, Horikoshi T, Sugita M, Yagishita T, Nukui H. Size of cerebral aneurysms and related factors in
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Mizutani T, Kojima H, Asamoto S, Miki Y. Pathological mechanism and three-dimensional structure of
patients with subarachnoid hemorrhage. Surg Neurol. 2004;61:239-245; discussion 245-237
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subarachnoid hemorrhage. Neurosurgery. 2004;54:342-347; discussion 347-348
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Figure Legends
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Figure 1. Intraoperative photograph (Fig. 1A and B) via interhemispheric approach and representative
400
photomicrographs of Case 1 (unruptured anterior communicating artery aneurysm): Elastica–Masson (Fig. 1C
401
and D), phosphor-tungstic acid hematoxylin (Fig. 1E), hematoxylin-eosin (Fig. 1F), and CD68 (Fig. 1G).
402
Pathological sections revealed subintimal and intramural fibrin deposition (arrow heads in Fig. 1D–F) and
403
monocyte infiltration (arrows in Fig. 1G). Scale bar in Figure 1C: 500 µm, in Figure 1D–F: 50 µm, and in
404
Figure 1G: 20 µm.
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Figure 2. Intraoperative photograph (Fig. 2A and B) via interhemispheric approach and representative
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photomicrographs of Case 2 (unruptured distal anterior cerebral artery aneurysm); Elastica–Masson (Fig. 2C),
408
phosphor-tungstic acid hematoxylin (Fig. 2D), hematoxylin-eosin (Fig. 2E), and CD68 (Fig. 2F). Pathological
409
sections revealed subintimal fibrin deposition (arrow heads in Fig. 2C–E) and monocyte infiltration (arrows in
410
Fig. 2F). Scale bar in Figure 2C: 200 µm, in Figure 2D and E: 50 µm, and in Figure 2F: 20 µm.
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Figure 3.
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Magnetic resonance angiography (Fig. 3A and B), intraoperative photograph (Fig. 3C), and representative
414
photomicrographs of Case 4 (unruptured middle cerebral artery aneurysm); Elastica–Masson (Fig. 3D and E),
415
hematoxylin-eosin (Fig. 3F), phosphor-tungstic acid hematoxylin (Fig. 3G), and CD68 (Fig. 3H). Pathological 22
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sections revealed subintimal and intramural fibrin deposition (arrow heads in Fig. 3E–G) and monocyte
417
infiltration (known as form cells; arrows in Fig. 3H). Scale bar in Figure 3D: 500 µm and in right panel of
418
Figure 3E–H: 50 µm
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Figure 4. Intraoperative photograph (Fig. 4A and B) via interhemispheric approach and representative
421
photomicrographs of Case 7 (unruptured anterior communicating artery aneurysm); Elastica–Masson (Fig. 4C
422
and D), hematoxylin-eosin (Fig. 4E), and CD68 (Fig. 4F). Pathological sections revealed fibrin deposition in
423
the peri-outer membrane (arrow heads in Fig. 4D and E) and monocyte infiltration (arrows in Fig. 4F). Scale
424
bar in Figure 4C: 500 µm, in Figure 4D and E: 50 µm, and in Figure 4F: 20 µm.
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Figure 5. Intraoperative photograph (Fig. 5A and B) and representative photomicrographs of Case 8
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(unruptured middle cerebral artery aneurysm); Elastica–Masson (Fig. 5C and D), phosphor-tungstic acid
428
hematoxylin (Fig. 5E), and CD68 (Fig. 5F). Black arrow head and black arrow in Figure 5A are two “humps”
429
and correspond with the pathological sites of those in Figure 5C. Pathological sections (Fig. 5D–F) revealed
430
fibrin deposition in the peri-outer membrane (red arrows in Fig. 5D and E) and monocyte infiltration (red
431
arrow head in Fig. 5F). Scale bar in Figure 5C: 500 µm and in Figure 5D–F: 50 µm.
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Figure 6. Intraoperative photograph (Fig. 6A) and representative photomicrographs of Case 12 (unruptured 23
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middle cerebral artery aneurysm); Elastica–Masson (Fig. 6B). Pathological sections revealed typical findings
435
of unruptured aneurysms; partially very thin wall, no fibrin deposition in the intramural layer. Scale bar in
436
Figure 6B: 200 µm.
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Figure 7. Theme of Natural History of unruptured saccular aneurysms and its pathology
439
Classified by Yonekura et al.
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Table 1. Review of patients having unruptured aneurysms in this study
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25
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NO;0, Yes;1
severe headache HT (op 4 months later) severe headache (op 1 month HT later) severe headache HT (op 2 months later) screening HT follow-up HL.HT, (AVM) AVM (radiation visual none
61
M
A-com
4
2
44
F
A2-3
7
3
54
F
A-com
5
4
56
F
MCA
5
4→5
5
58
F
A-com
8
3→8
6
60
F
IC(C2/3)
17
7
75
M
A-com
11
dementia
8
64
F
MCA
7
screening
9 10
53 59
M F
A-com IC-PC
6 4
follow-up (SAH) chronic headache
11
70
M
A-com
6
dizziness
12
54
F
MCA
5
chronic headache
13
74
M
MCA
4
14 15 16 17
76 54 64 56 61.8 8.2566
F M M F
A-com A-com IC(C2/3) IC-PC
5 5 5 4 6.46667 3.44065
SD
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NO;0, Yes;1
No;0, Mild;1, Severe;2
0
1
0
0
1
1
1
1
0
0
1
1
2
0
1
0
0
1
1
2
1
1
1
1
1
1
2
0
0
1
0
0
1
1
0
1
1
0
0
1
1
HT,HL
0
1
1
0
0
1
2
HT
0
1
1
1
0
1
1
SAH
1
none
0
1 1
1 1
0 0
0 0
0 0
0 0
none
0
0
1
0
0
0
0
HT, HL,
0
1
0
0
0
0
1
pAf
0
1
1
0
0
0
0
0 0 0 0
1 1 1 1
1 1 1 1
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
chronic headache HT chronic headache HT, smoking screening Marfan synd, HT dizziness smoking
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Average
dizziness
NO;0, Yes;1
0
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Growing
NO;0, Yes;1
multiple Myointimal Organized Subintimal Intramural Chronic Thinnin Past history and aneurysm hyperplasia laminar fibrin fibrin inflammati g of wall risk factor s (>200uM) thrombosis deposit deposition on (<50um)
SC
Age (Y) Gender Location
Reason for imaging
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Size (mm)
NO;0, Yes;1
ACCEPTED MANUSCRIPT
Disclosure: We certify that this manuscript has not been published and is not being submitted for publication.
The authors have no financial or institutional interest.
This manuscript has been read
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and agreed for submission by all of authors.
ACCEPTED MANUSCRIPT Highlights: We performed pathological analysis of 17 unruptured aneurysms. Our prior study observed subintimal fibrin deposition in most of ruptured aneurysms.
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This study demonstrated fibrin deposition in unruptured aneurysms with headaches.
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These may be newly formed aneurysms, which can result in rupture at an early stage.
1
S1878-8750(17)30092-X
DOI:
10.1016/j.wneu.2017.01.069
Reference:
WNEU 5166
To appear in:
World Neurosurgery
Received Date: 17 November 2016 Revised Date:
15 January 2017
Accepted Date: 17 January 2017
Please cite this article as: Hokari M, Nakayama N, Shimoda Y, Kiyohiro Houkin Effect of headache on the pathological findings of unruptured cerebral saccular aneurysms, World Neurosurgery (2017), doi: 10.1016/j.wneu.2017.01.069. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Abbreviations and Acronyms 3D-CTA: 3-dimensional computed tomographic angiography ACA: anterior cerebral artery
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A-com: anterior communicating artery EM: Elastica–Masson (EM) HE: hematoxylin-eosin
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ICA: internal carotid artery IC-IC: intracranial-intracranial
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MCA: middle cerebral artery PTAH: phosphor-tungstic acid hematoxylin
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SAH: subarachnoid hemorrhage
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ACCEPTED MANUSCRIPT Hokari
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Effect of headache on the pathological findings of unruptured cerebral saccular aneurysms
2
Masaaki Hokari, MD, PhD; Naoki Nakayama, MD, PhD; Yusuke Shimoda, MD; Kiyohiro Houkin, MD, PhD
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Department of Neurosurgery, Hokkaido University Graduate School of Medicine
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Running Title: Headache impact on unruptured aneurysms
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COI: There are no conflicts of interest to declare.
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Correspondence:
12
Masaaki Hokari, MD, PhD,
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Department of Neurosurgery, Hokkaido University Graduate School of Medicine, North 15 West 7, Kita-ku,
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Sapporo 060-8638, Japan
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TEL：+81-11-706-5987 FAX：+81-11-708-7737
16
E-mail: [email protected]
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Abstract
19
Background: Some patients with aneurysm exhibit warning headaches without minor bleeding, and this could
20
be caused by stretching of the aneurysm wall. Recently, our pathological study observed subintimal fibrin
21
deposition in a majority of the ruptured aneurysms. However, these findings were also observed in some
22
unruptured aneurysms. In this report, two unruptured aneurysms exhibited subintimal fibrin, and interestingly,
23
one of the patients experienced severe headache within 1 month before neuroimaging.
24
Objective: We performed pathological analysis of unruptured aneurysms and collected their various clinical
25
variables, including severe headache, to clarify the clinical characteristics of “dangerous” unruptured
26
aneurysms.
27
Methods: This study included unruptured saccular aneurysm samples (n = 17) that were resected after clipping.
28
We compared the differences in clinical variables, including warning headache, between aneurysms with and
29
without fibrin deposition.
30
Results: Fibrin deposition was present in the subintimal layer in four patients and in the peri-outer membrane
31
in four patients. Three of the four former patients experienced warning headaches, and one presented aneurysm
32
growth. Of the latter four patients, one exhibited aneurysm growth, while the others presented with relatively
33
large aneurysms. In the remaining nine aneurysms without fibrin deposition, monocyte infiltration was
34
observed in one, all aneurysms were small, and no patients experienced warning headaches or aneurysm
35
growth.
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Conclusion: Subintimal fibrin deposition is frequently observed in patients with aneurysm with warning
37
headaches. These pathological findings are clinically inspiring and may suggest that these aneurysms exhibit
38
rapid stretching by newly formed aneurysms, which can result in rupture at an early stage.
39
Keywords: cerebral aneurysms; pathology; headache
40
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Highlights:
42
We performed pathological analysis of 17 unruptured aneurysms.
43
Our prior study observed subintimal fibrin deposition in most of ruptured aneurysms.
44
This study demonstrated fibrin deposition in unruptured aneurysms with headaches.
45
These may be newly formed aneurysms, which can result in rupture at an early stage.
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Introduction
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Recent advances in noninvasive imaging techniques have resulted in increased detection of unruptured
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aneurysms. Although various surgical interventions have been suggested for prevention of future ruptures,1, 2
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there are some recommendations against them because of the relatively low risk of rupture.3, 4 Moreover, there
50
is some discrepancy between the low rupture rate of small unruptured aneurysms and the size of ruptured
51
aneurysms.5 According to previous reports,4, 6 the rupture rate does not remain constant after formation and
52
may be higher in the early stages. Therefore, ruptured aneurysms may be fundamentally different from stable
53
aneurysms that have remained unruptured for several years. Although it is clear that we should only perform
54
interventions for unruptured aneurysms that are at a high risk of rupture, prediction of aneurysmal ruptures has
55
not been promising till date. To clarify the mechanisms leading to their rupture, several pathological studies
56
examining human saccular aneurysms have been conducted and have proposed the notion that chronic
57
inflammation plays a role in aneurysmal wall degeneration and potentially increases the subsequent risk of
58
rupture.7-11 Frosen et al. reported that luminal thrombosis and chronic inflammation were observed more
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frequently in the ruptured aneurysm wall than in the unruptured wall.8, 9 In several clinical reports, the
60
existence of a laminar thrombus and thrombus in the aneurysm has been regarded as a risk factor of rupture in
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the dissecting, fusiform, or giant saccular aneurysms12-16.In those reports, thrombosis in the aneurysm change
62
in the time course between a few days and several months. However, the time course for formation of fibrin
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and the mechanism in the saccular non-giant aneurysms has not been recognized.
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Recently, our pathological study detected severe monocyte infiltration in the aneurysmal wall and subintimal
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fibrin deposition containing no erythrocytes in a majority of ruptured aneurysms resected within 24 h of
67
onset.17 This suggests that the fibrin components in the subintimal layer and chronic inflammation in the
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aneurysmal wall were present prior to rupture. The existence of subintimal fibrin deposition and monocyte
69
infiltration was also more frequently observed in 28 ruptured aneurysms compared with 12 unruptured
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aneurysms (92.9% and 100% in ruptured group versus 16.7% and 33.3% in unruptured group, respectively).
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However, pathological findings that were frequently observed in the ruptured aneurysm were also
occasionally observed in some unruptured aneurysms that were regarded as “dangerous” as they were at a high
73
risk of rupture. In our previous report,17 we observed two unruptured aneurysms with subintimal fibrin and
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interestingly, one of the patients presented with severe headache within 1 month before neuroimaging. An
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exhaustive systematic review reported that 10%–43% of subarachnoid hemorrhage (SAH) patients frequently
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experience a sudden headache (termed “warning headache” or “sentinel headache”)18 that precedes an episode
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of aneurysmal SAH. A majority of these episodes occur within 1 month before rupture, and these headaches
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are considered to represent minor bleeding into the subarachnoid space. However, some patients exhibit
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sentinel headaches without minor bleeding,19-21 and these may be caused by stretching or dissection of the
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aneurysm wall. Thus, based on these reports, unruptured aneurysms with subintimal fibrin deposition in
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patients experiencing severe headaches may be at a higher risk of rupture.
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The present study is a pathological analysis of 17 unruptured aneurysms. It compares various clinical
83
variables including severe headache between unruptured aneurysms with and without certain pathological
84
findings to clarify the clinical characteristics of “dangerous” unruptured aneurysms.
85
Patients and Methods
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Patients
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This study included unruptured saccular aneurysms (n = 17) that were resected after microsurgical clipping
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between 2010 and 2013 (Table 1). To retain the original state of saccular unruptured aneurysms as far as
90
possible, the aneurysms were fully exposed before clip application. The aneurysm sacs were not resected when
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full exposure was considered to be too dangerous, and all such aneurysms including those that were small or
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had a very thick neck were excluded.
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Clinical information including age, gender, aneurysm size, location, aneurysm growth, multiple aneurysms,
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history of SAH, history of hypertension, smoking, history of hyperlipidemia, and symptoms for neuroimaging
95
was collected from the patients’ medical records. The sizes of the aneurysms were measured using preoperative
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vascular imaging studies including either three-dimensional computed tomographic angiography (3D-CTA) or
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magnetic resonance angiography (MRA). Warning headache was defined as a sudden and unusually severe
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headache lasting at least 1 h followed by a symptom-free interval within 1 month prior to detection of
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aneurysm. Symptoms including warning headache, other chronic headaches, and vertigo were recorded using
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medical records that were based on a thorough interview of the patients and their relatives/accompanying
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persons. All quantitative clinical data have been expressed as mean ± SD. This study was approved by the
102
ethics committee of Hokkaido University (IRB No.011-0321) and written informed consent was waived
103
because of the retrospective design.
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Histology and Immunohistochemistry
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Histological examination was performed in a manner similar to the method described previously.17 Briefly,
107
following aneurysm resection, the specimens were gently washed with saline to remove any blood and fixed in
108
10% formalin. The specimens were sliced to a 3 µm thickness, and slides for classical histological staining
109
were prepared every 90 µm. The number of slices varied from five to twenty and depended on the size of the
110
aneurysm. For classical histological staining, hematoxylin-eosin (HE) and Elastica–Masson (EM) methods
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were used. We also performed phosphor-tungstic acid hematoxylin (PTAH) staining to detect and confirm
112
fibrin components in the specimens. PTAH staining was originally introduced by Mallory for glial fiber
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staining but has also been used for the demonstration of fibrin.22-26 It stains collagen pink and glial fibers,
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muscle fibers, and fibrin blue, although the mechanism is still largely unknown.24-26 As for
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immunohistochemistry, CD68 was used as a marker for macrophage infiltration. The de-paraffinized sections
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were processed through antigen retrieve for 15 min and then incubated with primary mouse monoclonal
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antibody against human CD68 (Dako, 1:100). Thereafter, the immunoreactivity was visualized by treating with
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Dako Envision kit HRP (DAB) (Dako). Finally, the sections were counterstained with hematoxylin.
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Histological analysis
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Histological analysis was performed to confirm pathological variables such as myointimal hyperplasia (>200
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µm), existence of fibrin deposition in the aneurysmal wall, and severe monocyte infiltration, as described
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previously.17 Briefly, by observing HE and EM all sections through an optical microscope (Olympus BX50),
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the existence of fibrin deposition was evaluated using PTAH and HE stainings. A hyaline-like structure was
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observed under the intimal layer in HE sections, and this was also seen in PTAH sections as a deep blue-
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stained layer. The number of CD68 positive cells in an area (100 µm × 100 µm) of the aneurysmal wall where
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active invasion of inflammatory cells was observed on HE was counted under 40× magnification. Severe
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infiltration by chronic inflammatory cells is defined as the presence of more than 50 CD68-positive cells in the
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area, while mild infiltration is defined as the presence of more than 10 CD68-positive cells. Histological
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analysis was conducted by M.H and Y.S.
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Statistics
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Fisher's test was performed to estimate whether a warning headache is associated with “dangerous”
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pathological findings, such as subintimal fibrin deposition or monocyte infiltration. Differences with a P value
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of <0.05 were considered statistically significant.
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Results
Clinical Data and Radiological Findings
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The characteristics of the patients and the aneurysms included in this study are shown in Table 1.
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The participants included 7 men and 10 women, and the mean age of the patients was 60.7 ± 8.8 years. This
142
was slightly younger than that of the participants of The Unruptured Cerebral Aneurysm Study of Japan
143
(UCAS Japan; 62.5 ± 10.3 years old). Moreover, in comparison with UCAS Japan (43.4%), a larger number of
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patients reported history of hypertension (64.7%). The percentage of smoking (17.6%) and history of
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hyperlipidemia (17.6%) were almost the same as those seen in UCAS Japan27 (14.1% and 16.8%, respectively).
146
Similar to UCAS Japan, headache (N = 7) and vertigo (N = 5) were the most common symptoms for imaging,
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and screening was also a typical reason for imaging. Other reasons for neuroimaging included dementia in one
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patient and visual disturbance in another patient. Four patients presented with a chronic headache, while three
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experienced a severe headache within 1 month before imaging (Cases 1–3). The mean size of aneurysms was
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6.4 ± 3.3 mm, and this was slightly bigger than those included in UCAS Japan, which is considered to be the
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largest cohort study examining unruptured cerebral aneurysms in Japan (5.7 ± 3.7 mm). With regard to location,
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eight aneurysms were anterior communicating artery (A-com), four were of middle cerebral artery (MCA),
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four were internal carotid artery (ICA), and one was of a distal anterior cerebral artery (ACA). The prevalence
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of characteristics such as location and size in this study may have been influenced by our decision to be safe
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with regard to full exposure and aneurysmal sac resection.
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Histology of cerebral saccular aneurysms and clinical course
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Deposition of fibrin was observed in 8 of 17 patients, all of whom (Cases 1–8) also exhibited chronic
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monocyte infiltration. Fibrin deposition was present in the subintimal layer in four of eight patients (Cases 1–
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4), and in the intramural layer (peri-outer membrane) in the remaining four patients (Cases 5–8). Among cases
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1–4, who presented with unruptured aneurysms with “dangerous” pathological findings, three patients
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experienced severe headache within 1 month before imaging (Cases 1–3) and one exhibited aneurysm growth
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(from 4 to 5 mm). Among cases 5–8, one patient (Case 5) exhibited aneurysm growth (from 3 to 8 mm), while
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the others (Cases 6–8) presented with relatively large aneurysms (≥7 mm) during initial neuroimaging. In
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these three cases, follow-up neuroimaging was not performed as the aneurysms were clipped within 6 months
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after diagnosis. Therefore, these aneurysms may be growing. In the remaining nine aneurysms without fibrin
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deposition (Cases 9–17), monocyte infiltration was observed in one case only, and all aneurysms were small
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(<6 mm). During 1 month before imaging, none of the nine patients (Cases 9–17) experienced warning
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headache or exhibited aneurysm growth. Fisher’s test revealed that a warning headache was associated with
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subintimal fibrin deposition (P = 0.006) but not with monocyte infiltration.
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Representative Cases
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Case 1: 10
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A 61-year-old man with hypertension presented at the hospital with severe frontal headache. Magnetic
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resonance image (MRI) and MRA revealed 4 mm A-com aneurysm with no subarachnoid hemorrhage. He
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underwent clipping and removal of the aneurysm 4 months later (Fig. 1A and B). No old subarachnoid
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hemorrhages were found during the surgery, and the pathological specimens revealed subintimal and
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intramural fibrin deposition (Fig. 1C–F) and monocyte infiltration (Fig. 1G).
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Case 2:
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A 44-year-old woman with hypertension presented at the hospital with a sudden, severe sudden headache. MRI
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and MRA examination revealed 5 mm distal ACA aneurysm with no subarachnoid hemorrhage, and this was
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confirmed by lumbar puncture. She underwent clipping and removal of the aneurysm 2 months later (Fig. 2A
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and B). No old subarachnoid hemorrhages were recognized during the surgery, and the pathological sections
183
revealed subintimal and intramural fibrin deposition (Fig. 2C-–E) and monocyte infiltration (Fig. 2F).
184
Case 4:
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MRI and MRA examination performed in a 56-year-old woman with hypertension for the purpose of screening
186
revealed a 4 mm MCA aneurysm and a 3 mm basilar artery aneurysm (Fig. 3A). Eleven months later, she
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underwent a follow-up MRI and MRA, which demonstrated MCA aneurysm growth from 4 to 5 mm (Fig. 3B).
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Therefore, she underwent clipping surgery and removal of the aneurysm (Fig. 3C). No old subarachnoid
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hemorrhages were found during the surgery, and pathological sections revealed subintimal and intramural
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fibrin deposition (arrow heads in Fig. 3D–G) and monocyte infiltration (known as form cells; arrows in Fig.
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3H).
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Case 7:
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A 75-year-old man with hypertension and hyperlipidemia underwent MRI and MRA examination for dementia,
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which revealed an 11 mm A-com aneurysm. He then underwent clipping surgery and removal of the aneurysm
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(Fig. 4A and B). No old subarachnoid hemorrhages were recognized during the surgery, and the pathological
196
sections revealed fibrin deposition in the intramural layer (peri-outer membrane; Fig. 4C–E) and monocyte
197
infiltration (Fig. 4F).
198
Case 8:
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A 64-year-old woman with hypertension underwent MRI and MRA examination for the purpose of screening,
200
which revealed a 7 mm MCA aneurysm. She then underwent clipping and removal of the aneurysm (Fig. 5A
201
and B). No old subarachnoid hemorrhages were recognized during the surgery, and the pathological sections
202
revealed fibrin deposition in the intramural layer (peri-outer membrane; Fig. 5C–E) and monocyte infiltration
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(Fig. 5F).
204
Case 12:
205
A 54-year-old woman with hypertension, hyperlipidemia, and smoking habit underwent MRI and MRA
206
examinations for a chronic headache, which revealed a 5 mm MCA aneurysm. She then underwent clipping
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surgery and removal of the aneurysm (Fig. 6A). No old subarachnoid hemorrhages were recognized during the
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surgery, and the pathological sections revealed typical findings of unruptured aneurysms, that is, partial thin
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walls with no fibrin deposition in the intramural layer (Fig. 6B).
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Discussion
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In this clinicopathological study, unruptured aneurysms with intramural fibrin deposition and monocyte
213
infiltration,17 which are usually observed in ruptured aneurysm specimens, were frequently observed in
214
patients experiencing severe headaches within 1 month before imaging. In addition to large aneurysms and
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aneurysm growth, severe headaches may also serve as a predictor for aneurysm rupture. Although no
216
association between severe headache and the mechanism of aneurysm rupture was demonstrated, the
217
pathological findings of the representative cases are clinically inspiring and arouse interest in the natural
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course of saccular aneurysms and the impact of aneurysm degeneration that may ultimately result in rupture.
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Risk Factors for Rupture of Unruptured Aneurysms and their Natural Course
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Previous studies have identified several factors including large size,27-32 location (A-com,6, 27 IC-PC,27 and
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posterior circulation27, 29-32), irregular protrusion of the aneurysm wall,27, 33 aneurysm growth,34 a history of
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SAH,29 smoking,30, 35 age,6, 32 race,32 and presence of multiple aneurysms6 as possible risk factors for rupture of
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an aneurysm. Furthermore, according to previous reports,4, 6 the rupture rate does not remain constant after
224
formation and may be higher in the early stages. In other words, aneurysms may be at a higher risk of rupture
225
shortly after formation. Sato et al. examined a mathematical model of the natural history of unruptured
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aneurysms and reported that some aneurysms bleed shortly after formation.4 With regard to the origin and
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growth of cerebral aneurysms, Yonekura et al. classified the natural course of unruptured aneurysms into the
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following four types: Type 1—aneurysm ruptures within a few days to a few months after formation; Type
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2—aneurysm builds up slowly for several months to several years after formation and ruptures during this
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process; Type 3—aneurysm keeps growing slowly for many years without rupturing; and Type 4—aneurysm
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grows to a certain size, probably under 5 mm in diameter, and thereafter remains unchanged.6 The difficulty in
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following Type 1 aneurysms clinically and radiologically from formation to rupture may explain the
233
discrepancy between the low rupture rate of small unruptured aneurysms and the size of ruptured aneurysms.5
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Some other previous reports have also suggested that a certain portion of acute SAH is derived from a recently
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formed aneurysm.36, 37 Mitchell et al. proved this with a mathematical model utilizing data from previously
236
published large studies and concluded that the duration of this high-risk period varies from 1 to 2 days to a
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maximum of approximately 8 weeks.36 After this initial period, the risk of rupture falls to a lower level.
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Natural Course of the Unruptured Aneurysm and its Pathology (Fig. 7)
239
The aneurysms accompanied by severe headache (Cases 1–3) were small (≤7 mm) and their pathological
240
findings including subintimal and intramural fibrin deposition that classified them as “dangerous.” Therefore,
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we speculate that the severe headaches in these cases (Cases 1–3) may be caused by rapid stretching or
242
dissection of the wall caused by newly formed aneurysms which, in turn, can result in rupture at an early stage
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(just before rupture in Type 1 by Yonekura et al.). The enlarging aneurysm with subintimal fibrin deposition
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observed in Case 4 is also considered to be at a relatively high risk of rupture and may be classified as Type 2
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The aneurysms exhibiting fibrin deposition in the intramural layer (peri-outer membrane) in Cases 5–8 may be
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classified as Type 3. Of these aneurysms, one was undergoing enlargement (Case 5) and others were already
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relatively large and may be growing (Cases 6–8). Interestingly, two “humps” (black arrow heads and black
248
arrows in Fig. 5A and C) were observed in Case 8, and fibrin deposition was seen in the peri-outer membrane
249
of the “hump” (black arrow head in Fig. 5A and C). We speculate that the walls of these humps may have been
250
thin, and the fibrin deposition may have actually been situated in the subintimal layer. To prevent rupture,
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aneurysmal wall remodeling may have then thickened the walls due to laminar thrombosis or myo-intimal
252
hyperplasia.8, 9
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The aneurysms in Cases 9–17 were all small (<7 mm), had stable pathology, and were considered to be “not
254
dangerous” as there was no fibrin deposition in the wall. These may be classified as Type 4.
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Impact of Headache on Unruptured Cerebral Saccular Aneurysms
256
Sentinel headaches occur 1 month before rupture, as mentioned before, and a majority of these episodes are
257
considered to represent minor bleeding into the subarachnoid space.18 Accurate diagnosis of previous
258
headaches by interview is difficult because of the inability to obtain complete information from patients in
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poor clinical conditions. Therefore, Oda et al. conducted neuroradiologic diagnosis of minor leaks using
260
T1-FLAIR mismatch and also found radiological minor leaks in patients without warning headaches.38 On the
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contrary, there are some patients with sentinel headaches not accompanied by minor bleeding,19-21 and these
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may be caused by stretching or dissection of the aneurysm wall. Therefore, de Falco suggested that MRA or
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3D-CTA should be performed to identify de novo small or enlarged aneurysms with high risk of rupture in
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patients with unusual, acute onset headaches, even if the CT and lumbar puncture examinations reveal negative
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findings.39 Interestingly, Ankeete et al. reported that both surgical clipping and endovascular embolization of
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unruptured aneurysms were associated with long-term improvement in self-reported quantitative headache
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scores. They then raised the question “When a patient presents to a neurosurgeon with headache and a
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diagnosis of unruptured saccular aneurysm, can we decide that the headaches are unrelated to the aneurysm
269
and are defined as ‘incidental’?” Although there are a limited number of reports examining patients with
270
unruptured saccular aneurysm with warning headaches,19-21 most of the patients with unruptured intracranial
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artery dissections complain of a headache, and it is well known that some of these rupture within a month.40-42
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Dissecting aneurysms are usually generated by sudden, widespread disruption of the internal elastic lamina and
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media, frequently accompanied by sudden, severe headaches.41, 42 However, previous pathological studies
274
examining saccular aneurysms have also demonstrated that the absence or fragmentation of internal elastica
275
lamina a generally observed in both ruptured and unruptured saccular aneurysms.7-10,
276
saccular aneurysms may be generated with relatively rapid disruption of the internal elastic lamina and media
277
at the bifurcation, resulting in severe headaches. Furthermore, it is interesting that three aneurysms with
278
subintimal fibrin deposition (Cases 1–3) were aneurysms at A-com or distal ACA. Ruptured A-com or distal
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ACA aneurysms are found more frequently than unruptured. Thus, it is likely that they rapidly grow and
280
rupture at an early stage, even when small in size.43-45
17
Therefore, some
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Limitations
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(1) This is a small-sized study; (2) histological analysis was not conducted by independent investigators; (3)
283
the presence of a severe recent headache (within 1 month before the aneurysm found) can only be determined
284
by interviews and relies heavily on recall; and (4) there are no established neuro-radiological diagnostic
285
procedures to prove aneurysm formation or acute expansion associated with headache.
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Conclusions
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This study demonstrated intramural fibrin deposition and monocyte infiltration in unruptured aneurysms, and
289
these findings were frequently observed in patients who experienced severe headaches within 1 month before
290
imaging. The pathological findings of aneurysms accompanied by severe headache are clinically inspiring and
291
arouse interest in the natural course of saccular aneurysms. It may be suggested that these aneurysms may
292
exhibit rapid stretching or dissection of the wall caused by newly formed aneurysms and can result in rupture
293
at an early stage.
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Acknowledgments
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The authors thank Yumiko Shinohe and Rika Nagashima deeply for their technical assistance. This study was
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supported by grant-in-aid from the Ministry of Education, Science and Culture of Japan (15K10287 and
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15K10284). 17
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Hokari M, Kuroda S, Nakayama N, Houkin K, Ishikawa T, Kamiyama H. Long-term prognosis in patients
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Figure Legends
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Figure 1. Intraoperative photograph (Fig. 1A and B) via interhemispheric approach and representative
400
photomicrographs of Case 1 (unruptured anterior communicating artery aneurysm): Elastica–Masson (Fig. 1C
401
and D), phosphor-tungstic acid hematoxylin (Fig. 1E), hematoxylin-eosin (Fig. 1F), and CD68 (Fig. 1G).
402
Pathological sections revealed subintimal and intramural fibrin deposition (arrow heads in Fig. 1D–F) and
403
monocyte infiltration (arrows in Fig. 1G). Scale bar in Figure 1C: 500 µm, in Figure 1D–F: 50 µm, and in
404
Figure 1G: 20 µm.
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Figure 2. Intraoperative photograph (Fig. 2A and B) via interhemispheric approach and representative
407
photomicrographs of Case 2 (unruptured distal anterior cerebral artery aneurysm); Elastica–Masson (Fig. 2C),
408
phosphor-tungstic acid hematoxylin (Fig. 2D), hematoxylin-eosin (Fig. 2E), and CD68 (Fig. 2F). Pathological
409
sections revealed subintimal fibrin deposition (arrow heads in Fig. 2C–E) and monocyte infiltration (arrows in
410
Fig. 2F). Scale bar in Figure 2C: 200 µm, in Figure 2D and E: 50 µm, and in Figure 2F: 20 µm.
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Figure 3.
413
Magnetic resonance angiography (Fig. 3A and B), intraoperative photograph (Fig. 3C), and representative
414
photomicrographs of Case 4 (unruptured middle cerebral artery aneurysm); Elastica–Masson (Fig. 3D and E),
415
hematoxylin-eosin (Fig. 3F), phosphor-tungstic acid hematoxylin (Fig. 3G), and CD68 (Fig. 3H). Pathological 22
ACCEPTED MANUSCRIPT Hokari
sections revealed subintimal and intramural fibrin deposition (arrow heads in Fig. 3E–G) and monocyte
417
infiltration (known as form cells; arrows in Fig. 3H). Scale bar in Figure 3D: 500 µm and in right panel of
418
Figure 3E–H: 50 µm
RI PT
416
419
Figure 4. Intraoperative photograph (Fig. 4A and B) via interhemispheric approach and representative
421
photomicrographs of Case 7 (unruptured anterior communicating artery aneurysm); Elastica–Masson (Fig. 4C
422
and D), hematoxylin-eosin (Fig. 4E), and CD68 (Fig. 4F). Pathological sections revealed fibrin deposition in
423
the peri-outer membrane (arrow heads in Fig. 4D and E) and monocyte infiltration (arrows in Fig. 4F). Scale
424
bar in Figure 4C: 500 µm, in Figure 4D and E: 50 µm, and in Figure 4F: 20 µm.
M AN U
SC
420
TE D
425
Figure 5. Intraoperative photograph (Fig. 5A and B) and representative photomicrographs of Case 8
427
(unruptured middle cerebral artery aneurysm); Elastica–Masson (Fig. 5C and D), phosphor-tungstic acid
428
hematoxylin (Fig. 5E), and CD68 (Fig. 5F). Black arrow head and black arrow in Figure 5A are two “humps”
429
and correspond with the pathological sites of those in Figure 5C. Pathological sections (Fig. 5D–F) revealed
430
fibrin deposition in the peri-outer membrane (red arrows in Fig. 5D and E) and monocyte infiltration (red
431
arrow head in Fig. 5F). Scale bar in Figure 5C: 500 µm and in Figure 5D–F: 50 µm.
AC C
EP
426
432
433
Figure 6. Intraoperative photograph (Fig. 6A) and representative photomicrographs of Case 12 (unruptured 23
ACCEPTED MANUSCRIPT Hokari
middle cerebral artery aneurysm); Elastica–Masson (Fig. 6B). Pathological sections revealed typical findings
435
of unruptured aneurysms; partially very thin wall, no fibrin deposition in the intramural layer. Scale bar in
436
Figure 6B: 200 µm.
RI PT
434
437
Figure 7. Theme of Natural History of unruptured saccular aneurysms and its pathology
439
Classified by Yonekura et al.
M AN U
SC
438
440
AC C
EP
TE D
441
24
ACCEPTED MANUSCRIPT Hokari
442
Table 1. Review of patients having unruptured aneurysms in this study
AC C
EP
TE D
M AN U
SC
RI PT
443
25
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
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AC C
EP
TE D
M AN U
SC
RI PT
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AC C
EP
TE D
M AN U
SC
RI PT
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AC C
EP
TE D
M AN U
SC
RI PT
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AC C
EP
TE D
M AN U
SC
RI PT
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AC C
EP
TE D
M AN U
SC
RI PT
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NO;0, Yes;1
severe headache HT (op 4 months later) severe headache (op 1 month HT later) severe headache HT (op 2 months later) screening HT follow-up HL.HT, (AVM) AVM (radiation visual none
61
M
A-com
4
2
44
F
A2-3
7
3
54
F
A-com
5
4
56
F
MCA
5
4→5
5
58
F
A-com
8
3→8
6
60
F
IC(C2/3)
17
7
75
M
A-com
11
dementia
8
64
F
MCA
7
screening
9 10
53 59
M F
A-com IC-PC
6 4
follow-up (SAH) chronic headache
11
70
M
A-com
6
dizziness
12
54
F
MCA
5
chronic headache
13
74
M
MCA
4
14 15 16 17
76 54 64 56 61.8 8.2566
F M M F
A-com A-com IC(C2/3) IC-PC
5 5 5 4 6.46667 3.44065
SD
EP
NO;0, Yes;1
No;0, Mild;1, Severe;2
0
1
0
0
1
1
1
1
0
0
1
1
2
0
1
0
0
1
1
2
1
1
1
1
1
1
2
0
0
1
0
0
1
1
0
1
1
0
0
1
1
HT,HL
0
1
1
0
0
1
2
HT
0
1
1
1
0
1
1
SAH
1
none
0
1 1
1 1
0 0
0 0
0 0
0 0
none
0
0
1
0
0
0
0
HT, HL,
0
1
0
0
0
0
1
pAf
0
1
1
0
0
0
0
0 0 0 0
1 1 1 1
1 1 1 1
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
chronic headache HT chronic headache HT, smoking screening Marfan synd, HT dizziness smoking
AC C
Average
dizziness
NO;0, Yes;1
0
TE D
1
RI PT
Growing
NO;0, Yes;1
multiple Myointimal Organized Subintimal Intramural Chronic Thinnin Past history and aneurysm hyperplasia laminar fibrin fibrin inflammati g of wall risk factor s (>200uM) thrombosis deposit deposition on (<50um)
SC
Age (Y) Gender Location
Reason for imaging
M AN U
Case
Size (mm)
NO;0, Yes;1
ACCEPTED MANUSCRIPT
Disclosure: We certify that this manuscript has not been published and is not being submitted for publication.
The authors have no financial or institutional interest.
This manuscript has been read
AC C
EP
TE D
M AN U
SC
RI PT
and agreed for submission by all of authors.
ACCEPTED MANUSCRIPT Highlights: We performed pathological analysis of 17 unruptured aneurysms. Our prior study observed subintimal fibrin deposition in most of ruptured aneurysms.
RI PT
This study demonstrated fibrin deposition in unruptured aneurysms with headaches.
AC C
EP
TE D
M AN U
SC
These may be newly formed aneurysms, which can result in rupture at an early stage.
1