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Detection of inflammation in aortic aneurysms with indium 111-oxine—labeled leukocyte imaging
Detection of inflammation in aortic aneurysms with indium 111-oxine–labeled leukocyte imaging Keiko Takahashi, MD,a Mitsumasa Ohyanagi, MD, PhD,a Kiyomitsu Ikeoka, MD, PhD,a Miho Masai, MD,a Hitoshi Naruse, MD, PhD,a Tadaaki Iwasaki, MD, PhD,a Minoru Fukuchi, MD, PhD,b and Takashi Miyamoto, MD, PhDc Background. The exact cause of aortic aneurysms is not completely understood. Histologically, the atherosclerotic lesions present in an aneurysm contain numerous inflammatory cells. This finding represents active atherosclerosis, which can cause lesion expansion. In this study we investigated the role of scintigraphy in the evaluation of inflammation in aortic aneurysms. Methods and Results. We performed imaging using indium 111-oxine–labeled leukocytes in 14 patients with aortic aneurysms (10 thoracic and 4 abdominal) diagnosed by computed tomography. Peripheral blood evidence of inflammation was assessed on the same day. In 8 patients who subsequently underwent graft replacement of the aneurysm, the excised specimen was examined for evidence of inflammatory infiltration and correlated with the scintigraphic findings. Scintigraphic accumulation of labeled leukocytes was present in 10 of the 14 patients. Although all patients had a small increase in the erythrocyte sedimentation rate, there was no significant difference in the erythrocyte sedimentation rate between patients with positive and negative scintigram results. In 5 of the 8 surgical patients with positive scintigram results, the resected specimens demonstrated numerous inflammatory cells in the adventitia of the aortic wall and atherosclerotic changes in the media. There was no correlation between the presence of periaortic inflammatory adhesions at the time of surgery and the scintigraphic results. Conclusions. The accumulation of In-111-oxine–labeled leukocytes is a potentially useful scintigraphic marker of inflammatory infiltration in aortic aneurysms. (J Nucl Cardiol 2001;8:165-70.) Key Words: Aneurysm • imflammation • indium 111-oxine–labeled leukocytes • scintigraphy
See related editorial, p 219 Several studies have analyzed the relationship between atherosclerosis and aortic aneurysms.1,2 Although immunologic, genetic, metabolic, and hemodynamic factors have been implicated in the pathogenesis of aortic aneurysms,3,4 the precise mechanism responsible for the development of aneurysms has not been determined. Various layers comprise an atherosclerotic lesion, From the First Department of Internal Medicine,a the Department of Nuclear Medicine,b and the Department of Thoracic and Cardiovascular Surgery,c Hyogo College of Medicine, Nishinomiya, Japan. Received for publication Jan 14, 2000; final revision accepted June 29, 2000. Reprint requests: Keiko Takahashi, MD, First Department of Internal Medicine, Hyogo College of Medicine, 1-1, Mukogawa-cho, Nishinomiya, Hyogo, 663-8501, Japan; [email protected]. Copyright © 2001 by the American Society of Nuclear Cardiology. 1071-3581/2001/$35.00 + 0 43/1/110209 doi:10.1067/mnc.2001.110209
and inflammatory cells are not typically found in layers that are covered by thick fibrous tissue. Casscells et al5 reported that active plaque eventually expands and ulcerates with consequent enlargement and thickening of the aortic wall. Studies of the natural history of aortic aneurysms have demonstrated that the chance of spontaneous rupture of an aneurysm that could have been repaired surgically is 50% to 70%.6 Patients with thoracic aortic aneurysms (TAAs) and a relatively great amount of aneurysmal atherosclerotic plaque are at increased risk for unfavorable vascular events.7,8 Furthermore, Waltson et al9 found that the degree of inflammatory cell infiltration in aortic aneurysms exceeds the degree expected as a simple response to mechanical irritation of the adventitia. Aneurysms are typically diagnosed by computed tomography (CT) or aortic arteriography. The degree of inflammation in the wall of the aneurysm can be determined in only about 33% of cases even when spiral CT is used, and it cannot be assessed further with more conventional methods.10 Ritchie et al11 used platelet scintig165
166
Takahashi et al Radiolabeled leukocytes in aortic aneurysms
Journal of Nuclear Cardiology March/April 2001
Figure 1. Example of positive scintigram results for accumulation of In-111-oxine–labeled leukocytes in an AAA. Left, Anterior view; right, posterior view.
Figure 2. Example of negative scintigram results for accumulation of In-111-oxine–labeled leukocytes in an AAA. Left, Anterior view; right, posterior view.
raphy to image aortic aneurysms and determined the relationship of the uptake of platelets to the clinical course of the aneurysm. We wanted to identify inflammation of the aortic wall in aneurysms. This study was performed to determine whether the inflammation of aortic aneurysm walls can be imaged with leukocyte scintigraphy. In addition, we compared the scintigraphic evidence of leukocyte uptake with the extent of inflammatory cell infiltration in tissues.
was transferred to a sterile test tube and centrifuged at 450g for 5 minutes to separate the leukocytes from the plasma. Saline solution was added, and the suspension was centrifuged again. The supernatant fluid was discarded, and the sedimented leukocytes were resuspended in previously isolated plasma. Next, 1 mCi of In-111-oxine (Nycomed Amersham Plc, Buckinghamshire, UK) was added to the preparation. After the washed leukocytes were incubated for 15 minutes, additional plasma was added, and the suspension was centrifuged. After the supernatant fluid was decanted, the labeled sedimented leukocytes were resuspended in plasma. The degree of leukocyte labeling was calculated as follows: Cell-associated activity/Total activity × 100%. Patients received infusions of approximately 0.5 mCi labeled leukocytes, and imaging was carried out 48 hours later with a Starcam 3000XCT gamma camera (General Electric, Milwaukee, Wis). Anterior and posterior whole-body views were each acquired for 15 minutes. A medium energy collimator was used to accommodate the energy spectrum of In-111. In some patients, establishing a distinction between the blood pool and the TAA was not possible in the images acquired after 24 hours. In contrast, identification of the structures was possible in the images acquired after 48 hours. The diameter of the aneurysm was measured by CT imaging. The markers of systemic inflammation were analyzed in another blood sample drawn on the day of imaging and included the leukocyte count, the C-reactive protein concentration, and the erythrocyte sedimentation rate (ESR).
METHODS Patient Selection The study included 14 patients (4 women and 10 men) with aortic aneurysms diagnosed by CT. The average age was 66 ± 7 (mean ± SD) years (Table 1). Informed consent was obtained from all patients before participation in the study.
Indium 111-oxine–Labeled Leukocyte Imaging Protocol Mixed leukocyte labeling was performed by use of the method of Thakur et al12 with autologous leukocytes. After 45 mL of venous blood was collected with a heparinized syringe and allowed to stand for 60 minutes, the supernatant
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Radioisotopic Angiography Protocol Radioisotopic angiography was performed with technetium 99m–labeled human serum albumin to determine the location of large blood vessels and to differentiate vertebral, aortic, and cardiac pool activity for each In-111-oxine–labeled leukocyte image.
Histopathologic Examination Protocol Of the 14 patients studied, 8 underwent aortic graft replacement. The walls of the excised aortic aneurysms were examined microscopically after hematoxylin and eosin staining to determine the extent of inflammation. The extent of tissue inflammation was graded as faint, moderate, or severe.
Data Analysis The accumulation of In-111-oxine–labeled leukocytes was determined visually from scintigrams and was graded as negative or positive. The peripheral blood leukocyte count, the C-reactive protein concentration, and the ESR were determined for patients with positive or negative scintigram results and are presented as mean ± SD. A χ2 test was used for statistical analysis. A value of P < .05 was considered significant.
RESULTS Imaging The accumulation of In-111-oxine–labeled leukocytes in the aortic aneurysms was confirmed in 10 patients (Figure 1), 3 with abdominal aortic aneurysms (AAAs) and 7 with TAAs (Figure 2). It was not influenced by sex, location of the aneurysm (Table 1), or diameter of the aneurysm (Table 2, Figure 3). This accumulation could be readily distinguished from surrounding osseous uptake and blood pool activity on the basis of the radioisotopic angiography results. All AAAs extended up to or included the common iliac artery bifurcation. It was possible to separate the activity in the aneurysm from that in the spine by use of the lateral image. Because all TAAs included the aortic arch, they were easily separated visually from the cardiac blood pool and sternal activity. There was a mildly elevated ESR in all patients, but there was no significant difference between patients with positive and negative scintigram results (Table 3). Furthermore, the relationship between the accumulation of In-111-oxine–labeled leukocytes and the degree of periaortic inflammatory adhesion observed at the time of surgery was analyzed to distinguish nonspecific inflammatory reactions in the tissue surrounding the aortic aneurysms from the accumulation of In-111-oxine–labeled leukocytes (Table 1). However, no clear correlation was found.
Figure 3. CT images. AAAs as shown on CT with positive scintigram results (top) and negative scintigram results (bottom).
Histologic Examination The results of the In-111-oxine–labeled leukocyte imaging were positive in 5 of the 8 patients who underwent surgery. Moderate-to-severe infiltration of inflammatory cells and a fibrous cap were present in the walls of the aortic aneurysms of patients with positive scintigram results. Inflammatory cells were present primarily in the adventitia, 1 of the 3 layers of the aortic wall (Figure 4). Only mild inflammatory cell infiltration was present in the layers of the aortic walls in patients with negative scintigram results (Table 1, Figure 5).
DISCUSSION We found that In-111-oxine–labeled leukocyte accumulation in aneurysms was associated with moderate-tosevere inflammatory cell infiltration in specimens resected from patients with aortic aneurysms. In this study we performed In-111-oxine–labeled leukocyte scintigraphy with a mixed-cell labeling method. Various scintigraphic approaches, such as gallium scintigraphy13
168
Takahashi et al Radiolabeled leukocytes in aortic aneurysms
Journal of Nuclear Cardiology March/April 2001
Figure 4. Histopathologic examination of an aortic specimen with positive scintigram results (top). Severe inflammatory cell infiltration is present in the adventitia of the aneurysmal aorta (bottom).
Figure 5. Histopathologic examination of an aortic specimen with negative scintigram results (top). Mild infiltration of inflammatory cells in the wall of the aortic aneurysm is noted (bottom).
and Tc-99m-hexamethylpropylene amine oxine–labeled leukocyte scintigraphy,14 have been used previously to diagnose inflammatory diseases. In-111-oxine–labeled leukocyte scintigraphy can detect persistent inflammation in vivo,15 and recent reports have estimated that the sensitivity of In-111-oxine–labeled leukocyte scintigraphy to detect inflammation is 84% to 96%, which suggests that In-111-oxine–labeled leukocyte scintigraphy may be used to detect vascular inflammatory disease.15 Moreover, the mixed-cell labeling method permits the localization of all inflammatory cells, including monocytes, macrophages, and lymphocytes, in the various layers of chronic inflammatory and atherosclerotic lesions.16 Ross17 characterized atherosclerosis as a slowly progressive chronic inflammatory process. Koch et al18 observed that, in contrast to the wall of a healthy aorta, the wall of an aortic aneurysm contains many areas with significant macrophage and lymphocyte infiltration. These authors also found that, as in general atherosclerosis, various cytokines are involved in the pathogenesis of
aneurysms, which suggests a causal link between aortic aneurysms and atherosclerosis.19 Accordingly, an active inflammatory form of atherosclerosis is likely to be present in aortic aneurysms. The expansion and ulceration of atherosclerotic plaques may result in the progression of an aneurysm,20 making the detection of inflammatory lesions in aneurysms clinically relevant. Inflammation of the aortic aneurysm wall and nonspecific periaortic inflammation may be superimposed on 2-dimensional scintigraphic images. Therefore we examined the relationship between the accumulation of In-111–labeled leukocytes and the degree of adhesion observed intraoperatively between the aortic aneurysm and surrounding tissues. However, no clear relationship was seen. In general, atherosclerosis leads to neointimal formation. Furthermore, the medium is compressed during aneurysm formation17 and is the region most likely to be damaged in dilated lesions such as aneurysms. When aortic medial disruption is severe and extensive as a result of previous endothelial and medial injuries, there is infiltration of inflammatory cells into the adventitia.21
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Table 1. Patient characteristics and imaging
Patient No.
Age (y)
Sex
Image*
Location†
1 2 3 4 5 6 7 8 9 10 11 12 13 14
67 63 72 63 77 64 77 55 57 66 57 76 66 67
M M M M F M M F M M F M F M
Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Negative Negative Negative Negative
AAA AAA TAA TAA TAA TAA AAA TAA TAA TAA AAA TAA TAA TAA
Histopathologic inflammation†
Perianeurysmal adhesion
+++ +++ +++ ++ ++
+ + + + +
+ + +
+ + +
*Positive or negative for accumulation of In-111-oxine–labeled leukocytes. †Classified as follows: +, faint; ++, moderate; and +++, severe.
Table 2. In-111-oxine–labeled leukocyte imaging and diameter of aneurysm (determined by CT)
Imaging results
n
Diameter of aneurysm (cm)
Positive Negative
10 4
5.4 ± 0.9 5.2 ± 0.5
Table 3. In-111-oxine–labeled leukocyte imaging and inflammation reaction
Imaging results
n
White blood cell count (/µL)
C-reactive protein (mg/dL)
ESR (mm/h)
Positive Negative
10 4
6710 ± 1092 6100 ± 529
0.78 ± 0.53 0.81 ± 0.54
39.1 ± 8.0 28.1 ± 8.1
In our study histopathologic analysis in patients with positive scintigram findings confirmed the presence of significant inflammatory cell infiltration into the adventitia of the aortic aneurysm (Figure 4). These observations suggest that the accumulation of indium-oxine–labeled leukocytes identifies active inflammatory lesions. According to a report by Freestone et al,22 the risk of aneurysm rupture increases as the diameter of the aneurysm increases and as the severity of inflammation in the vascular adventitia increases. In addition, preoperative information regarding the severity of inflammation in the walls of aortic aneurysms has been reported to be
an important predictor of treatment outcome and complications.23 Although there were only 14 patients in our study, there was a trend toward a relationship between outcome and histologic findings. We conclude that In111-oxine–labeled leukocyte imaging might be a practical way to assess aortic inflammation noninvasively. References 1. Davis CA, Pearce WH, Haines GK, Shah M, Koch AE. Increased ICAM-1 expression in aortic disease. J Vasc Surg 1993;18:875-80. 2. Yen HC, Lee FY, Chau LY. Analysis of the T cell receptor Vβ repertoire in human aortic aneurysms. Atherosclerosis 1997;135:29-36.
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Takahashi et al Radiolabeled leukocytes in aortic aneurysms
3. Capella JF, Paik DC, Yin NX, Gervasoni JE, Tilson MD. Complement activation and subclassification of tissue immunoglobulin G in the abdominal aortic aneurysm. J Surg Res 1996;65:31-3. 4. Ricci MA, Strindberg G, Slaiby JM, Guibord R, Bergersen LJ, Nichols P, et al. Anti-CD18 monoclonal antibody slows experimental aortic aneurysm expansion. J Vasc Surg 1996;23:301-7. 5. Casscells W, Hathorn B, David M, Krabach T, Vaughn WK, McAllister HA, et al. Thermal detection of cellular infiltrates in living atherosclerotic plaques: possible implications for plaque rupture and thrombosis. Lancet 1996;347:1447-9. 6. Thompson RW. Basic science of abdominal aortic aneurysms: emerging therapeutic strategies for an unresolved clinical problem. Curr Opin Cardiol 1996;11:504-18. 7. Kronzon I, Tunick PA. Atheromatous disease of the thoracic aorta: pathologic and clinical implications. Ann Intern Med 1997;126:629-37. 8. Coen A, Tzourio C, Bertrand B, Chauvel C, Bousser MG, Amarenco P. Aortic plaque morphology and vascular events. Circulation 1997;96: 3838-41. 9. Waltson LJ, Powell JT, Parums DV. Unrestricted usage of immunoglobulin heavy chain genes in B cells infiltrating the wall of atherosclerotic abdominal aortic aneurysms. Atherosclerosis 1997;135:65-71. 10. Errington ML, Ferguson JM, Gillespie IN, Connell HM, Ruckley CV, Wright AR. Complete pre-operative imaging assessment of abdominal aortic aneurysm with spiral CT angiography. Clin Radiol 1997;52:36977. 11. Ritchie JL, Stratton JR, Thiele B, Hamilton GW, Warrick LN, Huang TW, et al. Indium-111 platelet imaging for detection of platelet deposition in abdominal aneurysms and prosthetic arterial grafts. Am J Cardiol 1981;47:882-9. 12. Thakur M, Lavender P, Arnot R. Indium-111-labeled autologous leukocytes in man. J Nucl Med 1997;18:1014-21. 13. Seabold JE, Palestro CJ, Brown ML, Datz FL, Forstrom LA, Greenspan BS, et al. Procedure guideline for gallium scintigraphy in inflammation. Society of Nuclear Medicine. J Nucl Med 1997;38:994-7. 14. Datz FL, Seabold JE, Brown ML, Forstrom LA, Greenspan BS,
Journal of Nuclear Cardiology March/April 2001
15.
16.
17. 18.
19.
20.
21.
22.
23.
McAfee JG, et al. Procedure guideline for technetium-99m-HMPAOlabeled leukocyte scintigraphy for suspected infection/inflammation. J Nucl Med 1997;38:987-90. Seabold JE, Forstrom LA, Schauwecker DS, Brown ML, Datz FL, McAfee JG, et al. Procedure guideline for indium-111-leukocyte scintigraphy for suspected infection/inflammation. J Nucl Med 1997;38:997-1001. Volker W, Dorszewski A, Unruh V, Robenek H, Breithardt G, Buddecke E. Copper-induced inflammatory reactions of rat carotid arteries mimic restenosis/arteriosclerosis-like neointima formation. Atherosclerosis 1997;130:29-36. Ross R. The pathogenesis of atherosclerosis: a perspective for the 1990s. Nature 1993;362:801-9. Koch AE, Haines GK, Rizzo RJ, Radosevich JA, Pope RM, Robinson PG, et al. Human abdominal aortic aneurysms. Immunophenotypic analysis suggesting an immune-mediated response. Am J Pathol 1990;137:1199-213. Koch AE, Kunkel SL, Pearce WH, Shah MR, Parikh D, Evanoff HL, et al. Enhanced production of the chemotactic cytokines interleukin-8 and monocyte chemoattractant protein-1 in human abdominal aortic aneurysms. Am J Pathol 1993;142:1423-31. Montgomery DH, Ververis J, Mcgorisk G, Frohwein S, Martin RP, Taylor WR. Natural history of severe atheromatous disease of the thoracic aorta: a transesophageal echocardiographic study. J Am Coll Cardiol 1996;27:95-101. Freestone T, Turner RJ, Higman DJ, Lever MJ, Powell JT. Influence of hypercholesterolemia and adventitial inflammation on the development of aortic aneurysm in rabbits. Arterioscler Thromb Vasc Biol 1997;17:10-7. Freestone T, Turner RJ, Coady A, Hibman DJ, Greenhalgh RM, Powell JT. Inflammation and matrix metalloproteinases in the enlarging abdominal aortic aneurysm. Arterioscler Thromb Vasc Biol 1995;15: 1145-51. Todd GJ, DeRose JJ. Retroperitoneal approach for repair of inflammatory aortic aneurysms. Ann Vasc Surg 1995;9:525-34.
See related editorial, p 219 Several studies have analyzed the relationship between atherosclerosis and aortic aneurysms.1,2 Although immunologic, genetic, metabolic, and hemodynamic factors have been implicated in the pathogenesis of aortic aneurysms,3,4 the precise mechanism responsible for the development of aneurysms has not been determined. Various layers comprise an atherosclerotic lesion, From the First Department of Internal Medicine,a the Department of Nuclear Medicine,b and the Department of Thoracic and Cardiovascular Surgery,c Hyogo College of Medicine, Nishinomiya, Japan. Received for publication Jan 14, 2000; final revision accepted June 29, 2000. Reprint requests: Keiko Takahashi, MD, First Department of Internal Medicine, Hyogo College of Medicine, 1-1, Mukogawa-cho, Nishinomiya, Hyogo, 663-8501, Japan; [email protected]. Copyright © 2001 by the American Society of Nuclear Cardiology. 1071-3581/2001/$35.00 + 0 43/1/110209 doi:10.1067/mnc.2001.110209
and inflammatory cells are not typically found in layers that are covered by thick fibrous tissue. Casscells et al5 reported that active plaque eventually expands and ulcerates with consequent enlargement and thickening of the aortic wall. Studies of the natural history of aortic aneurysms have demonstrated that the chance of spontaneous rupture of an aneurysm that could have been repaired surgically is 50% to 70%.6 Patients with thoracic aortic aneurysms (TAAs) and a relatively great amount of aneurysmal atherosclerotic plaque are at increased risk for unfavorable vascular events.7,8 Furthermore, Waltson et al9 found that the degree of inflammatory cell infiltration in aortic aneurysms exceeds the degree expected as a simple response to mechanical irritation of the adventitia. Aneurysms are typically diagnosed by computed tomography (CT) or aortic arteriography. The degree of inflammation in the wall of the aneurysm can be determined in only about 33% of cases even when spiral CT is used, and it cannot be assessed further with more conventional methods.10 Ritchie et al11 used platelet scintig165
166
Takahashi et al Radiolabeled leukocytes in aortic aneurysms
Journal of Nuclear Cardiology March/April 2001
Figure 1. Example of positive scintigram results for accumulation of In-111-oxine–labeled leukocytes in an AAA. Left, Anterior view; right, posterior view.
Figure 2. Example of negative scintigram results for accumulation of In-111-oxine–labeled leukocytes in an AAA. Left, Anterior view; right, posterior view.
raphy to image aortic aneurysms and determined the relationship of the uptake of platelets to the clinical course of the aneurysm. We wanted to identify inflammation of the aortic wall in aneurysms. This study was performed to determine whether the inflammation of aortic aneurysm walls can be imaged with leukocyte scintigraphy. In addition, we compared the scintigraphic evidence of leukocyte uptake with the extent of inflammatory cell infiltration in tissues.
was transferred to a sterile test tube and centrifuged at 450g for 5 minutes to separate the leukocytes from the plasma. Saline solution was added, and the suspension was centrifuged again. The supernatant fluid was discarded, and the sedimented leukocytes were resuspended in previously isolated plasma. Next, 1 mCi of In-111-oxine (Nycomed Amersham Plc, Buckinghamshire, UK) was added to the preparation. After the washed leukocytes were incubated for 15 minutes, additional plasma was added, and the suspension was centrifuged. After the supernatant fluid was decanted, the labeled sedimented leukocytes were resuspended in plasma. The degree of leukocyte labeling was calculated as follows: Cell-associated activity/Total activity × 100%. Patients received infusions of approximately 0.5 mCi labeled leukocytes, and imaging was carried out 48 hours later with a Starcam 3000XCT gamma camera (General Electric, Milwaukee, Wis). Anterior and posterior whole-body views were each acquired for 15 minutes. A medium energy collimator was used to accommodate the energy spectrum of In-111. In some patients, establishing a distinction between the blood pool and the TAA was not possible in the images acquired after 24 hours. In contrast, identification of the structures was possible in the images acquired after 48 hours. The diameter of the aneurysm was measured by CT imaging. The markers of systemic inflammation were analyzed in another blood sample drawn on the day of imaging and included the leukocyte count, the C-reactive protein concentration, and the erythrocyte sedimentation rate (ESR).
METHODS Patient Selection The study included 14 patients (4 women and 10 men) with aortic aneurysms diagnosed by CT. The average age was 66 ± 7 (mean ± SD) years (Table 1). Informed consent was obtained from all patients before participation in the study.
Indium 111-oxine–Labeled Leukocyte Imaging Protocol Mixed leukocyte labeling was performed by use of the method of Thakur et al12 with autologous leukocytes. After 45 mL of venous blood was collected with a heparinized syringe and allowed to stand for 60 minutes, the supernatant
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Takahashi et al Radiolabeled leukocytes in aortic aneurysms
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Radioisotopic Angiography Protocol Radioisotopic angiography was performed with technetium 99m–labeled human serum albumin to determine the location of large blood vessels and to differentiate vertebral, aortic, and cardiac pool activity for each In-111-oxine–labeled leukocyte image.
Histopathologic Examination Protocol Of the 14 patients studied, 8 underwent aortic graft replacement. The walls of the excised aortic aneurysms were examined microscopically after hematoxylin and eosin staining to determine the extent of inflammation. The extent of tissue inflammation was graded as faint, moderate, or severe.
Data Analysis The accumulation of In-111-oxine–labeled leukocytes was determined visually from scintigrams and was graded as negative or positive. The peripheral blood leukocyte count, the C-reactive protein concentration, and the ESR were determined for patients with positive or negative scintigram results and are presented as mean ± SD. A χ2 test was used for statistical analysis. A value of P < .05 was considered significant.
RESULTS Imaging The accumulation of In-111-oxine–labeled leukocytes in the aortic aneurysms was confirmed in 10 patients (Figure 1), 3 with abdominal aortic aneurysms (AAAs) and 7 with TAAs (Figure 2). It was not influenced by sex, location of the aneurysm (Table 1), or diameter of the aneurysm (Table 2, Figure 3). This accumulation could be readily distinguished from surrounding osseous uptake and blood pool activity on the basis of the radioisotopic angiography results. All AAAs extended up to or included the common iliac artery bifurcation. It was possible to separate the activity in the aneurysm from that in the spine by use of the lateral image. Because all TAAs included the aortic arch, they were easily separated visually from the cardiac blood pool and sternal activity. There was a mildly elevated ESR in all patients, but there was no significant difference between patients with positive and negative scintigram results (Table 3). Furthermore, the relationship between the accumulation of In-111-oxine–labeled leukocytes and the degree of periaortic inflammatory adhesion observed at the time of surgery was analyzed to distinguish nonspecific inflammatory reactions in the tissue surrounding the aortic aneurysms from the accumulation of In-111-oxine–labeled leukocytes (Table 1). However, no clear correlation was found.
Figure 3. CT images. AAAs as shown on CT with positive scintigram results (top) and negative scintigram results (bottom).
Histologic Examination The results of the In-111-oxine–labeled leukocyte imaging were positive in 5 of the 8 patients who underwent surgery. Moderate-to-severe infiltration of inflammatory cells and a fibrous cap were present in the walls of the aortic aneurysms of patients with positive scintigram results. Inflammatory cells were present primarily in the adventitia, 1 of the 3 layers of the aortic wall (Figure 4). Only mild inflammatory cell infiltration was present in the layers of the aortic walls in patients with negative scintigram results (Table 1, Figure 5).
DISCUSSION We found that In-111-oxine–labeled leukocyte accumulation in aneurysms was associated with moderate-tosevere inflammatory cell infiltration in specimens resected from patients with aortic aneurysms. In this study we performed In-111-oxine–labeled leukocyte scintigraphy with a mixed-cell labeling method. Various scintigraphic approaches, such as gallium scintigraphy13
168
Takahashi et al Radiolabeled leukocytes in aortic aneurysms
Journal of Nuclear Cardiology March/April 2001
Figure 4. Histopathologic examination of an aortic specimen with positive scintigram results (top). Severe inflammatory cell infiltration is present in the adventitia of the aneurysmal aorta (bottom).
Figure 5. Histopathologic examination of an aortic specimen with negative scintigram results (top). Mild infiltration of inflammatory cells in the wall of the aortic aneurysm is noted (bottom).
and Tc-99m-hexamethylpropylene amine oxine–labeled leukocyte scintigraphy,14 have been used previously to diagnose inflammatory diseases. In-111-oxine–labeled leukocyte scintigraphy can detect persistent inflammation in vivo,15 and recent reports have estimated that the sensitivity of In-111-oxine–labeled leukocyte scintigraphy to detect inflammation is 84% to 96%, which suggests that In-111-oxine–labeled leukocyte scintigraphy may be used to detect vascular inflammatory disease.15 Moreover, the mixed-cell labeling method permits the localization of all inflammatory cells, including monocytes, macrophages, and lymphocytes, in the various layers of chronic inflammatory and atherosclerotic lesions.16 Ross17 characterized atherosclerosis as a slowly progressive chronic inflammatory process. Koch et al18 observed that, in contrast to the wall of a healthy aorta, the wall of an aortic aneurysm contains many areas with significant macrophage and lymphocyte infiltration. These authors also found that, as in general atherosclerosis, various cytokines are involved in the pathogenesis of
aneurysms, which suggests a causal link between aortic aneurysms and atherosclerosis.19 Accordingly, an active inflammatory form of atherosclerosis is likely to be present in aortic aneurysms. The expansion and ulceration of atherosclerotic plaques may result in the progression of an aneurysm,20 making the detection of inflammatory lesions in aneurysms clinically relevant. Inflammation of the aortic aneurysm wall and nonspecific periaortic inflammation may be superimposed on 2-dimensional scintigraphic images. Therefore we examined the relationship between the accumulation of In-111–labeled leukocytes and the degree of adhesion observed intraoperatively between the aortic aneurysm and surrounding tissues. However, no clear relationship was seen. In general, atherosclerosis leads to neointimal formation. Furthermore, the medium is compressed during aneurysm formation17 and is the region most likely to be damaged in dilated lesions such as aneurysms. When aortic medial disruption is severe and extensive as a result of previous endothelial and medial injuries, there is infiltration of inflammatory cells into the adventitia.21
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Table 1. Patient characteristics and imaging
Patient No.
Age (y)
Sex
Image*
Location†
1 2 3 4 5 6 7 8 9 10 11 12 13 14
67 63 72 63 77 64 77 55 57 66 57 76 66 67
M M M M F M M F M M F M F M
Positive Positive Positive Positive Positive Positive Positive Positive Positive Positive Negative Negative Negative Negative
AAA AAA TAA TAA TAA TAA AAA TAA TAA TAA AAA TAA TAA TAA
Histopathologic inflammation†
Perianeurysmal adhesion
+++ +++ +++ ++ ++
+ + + + +
+ + +
+ + +
*Positive or negative for accumulation of In-111-oxine–labeled leukocytes. †Classified as follows: +, faint; ++, moderate; and +++, severe.
Table 2. In-111-oxine–labeled leukocyte imaging and diameter of aneurysm (determined by CT)
Imaging results
n
Diameter of aneurysm (cm)
Positive Negative
10 4
5.4 ± 0.9 5.2 ± 0.5
Table 3. In-111-oxine–labeled leukocyte imaging and inflammation reaction
Imaging results
n
White blood cell count (/µL)
C-reactive protein (mg/dL)
ESR (mm/h)
Positive Negative
10 4
6710 ± 1092 6100 ± 529
0.78 ± 0.53 0.81 ± 0.54
39.1 ± 8.0 28.1 ± 8.1
In our study histopathologic analysis in patients with positive scintigram findings confirmed the presence of significant inflammatory cell infiltration into the adventitia of the aortic aneurysm (Figure 4). These observations suggest that the accumulation of indium-oxine–labeled leukocytes identifies active inflammatory lesions. According to a report by Freestone et al,22 the risk of aneurysm rupture increases as the diameter of the aneurysm increases and as the severity of inflammation in the vascular adventitia increases. In addition, preoperative information regarding the severity of inflammation in the walls of aortic aneurysms has been reported to be
an important predictor of treatment outcome and complications.23 Although there were only 14 patients in our study, there was a trend toward a relationship between outcome and histologic findings. We conclude that In111-oxine–labeled leukocyte imaging might be a practical way to assess aortic inflammation noninvasively. References 1. Davis CA, Pearce WH, Haines GK, Shah M, Koch AE. Increased ICAM-1 expression in aortic disease. J Vasc Surg 1993;18:875-80. 2. Yen HC, Lee FY, Chau LY. Analysis of the T cell receptor Vβ repertoire in human aortic aneurysms. Atherosclerosis 1997;135:29-36.
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