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Large solitary lytic skull vault lesions in adults: radiological review with pathological correlation
Journal Pre-proof Large solitary lytic skull vault lesions in adults: radiological review with pathological correlation
Tze Phei Kee, Lishya Liauw, Selvarajan Sathiyamoorthy, Hwei Yee Lee, Grace Siew Lim Tan, Wai Yung Yu PII:
S0899-7071(19)30220-7
DOI:
https://doi.org/10.1016/j.clinimag.2019.10.011
Reference:
JCT 8761
To appear in:
Clinical Imaging
Received date:
15 April 2019
Revised date:
29 September 2019
Accepted date:
17 October 2019
Please cite this article as: T.P. Kee, L. Liauw, S. Sathiyamoorthy, et al., Large solitary lytic skull vault lesions in adults: radiological review with pathological correlation, Clinical Imaging(2019), https://doi.org/10.1016/j.clinimag.2019.10.011
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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.
© 2019 Published by Elsevier.
Journal Pre-proof Title: Large Solitary Lytic Skull Vault Lesions in Adults: Radiological Review with Pathological Correlation Tze Phei Keea, Lishya Liauwa, Selvarajan Sathiyamoorthyb, Hwei Yee Leec, Grace Siew Lim Tana, Wai Yung Yud Department of Diagnostic Radiology, Singapore General Hospital, 169608, Singaporea Department of Anatomical Pathology, Singapore General Hospital, 169608, Singaporeb Department of Pathology, Tan Tock Seng Hospital, 308433, Singaporec Department of Neuroradiology, National Neuroscience Institute, 308433, Singapored
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1st author Given Name: Tze Phei Family Name: Kee
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Email: [email protected] Qualifications: MD, MRCS, FRCR, MMed
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2nd author
Family Name: Liauw
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Email: [email protected]
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Given Name: Selvarajan
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Qualifications: MD, PhD 3rd author
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Given Name: Lishya
Family Name: Sathiyamoorthy
Email: [email protected] Qualifications: MBBS, PGDCP, FRCPath, MCS, FAMS 4th author Given Name: Hwei Yee Family Name: Lee Email: [email protected] Qualifications: MBBS, FRCPath 5th author Given Name: Grace Siew Lim
Journal Pre-proof Family Name: Tan Email: [email protected] Qualifications: MBBS Last author Given Name: Wai Yung Family Name: Yu Email: [email protected] Qualifications: MBBS, FRCR
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Corresponding Author: Tze Phei Kee, MD, Department of Diagnostic Radiology, Singapore General Hospital, Outram Road, 169608, Singapore. Tel: (65) 6222 3322 Fax: 6224 9221 Email: [email protected] 16-digit ORCID – 0000-0002-4595-2801
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Funding: No funding was received for this study.
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Compliance with ethical standards
Conflict of Interest: The authors declare that they have no conflict of interest.
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Ethical approval: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki
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declaration and its later amendments or comparable ethical standards.
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Acknowledgement: N.A.
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Informed consent: For this type of study formal consent is not required.
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Large Solitary Lytic Skull Vault Lesions in Adults: Radiological Review with Pathological Correlation Type of manuscript – Pictorial Essay Introduction The approach to large solitary lytic skull vault lesions in adults is a challenge faced by radiologists. Large lesions can be misinterpreted for their aggressiveness which may lead to inappropriate investigation and treatment. It is therefore important to ascertain the nature of the lesions and narrow the differential diagnoses based on imaging findings. Optimal imaging assessment of skull vault lesions can be achieved using a
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combination of computed tomography (CT) and magnetic resonance imaging (MRI) with diffusion weighted imaging (DWI) [1]. We present cases of large solitary lytic skull vault lesions, and emphasize on the less typical imaging appearance of each cases. In addition, we correlate with pathological findings to achieve better
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understanding of the disease processes that underlie the imaging appearance.
Imaging Approach
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CT is invaluable in the assessment of bony lesions. The pattern of involvement of the bony margins and skull tables [2], [3] reflect their aggressiveness and aid in categorization of the lesions (Algorithm 1). For non-
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aggressive and slow-growing lesions, the bony margins are well-defined and sclerotic, with a narrow zone of transition [2], [4]. For highly-aggressive and rapid-growing lesions, the bony margins tend to be poorly-defined,
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with a wide zone of transition[2], [4], [5]. For the group of lesions of intermediate aggressiveness, the bony
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margins may be well-defined but non-sclerotic [3] (Algorithm 1). Expansion of the skull tables indicates an intradiploic origin, whilst aggressive lesions results in destruction of the skull tables.
Identifying lesions with individual characteristic imaging features, for example, characteristic matrix in osteosarcoma, beveled edges in Langerhans cells histiocytosis and permeative lytic appearance in lymphoma, enables radiologists to narrow the differential diagnoses. In addition, age predilection provides further refinement in the differential diagnoses.
MRI is superior in characterization of the soft tissue component and provides valuable information such as the presence of fat, hemorrhage and flow voids (Table 1). In addition to the conventional T1- and T2-weighted sequences, diffusion-weighted imaging has an increasing role in lesion characterization. Diffusion-weighted
Journal Pre-proof imaging evaluates the degree of water molecules diffusion through tissues. In general, mean apparent diffusion coefficient (ADC) value of malignant skull lesions is lower than that of benign lesions, with ADC cutoff values ranging from 0.7 to 1.10 × 10-3 mm2/s [1], [6], [7]. This can be explained by structural change in malignant tumors, such as enlarged nuclei and hyperchromatism, which lead to reduction in extracellular matrix and restricted diffusion of water molecules [7].
In spite of the categorization, some of the lesions may demonstrate variable aggressiveness with overlapping imaging features. Potential pitfalls for CT imaging include erosion of skull tables in larger benign lesions
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mimicking an aggressive pathology, and ‘sunburst’ matrix in osseous venous malformation and osteosarcoma, leading to diagnostic confusion. There are also potential pitfalls for ADC imaging, in that benign entities such as Langerhans cell histiocytosis and fibro-osseous lesion often demonstrate low ADC values due to high
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cellularity, whilst metastasis as a histologically diverse group of lesions can have a wide range of ADC values
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[6]–[8]. Understanding the similarities and distinguishing features of each pathology therefore play an important
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role in imaging assessment.
Non-aggressive Lesions
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Osseous Venous Malformation
Osseous venous malformation (formerly hemangioma) is a benign vascular bone tumor containing capillaries,
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venous and cavernous vascular channels (Fig. 1C), most commonly occurring in middle-aged females [9], with
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predilection for the frontal and parietal bones [2], [3].
As a slow-growing intradiploic lesion, an osseous venous malformation has well-defined sclerotic margins on CT. It demonstrates expansion of the outer table with relative sparing of the inner table.[2], [4]. It contains trabecular matrix radiating from the center to the periphery of the lesion, resulting in a “honeycomb” or “sunburst” appearance (Fig.1A & B) [2], [10]. However, ‘sunburst’ matrix is also described in osteosarcomas (Fig. 5) making this a potential pitfall. The age of the patient is an important consideration in that osteosarcomas are typically described in young patients, whereas osseous venous malformations occur in middle-aged to older patients.
Journal Pre-proof On MRI, there is mixed hyperintensity (fatty tissue) and hypointensity (iron) on T1-weighted images, with heterogeneous enhancement; hyperintensity on T2-weighted images is due to slow flow or pooling of blood. Variable lesional signal intensity in the presence of hemorrhage depends on the age of blood products [2], [11]. Osseous venous malformations have high ADC values [8].
Fibrous dysplasia Fibrous dysplasia is characterized by replacement of normal cancellous bone with abnormal fibrous tissue
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containing immature woven bone (Fig. 2F). It is most commonly seen in adolescent and young adults [2]. Calvarial involvement is rare, with frontal and temporal bones being most common [12]. Fibrous dysplasia commonly crosses bony sutures without interruption [13].
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Similar to osseous venous malformations, fibrous dysplasia is an intradiploic lesion causing expansion of the
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outer table while conserving the contour of the inner table (Fig. 2A & B) [2], [12]. It tends to show sclerotic margins due to its slow growing nature. Fibrous dysplasia typically demonstrates ground-glass matrix on CT
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(due to woven bone); it can also show a mixed pattern of ground glass, lytic or sclerotic appearance depending
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on the phase [12].
On MRI, low signal intensity on T1 - and T2-weighted images can be seen in ossified or fibrous portions. In the
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active phase, the signal intensity and enhancement is usually heterogeneous depending on the fibrous tissue
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density, intra-lesional cellularity, and hemorrhagic (Fig. 2C) or cystic components [11], [13]. The solid component of fibrous dysplasia has low ADC value (Fig. 2D & E) due to the presence of abundant collagenproducing fibroblastic cells and a dense network of collagen fibers within the extracellular matrix [6]. In our patient the presence of intralesional hemorrhage, in keeping with active phase, along with low ADC value, could mimic an aggressive lesion. The preserved contour of the inner table in our patient points to the diagnosis of a benign lesion.
Epidermoid and Dermoid Epidermoids and dermoids are caused by inclusion of ectodermal remnants within the diploic space. Epidermoids only contain squamous epithelium, while dermoids contain other skin elements such as hair, sebaceous and sweat glands, and squamous epithelium. Epidermoids are commonly found in the third to sixth
Journal Pre-proof decade, while dermoids are commonly seen in childhood [3]. Epidermoids are typically lateral in location, commonly in the temporal and parietal bones whilst dermoids are usually found in the midline or related to sutures [9]–[11]. On CT, both epidermoids and dermoids demonstrate well-defined sclerotic margins due to their slow-growing nature [9]–[11]. On MRI, epidermoids demonstrate hypointense signal on T1-weighted images, hyperintense signal on T2-weighted images, without enhancement[4]. Dermoids demonstrate signal intensity characteristics of lipid material, although some may demonstrate signal heterogeneity in view of complex composition, along with an enhancing thick wall [9]–[11]. Both epidermoids and dermoids demonstrate intermediate or low ADC
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values due to high viscosity [8].
Lesions of Intermediate Aggressiveness
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Intraosseous Meningioma
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Intraosseous meningiomas are a rare subtype of meningioma, comprising about 2% of all meningiomas [14]. Its proposed origin is trapping of arachnoid cells within the cranial sutures in the developing calvarium (either
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developmental or result of trauma) which explains its predisposed site near the sutures [15], [16]. Proliferation of pluripotent embryonal precursor cells in the bone capable of meningothelial differentiation is the other
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postulation of its origin (Fig. 3C) [17].
The age predilection for intra-osseous meningiomas is middle-aged, with near equal gender distribution (in
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contrast to intradural meningioma which shows female predominance) [3]. The majority of intra-osseous
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meningiomas are osteoblastic in nature and the osteolytic subtype is rare [18]. Figure 3A and B demonstrates an osteolytic intraosseous meningioma causing expansion of both the inner and outer skull tables with well-defined, non-sclerotic margins (Fig. 3A & B)[18]. The soft tissue component of intra-osseous meningioma can be iso- to hyper-dense on CT, with avid enhancement [18]. On MRI, the soft tissue component is hypo- to iso-intense on T1-weighted images and iso- or hyper-intense on T2-weighted images with avid enhancement [18], [19]. Calvarial meningiomas have variable ADC values [8], with atypical or malignant subtypes showing lower ADC values compared to the benign subtype [20]. The differential diagnosis for an intra-diploic lesion with thinned and expanded skull tables include osseous venous malformation, Langerhans cells histiocystosis, metastasis and plasmacytoma. Assessing the proximity to sutures, matrix and pattern of skull table involvement will narrow down the differential diagnosis.
Journal Pre-proof Plasmacytoma Plasmacytomas are clonal proliferations of plasma cells that are cytologically and immunophenotypically identical to plasma cell myeloma but manifest as localized disease (Fig. 4C) [21]. Craniocerebral localization is rare and can arise from the skull (intramedullary) or dura (extramedullary) [21]. Parietal bone is the most commonly affected site [21]. Patients who develop plasmacytomas are generally younger than those who develop multiple myeloma [11]. On CT, plasmacytomas cause lytic destruction of the skull tables with well-defined, non-sclerotic margins (Fig. 4B) [3]. The soft tissue component is hyperdense with avid enhancement (Fig. 4A) [22]. On MRI, the soft tissue
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component is hypo- to iso-intense on T1-weighted images and iso- to hyper-intense on T2-weighted images, with solid homogenous enhancement [3], [21]. Flow voids can be found in plasmacytoma, which may lead to confusion with the other hypervascular lesions such as haemangiopericytoma, however, flow voids are usually
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more abundant in the latter [22]. Plasmacytomas often demonstrate low ADC values due to the densely packed
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plasma cells [6].
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Langerhans cell histiocytosis
Langerhans cell histiocytosis (LCH) is a multisystemic disorder characterized by abnormal clonal proliferation
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of Langerhans cells in various tissues (Fig. 5D). LCH is most frequently found in children or young adults, with a slight male dominance [10], [23]. The parietal bone is most frequently affected, followed by the frontal bone
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[23]. LCH can present as multiple lesions in the skull or less commonly as a solitary lesion [23].
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Whilst there is a younger predominance, it has to be considered in older adults, in which the top differential diagnosis is metastasis (Fig. 5). On CT, LCH is an intradiploic lytic lesion with well-defined non-sclerotic margins. It may demonstrate beveled edges (Fig. 5A), and button sequestrum (central remnant intact bone), which helps to differentiate from more aggressive etiologies [10]. On MR, the soft tissue component is hypo- to iso-intense on T1-weighted images and hyperintense on T2-weighted images with marked homogenous contrast enhancement [2], [23]; LCH has low ADC values due to high cellularity (Fig. 5B & C) [8].
Aneurysmal bone cyst An aneurysmal bone cyst (ABC) is a benign bone tumor, composed of numerous blood-filled spaces separated by connective tissue septa, and rarely affects the skull [19]. It can be a primary lesion, which is commonly
Journal Pre-proof encountered in children and adolescence; or a secondary lesion that arises from an underlying pathology (e.g., fibrous dysplasia, chondroblastoma, osteoblastoma and giant cell tumor) [24]. ABCs have an osteolytic appearance on CT causing expansion of the skull tables with well-defined nonsclerotic margins. They are multiloculated with fluid-fluid levels giving the characteristics “soap bubble” appearance, evident on both CT and MRI [19], [25]. The internal septations may enhance [5]. ABCs are reported to have high ADC values [26].
Highly-aggressive Lesions
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Giant cell tumor Giant cell tumors (GCT) are benign tumors of the bone, resulting from over-proliferation of osteoclasts (Fig. 6D). They tend to be locally invasive and aggressive, and have a peak prevalence in the third decade of life.
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Only 2% of these lesions present in the head and neck, with the most common sites being the sphenoid and
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temporal bones [5].
On CT, GCTs cause lytic expansion of the skull tables with poorly defined margins (Fig. 6B) and heterogeneous
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soft tissue components (Fig. 6A) [5]. On MRI, the soft tissue is hypo- to iso-intense on T1-weighted imaging and markedly hypointense on T2-weighted imaging due to hemosiderin deposition or fracture (Fig. 6C), with
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heterogeneous contrast enhancement [5], [27] and ADC values of approximately 1.21 × 10-3 mm2/s [6]. GCTs
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Lymphoma
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may coexist with ABCs in 14-39% of cases [5].
Osseous lymphoma is commonly due to non-Hodgkin lymphoma. Primary osseous lymphoma has predilection in the appendicular skeleton whilst secondary osseous lymphoma preferentially affects the axial skeleton. Primary lymphoma of the skull vault is extremely rare [28]. Radiographic features of osseous lymphoma are variable, with permeative lytic destruction being the most common appearance [28]. It has been suggested that lymphoma cells infiltrate the spaces within the diploe and extend along the emissary veins to infiltrate the soft tissues on either side of the bone causing the permeative lytic appearance on CT (Fig. 7A) [29]. We include a case of secondary osseous lymphoma affecting the skull vault. The soft tissue component is homogeneously iso- to hyper-dense on CT (Fig. 7B) [29], [30]. On MRI, the soft tissue is hypo- to iso-intense on T1-weighted imaging and iso- to hyper-intense on T2-weighted imaging with homogeneous enhancement and low ADC values due to hypercellularity [8], [29], [30].
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Metastasis Metastasis is the commonest cause of a lytic calvarial lesion in older adults [3]. Although frequently multiple, calvarial metastasis has to be considered in a solitary calvarial lesion. Single and expanded lytic calvarial metastasis commonly arises from a thyroid or renal primary [19]. On CT, there is lytic destruction of the skull tables, with poorly-defined margins due to the aggressive nature (Fig. 8B). The soft tissue component has variable density and enhancement, and is often heterogeneous (Fig. 8A) [12]–[14]. On MRI, the soft tissue is hypointense on T1-weighted images (replacing the normal T1W
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hyperintense bone marrow) and hyperintense on T2-weighted images, with avid heterogeneous contrast enhancement [12]–[14]. There is a wide range of ADC values for calvarial metastasis depending on primary histology, with the majority of them showing restricted diffusion [8], [20]. However, there is absence of
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restricted diffusion in our case of a calvarial metastasis (Fig. 8C), which is attributed to the abundance of colloid
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(Fig. 8D).
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Osteosarcoma
Osteosarcoma is a malignant mesenchymal neoplasm in which the tumor cells directly produce osteoid or
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immature bone (Fig. 9B). Calvarial osteosarcoma is rare, occur predominantly in the third and fourth decades of life, as opposed to osteosarcoma in the extremities in which the age predilection is in adolescence [10], [32].
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On CT, osteosarcoma causes lytic destruction of the skull tables with poorly-defined margins. It contains
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variable amount of osteoid mineralization with a “sunburst” appearance (Fig. 9A), which is also seen in osseous venous malformation. The bony margins is a differentiating feature in that osteosarcomas tend to have illdefined margins while osseous venous malformations have well-defined sclerotic margins. [10], [32], [33]. On MRI, the soft tissue component is hypo- to iso-intense on T1-weighted images and heterogeneous on T2weighted images, with marked heterogeneous contrast enhancement [3], [32], [33]. It demonstrates variable ADC values [6], with high ADC values seen in the chondroblastic subtype of osteosarcoma [26] and in the presence of necrotic content [34].
Hemangiopericytoma Intracranial hemangiopericytoma is a neoplasm that arises from the pericytes originating in the meninges (Fig. 10D). Hemangiopericytoma is a dural-based hypervascular mass that is frequently associated with focal
Journal Pre-proof calvarial destruction and may mimic an aggressive primary calvarial lesion. It is most commonly located along the falx, tentorium, or dural sinuses. On CT, hemangiopericytoma can cause lytic destruction of the skull tables, with poorly defined margins (Fig. 10B). The extra-axial soft tissue component is hyperdense with avid enhancement (Fig. 10A) [2], [35].On MRI, the soft tissue demonstrates iso- to slightly hyper-intense on T1-weighted and T2-weighted imaging, heterogeneous avid enhancement and foci of central necrosis [35]. Prominent internal flow voids on T2weighted images is a typical feature (Fig. 10C) [2], [35]. Hemangiopericytoma has low ADC values due to
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hypercellularity and dense interstitium [36].
CONCLUSION
There is a wide range of differential diagnoses for large solitary lytic calvarial lesions in adults, with variable
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aggressiveness and overlapping features. Assessing the pattern of bony involvement on CT, focusing on the
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bony margins and skull table involvement, as illustrated in our algorithm, aids in assessment of aggressiveness. When there are overlapping features, knowledge of the distinguishing features of the various bony lesions
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narrows the differential diagnoses. MRI with DWI is superior in characterization of the soft tissue component and lesion cellularity. Correlating the imaging manifestations with pathological features enables radiologists to
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Figure Legends Figure 1A – C. Osseous venous malformation in a 92-year-old female.
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A,B. CT bone (A) and soft tissue (B) windows demonstrate a well-defined expansile lytic lesion with sclerotic margin, containing radiating trabecular matrix of “sunburst” appearance . Intra-operatively, there are lakes of
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blood spaces noted within the tumor. The tumor is adherent to the dura.
C. Photomicrographic section: The lesion is composed of numerous dilated vascular spaces engorged with
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blood (black arrow), interspersed among the branching trabeculae of the cortical bone (open arrow).
Figure 2A – F. Fibrous dysplasia in a 43-year-old male.
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A,B. CT (A) bone and (B) soft tissue windows demonstrate diploic expansion with bowing of the outer skull table and relative preserved contour of the inner table. The margins are well-defined and part-sclerotic.
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C – E. The central hyperdense component seen on CT (B, arrow) corresponds to the susceptibility focus on
(D,E).
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gradient echo sequence (C, arrow) consistent with hematoma. The lesion demonstrates restricted diffusion
F. Photomicrographic section shows irregular curvilinear trabeculae of woven bone (arrows) and fibrous tissue (asterisks) consistent with a fibro-osseous lesion.
Figure 3A & B. Intraosseous meningioma in a 61-year-old male. A,B. CT (A) bone and (B) soft tissue windows demonstrate an expansile intradiploic osteolytic isodense mass centered at the coronal suture, with thinning and disruption of the inner and outer skull tables. The lesion demonstrates well-defined non-sclerotic margins. The soft tissue is isodense on CT and a greyish soft tumor involving the dura with both intra- and extra-dural components was evident intraoperatively.
Journal Pre-proof C. Photomicrographic section: The tumor is composed of spindle to polygonal meningothelial-like cells (arrows). Tumor infiltrates the bony trabeculae (asterisk).
Figure 4A – C. Plasmacytoma in a 30-year-old female. A,B. CT (A) soft tissue and (B) bone windows demonstrate a large homogeneously enhancing mass centered in the left parietal bone causing lytic destruction of the inner and outer skull tables with well-defined nonsclerotic margins. A very vascular tumor is noted intraoperatively, eroding through the outer table and adherent to dura.
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C. Photomicrographic section demonstrates sheets of malignant plasma cells (long arrow) with dural tissue
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(short arrow) and bony spicule (open arrow).
Figure 5A – D. Langerhans cell histiocytosis in a 67-year-old female.
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A – C. MRI brain demonstrates a lesion centered in right temporal bone, (A) isointense on T1-weighted image
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and mildly hyperintense on T2-weighted image with avid enhancement (not shown), and (B,C) restricted diffusion. Note is made of unequal involvement of the inner and outer skull tables (beveled edges).
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D. Photomicrographic section reveals lesional Langerhans cells with oval indented and grooved nuclei and eosinophilic cytoplasm (long arrows). Large numbers of eosinophils (short arrows) are present among the
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Langerhans cells. The Langerhans cells are diffusely positive for S100 protein and CD1a (not shown).
Figure 6A – D. Giant cell tumor in a 26-year-old female. A,B. CT brain soft tissue (A) and bone windows (B) demonstrate a large expansile iso- to hyper-dense soft tissue with internal cystic component centered in the left temporal bone. There is severe thinning and disruption of the skull tables, with poorly-defined margins. C. The lesion shows markedly low signal on T2-weighted images with corresponding blooming of GRE (not shown) and internal fluid components. Intra-operatively, a large extradural tumor with bone erosion of the squamous temporal bone, zygomatic arch and glenoid fossa is noted with dural attachment. D. Photomicrographic section: The tumor is composed of sheets of osteoclastic type multinucleate cells (black arrows) and stromal mononuclear cells (red arrows), with features of fracture within the lesion including reactive woven bone formation.
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Figure 7A & B. Diffuse large B-cell lymphoma in a 46-year-old male (histologically proven on peritoneal nodule). CT (A) bone and (B) soft tissue windows demonstrate large hyperdense mass centered in the right frontoparietal bone with permeative lytic calvarial destruction.
Figure 8A – D. Metastatic follicular thyroid carcinoma in a 44-year-old male. A,B. CT (A) soft tissue and (B) bone windows demonstrate soft tissue mass of heterogenous density with poorly-defined lytic destruction of the left parietal bone.
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C. No corresponding restricted diffusion as shown on ADC due to abundance of colloid as confirmed on histology. A vascular tumor with scalp infiltration, bone erosion and dural attachment is noted intraoperatively.
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D. Photomicrographic section: The tumor is composed of destroyed bony trabeculae and numerous follicles
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containing colloid (arrows).
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Figure 9A & B. Conventional osteoblastic osteosarcoma in a 31-year-old male. A. CT soft tissue window shows an isodense mass centered in the right fronto-temporal bone with poorly-
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defined lytic calvarial destruction and central spiculated osteoid mineralization of sunburst pattern. B. Photomicrographic section reveals cellular proliferation of malignant-looking epithelioid to spindle tumor
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cells with enlarged, pleomorphic nuclei and high nuclear cytoplasmic ratios. The tumor cells are surrounded by
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disorganized trabeculae of neoplastic woven bone producing a coarse lace-like pattern (arrows).
Figure 10A – D. Hemangiopericytoma in a 72-year-old female. A,B. CT brain (A) soft tissue and (B) bone windows demonstrate a large well-circumscribed avidly enhancing tumor with poorly-defined calvarial destruction. Note the presence of a left retrobulbar intraconal mass which is well-circumscribed with avid enhancement. C. MRI brain reveals a predominantly isointense mass on T1- (not shown) and T2-weighted images with presence of flow voids (arrows). Pre-operative embolization of the supplying arteries followed by tumor excision. Intra-operatively, the tumor is very vascular with muscle invasion and bone erosion. D. Photomicrographic section demonstrates patternless sheets of tumor cells with mitosis (arrow).
Journal Pre-proof Algorithm 1. CT Imaging Approach to Large Solitary Lytic Skull Vault Lesions in Adults.
Table 1: A Summary of MR Imaging Characteristics of the Pathology for Large Solitary Lytic Skull Vault Lesions in Adults. Pathology
MRI T2-weighted
Contrast enhancement
ADC value
Osseous Venous Malformation
Mixed foci of hypoand hyper-intensity
Hyperintense
Avid heterogenous
High
Fibrous Dysplasia
Variable (depends on phases)
Variable (depends on phases)
Variable
Low
Epidermoid
Hypointense
Hyperintense
None
Low
Dermoid
Hyperintense
Hyperintense
Low
Meningioma
Hypo- to iso-intense
Iso- to hyper-intense
Variable
Plasmacytoma
Hypo- to iso-intense
Langerhans cell histiocytosis Aneurysmal bone cyst
Hypo- to iso-intense
Iso-to hyper-intense +/- flow voids Hyperintense
Thick enhancing wall Avid homogenous Avid homogenous Avid homogenous
Low
Low
High
Heterogenous
Variable
Lymphoma
Hypo- to iso-intense
Iso- to hyper-intense
Avid homogenous
Low
Metastasis
Hypointense
Hyperintense
Variable
Hypo- to iso-intense
Heterogenous
Avid heterogenous Avid heterogenous Avid heterogenous
Iso- to slightly hyperintense
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Hemangiopericytoma
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Osteosarcoma
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Mixed hypo- and hyper-intense, fluidfluid levels Hypointense
Internal septations may enhance
Giant cell tumor
Mixed hypo- and hyper-intense components Hypo- to iso-intense
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T1-weighted
Iso- to slightly hyperintense +/- flow voids
Variable Low
Journal Pre-proof Highlights
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Evaluation of solitary lytic skull vault lesion using a CT diagnostic algorithm is discussed. The utility of MRI with DWI aids in characterization of the soft tissue component. Imaging correlation with pathological features improves understanding of the disease processes.
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Tze Phei Kee, Lishya Liauw, Selvarajan Sathiyamoorthy, Hwei Yee Lee, Grace Siew Lim Tan, Wai Yung Yu PII:
S0899-7071(19)30220-7
DOI:
https://doi.org/10.1016/j.clinimag.2019.10.011
Reference:
JCT 8761
To appear in:
Clinical Imaging
Received date:
15 April 2019
Revised date:
29 September 2019
Accepted date:
17 October 2019
Please cite this article as: T.P. Kee, L. Liauw, S. Sathiyamoorthy, et al., Large solitary lytic skull vault lesions in adults: radiological review with pathological correlation, Clinical Imaging(2019), https://doi.org/10.1016/j.clinimag.2019.10.011
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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.
© 2019 Published by Elsevier.
Journal Pre-proof Title: Large Solitary Lytic Skull Vault Lesions in Adults: Radiological Review with Pathological Correlation Tze Phei Keea, Lishya Liauwa, Selvarajan Sathiyamoorthyb, Hwei Yee Leec, Grace Siew Lim Tana, Wai Yung Yud Department of Diagnostic Radiology, Singapore General Hospital, 169608, Singaporea Department of Anatomical Pathology, Singapore General Hospital, 169608, Singaporeb Department of Pathology, Tan Tock Seng Hospital, 308433, Singaporec Department of Neuroradiology, National Neuroscience Institute, 308433, Singapored
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1st author Given Name: Tze Phei Family Name: Kee
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Email: [email protected] Qualifications: MD, MRCS, FRCR, MMed
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2nd author
Family Name: Liauw
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Email: [email protected]
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Given Name: Selvarajan
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Qualifications: MD, PhD 3rd author
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Given Name: Lishya
Family Name: Sathiyamoorthy
Email: [email protected] Qualifications: MBBS, PGDCP, FRCPath, MCS, FAMS 4th author Given Name: Hwei Yee Family Name: Lee Email: [email protected] Qualifications: MBBS, FRCPath 5th author Given Name: Grace Siew Lim
Journal Pre-proof Family Name: Tan Email: [email protected] Qualifications: MBBS Last author Given Name: Wai Yung Family Name: Yu Email: [email protected] Qualifications: MBBS, FRCR
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Corresponding Author: Tze Phei Kee, MD, Department of Diagnostic Radiology, Singapore General Hospital, Outram Road, 169608, Singapore. Tel: (65) 6222 3322 Fax: 6224 9221 Email: [email protected] 16-digit ORCID – 0000-0002-4595-2801
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Funding: No funding was received for this study.
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Compliance with ethical standards
Conflict of Interest: The authors declare that they have no conflict of interest.
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Ethical approval: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki
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declaration and its later amendments or comparable ethical standards.
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Acknowledgement: N.A.
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Informed consent: For this type of study formal consent is not required.
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Large Solitary Lytic Skull Vault Lesions in Adults: Radiological Review with Pathological Correlation Type of manuscript – Pictorial Essay Introduction The approach to large solitary lytic skull vault lesions in adults is a challenge faced by radiologists. Large lesions can be misinterpreted for their aggressiveness which may lead to inappropriate investigation and treatment. It is therefore important to ascertain the nature of the lesions and narrow the differential diagnoses based on imaging findings. Optimal imaging assessment of skull vault lesions can be achieved using a
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combination of computed tomography (CT) and magnetic resonance imaging (MRI) with diffusion weighted imaging (DWI) [1]. We present cases of large solitary lytic skull vault lesions, and emphasize on the less typical imaging appearance of each cases. In addition, we correlate with pathological findings to achieve better
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understanding of the disease processes that underlie the imaging appearance.
Imaging Approach
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CT is invaluable in the assessment of bony lesions. The pattern of involvement of the bony margins and skull tables [2], [3] reflect their aggressiveness and aid in categorization of the lesions (Algorithm 1). For non-
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aggressive and slow-growing lesions, the bony margins are well-defined and sclerotic, with a narrow zone of transition [2], [4]. For highly-aggressive and rapid-growing lesions, the bony margins tend to be poorly-defined,
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with a wide zone of transition[2], [4], [5]. For the group of lesions of intermediate aggressiveness, the bony
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margins may be well-defined but non-sclerotic [3] (Algorithm 1). Expansion of the skull tables indicates an intradiploic origin, whilst aggressive lesions results in destruction of the skull tables.
Identifying lesions with individual characteristic imaging features, for example, characteristic matrix in osteosarcoma, beveled edges in Langerhans cells histiocytosis and permeative lytic appearance in lymphoma, enables radiologists to narrow the differential diagnoses. In addition, age predilection provides further refinement in the differential diagnoses.
MRI is superior in characterization of the soft tissue component and provides valuable information such as the presence of fat, hemorrhage and flow voids (Table 1). In addition to the conventional T1- and T2-weighted sequences, diffusion-weighted imaging has an increasing role in lesion characterization. Diffusion-weighted
Journal Pre-proof imaging evaluates the degree of water molecules diffusion through tissues. In general, mean apparent diffusion coefficient (ADC) value of malignant skull lesions is lower than that of benign lesions, with ADC cutoff values ranging from 0.7 to 1.10 × 10-3 mm2/s [1], [6], [7]. This can be explained by structural change in malignant tumors, such as enlarged nuclei and hyperchromatism, which lead to reduction in extracellular matrix and restricted diffusion of water molecules [7].
In spite of the categorization, some of the lesions may demonstrate variable aggressiveness with overlapping imaging features. Potential pitfalls for CT imaging include erosion of skull tables in larger benign lesions
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mimicking an aggressive pathology, and ‘sunburst’ matrix in osseous venous malformation and osteosarcoma, leading to diagnostic confusion. There are also potential pitfalls for ADC imaging, in that benign entities such as Langerhans cell histiocytosis and fibro-osseous lesion often demonstrate low ADC values due to high
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cellularity, whilst metastasis as a histologically diverse group of lesions can have a wide range of ADC values
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[6]–[8]. Understanding the similarities and distinguishing features of each pathology therefore play an important
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role in imaging assessment.
Non-aggressive Lesions
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Osseous Venous Malformation
Osseous venous malformation (formerly hemangioma) is a benign vascular bone tumor containing capillaries,
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venous and cavernous vascular channels (Fig. 1C), most commonly occurring in middle-aged females [9], with
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predilection for the frontal and parietal bones [2], [3].
As a slow-growing intradiploic lesion, an osseous venous malformation has well-defined sclerotic margins on CT. It demonstrates expansion of the outer table with relative sparing of the inner table.[2], [4]. It contains trabecular matrix radiating from the center to the periphery of the lesion, resulting in a “honeycomb” or “sunburst” appearance (Fig.1A & B) [2], [10]. However, ‘sunburst’ matrix is also described in osteosarcomas (Fig. 5) making this a potential pitfall. The age of the patient is an important consideration in that osteosarcomas are typically described in young patients, whereas osseous venous malformations occur in middle-aged to older patients.
Journal Pre-proof On MRI, there is mixed hyperintensity (fatty tissue) and hypointensity (iron) on T1-weighted images, with heterogeneous enhancement; hyperintensity on T2-weighted images is due to slow flow or pooling of blood. Variable lesional signal intensity in the presence of hemorrhage depends on the age of blood products [2], [11]. Osseous venous malformations have high ADC values [8].
Fibrous dysplasia Fibrous dysplasia is characterized by replacement of normal cancellous bone with abnormal fibrous tissue
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containing immature woven bone (Fig. 2F). It is most commonly seen in adolescent and young adults [2]. Calvarial involvement is rare, with frontal and temporal bones being most common [12]. Fibrous dysplasia commonly crosses bony sutures without interruption [13].
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Similar to osseous venous malformations, fibrous dysplasia is an intradiploic lesion causing expansion of the
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outer table while conserving the contour of the inner table (Fig. 2A & B) [2], [12]. It tends to show sclerotic margins due to its slow growing nature. Fibrous dysplasia typically demonstrates ground-glass matrix on CT
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(due to woven bone); it can also show a mixed pattern of ground glass, lytic or sclerotic appearance depending
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on the phase [12].
On MRI, low signal intensity on T1 - and T2-weighted images can be seen in ossified or fibrous portions. In the
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active phase, the signal intensity and enhancement is usually heterogeneous depending on the fibrous tissue
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density, intra-lesional cellularity, and hemorrhagic (Fig. 2C) or cystic components [11], [13]. The solid component of fibrous dysplasia has low ADC value (Fig. 2D & E) due to the presence of abundant collagenproducing fibroblastic cells and a dense network of collagen fibers within the extracellular matrix [6]. In our patient the presence of intralesional hemorrhage, in keeping with active phase, along with low ADC value, could mimic an aggressive lesion. The preserved contour of the inner table in our patient points to the diagnosis of a benign lesion.
Epidermoid and Dermoid Epidermoids and dermoids are caused by inclusion of ectodermal remnants within the diploic space. Epidermoids only contain squamous epithelium, while dermoids contain other skin elements such as hair, sebaceous and sweat glands, and squamous epithelium. Epidermoids are commonly found in the third to sixth
Journal Pre-proof decade, while dermoids are commonly seen in childhood [3]. Epidermoids are typically lateral in location, commonly in the temporal and parietal bones whilst dermoids are usually found in the midline or related to sutures [9]–[11]. On CT, both epidermoids and dermoids demonstrate well-defined sclerotic margins due to their slow-growing nature [9]–[11]. On MRI, epidermoids demonstrate hypointense signal on T1-weighted images, hyperintense signal on T2-weighted images, without enhancement[4]. Dermoids demonstrate signal intensity characteristics of lipid material, although some may demonstrate signal heterogeneity in view of complex composition, along with an enhancing thick wall [9]–[11]. Both epidermoids and dermoids demonstrate intermediate or low ADC
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values due to high viscosity [8].
Lesions of Intermediate Aggressiveness
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Intraosseous Meningioma
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Intraosseous meningiomas are a rare subtype of meningioma, comprising about 2% of all meningiomas [14]. Its proposed origin is trapping of arachnoid cells within the cranial sutures in the developing calvarium (either
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developmental or result of trauma) which explains its predisposed site near the sutures [15], [16]. Proliferation of pluripotent embryonal precursor cells in the bone capable of meningothelial differentiation is the other
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postulation of its origin (Fig. 3C) [17].
The age predilection for intra-osseous meningiomas is middle-aged, with near equal gender distribution (in
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contrast to intradural meningioma which shows female predominance) [3]. The majority of intra-osseous
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meningiomas are osteoblastic in nature and the osteolytic subtype is rare [18]. Figure 3A and B demonstrates an osteolytic intraosseous meningioma causing expansion of both the inner and outer skull tables with well-defined, non-sclerotic margins (Fig. 3A & B)[18]. The soft tissue component of intra-osseous meningioma can be iso- to hyper-dense on CT, with avid enhancement [18]. On MRI, the soft tissue component is hypo- to iso-intense on T1-weighted images and iso- or hyper-intense on T2-weighted images with avid enhancement [18], [19]. Calvarial meningiomas have variable ADC values [8], with atypical or malignant subtypes showing lower ADC values compared to the benign subtype [20]. The differential diagnosis for an intra-diploic lesion with thinned and expanded skull tables include osseous venous malformation, Langerhans cells histiocystosis, metastasis and plasmacytoma. Assessing the proximity to sutures, matrix and pattern of skull table involvement will narrow down the differential diagnosis.
Journal Pre-proof Plasmacytoma Plasmacytomas are clonal proliferations of plasma cells that are cytologically and immunophenotypically identical to plasma cell myeloma but manifest as localized disease (Fig. 4C) [21]. Craniocerebral localization is rare and can arise from the skull (intramedullary) or dura (extramedullary) [21]. Parietal bone is the most commonly affected site [21]. Patients who develop plasmacytomas are generally younger than those who develop multiple myeloma [11]. On CT, plasmacytomas cause lytic destruction of the skull tables with well-defined, non-sclerotic margins (Fig. 4B) [3]. The soft tissue component is hyperdense with avid enhancement (Fig. 4A) [22]. On MRI, the soft tissue
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component is hypo- to iso-intense on T1-weighted images and iso- to hyper-intense on T2-weighted images, with solid homogenous enhancement [3], [21]. Flow voids can be found in plasmacytoma, which may lead to confusion with the other hypervascular lesions such as haemangiopericytoma, however, flow voids are usually
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more abundant in the latter [22]. Plasmacytomas often demonstrate low ADC values due to the densely packed
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plasma cells [6].
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Langerhans cell histiocytosis
Langerhans cell histiocytosis (LCH) is a multisystemic disorder characterized by abnormal clonal proliferation
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of Langerhans cells in various tissues (Fig. 5D). LCH is most frequently found in children or young adults, with a slight male dominance [10], [23]. The parietal bone is most frequently affected, followed by the frontal bone
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[23]. LCH can present as multiple lesions in the skull or less commonly as a solitary lesion [23].
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Whilst there is a younger predominance, it has to be considered in older adults, in which the top differential diagnosis is metastasis (Fig. 5). On CT, LCH is an intradiploic lytic lesion with well-defined non-sclerotic margins. It may demonstrate beveled edges (Fig. 5A), and button sequestrum (central remnant intact bone), which helps to differentiate from more aggressive etiologies [10]. On MR, the soft tissue component is hypo- to iso-intense on T1-weighted images and hyperintense on T2-weighted images with marked homogenous contrast enhancement [2], [23]; LCH has low ADC values due to high cellularity (Fig. 5B & C) [8].
Aneurysmal bone cyst An aneurysmal bone cyst (ABC) is a benign bone tumor, composed of numerous blood-filled spaces separated by connective tissue septa, and rarely affects the skull [19]. It can be a primary lesion, which is commonly
Journal Pre-proof encountered in children and adolescence; or a secondary lesion that arises from an underlying pathology (e.g., fibrous dysplasia, chondroblastoma, osteoblastoma and giant cell tumor) [24]. ABCs have an osteolytic appearance on CT causing expansion of the skull tables with well-defined nonsclerotic margins. They are multiloculated with fluid-fluid levels giving the characteristics “soap bubble” appearance, evident on both CT and MRI [19], [25]. The internal septations may enhance [5]. ABCs are reported to have high ADC values [26].
Highly-aggressive Lesions
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Giant cell tumor Giant cell tumors (GCT) are benign tumors of the bone, resulting from over-proliferation of osteoclasts (Fig. 6D). They tend to be locally invasive and aggressive, and have a peak prevalence in the third decade of life.
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Only 2% of these lesions present in the head and neck, with the most common sites being the sphenoid and
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temporal bones [5].
On CT, GCTs cause lytic expansion of the skull tables with poorly defined margins (Fig. 6B) and heterogeneous
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soft tissue components (Fig. 6A) [5]. On MRI, the soft tissue is hypo- to iso-intense on T1-weighted imaging and markedly hypointense on T2-weighted imaging due to hemosiderin deposition or fracture (Fig. 6C), with
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heterogeneous contrast enhancement [5], [27] and ADC values of approximately 1.21 × 10-3 mm2/s [6]. GCTs
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Lymphoma
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may coexist with ABCs in 14-39% of cases [5].
Osseous lymphoma is commonly due to non-Hodgkin lymphoma. Primary osseous lymphoma has predilection in the appendicular skeleton whilst secondary osseous lymphoma preferentially affects the axial skeleton. Primary lymphoma of the skull vault is extremely rare [28]. Radiographic features of osseous lymphoma are variable, with permeative lytic destruction being the most common appearance [28]. It has been suggested that lymphoma cells infiltrate the spaces within the diploe and extend along the emissary veins to infiltrate the soft tissues on either side of the bone causing the permeative lytic appearance on CT (Fig. 7A) [29]. We include a case of secondary osseous lymphoma affecting the skull vault. The soft tissue component is homogeneously iso- to hyper-dense on CT (Fig. 7B) [29], [30]. On MRI, the soft tissue is hypo- to iso-intense on T1-weighted imaging and iso- to hyper-intense on T2-weighted imaging with homogeneous enhancement and low ADC values due to hypercellularity [8], [29], [30].
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Metastasis Metastasis is the commonest cause of a lytic calvarial lesion in older adults [3]. Although frequently multiple, calvarial metastasis has to be considered in a solitary calvarial lesion. Single and expanded lytic calvarial metastasis commonly arises from a thyroid or renal primary [19]. On CT, there is lytic destruction of the skull tables, with poorly-defined margins due to the aggressive nature (Fig. 8B). The soft tissue component has variable density and enhancement, and is often heterogeneous (Fig. 8A) [12]–[14]. On MRI, the soft tissue is hypointense on T1-weighted images (replacing the normal T1W
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hyperintense bone marrow) and hyperintense on T2-weighted images, with avid heterogeneous contrast enhancement [12]–[14]. There is a wide range of ADC values for calvarial metastasis depending on primary histology, with the majority of them showing restricted diffusion [8], [20]. However, there is absence of
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restricted diffusion in our case of a calvarial metastasis (Fig. 8C), which is attributed to the abundance of colloid
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(Fig. 8D).
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Osteosarcoma
Osteosarcoma is a malignant mesenchymal neoplasm in which the tumor cells directly produce osteoid or
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immature bone (Fig. 9B). Calvarial osteosarcoma is rare, occur predominantly in the third and fourth decades of life, as opposed to osteosarcoma in the extremities in which the age predilection is in adolescence [10], [32].
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On CT, osteosarcoma causes lytic destruction of the skull tables with poorly-defined margins. It contains
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variable amount of osteoid mineralization with a “sunburst” appearance (Fig. 9A), which is also seen in osseous venous malformation. The bony margins is a differentiating feature in that osteosarcomas tend to have illdefined margins while osseous venous malformations have well-defined sclerotic margins. [10], [32], [33]. On MRI, the soft tissue component is hypo- to iso-intense on T1-weighted images and heterogeneous on T2weighted images, with marked heterogeneous contrast enhancement [3], [32], [33]. It demonstrates variable ADC values [6], with high ADC values seen in the chondroblastic subtype of osteosarcoma [26] and in the presence of necrotic content [34].
Hemangiopericytoma Intracranial hemangiopericytoma is a neoplasm that arises from the pericytes originating in the meninges (Fig. 10D). Hemangiopericytoma is a dural-based hypervascular mass that is frequently associated with focal
Journal Pre-proof calvarial destruction and may mimic an aggressive primary calvarial lesion. It is most commonly located along the falx, tentorium, or dural sinuses. On CT, hemangiopericytoma can cause lytic destruction of the skull tables, with poorly defined margins (Fig. 10B). The extra-axial soft tissue component is hyperdense with avid enhancement (Fig. 10A) [2], [35].On MRI, the soft tissue demonstrates iso- to slightly hyper-intense on T1-weighted and T2-weighted imaging, heterogeneous avid enhancement and foci of central necrosis [35]. Prominent internal flow voids on T2weighted images is a typical feature (Fig. 10C) [2], [35]. Hemangiopericytoma has low ADC values due to
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hypercellularity and dense interstitium [36].
CONCLUSION
There is a wide range of differential diagnoses for large solitary lytic calvarial lesions in adults, with variable
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aggressiveness and overlapping features. Assessing the pattern of bony involvement on CT, focusing on the
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bony margins and skull table involvement, as illustrated in our algorithm, aids in assessment of aggressiveness. When there are overlapping features, knowledge of the distinguishing features of the various bony lesions
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narrows the differential diagnoses. MRI with DWI is superior in characterization of the soft tissue component and lesion cellularity. Correlating the imaging manifestations with pathological features enables radiologists to
Z. Tu, Z. Xiao, Y. Zheng, and H. Huang, “Benign and malignant skull-involved lesions : discriminative
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Figure Legends Figure 1A – C. Osseous venous malformation in a 92-year-old female.
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A,B. CT bone (A) and soft tissue (B) windows demonstrate a well-defined expansile lytic lesion with sclerotic margin, containing radiating trabecular matrix of “sunburst” appearance . Intra-operatively, there are lakes of
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blood spaces noted within the tumor. The tumor is adherent to the dura.
C. Photomicrographic section: The lesion is composed of numerous dilated vascular spaces engorged with
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blood (black arrow), interspersed among the branching trabeculae of the cortical bone (open arrow).
Figure 2A – F. Fibrous dysplasia in a 43-year-old male.
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A,B. CT (A) bone and (B) soft tissue windows demonstrate diploic expansion with bowing of the outer skull table and relative preserved contour of the inner table. The margins are well-defined and part-sclerotic.
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C – E. The central hyperdense component seen on CT (B, arrow) corresponds to the susceptibility focus on
(D,E).
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gradient echo sequence (C, arrow) consistent with hematoma. The lesion demonstrates restricted diffusion
F. Photomicrographic section shows irregular curvilinear trabeculae of woven bone (arrows) and fibrous tissue (asterisks) consistent with a fibro-osseous lesion.
Figure 3A & B. Intraosseous meningioma in a 61-year-old male. A,B. CT (A) bone and (B) soft tissue windows demonstrate an expansile intradiploic osteolytic isodense mass centered at the coronal suture, with thinning and disruption of the inner and outer skull tables. The lesion demonstrates well-defined non-sclerotic margins. The soft tissue is isodense on CT and a greyish soft tumor involving the dura with both intra- and extra-dural components was evident intraoperatively.
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Figure 4A – C. Plasmacytoma in a 30-year-old female. A,B. CT (A) soft tissue and (B) bone windows demonstrate a large homogeneously enhancing mass centered in the left parietal bone causing lytic destruction of the inner and outer skull tables with well-defined nonsclerotic margins. A very vascular tumor is noted intraoperatively, eroding through the outer table and adherent to dura.
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C. Photomicrographic section demonstrates sheets of malignant plasma cells (long arrow) with dural tissue
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(short arrow) and bony spicule (open arrow).
Figure 5A – D. Langerhans cell histiocytosis in a 67-year-old female.
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A – C. MRI brain demonstrates a lesion centered in right temporal bone, (A) isointense on T1-weighted image
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and mildly hyperintense on T2-weighted image with avid enhancement (not shown), and (B,C) restricted diffusion. Note is made of unequal involvement of the inner and outer skull tables (beveled edges).
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D. Photomicrographic section reveals lesional Langerhans cells with oval indented and grooved nuclei and eosinophilic cytoplasm (long arrows). Large numbers of eosinophils (short arrows) are present among the
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Langerhans cells. The Langerhans cells are diffusely positive for S100 protein and CD1a (not shown).
Figure 6A – D. Giant cell tumor in a 26-year-old female. A,B. CT brain soft tissue (A) and bone windows (B) demonstrate a large expansile iso- to hyper-dense soft tissue with internal cystic component centered in the left temporal bone. There is severe thinning and disruption of the skull tables, with poorly-defined margins. C. The lesion shows markedly low signal on T2-weighted images with corresponding blooming of GRE (not shown) and internal fluid components. Intra-operatively, a large extradural tumor with bone erosion of the squamous temporal bone, zygomatic arch and glenoid fossa is noted with dural attachment. D. Photomicrographic section: The tumor is composed of sheets of osteoclastic type multinucleate cells (black arrows) and stromal mononuclear cells (red arrows), with features of fracture within the lesion including reactive woven bone formation.
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Figure 7A & B. Diffuse large B-cell lymphoma in a 46-year-old male (histologically proven on peritoneal nodule). CT (A) bone and (B) soft tissue windows demonstrate large hyperdense mass centered in the right frontoparietal bone with permeative lytic calvarial destruction.
Figure 8A – D. Metastatic follicular thyroid carcinoma in a 44-year-old male. A,B. CT (A) soft tissue and (B) bone windows demonstrate soft tissue mass of heterogenous density with poorly-defined lytic destruction of the left parietal bone.
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C. No corresponding restricted diffusion as shown on ADC due to abundance of colloid as confirmed on histology. A vascular tumor with scalp infiltration, bone erosion and dural attachment is noted intraoperatively.
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D. Photomicrographic section: The tumor is composed of destroyed bony trabeculae and numerous follicles
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containing colloid (arrows).
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Figure 9A & B. Conventional osteoblastic osteosarcoma in a 31-year-old male. A. CT soft tissue window shows an isodense mass centered in the right fronto-temporal bone with poorly-
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defined lytic calvarial destruction and central spiculated osteoid mineralization of sunburst pattern. B. Photomicrographic section reveals cellular proliferation of malignant-looking epithelioid to spindle tumor
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cells with enlarged, pleomorphic nuclei and high nuclear cytoplasmic ratios. The tumor cells are surrounded by
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disorganized trabeculae of neoplastic woven bone producing a coarse lace-like pattern (arrows).
Figure 10A – D. Hemangiopericytoma in a 72-year-old female. A,B. CT brain (A) soft tissue and (B) bone windows demonstrate a large well-circumscribed avidly enhancing tumor with poorly-defined calvarial destruction. Note the presence of a left retrobulbar intraconal mass which is well-circumscribed with avid enhancement. C. MRI brain reveals a predominantly isointense mass on T1- (not shown) and T2-weighted images with presence of flow voids (arrows). Pre-operative embolization of the supplying arteries followed by tumor excision. Intra-operatively, the tumor is very vascular with muscle invasion and bone erosion. D. Photomicrographic section demonstrates patternless sheets of tumor cells with mitosis (arrow).
Journal Pre-proof Algorithm 1. CT Imaging Approach to Large Solitary Lytic Skull Vault Lesions in Adults.
Table 1: A Summary of MR Imaging Characteristics of the Pathology for Large Solitary Lytic Skull Vault Lesions in Adults. Pathology
MRI T2-weighted
Contrast enhancement
ADC value
Osseous Venous Malformation
Mixed foci of hypoand hyper-intensity
Hyperintense
Avid heterogenous
High
Fibrous Dysplasia
Variable (depends on phases)
Variable (depends on phases)
Variable
Low
Epidermoid
Hypointense
Hyperintense
None
Low
Dermoid
Hyperintense
Hyperintense
Low
Meningioma
Hypo- to iso-intense
Iso- to hyper-intense
Variable
Plasmacytoma
Hypo- to iso-intense
Langerhans cell histiocytosis Aneurysmal bone cyst
Hypo- to iso-intense
Iso-to hyper-intense +/- flow voids Hyperintense
Thick enhancing wall Avid homogenous Avid homogenous Avid homogenous
Low
Low
High
Heterogenous
Variable
Lymphoma
Hypo- to iso-intense
Iso- to hyper-intense
Avid homogenous
Low
Metastasis
Hypointense
Hyperintense
Variable
Hypo- to iso-intense
Heterogenous
Avid heterogenous Avid heterogenous Avid heterogenous
Iso- to slightly hyperintense
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Hemangiopericytoma
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Osteosarcoma
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Mixed hypo- and hyper-intense, fluidfluid levels Hypointense
Internal septations may enhance
Giant cell tumor
Mixed hypo- and hyper-intense components Hypo- to iso-intense
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T1-weighted
Iso- to slightly hyperintense +/- flow voids
Variable Low
Journal Pre-proof Highlights
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Evaluation of solitary lytic skull vault lesion using a CT diagnostic algorithm is discussed. The utility of MRI with DWI aids in characterization of the soft tissue component. Imaging correlation with pathological features improves understanding of the disease processes.
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