Imaging Findings of Various Calvarial Bone Lesions with a Focus on Osteolytic Lesions 다양한 두개골 병변의 영상소견: 골용해성 병변을 중심으로

Home , Exostosis, Vertex (anatomy)

Pictorial Essay pISSN 1738-2637 / eISSN 2288-2928 J Korean Soc Radiol 2016;74(1):43-54 http://dx.doi.org/10.3348/jksr.2016.74.1.43

Younghee Yim, MD1, Won-Jin Moon, MD1*, Hyeong Su An, MD1, Joon Cho, MD2, Myung Ho Rho, MD3 Departments of 1Radiology, 2Neurosurgery, Konkuk University Medical Center, Konkuk University School of Medicine, Seoul, Korea 3Department of Radiology, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea

In this review, we present computed tomography (CT) and magnetic resonance imaging (MRI) findings of various calvarial lesions on the basis of their imaging pat- Received April 14, 2015 terns and list the differential diagnoses of the lesions. We retrospectively reviewed Revised June 16, 2015 Accepted July 19, 2015 256 cases of calvarial lesion (122 malignant neoplasms, 115 benign neoplasms, and *Corresponding author: Won-Jin Moon, MD 19 non-neoplastic lesions) seen in our institutions, and classified them into six cat- Department of Radiology, Konkuk University Medical Center, Konkuk University School of Medicine, egories based on the following imaging features: generalized skull thickening, focal 120-1 Neungdong-ro, Gwangjin-gu, Seoul 05030, Korea. skull thickening, generalized skull thinning, focal skull thinning, single lytic lesion, Tel. 82-2-2030-5544 Fax. 82-2-2030-5549 and multiple lytic lesions. Although bony lesions of the calvarium are easily identi- E-mail: [email protected] fied on CT, bone marrow lesions are better visualized on MRI including diffusion- This is an Open Access article distributed under the terms weighted imaging or fat-suppressed T2-weighted imaging. Careful interpretation of of the Creative Commons Attribution Non-Commercial calvarial lesions based on pattern recognition can effectively narrow a range of License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distri- possible diagnoses. bution, and reproduction in any medium, provided the original work is properly cited. Index terms Skull Neoplasms Magnetic Resonance Imaging Tomography, X-Ray Computed Diagnosis, Differential Retrospective Studies Bone Disease Bone Marrow Disease

INTRODUCTION tastases are the most common malignant lesions, multiple myeloma is more common in our database because of errors in In this article, we reviewed our institutional database and ra- coding and also because our institution is renowned for treating diology department database of images taken from 2005 to hematologic malignancies. We retrospectively reviewed the im- 2013 and retrieved the records of 256 patients who underwent aging findings of CT and MRI for these calvarial lesions, and, brain CT or MRI and were later diagnosed with tumorous or using a categorical imaging approach, we briefly described and nontumorous calvarial lesions (122 malignant neoplasms, 115 illustrated the imaging findings of representative osteolytic cal- benign neoplasms, 19 non-neoplastic lesions). The majority of varial lesions. The Institutional Review Board approved this patients either had multiple myelomas (n = 108, 42.2%) or be- retrospective review, and the requirement of informed consent nign osteomas (n = 99, 38.7%) (Table 1). Though calvarial me- was waived.

Table 1. Calvarial Lesions from Our Institution Database (n = 256) Table 2. Categories and Pathologies Based on Involvement Pattern of Calvarial Lesions No. of Cases (%) Calvarial Lesions Malignant neoplasm 122 (47.7) Category Lesions Multiple myeloma 108 Lytic Metastasis 7 Single Histiocytosis-X, osseous hemangioma, epidermoid and Lymphoma 3 demoid cyst, desmoplastic fibroma, aretic meningocele, Rhabdomyosarcoma 1 gorham disease, osteosarcoma/chondrosarcoma, Mesenchymal chondrosarcoma 1 osteomyelitis, arachnoid granulation, intraosseous Langerhans cell histiocytosis 2 meningioma, fibrous dysplasia, neurofibromatosis Benign neoplasm 115 (44.9) type 1, burr-hole Osteoma 99 Multiple Multiple myeloma, metastasis, lymphoma Fibrous dysplasia 5 Thickening Meningioma 4 Diffuse Acromegaly, shunted hydrocephalus, phenytoin induced Osseous hemangioma 2 hyperostosis, Paget's disease, chronic hemolytic anemia Plexiform neurofibroma 1 Focal Metastasis, osteoma, fibrous dysplasia, meningioma, Desmoplastic fibroma 1 chronic calcified hematoma, hyperostosis frontalis Inflammatory myofibroblastic tumor 1 interna Lipoma 1 Thinning Chordoid tumor 1 Generalized Prominent convolutional marking, craniosynostosis, Non-neoplastic lesion 19 (7.4) lacunar skull, long-stnding hydrocephalus, normal Epidermoid/dermoid cyst 3 parietal thinning Cephalhematoma 3 Focal Secondary thinning due to benign tumor, Parry Romberg Skull thinning due to arachnoid cyst 2 syndrome Benign parietal thinning 2 Parry Romberg syndrome 1 ingly, we can simplify the classification system into six categories Atertic meningocephalocele 1 Interparietal foramina 1 based on three main features. We suggest that calvarial lesions Gorham disease 1 are classified into calvarial thickening, thinning, and lytic lesion. Phenytoin induced hyperostosis 1 When the calvarial lesions fall into the ‘thickening’ or ‘thinning’ Depressed fracture 1 categories, they can be further subdivided into focal or general- Acromegaly 1 ized lesions. The lytic category can be subdivided into either sin- Exostosis 1 Peripheral low-flow vascular malformation 1 gle or multiple lesions. Furthermore, we can expect to get addi- Data are presented as numbers of patients with percentages in parentheses. tional information about matrix characteristics with contrast enhancement and diverse advanced MR sequences such as dif- CATEGORICAL APPROACH TO IMAGING fusion-weighted imaging (DWI) (3), perfusion-weighted imag- DIAGNOSIS ing, and MR spectroscopy. A flowchart for a systematic approach to imaging diagnosis of calvarial lesions is provided in Table 2. With increasing frequency, CT and MRI have been incorpo- rated into the basic imaging tools for evaluating calvarial le- Single or Multiple Osteolytic Lesions sions. Therefore, it is useful to categorize diagnostic features of images taken not by conventional radiography but by CT and Multiple Myeloma MRI (1, 2). It is possible to categorize 8 different types of cal- Multiple myeloma is characterized as multiple osteolytic le- varial lesions based on 4 key features: thickening or thinning of sions due to the malignant proliferation of osteoclast-activating calvarial bone, sclerosis or lysis of bone, focal or generalized le- factors triggered by myeloma. Plain radiography of multiple sions, and, finally, singularity or multiplicity of lesions. On CT myeloma patients is characterized by a subcortical circular or and MRI, sclerotic lesions appear as thickening of calvarial bone elliptical radiolucent shadow, and the axial skeleton is the pre- (either the inner/outer tables, or bone marrow, or both). Accord- dominant site of the abnormality. CT shows punched-out le-

44 J Korean Soc Radiol 2016;74(1):43-54 jksronline.org Younghee Yim, et al sions with soft tissue masses and fractures. On MRI, multiple or sometimes as diffusely destructive on bone algorithm CT (2). myeloma presents with low-to-intermediate signal intensity on Hypointense infiltrating foci are seen on T1-weighted images as T1-weighted images, high signal intensity on T2-weighted im- metastases replace hyperintense normal yellow marrow. Most ages, and high signal intensity on DWI (4). The lesions enhance skull metastases are hyperintense compared to bone marrow on strongly following contrast administration. Four different imag- T2-weighted images and appear clearly on fat-saturated con- ing patterns may appear: normal-looking marrow, a micro nodu- trast-enhanced T1-weighted images (Fig. 2). DWI is helpful for lar pattern (also described as variegated or salt and pepper le- the detection of bone marrow involvement of the calvarium (3). sions), a focal pattern, or a diffuse pattern (Fig. 1) (1, 2). Langerhans Cell Histiocytosis Osteolytic Metastases Langerhans cell histiocytosis (LCH) is an uncontrolled mono- Metastases take various forms; they can be seen as either os- clonal proliferation of abnormal Langerhans cells involving any teoblastic or osteolytic lesions on plain radiograph. When ap- organ. When LCH involves the skull, it manifests as a small soft pearing as single or multiple lytic lesions, metasteses are usually tissue calvarial mass with lytic defect and beveled edge more on seen as one or more relatively circumscribed intraosseous lesions the inner table than the outer table on plain radiograph and CT

A B Fig. 1. A 70-year-old male with multiple myeloma. On lateral skull radiograph (A) and axial CT (B), multiple punch-out osteolytic lesions in the skull (salt and pepper) are seen, a pathognomonic finding of multiple myeloma.

A B C Fig. 2. A 70-year-old female with renal cell carcinoma. A. On contrast-enhanced CT, two huge osteolytic soft tissue masses with extreme enhancement in right parietooccipital and left frontotemporal bone are seen (arrows). B. On lateral skull radiograph, two huge osteolytic lesions (arrows) are seen. C. On MRI, huge soft tissue metastatic tumors show heterogeneous signal intensity on diffusion-weighted imaging (arrows). jksronline.org J Korean Soc Radiol 2016;74(1):43-54 45 Imaging Findings of Various Calvarial Bone Lesions with a Focus on Osteolytic Lesions scans. It is often seen as bilateral soft tissue masses with bone time. They show intact inner and outer tables; the outer table destruction. On MRI, LCH presents as an enhancing soft tissue tends to be more expanded than the inner table. Trabecular th- mass on contrast-enhanced T1-weighted images with vivid en- ickening with radiating spicules is also commonly seen. MRI sig- hancement of the pituitary infundibulum and stalk thickening nal strength depends on the quantity of slow-moving venous (Fig. 3) (5-7). blood, the proportion of red to fatty marrow, and hypointense trabeculae (8). Osseous hemangiomas are typically hyperintense Osseous Hemangioma on T1-weighted images and heterogeneously hyperintense on Osseous hemangiomas are benign skull lesions composed of T2-weighted images. They enhance intensely, heterogeneously, predominantly vascular entities. On plain radiographs and CT or minimally on contrast-enhanced CT or MRI (Fig. 4) (8, 9). scans, they present as sharply defined expansile lesions, which may include a periosteal reaction and be surrounded by a thin Epidermoid and Dermoid Cysts peripheral sclerotic rim, as is the case approximately 30% of the Epidermoid and dermoid cysts are ectodermal inclusion cysts

A B C D Fig. 3. A 4-year-old girl with Langerhans cell histiocytosis. A. On lateral skull radiograph, a focal osteolytic lesion (arrow) is visible. B. Non-contrast CT shows a localized osteolytic lesion with beveled edges in the right frontal bone (arrow). C, D. On MRI, the osteolytic mass shows heterogeneous signal intensity on a T2-weighted image (arrow) (C) and marked enhancement with focal cystic change on the gadolinium-enhanced T1-weighted image (arrow) (D).

A B C Fig. 4. A 45-year-old male with osseous hemangioma. A. On lateral skull radiograph, a small osteolytic lesion (arrow) is seen in the right parietal skull. B, C. A focal mass is detected with non-enhancing low signal intensity (arrow) on coronal gadolinium-enhanced T1-weighted MR image (B) and high signal intensity (arrow) on coronal T2-weighted MR image (C).

46 J Korean Soc Radiol 2016;74(1):43-54 jksronline.org Younghee Yim, et al lined by epithelium. They occur inside the orbit, in the calvarial gocyte or arachnoid cap cells in the cranial sutures may cause diploic space, and intracranially (9). They typically appear as en- primary intraosseous meningiomas (10). Approximately 68% of capsulated unilocular cystic lesions with a signal intensity that primary extradural meningiomas involve the calvarium (11). Pri- depends on their components (1). On plain radiograph and CT mary extradural meningiomas typically present with slow scalp scans, epidermoids appear as intradiploic, expansile, osteolytic swelling and do not show any neurologic symptoms or signs, lesions with smooth sclerotic margins while dermoids appear as unless the lesion extends through the inner table and compresses expansile, osteolytic midline lesions. On CT, dermoids contain a intracranial structures (12). On plain radiograph and CT, well- soft-tissue component extending to overlying skin and intracra- defined radiolucent, osteolytic lesions can be seen. On MRI, me- nial areas. Usually epidermoids have a fluid-like signal intensity ningiomas are usually hypo- to isointense on T1-weighted im- on MRI. Dermoids have a heterogeneous appearance with var- ages and iso- to hyperintense or sometimes heterogeneously ied signal intensities depending on their various compositions. intense on T2-weighted images. Contrast enhancement generally Since dermoids contain fatty tissue, they show low attenuation enhances evenly and often produces a dural tail (Fig. 6) (2). on CT and high signal intensity on T1-weighted images (Fig. 5) (1, 6, 9). Enhancement is generally absent although mild pe- Fibrous Dysplasia ripheral enhancement can be seen in about 25% of cases. Fibrous dysplasia is characterized as the replacement of normal cancellous bone with abnormal fibrous tissue (13). On plain Intraosseous Meningioma radiograph, they appear as ground-glass sclerotic lesions or cystic When a meningioma invades overlying bone, it can create an lesions commonly crossing bony sutures. They may involve mul- osteolytic bone lesion. Infrequently, meningioma arises initially tiple calvarial bones (14), tending to cause the outer table to bulge in the calvarium. It is thought that trapping of ectopic menin- while conserving the shape of the inner table (15). CT scans

A B C D E Fig. 5. A 13-year-old boy with epidermoid cyst of the skull. Lateral skull radiograph (A) and axial CT (B) show a large lucent area with well-defined sclerotic margin (arrow) in the right parietal bone. The lesion shows heterogeneous bright signal intensity on coronal T2-weighted image (arrow) (C), and shows thin wall enhancement on non-contrast (arrow) (left in D) and contrast-enhanced T1-weighted images (arrow) (right in E).

A B C D Fig. 6. A 58-year-old female with intracalvarial meningioma. A. A small well-defined radiolucent lesion (arrow) is seen on lateral skull radiograph. B. The pre-contrast CT scan shows a well-defined mildly expansile osteolytic meningioma (arrow) on the right parietal bone. C, D. This mass shows iso-signal intensity (C) on T2-weighted image (arrow) and contrast enhancement (arrow) (D) when gadolinium is applied. jksronline.org J Korean Soc Radiol 2016;74(1):43-54 47 Imaging Findings of Various Calvarial Bone Lesions with a Focus on Osteolytic Lesions show a degree of hazy and intradiploic density. On T1-weighted cases of skull lymphomas produced isointense signals on pre- images, they are usually hypointense, but more fibrous areas can contrast T1-weighted images with intense enhancement with be isointense. On T2-weighted images, they show various sig- contrast. However, MR imaging does not diagnose lymphoma nals, depending on their cellularity: those that are more fibrous accurately because it can mimic metastatic carcinoma, osteomy- with fewer bony trabeculae and less cellularity exhibit relatively elitis, or in some cases, meningioma (Fig. 8) (18). high signal intensities, while more osseous and cellular matrices can show relatively low signal intensities (16). Contrast enhance- Desmoplastic Fibroma ment produces a variable range of intensities depending on le- Desmoplastic fibroma is a rare benign bone tumor which orig- sion stage; there can be homogeneous, central or peripheral en- inates from fibrous tissue, and a majority of cases are seen in hancement (Fig. 7). those younger than 30 years of age. Desmoplastic fibroma most commonly occurs in the metaphyses of the long bones, the man- Lymphoma dible, and the pelvis, whereas the maxilla, calvaria, sternum, and Malignant lymphoma may originate in the skull and extend vertebrae are less frequently affected. Simple radiographs show to outside the cranium (17). Presenting as nonspecific osteolytic an expansile, osteolytic lesion with a trabeculated or bubbly ap- lesions on plain radiograph, on CT scans they instead appear as pearance. At times, the tumor may have a very aggressive radio- extra-intra cranial isodense lesions in the cranial vault or ho- graphic appearance with bone destruction, cortical erosion, or mogenous masses with sharp margins. On MR, most reported soft-tissue invasion (19, 20). The dense connective tissue and hy-

A B C D Fig. 7. A 35-year-old male with fibrous dysplasia. A. On non-contrast CT, an expansile lesion (arrow) with internal ground-glass opacity emerging from the occipital bone is seen. B, C. On coronal T1-weighted image (B) and T2-weighted image (C), the lesion shows iso signal intensity (arrow) and mixed signal intensity (arrow), respectively. D. It shows heterogeneous but marked enhancement (arrow) when gadolinium is added.

A B C Fig. 8. A 59-year-old male with skull lymphoma. A. On axial gadolinium-enhanced T1-weighted MR images, multiple homogeneous enhancing mass lesions are seen in both parietal bones (arrow in right parietal bone lesion). B, C. The lesions show hyperintensity on diffusion-weighted imaging (arrow) (B) and iso signal intensity on the T2-weighted image (arrow) (C).

48 J Korean Soc Radiol 2016;74(1):43-54 jksronline.org Younghee Yim, et al percellular regions have intermediate signal intensity on T1-wei- weighted images and high signals on T2-weighted images and ghted images and heterogenous signal intensity on T2-weighted heterogeneous enhancement after contrast injection. On MR ve- images (Fig. 9) (19). nography, a vertically positioned straight sinus equivalent (persistent falcine vein) is seen (Fig. 10) (21). Atretic Meningocehalocele Atretic cephalocele is composed of dura, fibrous tissue, and Gorham Disease dysplastic brain tissue. Oval or elongated defects are observable Gorham disease is an intraosseous neoplastic proliferating dis- on plain skull radiographs. On CT scans, a subgaleal soft tissue ease of hemangiomatous or lymphagiomatous tissue with pro- mass with “spinning top” configuration is seen. On MRI, a sub- gressive massive osteolysis. The first stage involves vascular pro- cutaneous scalp mass with intracranial extension through skull liferation in connective tissue; in the second stage, fibrous tissue and dura may be seen as having heterogeneous signals on T1- replaces the absorbed bone without regeneration of the bone

A B C Fig. 9. A 1-year-old girl with desmoplastic fibroma. A. A focal osteolytic lesion with sclerotic border (arrow) is seen near the right coronal suture on non-contrast CT. B, C. The lesion shows prominent enhancement on the gadolinium-enhanced T1-weighted image (arrow) (B), but shows low signal intensity relative to brain parenchyma on diffusion-weighted imaging (arrow) (C).

A B C Fig. 10. A 45-year-old man with atretic cephalocele and persistent falcine sinus. Coronal plain radiograph (A) shows a well-defined bony defect (arrow) in the interparietal region. On a T2-weighted image(B) , a U-shaped hypointense subscalp lesion (arrows) which extends to a congenital bony defect is detected. Anomalous persistent falcine sinus is noted as well (open arrow). On contrast-enhanced MR venograph, marked stenosis (arrow) of the persistent falcine sinus (open arrow) at the junction of the falcine and superior sagittal sinuses is noted (C). Reprinted from Cho J, Kim MY, Roh HG, Moon WJ. MR images of spontaneously involuted atretic cephalocele concomitant with persistent falcine sinus in an adult. J Korean Soc Magn Reson Med 2006;10:117-120; with permission. jksronline.org J Korean Soc Radiol 2016;74(1):43-54 49 Imaging Findings of Various Calvarial Bone Lesions with a Focus on Osteolytic Lesions matrix. On CT scans, radiolucent foci in the intramedullary or Neurofibromatosis Type 1 subcortical regions are seen and the gradual disappearance of Neurofibromatosis type 1 is a multisystem neurocutaneous bone may be apparent. MR imaging of Gorham disease involv- disorder that is one of the most common inherited autosomal ing the calvaria has not been widely reported, but a reticular pat- dominant central nervous system disorders. The radiographic tern on a contrast enhanced fat-suppressed T1-weighted image spectrum includes focal areas of abnormal signal intensity in was reported (16). deep grey or white matter, optic nerve glioma, progressive sphe- noid wing dysplasia, lambdoid suture defects, dural calcifica- Burr Hole tion at the vertex, buphthalmos, and in rare cases, the Moyam- Burr holes appear as well-defined defects in the inner and out- oya phenomenon (28). er tables of the skull vault on CT or simple radiograph. On contrast-enhanced MR images, the margins of the burr hole usually Focalized or Generalized Thickening of the Calvarium show enhancement, and in some cases, diffuse enhancement with a filling of the plunge defect may be seen. Defects caused by Osteoblastic Metastasis plunging may show high signal intensity on T2-weighted images, Osteoblastic metastases arise from hematogenous spread from which is referred to as a “mushroom sign” (22). primary cancers. In such instances, they are often seen without benign sclerotic borders. On CT scans, metastatic lesions are Others usually seen as enhancing masses centered in bone with osseous destruction and most are lytic, though a few are sclerotic (e.g., Skull Osteosarcoma prostate lesions). Osteoblastic metastases appear as hypointense Skull osteosarcomas show nonspecific radiological features, lesions on both T1-weighted and T2-weighted images without for example, they can be either osteolytic, osteoblastic, or mixed significant enhancement and appear positive on DWI (2, 29). in involvement pattern. However, spicular calcification tends to be seen, and a sun burst appearance exists in 25% to 31% of cases Osteoma (23). Bone destruction and mineralization of the tumors may in- Osteomas are benign, slow-growing tumors usually found in- dicate an osteogenic sarcoma (24). cidentally (30). They are the most common benign osseous tumors in the calvarium, and are mainly found in the outer table of Osteomyelitis the skull (31). They appear as dense oval lesions on radiographs. Osteomyelitis of the calvarium may occur as a consequence of On CT images, they appear as very hyperdense sclerotic masses trauma or as a complication of sinus sepsis. Pus in the bone can with clear-cut outlines that grow from, and attach to, the external spread either into the cranium or outward into subgaleal or sub- aspect of the cortical bone. They are homogeneously hypointense cutaneous planes where it can form abscesses, visible as osteo- on T1-weighted images, heterogeneously hypointense on T2- lytic lesions on CT (25). weighted images, and do not show contrast enhancement (2).

Arachnoid Granulation Fibrous Dysplasia Arachnoid granulations usually present as sharply marginat- Fibrous dysplasia can be seen as calvarial thickening because it ed, lucent, occipital bone lesions adjacent to the transverse sinus. tends to cause the outer table to bulge while conserving the shape They generally appear as hypointense or isointense relative to the of the inner table (15). brain parenchyma on T1-weighted images and hyperintense on T2-weighted images and show minimal heterogeneous contrast Meningioma enhancement (26, 27). Usually benign, meningiomas arising from the dura can cause hyperostosis. On plain radiograph and CT, 75% of cases appear as round or smoothly lobulated masses that are hyperdense com-

50 J Korean Soc Radiol 2016;74(1):43-54 jksronline.org Younghee Yim, et al pared to the cerebral cortex. 25% of cases demonstrate calcifica- Chronic Hemolytic Anemia tion. Hyperostosis on bone algorithm CT is often seen (32). Patients with hemolytic anemia have red marrow hyperplasia, causing the widening of the diploic space; the outer table thins Acromegaly or is completely obliterated. Before diploic widening, a coarse Growth hormone hypersecretion can manifest as generalized granular or stippled pattern can be seen in the upper parietal re- thickening of the skull. Bony abnormalities associated with gr- gion. When the hyperplastic marrow perforates or destroys the owth hormone include sella turcica alterations, prominence and outer table, new bony spicules perpendicular to the inner table enlargement of frontal and maxillary sinuses, excessive pneuma- are seen as “hair-on-end” signs (38). tization of the mastoids, prominence of the occipital protuber- ance, thickening or, less commonly, thinning of the cranial vault, Chronic Calcific Cephalhematoma enlargement and elongation of the mandible, and widening of Cephalhematoma that is not absorbed within a month begins the mandibular angle (32). to ossify where the periosteum is lifted and the ossification grad- ually covers the surface of the hematoma. The thick band-like Others ossification mimics doubling of the skull, so it is referred to as a “double skull sign” (39). On CT and radiograph, it appears as a Shunted Hydrocephalus uniform, densely calcified mass located immediately adjacent Chronic intracranial hypotension or prolonged ventricular to the outer table, within the periosteum (1). shunting for hydrocephalus can cause diffuse thickening of all bones of the neurocranial vault. This happens because outward Hyperostosis Frontalis Interna pressure needed to expand the cranium is missing, so the inner Hyperostosis frontalis interna is a benign condition which th- table of the skull bone grows instead. On simple radiographs ickens the inner table of the frontal bone. Though the etiology and CT scans, the entire cranial vault thickening can be seen (33). is not clearly known, estrogen signaling is thought to be involved. The hyperostotic bone tends to be less dense on simple radio- Dilantin Therapy graphs or on CT than are normal cortical bones (40, 41). Dilatin (Diphenylhydantoin) is widely used for the manage- ment of patients with epileptic convulsions. Dilatin has recently Focal or Generalized Thinning of the Calvarium been shown to stimulate osteoblast proliferation in approximately 34% of patients. The degree of skull thickening is correlated Prominent Convolutional Marking (Copper-Beaten Skull) with frontal bossing and degree of facial coarsening (34). The in- Prominent convolutional marking is widely considered to be crease in the thickness of the calvarium is mainly presented in a reflection of normal brain growth. The growing brain exerts a the diploic space (35). continuous pulsatile pressure on the cranium, producing a gyral pattern on plain radiographs which is known as the copper-beat- Paget Disease en pattern (42). Paget disease, also known as osteitis deformans, can cause chronic metabolic skeletal disorders (2) characterized by bony Craniosynostosis expansion with variable destruction with or without sclerosis. Craniosynostosis is a rare, complex condition defined as a The characteristics of CT and MR are a loss of normal trabecu- premature fusion of one or more of the cranial sutures (43). Pri- lae from lysis, a disorganized pattern of trabecular thickening, mary craniosynostosis is due to a developmental error during and, finally, sclerosis when the disease is in the blastic phase. embryogenesis, while secondary craniosynostosis is due to me- Since a majority of cases are seen in the mixed phase, the yellow chanical or metabolic causes (44). In plain radiographs, perisu- marrow signal intensity is maintained regardless of the MR se- tural sclerosis, localized breaking, bony bridging, and absence of quence (36, 37). the suture are primary signs of craniosynostosis. When raised jksronline.org J Korean Soc Radiol 2016;74(1):43-54 51 Imaging Findings of Various Calvarial Bone Lesions with a Focus on Osteolytic Lesions intracranial pressure is maintained over long, fingerprinting and life-threatening lesions such as bone metastases. While bony le- copper beating can be seen (45). sions of the calvarium are easily identified using brain CTs, bone marrow lesions can be visualized better on brain MRIs than on Lacunar Skull brain CTs. Diffusion-weighted MRI is helpful in detection and Lacunar skull is characterized as a dysplasia of the membra- diagnosis of bone marrow lesions. The categorical imaging ap- nous bone caused by mesenchymal abnormality and is associat- proach presented here will be helpful in narrowing the list of ed with neural tube defects, especially myelomeningocele with possible diagnoses of calvarial lesions. Chiari II malformation. It is seen as a well-defined lucent lesion (having a scooped-out appearance) which corresponds to the Acknowledgments nonossified fibrous bone (32). This study was supported by Konkuk University in 2015 and by a grant of the Korea Healthcare technology R&D Project, Long-Standing Hydrocephalus Ministry of Health and Welfare, Republic of Korea (HI12C0713). Regardless of the cause of hydrocephalus, increased intracranial pressure may result in diffuse calvarial thinning with or wi- References thout deformity when it is not treated properly (33). 1. Lloret I, Server A, Taksdal I. Calvarial lesions: a radiological Normal Parietal Thinning approach to diagnosis. Acta Radiol 2009;50:531-542 Parietal thinning is an uncommon condition which can be 2. Garfinkle J, Melançon D, Cortes M, Tampieri D. Imaging caused by either non-progressive congenital dysplasia of the di- pattern of calvarial lesions in adults. Skeletal Radiol 2011; pole or acquired and progressive diseases such as tumors, diabe- 40:1261-1273 tes, long-standing steroid therapy, or osteoporosis. The bilateral 3. Moon WJ, Lee MH, Chung EC. Diffusion-weighted imaging parietal bones show symmetrical thinning (involving the outer with sensitivity encoding (SENSE) for detecting cranial bone tables and diploe) with a scalloped appearance while the inner marrow metastases: comparison with T1-weighted images. table is usually intact (46, 47). Korean J Radiol 2007;8:185-191 4. Sommer G, Klarhöfer M, Lenz C, Scheffler K, Bongartz G, Secondary Thinning due to Benign Tumors Winter L. Signal characteristics of focal bone marrow le- Benign tumors or slow growing cysts can result in overlying sions in patients with multiple myeloma using whole body skull thinning because of a chronic pressure effect. Smooth-mar- T1w-TSE, T2w-STIR and diffusion-weighted imaging with gined calvarial thinning without periosteal reaction or new bone background suppression. Eur Radiol 2011;21:857-862 formation suggests that the underlying lesion is benign. 5. Prayer D, Grois N, Prosch H, Gadner H, Barkovich AJ. MR imaging presentation of intracranial disease associated with Parry Romberg Syndrome Langerhans cell histiocytosis. AJNR Am J Neuroradiol 2004; Parry Romberg syndrome is rare neurocutaneous disorder 25:880-891 also known as progressive hemifacial atrophy. One side of the 6. Willatt JM, Quaghebeur G. Calvarial masses of infants and face, including the skin, subcutaneous tissue, muscles, cartilage, children. A radiological approach. Clin Radiol 2004;59: and underlying bony structures, becomes slowly and progres- 474-486 sively atrophic. Radiologic findings include bone and soft-tissue 7. Kilborn TN, Teh J, Goodman TR. 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다양한 두개골 병변의 영상소견: 골용해성 병변을 중심으로

임영희1 · 문원진1* · 안형수1 · 조 준2 · 노명호3

이 임상화보의 목적은 다양한 두개골 병변을 병변의 양상에 따라 분류하여 컴퓨터단층촬영과 자기공명영상소견을 보여주 고 감별진단을 제시하는 것이다. 256예의 두개골 병변 증례(122 악성종양, 115 양성종양, 19 비종양성 병변)를 후향적으 로 분석하였으며 이를 다음과 같은 여섯 가지 분류로 나누었다: 전반적 두개골비후, 국소적 두개골비후, 전반적 두개골 위 축, 국소적 두개골 위축, 단발성 용골성 병변, 다발성 용골성 병변. 두개골의 골병변은 컴퓨터단층촬영으로 잘 찾아낼 수 있으나, 골수병변의 진단은 확산강조영상이나 지방억제 T2 강조영상과 같은 자기공명영상이 좀 더 우수하다. 침범패턴에 따른 두개골 병변의 세심한 판독이 감별진단의 범위를 줄이면서 정확한 진단으로 이끌 수 있다.

건국대학교 의학전문대학원 건국대학교병원 1영상의학교실, 2신경외과학교실, 3성균관대학교 의과대학 강북삼성병원 영상의학교실

54 J Korean Soc Radiol 2016;74(1):43-54 jksronline.org