Schwannomas or neurilemomas are relatively frequent benign tumors; however, intraosseous schwannomas are rare. The most common site for intraosseous schwannoma is the mandible. Other sites include the vertebra, ulna, humerus, femur, tibia, patella, scapula, rib, and small bones of the hands. The skull vault is a rare site for intraosseous schwannoma.
This article presents a case of intraosseous schwannoma in the frontal bone in an 11-year-old boy.
| Figure 1: CT scan of the skull showing an intradiploic hypodense mass in the left frontal bone with focal cortical break of the outer table. |
An 11-year-old boy presented with forehead swelling that increased progressively during a period of 2 years. The swelling was greater on the left side. The swelling was not associated with any pain, headaches, visual disturbances, or neurological deficit. The patients history was normal.
On physical examination, the patient had swelling of forehead that was greater above the left eyebrow. The swelling measured 3×3 cm in size and was nontender, hard, and noncompressible. There was no local rise of temperature, and the overlying skin was normal. The differential diagnosis included osteoma and fibrous dysplasia. Laboratory studies including serum electrolytes as well as liver and renal function tests were normal.
A skull radiograph showed a lytic lesion in the frontal bone with some sclerosis at the rim. Noncontrast axial and coronal computed tomography (CT) of the paranasal sinuses demonstrated a 3×3×1.5-cm intradiploic lesion in the left frontal bone. The lesion was hypodense and expansile with trabeculations, and there was focal cortical break of the outer table with mild overlying soft-tissue swelling. There was no periosteal reaction. The bilateral frontal sinuses were not pneumatized, and the bilateral ethmoid, sphenoid, and maxillary sinuses were clear. The brain parenchyma visualized was normal (Figure 1). The appearance on CT was that of a hemangioma in the frontal bone.
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Figure 2: Photomicrograph of the tumor showing a hypercellular area with Verocay bodies (hematoxylin-eosin, original magnification ×20).
Intraoperatively, the lesion was an intradiploic firm swelling that abutted the left supraorbital ridge. The underlying dura was intact. The lesion was excised, and a calvarial bone graft was placed. The postoperative period was unremarkable, and 6 months after excision of the lesion, the patient was well.
Grossly, the excised bone piece measured 5×4 cm. The cut surface had a greyish-white lesion that was focally congested. No areas of necrosis or hemorrhage were seen. Microscopically, the tumor was circumscribed with few intervening bony trabeculae. It was cellular, composed of spindle-shaped cells with prominent nuclear palisading and numerous Verocay bodies. The cells showed minimal pleomorphism and had bland chromatin with inconspicuous nucleoli (Figure 2). Only a few hypocellular areas were present. There was no increase in mitosis, and no necrosis was noted.
To confirm the diagnosis, immunohistochemistry was performed. The sections were treated with monoclonal antibodies (Dako Corp, Carpinteria, California). Staining was performed for vimentin (1:200), S-100 (1:400), glial fibrillary acidic protein (1:100), and smooth muscle actin (1:400) using the peroxidase-antiperoxidase method. Cells were positive for S-100 and vimentin while being negative for glial fibrillary acidic protein and smooth muscle actin.
The sample for electron microscopy was obtained from paraffin-embedded tissue; therefore, the ultrastructural details could not be defined fully. However, the tumor cells showed distinct cytoplasmic membrane coated by amorphous band of basal lamina (Figure 3). Based on these findings, the lesion was labeled as an intraosseous schwannoma.
Figure 3: Electron microphotograph of the tumor cells showing a distinct cytoplasmic membrane coated by an amorphous band of basal lamina (arrows) (uranyl acetate and lead citrate, original magnification ×10,000).
Schwannomas or neurilemomas are relatively frequent benign tumors that arise from the nervous system, comprising 1% to 10% of all soft-tissue tumors.1 Intraosseous schwannoma is a rare neoplasm. In one large series, schwannoma accounted for <0.2% of primary bone tumors.2
Schwannomas are associated almost exclusively with sensory nerves3,4; therefore, the low density of sensory nerve fibers within bone may account for the exceedingly rare occurrence of intraosseous schwannoma.4 Schwannomas can involve bone by 3 mechanisms: extraosseous tumors can cause secondary erosion of bone; tumors can arise within the nutrient canal and grow in a dumbbell-shaped configuration, enlarging the canal; and tumors can arise centrally within bone.4
Intraosseous schwannomas affect males and females equally, with patient age ranging from 2 to 65 years.5 The majority of intraosseous schwannomas have been located in the mandible, followed by the sacrum. Other sites include the vertebra, ulna, humerus, femur, tibia, patella, scapula, rib, and small bones of the hands.5-8
The skull vault is a rare site for intraosseous schwannoma. Only 4 cases of intraosseous schwannoma in the skull vault have been reported previously (Table).9-11 In addition, Unni et al12 reported 2 cases of intraosseous neurilemoma of the skull; however, no detailed information was given.
Radiologically, intraosseous schwannomas are lytic, sharply demarcated defects that often expand the involved bone. Perilesional sclerosis may surround the area of central lucency.5 Histologic features of intraosseous schwannomas are similar to that observed for soft-tissue schwannomas including Antoni type A areas (compactly arranged spindle-shaped cells with palisading or Verocay bodies) and Antoni type B areas (widely separated cells with loose intervening collagenous matrix). In our patient, typical radiologic and histologic findings including immunohistochemistry and electron microscopy results led to a diagnosis of intraosseous schwannoma.
- Hagiwara K, Higa T, Miyazato H, Nonaka S. A case of a giant schwannoma on the extremities. J Dermatol. 1993; 20(11):700-702.
- Fawcett KJ, Dahlin DC. Neurilemmoma of bone. Am J Clin Pathol. 1967; 47(6):759-766.
- Escourolle R, Poirier J. Manual of Basic Neuropathology. Philadelphia, PA: WB Saunders Co; 1971.
- De la Monte SM, Dorfman HD, Chandra R, Malawer M. Intraosseous schwannoma: histologic features, ultrastructure, and review of the literature. Hum Pathol. 1984; 15(6):551-558.
- Fechner RE, Mills SE. Tumors of the bones and joints. In: Rosai J, ed. Atlas of Tumor Pathology, Third Series. Washington, DC: Armed Forces Institute of Pathology; 1993.
- Gordon EJ. Solitary intraosseous neurilemmoma of the tibia: review of intraosseous neurilemmoma and neurofibroma. Clin Orthop Relat Res. 1976; (117):271-282.
- Chi AC, Carey J, Muller S. Intraosseous schwannoma of the mandible: a case report and review of the literature. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2003; 96(1):54-65.
- Gine J, Calmet J, Sirvent JJ, Domenech S. Intraosseous neurilemmoma of the radius: a case report. J Hand Surg Am. 2000; 25(2):365-369.
- Celli P, Cervoni L, Colonnese C. Intraosseous schwannoma of the vault of the skull. Neurosurg Rev. 1998; 21(2-3):158-160.
- Ersahin Y, Mutluer S, Demirtas E. Intraosseous neurinoma of the parietal bone. Childs Nerv Syst. 2000; 16(3):181-183.
- Schiffer J, Reif R, Lahat E, Bar-Iojai A, Starinski R. Intraosseous neurilemmoma of skullsingle case report. Neurochirurgia (Stuttg). 1991; 34(6):178-179.
- Unni KK. Dahlins Bone Tumors: General Aspects and Data on 11,087 Cases. 5th ed. Philadelphia, PA: Lippincott-Raven; 1986.
Drs Goyal, Saikia, Vashishta, and Gulati are from the Department of Pathology and Dr Sharma is from the Department of Plastic Surgery, Post Graduate Institute of Medical Education and Research, Chandigarh, India.
Drs Goyal, Saikia, Vashishta, Gulati, and Sharma have no relevant financial relationships to disclose.
Correspondence should be addressed to: Uma Nahar Saikia, MD, Department of Histopathology, Post Graduate Institute of Medical Education and Research, Chandigarh, India.