An Unexpected Occipital Tumor.

Our patient was a 68-year-old, right-handed woman who had been in her usual state of health until early 1997 when she was diagnosed with a colonic carcinoma that was resected at another institution. Two days after the surgery, she developed complete blindness. She was placed on phenytoin, and several weeks later her vision returned. Subsequently, she experienced pain localized in the occipital area, which was worse when lying in the supine position.

On physical examination there was tenderness on palpation of the occiput, with moderate restriction to the range of head motion in all directions. Deep tendon reflexes were 2++ throughout. No pathologic reflexes were found. She had normal strength. Gait was normal and cerebellar function was intact.

An evaluation using nonenhanced computed axial tomography showed a markedly thickened sclerotic occipital bone that measured 7 cm in thickness, with a portion of the hyperostotic area projecting into the posterior fossa. There was also an intraosseous soft tissue nodular density measuring 2.0 cm. Multiple areas of increased density were evident within the soft tissue component. Magnetic resonance imaging studies revealed a striking difference between the density of the normal bone of the cranium and the pathologic occipital bone, which was better visualized in the sagittal view of TI-weighted sequences without gadolinium (Figure 1). Also with the magnetic resonance imaging (sagittal and coronal T1-weighted sequences without gadolinium), we noted a soft tissue density lesion located within the bone that did not show any connection with the dura or the extracranial soft tissues.

[Figure 1 ILLUSTRATION OMITTED]

At surgery, there was a significant deformity of the cranial vault at the level of the occiput and first and second cervical vertebrae. Bur holes could not be drilled, as the craniotome was not long enough to penetrate this area of thickened skull. The entire lesion was removed with great technical difficulty owing to the extreme hardness of the bone. The patient's immediate postoperative course was uneventful, and there was no neurologic deficit. She made a complete recovery and was discharged 3 days after surgery.

Histologic examination revealed that the specimen consisted of a fragment of extremely thick, dense bone measuring 6.0 x 5.0 x 3.5 cm. There was an excavated tumor cavity that measured 1.9 cm, within which there were fragments of tan, finely vascularized tissue corresponding to the tumor bed (Figure 2, arrow). Low-power histologic examination with hematoxylin-eosin stains showed a neoplasm composed of spindle cells growing in a somewhat whorled pattern, suggestive of meningothelial cells (Figure 3). In some areas there were cells showing clear cytoplasm, similar to histiocytes intermixed with meningothelial cells. Closer examination of these cells demonstrated features of xanthoma cells. Special stains used to better characterize the neoplasm included glial fibrillary acidic protein and epithelial membrane antigen immunoperoxidase stains; the tumor cells were positive for epithelial membrane antigen (Figure 4) and negative for glial fibrillary acidic protein immunohistochemical stains. Also, a periodic acid-Schiff reaction demonstrated minute amounts of periodic acid-Schiff-positive material within some of the scattered cells.

[Figures 2-4 ILLUSTRATION OMITTED]

What is your diagnosis?

Pathologic Diagnosis: Intraosseous Hyperostotic Occipital Meningioma 

Meningiomas usually pose no diagnostic difficulty to the clinician, radiologist, or pathologist. Nevertheless, at times the clinical presentation and the radiologic appearance may be unusual. When these neoplasms occur in an unusual location, the differential diagnosis becomes a difficult clinicopathologic exercise.

In general, neoplasms of the occipital bone are rather infrequent when compared to other bones of the skull. Neoplasms that may occur in the occipital bone include such diverse entities as chondroblastoma, ossifying fibroma, atypical juvenile xanthogranuloma of childhood, epidermoid tumor, giant cell tumor in the background of von Recklinghausen disease, melanotic neuroectodermal tumor of infancy, and primary lymphoma.

In their review article of calvarial meningiomas, Oka et al[1] made no mention of a meningioma of the occipital bone. From the radiological perspective, intraosseous meningiomas of the occipital bone have not been reported. McWhorter et al[2] reported a case of an extracranial meningioma that presented as a lytic parietal lesion. The radiologic differential diagnosis included eosinophilic granuloma, hemangioma, and epidermoid tumor. Pearl et al reported a similar case in the frontal bone, and in their opinion in such cases the differential diagnosis should also include metastatic carcinoma, myeloma, fibrous dysplasia, and osteogenic sarcoma. Azar-Kia et al[4] gathered several cases of intraosseous meningiomas and reviewed mainly the radiologic appearance of these neoplasms. In their series, the distribution of the neoplasms was as follows: 4 frontal, 4 frontoparietal, 2 temporal, and 2 parietal. No occipital tumors were reported.[4] Pompili et al[5] reported a meningioma occurring in the orbital roof. Their case had no associated hyperostosis, but, interestingly enough, demonstrated a "shell" that gave the radiologic image of a calcified mass.

The pathogenesis of the hyperostosis associated with meningiomas has been studied by different researchers. In 1922, Cushing proposed that hyperostosis was due to invasion of the bony canaliculi by meningioma, with resultant new bone formation due to stimulated osteoblastic activity.[4] Kolodny and Schlesinger thought that hyperostosis was caused by venous stasis in the bone/More recently, at least 3 other mechanisms have been proposed to explain this abnormal bone overgrowth. Heick et al[6] stated that this phenomenon occurs for various reasons, including (1) calcification of the tumor, (2) formation of osteoid spiculae, and (3) genuine ossification of the meningioma and osteolytic activity. In these proposed mechanisms, a mineralization path is necessary for calcification/ossification to occur, and the authors believe that alkaline phosphatase plays an important role in this path. However, they cannot fully prove the effects of alkaline phosphatase in bone and also could not determine the effects of other growth factors in the development of hyperostosis.[6] The pathophysiologic mechanisms are the subject of further research.[3]

Meningiomas display an immunohistochemical profile that is helpful when differentiating them from other neoplasms in the central nervous system. Glial fibrillary acidic protein is usually negative in meningiomas, but positive in glial and astrocytic neoplasms. Epithelial membrane antigen positivity in a cytoplasmic pattern is a characteristic of meningioma; this feature may help when schwannoma is part of the differential diagnosis.[7]

This case is remarkable for 2 reasons, namely, the previously unreported occipital location of the lesion and the striking radiologic appearance caused by the presence of such florid hyperostosis that caused not only clinical symptoms but also complicated the surgical approach. Although meningiomas in this location are extremely rare, these neoplasms should be included in the clinicopathologic differential diagnosis when dealing with neoplastic processes in this particular location.

References

[1.] Oka K, Hirikawa K, Yoshida S, Tomogana M. Primary calvarial meningiomas. Surg Neurol. 1989;32:304-310.

[2.] McWhorter KM, Ghatak NR, Kelly DL. Extracranial meningioma presenting as a lyric skull lesion. Surg Neurol. 1976;5:223-224.

[3.] Pearl GS, Takei Y, Parent AD, Boehm WM Jr. Primary intraosseous meningioma presenting as a solitary osteolytic skull lesion: case report. Neurosurgery. 1979;4:269-270.

[4.] Azar-Kia B, Sarwar M, Marc JA, Schechter MM. Intraosseous meningioma. Neuroradiology. 1974;6:246-253.

[5.] Pompili A, Caroli F, Cattani F, lachetti M. Intradiploic meningioma of the orbital roof. Neurosurgery. 1983;12:565-568.

[6.] Heick A, Mosdal C, Jorgensen K, Klinken L. Localized cranial hyperostosis of meningiomas: a result of neoplastic enzymatic activity? Acta Neurol Stand. 1993;87:243-247.

[7.] Burger PC, Scheithauer BW. Meningiomas. In: Tumors of the Central Nervous System. Washington, DC: Armed Forces Institute of Pathology; 1994:272-274. Atlas of Tumor Pathology; 3rd series, fascicle 10.

Accepted for publication May 5, 2000.

From the Arkadi M. Rywlin, MD, Department of Pathology and Laboratory Medicine (Drs Castellano-Sanchez, Alexis, and Poppiti) and the Departments of Neurosurgery (Dr Nanes) and Radiology (Dr Villalobos), Mount Sinai Medical Center, Miami Beach, Fla; and the University of Miami School of Medicine, Miami, Fla (Drs Castellano-Sanchez, Alexis, and Poppiti).

Reprints: Amilcar A. Castellano-Sanchez, MD, Arkadi M. Rywli, MD, Department of Pathology and Laboratory Medicine, Blum Bldg, Rm 201, Mount Sinai Medical Center, 4300 Alton Rd, Miami Beach, FL 33240 (e-mail: [e-mail]).