A sixty-three year old woman presented with progressive pain and thickening of the right skull frontal bone. Physical examination revealed a swelling of the right frontal region about 12 cm in diameter; the lesion was not adherent to the overlying skin and was not mobile or tender. The patient had no neurologic deficit but she complained of a sensation of pressure in the right eye, occasionally feeling unable to open it. Laboratory studies were unremarkable.
Plain x-ray films revealed a large, sclerotic lesion involving the right side of the frontal bone of the skull, extending to the unilateral frontal sinus (Fig. 1). Further imaging with CT scan showed a diffuse sclerotic right-sided frontal lesion measuring approximately 9.5 x 12 x 1.5 cm involving the diploe with extensive mature periosteal new bone formation along the external table of the right frontal bone (Fig. 2a-c). The lesion extended across the midline and into the right frontal sinus. An MRI scan confirmed the osseous nature of the tumour and the absence of infiltration of the brain parenchyma (Fig. 3a, b).
After biopsy of the lesion for histological diagnosis (see below), follow-up imaging showed progressive periosteal bone formation on the external table of the calvarium. Four months after the biopsy, a right frontal craniotomy with mesh cranioplasty was performed with resection of the calvarial tumour but not the mass in the frontal sinus. The patient made a good post-operative recovery and has remained clinically well with follow up imaging over 3 years showing that the residual tumour has not increased in size.
Histopathology of the fixed, decalcified biopsy and resection specimens showed similar features. There was abundant thickened organised reactive woven and lamellar bone with numerous thickened bone trabeculae separated by dense collagenous fibrous tissue containing scattered cells with wavy, spindle-shaped or ovoid vesicular nuclei between bone trabeculae and in Haversian channels (Fig. 4a, b). There were also numerous scattered cells with vacuolated cytoplasm and focally small meningotheliomatous whorls of cells with vesicular nuclei in fat and fibrous tissue (Fig. 4c, d). The tumour involved cortical and medullary bone and the dura but had not spread into superficial soft tissue beyond the periosteum. Immunohistochemistry showed that the lesional cells strongly expressed epithelial membrane antigen (EMA), vimentin and progesterone receptor (PR) (Fig. 5a-c). A few cells reacted for CD99 and podoplanin. There was no staining for estrogen receptor, CD45, CD68, CD10, chromogranin, Melan A, HMB45, CD34, CDK4, SATB2, desmin, smooth muscle/muscle actin, GFAP, NSE, cytokeratin (CK7-, CK20-), Brachyury, S100, DMP-1 CD31, CD34 or factor 8. There was a low Ki-67 proliferation index. The morphological features and strong expression of EMA and PR were considered to be consistent with the diagnosis of a partly fibroblastic intraosseous meningioma. (WHO Grade I).