Mount meningioma with tumor cap.

The association between meningioma and hyperostosis of adjacent calvarium is well established. However, the cause of hyperostosis is still not certain. Various authors in the past have tried to explain this phenomenon by preceding trauma or by bone irritation by the tumor without bone invasion, while some believe it to be because of stimulation of osteoblasts in normal bone by factors secreted by tumor cells. There are still others who believe it to be secondary to production of bone by the tumor itself, while some have hypothesised that vascular disturbances secondary to the tumor result in hyperostosis. The authors wish to report a case of parasagittal meningioma in which the bone overlying the meningioma was so hyperostotic that it appeared to look like a 'mountain'. In addition, the tumor appeared to invade through the bone to form a 'tumor cap' over the hyperostotic bone.