Venous hemodynamics of arteriovenous meningeal fistulas in the posterior cranial fossa.

The etiology of arteriovenous meningeal fistulas (AVMFs) of the posterior fossa often remains unclear. Analyses of three personal cases, however, suggest a change in venous hemodynamics due to a primary lesion, the cases being of sinus thrombosis, intracerebral abscess with oedema and arteriovenous malformation. It is suggested that increase of venous pressure in the posterior fossa leads to increased drainage and, consequently, to dilatation of infratentorial veins and of meningeal branches of the external carotid and vertebral artery. Clinical findings and anatomical facts underlying AVMF lesions tend to confirm the view that the concept of a congenital malformation decompensating with age cannot be upheld for all AVMFs, especially when located in the posterior fossa and when clinical symptoms arise in middle age. It is proposed that a pressure activated mechanism of growth results in widening of normally insignificantly small dural vessels.