[Surgery of AVM of the inferior medullary velum by the uvulotonsillar approach--advantage of moving of the cerebellar tonsil: technical case report].

An incidentally found arteriovenous malformation (AVM) of the inferior medullary velum behind the medulla was removed by the lateral approach to the fourth ventricle originally described by Seeger in 1980. A wide posterior fossa craniotomy was performed to move the cerebellar tonsil laterally with C-1 laminectomy. The tela chroidea and inferior medullary velum, the two main sheets of tissue that form the lower half of the roof of the fourth ventricle can be exposed by gently displacing the tonsils laterally without splitting the vermis. Both the cerebellomedullary and uvulotonsillar spaces were exposed. Because the lateral cerebellomedullary cistern was also exposed, the moving of the cerebellar tonsil in a lateral direction was easy to do without injuring the cerebellar tissues. The nidus was located mainly in the extrapial plane that received feeding arteries from the posterior inferior cerebellar artery. The nidus was removed in a dry field without bleeding. This report is the first report of surgical removal of unruptured AVM of the inferior medullary velum through the so-called telovelar or transcerebellomedullary fissure approach. We propose to call this approach the uvulotonsillar approach to emphasize the dissecting plane between the uvula and the tonsil.