Dural arteriovenous malformation of the skull base with intraosseous vascular nidus. Report of two cases.

Intracranial arteriovenous malformations (AVM's) have been classified as pure pial, pure dural, and mixed pial and dural. Dural AVM's are relatively uncommon, with 377 cases documented up to 1990. These lesions were believed to be situated within the walls of the sinuses, but during the last decade researchers discovered a small subgroup of dural AVM's in extrasinusal locations such as the skull base and tentorium. Two of the 17 patients who were studied between 1976 and 1993 had dural AVM's that were entirely intraosseous except for their venous drainage, which was via the dural venous sinuses. Although such intraosseous dural AVM's have not been previously described, the authors elected to group these malformations with dural AVM's because their venous drainage was intracranial and angiograms revealed identical features.