Mixed vascular malformations of the brain: clinical and pathogenetic considerations.

The clinical relevance of any scheme for classification of vascular malformations of the brain remains controversial. Widely accepted pathologic classifications include discrete venous, arteriovenous, capillary, and cavernous malformations. Of 280 cases of possible vascular malformations evaluated by a single cerebrovascular service during a 5-year period, 14 were instances of mixed vascular malformations including definite features of more than one pathologically discrete type of malformation within the same lesion. There were six instances of mixed cavernous and venous malformations in the same lesion; in all instances, the cavernous malformation accounted for the clinical presentation. There were three cases of mixed venous and arteriovenous malformations (arterialized venous malformations), presenting with the typical histoarchitectural appearance of a venous malformation, but with arteriovenous shunting; all cases were symptomatic, two with hemorrhage and one with focal neurological symptoms. There were five cases of predominantly cavernous malformations with features of arteriovenous malformation or capillary telangiectasia in the same lesion. These five cases presented clinically as angiographically occult lesions indistinguishable from a cavernous malformation. Lesions including a venous malformation were recognizable preoperatively because of characteristic imaging features of the venous malformation. Other mixed vascular malformations were indistinguishable on diagnostic studies from pure cavernous malformations. Of the 14 mixed vascular malformations, 11 included a cavernous malformation that was usually responsible for the symptomatic presentation. In the other three cases, manifestations of clinical lesions were due to arteriovenous shunting within a venous malformation. We conclude that mixed vascular malformations of the brain are rare entities with distinct clinical, radiological, and pathological profiles. Their identification generates several hypotheses about common pathogenesis or causation-evolution among different types of lesions.