OBJECTIVE:Histological and radiological classification of vascular malformations has previously been attempted in an effort to understand their nature and predict their biological behavior. There exists a subgroup of vascular malformations that are angiographically occult and share a common magnetic resonance imaging (MRI) appearance but may differ in their behavior. We sought to determine any correlation between MRI features and final histopathological diagnosis.METHODS:We reviewed our series of 72 patients with angiographically occult vascular malformations operated on at Stanford University Medical Center between 1988 and 1993. Radiographic magnetic resonance images and histopathological specimens were retrospectively evaluated for various diagnostic features.RESULTS:Our data indicate that lesions exhibiting a ring of hemosiderin are associated with the presence of a cavernous malformation (CM) component (86% of CMs versus 33% of non-CM lesions). A lesion associated with edema, mass effect, or a single prominent blood product on MRI correlates with the presence of an arteriovenous malformation (AVM) component. Sixty-three percent of AVMs and 80% of lesions with partial AVM components showed edema, compared with 8% of CMs and 0% of venous malformations. Sixty percent of AVMs and 63% of lesions with partial AVM components showed a single prominent blood product, compared with 8% of CMs and 0% of venous malformations. Finally, 60% of AVMs exhibited mass effect, compared with 20% of CMs. Additionally, an expansile hemorrhage is suggestive of an AVM.CONCLUSION:This study is the first to demonstrate that a particular MRI appearance of an angiographically occult vascular malformation is suggestive of an AVM component. This may have important implications with regard to the behavior of the lesion and planning of future treatment.