The nature and fate of punctate (type IV) cavernous malformations.

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Four types of cavernous malformations (Types I-IV) have been described on the basis of their magnetic resonance imaging (MRI) appearance. The nature of the Type IV cavernous malformation is unclear. It has been suggested that these small lesions, which are well observed only on gradient echo MRI scans, are capillary telangiectasias. We sought to understand the relationship of Type IV cavernous malformations to the other cavernous malformation subtypes. We examined serial MRI scans obtained between 1987 and 2000 from 68 patients with more than 228 cavernous malformations. Sixteen patients harbored Type IV cavernous malformations (total, >114 Type IV lesions). Spin echo T1-weighted, T2-weighted, proton density, and (when available) gradient echo MRI scans were reviewed. Cavernous malformations that met the Zabramski criteria for Type IV (poorly observed on T1- and T2-weighted images) were reviewed in serial scans from individual patients to characterize their radiographic behavior over time. Type IV cavernous malformations were best observed on gradient echo images and have an MRI appearance distinct from capillary telangiectasias. Proton density images demonstrate more Type IV lesions than T1- and T2-weighted images, but far fewer Type IV lesions than gradient echo images. When observed on T1- and T2-weighted images, Type IV cavernous malformations are generally punctate and hypointense. These lesions rarely enhance with gadolinium. Four of the Type IV cavernous malformations observed serially evolved into Type I and Type II cavernous malformations, for an approximate rate of progression of 0.05 per patient year. Although most Type IV cavernous malformations remain stable over time, a small subset of these lesions progress into Types I and II cavernous malformations.