The nature and fate of punctate (Type IV) cavernous malformations

OBJECTIVE: Four types of cavernous malformations (Types I-IV) have been des cribed on the basis of their magnetic resonance imaging (MRI) appearance. T he nature of the Type IV cavernous malformation is unclear. It has been sug gested that these small lesions, which are well observed only on gradient e cho MRI scans, are capillary telangiectasias. We sought to understand the r elationship of Type IV cavernous malformations to the other cavernous malfo rmation subtypes. METHODS: We examined serial MRI scans obtained between 1987 and 2000 from 6 8 patients with more than 228 cavernous malformations. Sixteen patients har bored Type IV cavernous malformations (total, > 114 Type IV lesions). Spin echo T1-weighted, T2-weighted, proton density, and (when available) gradien t echo MRI scans were reviewed. Cavernous malformations that met the Zabram ski criteria for Type IV (poorly observed on T1- and T2-weighted images) we re reviewed in serial scans from individual patients to characterize their radiographic behavior over time. RESULTS: Type IV cavernous malformations were best observed on gradient ech o images and have an MRI appearance distinct from capillary telangiectasias . Proton density images demonstrate more Type IV lesions than T1- and T2-we ighted images, but far fewer Type IV lesions than gradient echo images. Whe n observed on T1- and T2-weighted images, Type IV cavernous malformations a re generally punctate and hypointense. These lesions rarely enhance with ga dolinium. Four of the Type IV cavernous malformations observed serially evo lved into Type I and Type II cavernous malformations, for an approximate ra te of progression of 0.05 per patient year. CONCLUSION: Although most Type IV cavernous malformations remain stable ove r time, a small subset of these lesions progress into Types I and II cavern ous malformations.