Posterior fossa venous angiomas with drainage through the brain stem.

PURPOSE To describe 11 cases of posterior fossa venous angiomas with drainage through the brain stem. METHODS Eleven cases of posterior fossa venous angioma with drainage through the brain stem were evaluated using MR. Correlation with known routes of venous drainage for the cerebellum and brain stem is made. RESULTS Six of the 11 venous angiomas were found in the cerebellum, four in the brain stem; one involved both the cerebellum and brain stem. The cerebellar venous angiomas drained to subependymal veins about the fourth ventricle and dorsal pons. These then connected with an enlarged transmesencephalic or transpontine vein, to drain anteriorly to the anterior pontine veins. The brain stem angiomas had variable drainage depending on location. Evidence of hemorrhage was seen in five cases. CONCLUSION Cerebellar and brain stem venous angiomas have several potential routes of drainage, including an enlarged vein traversing the pons, midbrain, or medulla. A knowledge of the normal venous anatomy of this region helps to understand the occurrence of these uncommon routes of venous drainage.