Classification of medullary venous malformations in the temporal lobe: according to location and drainage pathway

Medullary venous malformation (MVM) is rare in the temporal lobe, and the radiologic characteristics of temporal MVM have not yet been clarified. In 12 previously reported cases with satisfactory angiographic or magnetic resonance information as well as two newly reported here, we analyzed the specific location and hemodynamics of temporal lobe MVMs, particularly with respect to venous drainage. Temporal lobe MVM typically were seen in the superior lateral portion of the temporal lobe near either the atrium or the inferior horn of the lateral ventricle. Venous drainage was classified into two main patterns: deep (three cases) and superficial (11 cases). Superficial drainage could be divided into two subtypes: lateral and anterior. Dilated deep medullary veins converged toward either the lateral wall of the atrium or the inferior horn of the lateral ventricle. In the deep-drainage type, medullary veins drained into subependymal veins such as the inferior ventricular vein and the lateral atrial vein, and then emptied into the basal vein of Rosenthal. The anastomotic lateral mesencephalic vein was involved in one case as a variant of the basal vein. When the subependymal veins and/or the basal vein of Rosenthal or transverse sinus were hypoplasic, the medullary veins drained into either the Sylvian veins (anterior superficial type) or the vein of Labbé (lateral superficial type) through a characteristic large transcerebral vein. Drainage of temporal lobe MVM can be classified as deep, lateral superficial, or anterior superficial.