Venous Preservation in the Anterior Transpetrosal Approach

Background: An anterior transpetrosal approach (ATPA) may interrupt some types of the drainage routes of the superficial middle cerebral vein (SMCV). To preserve the SMCV, we proposed the classification of the SMCV according to the surgical variation of the ATPA. Methods: The drainage patterns of the SMCV were examined in 47 patients treated via ATPA by three-dimensional CT angiography (3DCTA). Results: The drainage patterns of the SMCV were classified into three types. Type1 (cavernous/absent, 68.7%) includes cavernous drainage or absence of the SMCV. In this type, a typical epidural ATPA is possible. Type2 (sphenobasal) includes the sphenobasal vein. In case of drainage to the medial and/or anterior side of the ovale (type 2a, 8.3%), we can perform a typical ATPA. However, in the case of drainage to the posterolateral side of the ovale (type 2b, 4.1%), ATPA should be modified as previously reported. Type3 (middle fossa) includes the other drainage types. In this type, we should first confirm the vein or sinus from the subdural side. In the vein type, we can perform a typical epidural ATPA (type 3a, 14.6%). In the sinus type, we should then check whether we can peel off the basal dura from the middle fossa. If we can peel off the basal dura, we should consider the modification of the dural incision according to the transitional region from vein to sinus (type 3b, 2%). If we cannot peel off the basal dura of the temporal, subdural anterior petrosectomy is required (type 3c, 2%).