Various patterns of the middle cerebral vein and preservation of venous drainage during the anterior transpetrosal approach

OBJECTIVE: The drainage of the superficial middle cerebral vein (SMCV) has previously been classified into 4 subtypes. Extradural procedures and dural incisions during the anterior transpetrosal approach (ATPA) may interrupt the route of drainage from the SMCV. In this study, the authors examined the relationship between anatomical variations in the SMCV and the corresponding surgical modifications to the ATPA that are necessary for venous preservation. METHODS: This study included 48 patients treated via the ATPA in whom the SMCV was examined using 3D CT venography. The drainage patterns of the SMCV were classified into 3 types: cavernous or absent (Type 1), sphenobasal (Type 2), and sphenopetrosal (Type 3). Type 2 was subdivided into medial (Type 2a) and lateral (Type 2b), and Type 3 was subdivided into vein (Type 3a), vein and sinus (Type 3b), and sinus (Type 3c). The authors performed 3 ATPA modifications to preserve the SMCV: epidural anterior petrosectomy with subdural visualization of the sphenobasal vein (SBV), modification of the dural incision, and subdural anterior petrosectomy. Standard ATPA can be performed with Type 1, Type 2a, and Type 3a drainage. With Type 2b drainage, an epidural anterior petrosectomy with subdural SBV visualization is appropriate. The dural incision should be modified in Type 3b. With Type 3c, a subdural anterior petrosectomy is required. RESULTS: The frequency of each type was 68.7% (33/48) in Type 1, 8.3% (4/48) in Type 2a, 4.2% (2/48) in Type 2b, 14.6% (7/48) in Type 3a, 2.1% (1/48) in Type 3b, and 2.1% (1/48) in Type 3c. No venous complications were found. CONCLUSIONS: The authors propose an SMCV modified classification based on ATPA modifications required for venous preservation.