Epidural Anterior Petrosectomy with Subdural Visualization of Sphenobasal Vein via the Anterior Transpetrosal Approach

The drainage of the superficial middle cerebral vein (SMCV) is classified into four subtypes. The sphenobasal vein (SBV) drains from the SMCV to the pterygoid venous plexus at the temporal skull base. Epidural procedures in the standard anterior transpetrosal approach (ATPA) may damage the route of the SBV. We report a case in which modified surgical procedures via the ATPA were used to preserve the SBV. A 45-year-old male complained of right facial pain. Magnetic resonance (MR) images revealed a right cerebellopontine tumor suggestive of an epidermoid cyst. Right carotid angiography revealed that the SMCV drained into the pterygoid venous plexus via the SBV. The convexity dura mater of the temporal lobe was cut and the anterior part of the temporal lobe was retracted subdurally. The basal dura of the temporal lobe posterior to the SBV vein was visualized and cut subdurally. The posterior part of the temporal lobe was retracted epidurally. After dissecting, the dura mater medial to the greater petrosal nerve and to the edge of the petrous apex, the petrous apex was exposed and drilled out without injuring the SBV. The superior petrous sinus and the tentorium were cut. The tumor was compressed at the root exit zone of the trigeminal nerve. The tumor was removed grossly and totally. The modified ATPA (epidural anterior petrosectomy with subdural visualization of sphenobasal vein) is effective to preserve the SBV.