Middle Fossa Approach

The middle fossa approach, as described by House in 1961 involves an extradural subtemporal approach with microneurosurgical unroofing of the internal auditory canal. This approach is limited to the excision of small intracanalicular tumors that have not escaped the confines of the internal auditory canal. It is usually performed in patients in whom hearing remains at a functional level, providing a chance of hearing preservation.

Subtemporal-Transtentorial Approach

The subtemporal-transtentorial approach as described by Rosomoff, uses a craniotomy centered low over the petrous ridge, extending anteriorly over the middle cranial fossa, superiorly to the parietal boss and posteriorly to a point midway between the mastoid process and the inion. A U-shaped dural flap based on the transverse sinus is made. The temporal lobe is retracted anteriorly and the occipital lobe is retracted posteriorly. At this point it may be necessary to divide the vein of Labbe or possibly several smaller veins draining the temporal and occipital lobes. The petrous ridge and superior petrosal sinus are followed to the edge of the tentorium, where the trochlear nerve can be identified. The tentorium is opened close to the petrosal sinus and this opening is angled back to a point behind the entrance of the trochlear nerve. Retraction of the divided tentorium provides adequate exposure of the cerebellopontine angle. In the removal of an acoustic tumor, the superior petrosal sinus is ligated and a dural flap is turned over the acoustic meatus. The roof of the canal is drilled away and the tumor is dissected free of the nerves. A technique of internal decompression with mobilization is used to remove the remaining tumor. Complications of this approach include possible injury to the trochlear nerve, inadequate exposure of the lower pole of the tumor, postoperative seizures, and temporal lobe dysfunction.