32Total Removal of a Large Vestibular Schwannoma with Hearing Preservation

A 45-year-old man complaining of dizziness was referred to our hospital with a large mass in the right cerebellopontine angle on the computed tomographic (CT) scan. On admission, the patient exhibited no neurological abnormality. Subsequent magnetic resonance imaging (MRI) showed a large enhancing mass, 3.5 cm in maximal diameter, in the right cerebellopontine angle (Fig. 32–1). A CT scan with bone windows showed a slight enlargement of the right internal auditory canal. On audiometrical examinations, the patient’s pure-tone average (PTA) (the average of thresholds at 500, 1000, and 2000 Hz) was 25 dB, the speech discrimination (SD) was 100% at 70 dB, and the brain stem auditory evoked potential (BAEP) was normal on both sides. The tumor was diagnosed as a vestibular schwannoma.

Surgical Technique

The patient was placed in the lateral position and the upper part of the body was elevated 15 degrees, with forward flexion of the head. A vertical skin incision was made 1 cm medial to the mastoid process. A suboccipital craniotomy (5 × 4 cm) was performed in the usual manner to expose the genu of the transverse and sigmoid sinuses. After the dura was opened, the lateral medullary cistern was opened and cerebrospinal fluid (CSF) was allowed to drain.

Under the microscope, the arachnoid was dissected from the tumor capsules carefully to prevent injury to the vessels on the cerebellar and brain stem sides. The tumor capsule, which was safely defined with facial stimulation by the Silverstein Facial Nerve Monitor/Stimulator (Medical Electronics, USA), was coagulated and opened. The tumor was then internally debulked with ultrasonic aspiration. After debulking, the arachnoid was dissected to expose the inferior tumor capsule. The ninth, tenth, and eleventh cranial nerves, which were covered by arachnoid, were identified. Internal decompression, arachnoid dissection, and removal of the tumor capsule were performed repeatedly. Superiorly, the tumor extended to the cerebellar tent. The petrosal vein and the fourth and fifth cranial nerves, which were covered by arachnoid, were identified. A cranial nerve bundle, which was seen inferomedially, was identified with the cochlear nerve by recording of the direct cochlear nerve action potentials. The cochlear nerve was dissected toward the internal auditory canal, preserving the branches of the anterior inferior cerebellar artery along the cochlear nerve. The seventh cranial nerve was identified anterior to the cochlear nerve through electrical stimulation. Sharp dissection separated the facial nerve from the tumor capsule toward the internal auditory canal. After the tumor on the brain stem side was removed, the operating table was rotated so that we could see the internal auditory canal. The posterior wall of the internal auditory canal was removed with a diamond burr on the high-speed drill. The tumor in the internal auditory canal was removed through sharp dissection with microscissors and a thin dissector. Bleeding along the nerves occurred, but stopped spontaneously with saline irrigation and the placement of oxidized cellulose (Surgicel®). The final intraoperative view showed that the fourth, fifth, sixth, seventh, cochlear, ninth, tenth, and eleventh cranial nerves were identified and preserved (Fig. 32–2

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