Removal of Vestibular Schwannoma

The retromastoid suboccipital approach can be used for any size tumor with or without attempts to preserve hearing. This technique allows the tumor and the important structures medial and lateral to it to be in full view in the surgical field. In general, an incision is made to the tip of the mastoid eminence. After separation of the underlying muscles, a bony opening is made, extending laterally to the sigmoid sinus. The surgeon carefully tries to preserve the planes of the arachnoid over the tumor, to protect the delicate cranial nerves and brainstem. To the right, the fifth cranial nerve and petrosal vein are seen; toward the lower portion of the field, the glossopharyngeal (IX), vagus (X), and accessory (XI) nerves are visible.

When the tumor grows in the posterior portion of the canal, the facial nerve tends to be pushed forward. Knowing this relationship is important in preserving the facial nerve, which is markedly flattened and often quite adherent just medial to the internal auditory meatus. The vestibular nerves, from which the tumor is arising, must be sectioned. If hearing has not already been irreversibly damaged, preservation of hearing may be attempted by minimizing manipulation of the cochlear nerve and protecting the labyrinthine artery, which may be a source of blood supply to the tumor. The anterior inferior cerebellar artery, which supplies the lateral portion of the brainstem and cerebellar peduncles, is another important structure to which the surgeon must be mindful.

With a larger tumor, the capsule is gutted at an early stage to facilitate atraumatic manipulation. In the second drawing above, the 9th, 10th, and 11th cranial nerve complex is visible, passing through the jugular foramen with the accompanying sigmoid sinus. The bottom drawing at right illustrates a view after the tumor has been excised. The labyrinthine artery has been preserved, and the relationship of the four main nerves in the canal is seen. Because a CSF leak through the lateral portion of the canal can develop, the lateral canal is plugged with fat and bone wax.

For patients who are not surgical candidates, stereotactic radiosurgery (SRS) and stereotactic fractionated radiotherapy have been used. Stereotactic radiosurgery focuses the beams in a single dose to a discrete tumor volume in an effort to decrease the risk of damage to neighboring structures. One large series documented a 97% tumor control rate at 10 years with SRS. Fractionated stereotactic radiation focuses the radiotherapy over a series of treatments to minimize the risk of damage to critical structures. One prospective study comparing SRS with stereotactic radiotherapy documented a 97% tumor control rate for both treatments with a higher rate of hearing preservation with the fractionated stereotactic radiotherapy. Potential concerns for radiotherapy is the risk of cranial nerve injury, secondary tumor formation, and scarring, rendering future surgeries more precarious.

Finally, conservative management is used in select patients, especially those with small symptomatic tumors or who are deemed poor candidates for immediate intervention. In these patients, close monitoring with surveillance MRIs is warranted.

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Sep 2, 2016 | Posted by in NEUROLOGY | Comments Off on Removal of Vestibular Schwannoma
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