Usefulness of an Inferolateral Suboccipital Infrafloccular Approach in Hearing Preservation during MVD for Hemifacial Spasm

Purpose: To evaluate the usefulness of using an inferolateral suboccipital infrafloccular approach to prevent hearing loss during microvascular decompression (MVD) for hemifacial spasm (HFS) in a center not equipped with intraoperative monitoring facilities.

Methods: Our center is the first to start epilepsy surgery in Eastern India where there are likely to be around 100,000 patients with intractable epilepsy. We decided that if we were to start MVD for HFS safely in our center presently not equipped with neuromonitoring facilities, we would have to use a skull base approach that would minimize retraction of the cerebellum and thereby minimize injury to the eighth nerve. We chose patients, after appropriate informed consent, with severe HFS who either could not afford Botox or who were tired of repeated injections. We used an inferolateral suboccipital approach involving bony removal from the incisura mastoidea down as far laterally as the posterior condylar foramen and as far caudally as the foramen magnum. The bony removal involved exposing the medial border of the inferior half of the sigmoid sinus. The park bench positioning of the patient involved lateral flexion at the upper cervical spine and the head was positioned vertex down in order to open up the required area. This approach allowed inspection of the root-entry zone of the seventh nerve which is blocked laterally by the flocculus and the eighth nerve from a caudolateral infrafloccular direction between the flocculus and the glossopharyngeal nerve. Retraction of the flocculus is made in a caudorostral direction perpendicular to the eighth nerve.

Results: We have used this approach in five patients. None of these patients had any postoperative hearing deterioration. Excellent results for HFS were achieved in four. One patient with an atypical vascular loop between the seventh and the eighth nerve had only temporary partial relief lasting 6 months but had no hearing deterioration.

Conclusions: This approach probably minimizes the risk of hearing deterioration during MVD for HFS. This also demonstrates the importance of the skull base philosophy for even what is considered functional neurosurgery. This is very important because of the growing replacement of treatment of skull base lesions by endovascular techniques and radiosurgery. But in any case, to be a good neurosurgeon, understanding of the skull base anatomy and philosophy is imperative.