Anatomic considerations in vestibular neuritis

Hypothesis: The authors believe that anatomic differences render the superi or division of the vestibular nerve more susceptible to injury during vesti bular neuritis. The purpose of the study was to investigate anatomic differ ences between the superior vestibular nerve and singular nerve canals. Background: Previous studies of temporal bones have revealed vestibular ner ve degeneration in patients with vestibular neuritis. Although the cause of this degeneration has not been established, it has been noted that the sup erior division of the vestibular nerve is preferentially affected, with spa ring of the inferior division. The superior vestibular nerve and the singul ar nerve, a branch of the inferior vestibular nerve, both pass through cana ls interlaced with bony networks before reaching the peripheral receptors. Methods: The authors performed histologic analysis of 40 normal temporal bo nes randomly selected from their temporal bone library. With a micrometer, measurements were taken of the individual canals. The ratio of the total bo ny spicule component to the total canal width was obtained for both the sup erior vestibular nerve and the singular nerve. The length of the canals was also measured. Arteriole:arteriolar canal ratios of the superior vestibula r nerve and singular nerve were obtained. Results: The bony channel of the singular nerve had an average length of 0. 59 mm, and the average length of the superior vestibular nerve was 2.30 mm (p < 0.001). The ratio of total bony spicule width to total canal width was significantly smaller (p < 0.05) for the singular nerve (0.30 mm) compared with the superior vestibular nerve (0.14 mm). The arteriole: arteriolar ca nal ratio was significantly smaller (p < 0.05) for the singular nerve (0.45 mm) than for the superior vestibular nerve (0.54 mm). Conclusion: The bony canal of the superior vestibular nerve is longer than the singular nerve canal. Additionally, the superior vestibular nerve and a rteriole travel through a relatively narrower passage than the singular ner ve and its vascular supply. From an anatomic standpoint, this renders the s uperior division of the vestibular nerve more susceptible to entrapment and possible ischemic labyrinthine changes.