Elevation of internal auditory canal pressure by vestibular schwannomas

Objective: The exact mechanism of hearing loss, the most common presenting symptom in patients with vestibular schwannomas, remains unclear. To test w hether increased pressure in the internal auditory canal from tumor growth is responsible for this clinical finding, the intracanalicular pressure in patients harboring these tumors was measured. Study Design: Prospective study. Setting: Tertiary referral hospital. Patients: Fifteen consecutive patients undergoing a retrosigmoid approach f or resection of vestibular schwannomas were included in the study. Intervention: The intracanalicular pressure in every patient was measured b y introducing a pressure microsensor into the internal auditory canal. The pressure readings, which were performed before tumor resection, were then c orrelated with tumor size and respective preoperative hearing status. Results: Placement of the pressure monitor into the internal auditory canal revealed a biphasic waveform in every patient. Whereas the mean intracanal icular pressure was 20 nun Hg, there was significant variability among pati ents (range, 1-45 mm Hg). The intracanalicular pressure directly correlated with the amount of tumor in the internal auditory canal (r > 0.63, p < 0.0 12) but not with the total tumor size (r less than or equal to 0.40, p > 0. 075). Furthermore, eight patients with class A preoperative hearing (Americ an Academy of Otolaryngology-Head and Neck Surgery classification) had lowe r intracanalicular pressures than did five patients with class B hearing (1 6 +/- 5 vs. 28 +/- 4). Although this observation suggested an inverse corre lation between the intracanalicular pressure and hearing function, the diff erence between the two groups was not statistically significant (p = 0.14). Conclusion: Pressure on the cochlear nerve as a result of tumor growth in t he internal auditory canal may be responsible for hearing loss in patients with vestibular schwannomas. Modification of surgical techniques to address the elevated intracanalicular pressure may be beneficial in improving hear ing preservation in these patients.