title: Elevation of internal auditory canal pressure by vestibular schwannomas.
abstract: OBJECTIVE
  The exact mechanism of hearing loss, the most common presenting symptom in patients with vestibular schwannomas, remains unclear. To test whether 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.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  Tertiary referral hospital.
  
  
  METHODS
  Fifteen consecutive patients undergoing a retrosigmoid approach for resection of vestibular schwannomas were included in the study.
  
  
  METHODS
  The intracanalicular pressure in every patient was measured by introducing a pressure microsensor into the internal auditory canal. The pressure readings, which were performed before tumor resection, were then correlated 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 intracanalicular pressure was 20 mm Hg, there was significant variability among patients (range, 1-45 mm Hg). The intracanalicular pressure directly correlated with the amount of tumor in the internal auditory canal (r > 0.63, p < 0.012) but not with the total tumor size (r </= 0.40, p > 0.075). Furthermore, eight patients with class A preoperative hearing (American Academy of Otolaryngology-Head and Neck Surgery classification) had lower intracanalicular pressures than did five patients with class B hearing (16 +/- 5 vs. 28 +/- 4). Although this observation suggested an inverse correlation between the intracanalicular pressure and hearing function, the difference between the two groups was not statistically significant (p = 0.14).
  
  
  CONCLUSIONS
  Pressure on the cochlear nerve as a result of tumor growth in the 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 hearing preservation in these patients.
authors.affiliation: Department of Neurologic Surgery, University of Wisconsin School of Medicine, Madison, Wisconsin 53792-3232, USA.
authors.forename: B
authors.initials: B
authors.lastname: Badie
authors.forename: G M
authors.initials: GM
authors.lastname: Pyle
authors.forename: P H
authors.initials: PH
authors.lastname: Nguyen
authors.forename: E J
authors.initials: EJ
authors.lastname: Hadar
mesh_terms: D003056:Cochlear Nerve / Q000503:physiopathology; D003389:Cranial Nerve Diseases / Q000209:etiology / Q000503:physiopathology; D007758:Ear, Inner / Q000473:pathology*; D006801:Humans; D009464:Neuroma, Acoustic / Q000150:complications / Q000473:pathology*; D011446:Prospective Studies; D013069:Speech Reception Threshold Test