Long Term Hearing Preservation in Acoustic Neuroma Surgery - Not always a Sure Thing

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Contact: Kenneth Satterfield561-447-5521 (May 9-14, 2002)703-519-1563[email protected]

Long Term Hearing Preservation in Acoustic Neuroma Surgery - Not always a Sure Thing

Boca Raton, FL -- Acoustic neuromas or schwannoma are benign neoplasms or tumors located in the intracranial segment of the eighth cranial nerve, producing cerebellar, lower cranial nerve, and brainstem signs and symptoms. These symptoms can include progressive and sudden hearing loss as well as balance disorders. Surgical intervention or medical management may be indicated for treating this condition.

For those undergoing acoustic neuroma surgery, the current success rates for hearing preservation in selected patients range from 15 to 68 percent. This spread may be a result of varying definitions applied to successful hearing preservation. Although much has been published on hearing preservation after acoustic neuroma surgery, the literature on the natural history of long-term hearing preservation is sparse.

Certain factors affect the likelihood of successful hearing preservation in the early post-operative period. These are well reported and include size of tumor, pre-operative hearing thresholds, intact stapedial reflex. However, no study has determined whether these or other pre-operative factors have any bearing on long-term hearing preservation.

This study examined whether there are any changes over the long term and if present, whether these same changes are mirrored in the opposite unoperated ear. In addition, the researchers hoped to identify factors that might predispose patients to an accelerated hearing loss over time.

The authors of the study, " Acoustic Neuroma Surgery: The Results of Long-term Hearing Preservation," are Gerard H Chee, FRCS, Julian M Nedzelski, MD FRCS(C), and David Rowed, MD FRCS(C), all from the Sunnybrook & Women's College Health Science Centre, Toronto, Ontario, Canada. Their findings will be presented May 10, 2002, at the Annual Meeting of the American Neurotology Society http://itsa.ucsf.edu/~ajo/ANS/ANS.html, at the Boca Raton Resort & Club, Boca Raton, FL.

Methodology: A retrospective chart review was performed for 126 patients with tumors smaller than 2cm (within the cerebellopontine angle) who underwent surgery between 1978 and 1997. Tumors removed had dimensions larger than 1.5cm (cerebellopontine angle) via the translabyrinthine approach regardless of preoperative hearing acuity. Hearing preservation was successful in 43 patients (34.1 percent).

Of the 43 patients, 30 with a minimum of 36 months follow-up make up the study group. The cohort consisted of 17 males and 13 females. The mean age at surgery was 47.3 years (range 32 to 64). There were 13 right-sided tumors and 17 left-sided ones. The follow-up period was from the date of surgery to the last audiogram. The average follow-up period was 113.6 months. Thirteen patients had more than a 10-year follow-up.

Outcome measures include Speech Reception Thresholds (SRT), Speech Discrimination Scores (SDS), and pure tone audiogram (PTA) (0.5, 1 & 2 kHz). All patients had pre-operative audiograms performed within six months of surgery. Post-operatively, audiograms were performed at one month, six months, one year and yearly after that where appropriate. The results were recorded as pre-operative, early post-operative (first post-operative audiogram), and late post-operative (last post-operative audiogram). Hearing change in the operated ear was compared to hearing change in the unoperated ear to control for other possible causes of progressive sensorineural hearing loss. A significant change was defined as a decline of 15dB or more on pure-tone audiogram and/or significant change in speech discrimination.

Results: Twelve patients (40 percent) demonstrated significant hearing deterioration over time. The results demonstrate there are significant differences in the operated ear comparing the early and late post-operative intervals. Similar significant differences are seen in the unoperated ear over time (i.e. early vs. late post-operative periods). There are also significant differences in the means for all three parameters between the operated and unoperated ear when compared in the early post-operative to the late post-operative period. However, most importantly, when the changes in the unoperated ear are taken into account, the changes in the means on SRT and PTA over time in the operated ear remain significant.

Conclusions: The present study conclusively demonstrates that in a considerable proportion of patients, hearing preserved after acoustic neuroma surgery deteriorates at an accelerated pace as compared with the unoperated ear. Of the 30 patients in the series, 12 (40 percent) realized a significant worsening in hearing thresholds. As a group, changes in the SRT and PTA were statistically significant between the early and late post-operative period after taking changes in the unoperated ear into account. Hearing preservation is a realistic goal in selected patients undergoing acoustic neuroma surgery. Patients should be informed of the possibility that preserved hearing may worsen at a faster rate than that of the unoperated ear.

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