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Hearing conservation surgery for acoustic tumors--a clinical-pathologic correlative study.

It has been estimated that hearing conservation is possible in 50% of patients with tumors extending medial to the porus acusticus 1.5 cm or less and who maintain speech discrimination scores of 80% or greater. Others have indicated that a hearing level of 30 dB or less and 80% discrimination are ideal candidates for hearing preservation surgery. Twenty-two cases of solitary schwannoma of the eighth nerve are reviewed in which adequate tissue was available for histologic fiber analysis, using the established preoperative predictive criteria for hearing preservation surgery. We describe the histology found in patients meeting these preoperative criteria. The tumors in ten cases measured less than 1.5 cm; five cases had a discrimination score of 80% or greater; and four cases had a pure-tone average of 30 dB or less. Only three cases satisfied any two criteria and only one case satisfied all three criteria. All cases had significant fiber destruction and tumor infiltration. The one case that met all three criteria demonstrated severe tumor infiltration within the cochlear nerve and the trunk of the eighth nerve; in two of five subserial en block tumor-nerve cross-sections no fibers could be identified crossing the tumor. Histologic data suggests that completely removing the tumor while attempting to preserve hearing may be beyond present surgical capabilities. They further suggest that the present preoperative criteria for selection of patients for hearing preservation are inadequate.