Histopathologic findings of acoustic neuromas (from the temporal bone collection at the University of Minnesota)
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Objective: To describe the diverse histopathological findings of acoustic neuroma (AN) cases including: nerve origin, microscopic characteristics of the tumor, status of facial and cochlear nerves, changes of cochlear and vestibular structures, and associated pathologies. Design: From the 1700 temporal bones at the University of Minnesota, we selected temporal bones from patients with AN. Clinical charts were reviewed, and temporal bones which had been previously sectioned and stained with hematoxylin and eosin were examined using light microscopy. Subjects: Of the 1700 temporal bones, 13 temporal bones from 13 patients had histopathologic evidence of AN. The ages of the patients ranged from 44 to 86 years (mean age 69.61). Eleven (84.6%) of the temporal bones were from males and two (15.4%) from females. The left temporal bone was affected in 10 patients and the right in 3. Results: Audiograms were available in 6 cases, four had high frequency sensorineural hearing loss, one had profound sensorineural hearing loss at all frequencies, and one had total hearing loss. The origin of the tumor was the vestibular nerve in ten temporal bones (seven bones from superior vestibular nerve and three bones from inferior vestibular nerve) and the cochlear nerve in two temporal bones. Since one patient was surgically treated, only residual tumor was detected extrameatally. It was therefore not possible to determine the origin of the tumor. Microscopic characteristics of the tumors were Antoni type A in 12 temporal bones, and Antoni type B in one. The intracanalicular tumor length ranged in from 1.00 mm to 14.40 mm and the width from 0.55 mm to 7.00 mm. Although the origin of the tumor was determined as coming from the superior or inferior vestibular nerve, in most cases both nerves were affected; either invaded or compressed by the involved nerve. Cochlear nerves were generally compressed by tumors and had a ribbon-like appearance. In one temporal bone a facial neuroma in the internal auditory meatus was found with AN, and in other temporal bone several differ-ent middle and inner ear pathologies such as cholestatoma, cholestreol granulaoma, otosclerosis, and Scheibe's dysplasia were also detected. Most of the temporal bones showed well-preserved vestibular structures, but the cochlear structures contained artifactual changes from processing and a decrease in spiral ganglion cells in the basal turn. Conclusions: In a patient who presents with sensorineural hearing loss, we should consider the possibility of AN. However, in a patient who presents with facial weakness or paralysis, the possibility of a combination of AN and facial neuroma should be considered. Furthermore because the cochlear nerve can be compressed or deformed special car-e must be taken during the dissection of the tumor.