Brainstem response in cerebellopontine angle tumors.

Abstract

To evaluate the auditory brainstem response (ABR) findings in cerebellopontine angle (CPA) tumors and focus on those with normal ABR results. This was a retrospective evaluation of ABR findings. All subjects with diagnosed CPA tumors who were referred for treatment were included. All 309 patients with radiographically confirmed (computed tomography or magnetic resonance imaging [MRI]) CPA tumors (153 before 1993 and 156 after 1993). All patients underwent complete audiologic examination, electronystagmography, ABR testing, and ipsilateral transtympanic electrocochleography. All tumors were histologically confirmed. The patients were categorized according to ABR results (normal or pathologic findings or no response); according to histology (vestibular schwannomas or meningiomas); and according to tumor size by MRI (small, up to 15 mm; medium, 16-25 mm; large, 26-40 mm; and very large, over 40 mm). Normal ABR results were found in 18.4%; pathologic ABR results in 31.4%; and no response in 50.2%. Small vestibular schwannomas (under 15 mm) showed a higher incidence of normal ABR results (41.7%). CPA tumors with normal ABR results (n = 57) caused no hearing loss (n = 12), symmetrical hearing loss (n = 11), or ipsilateral hearing loss with Short Increment Sensitivity Index 100% and normal acoustic reflex (cochlear deafness, n = 34). Caloric response was normal in 59.7% of these tumors. Because validation of ABR as screening for acoustic tumors is based on diagnosed tumors, and because MRI allows detection of very small tumors, the incidence of normal ABR increases and its sensitivity would be expected to decrease. ABR is not sufficient for early detection of small CPA tumors.