Brainstem response in cerebellopontine angle tumors

Objective: To evaluate the auditory brainstem response (ABR) findings in ce rebellopontine angle (CPA) tumors and focus on those with normal ABR result s. Study Design: This was a retrospective evaluation of ABR findings. All subj ects with diagnosed CPA tumors who were referred for treatment were include d. Patients: All 309 patients with radiographically confirmed (computed tomogr aphy or magnetic resonance imaging [MRI]) CPA rumors (153 before 1993 and 1 56 after 1993). Intervention: All patients underwent complete audiologic examination, elect ronystagmography. ABR testing, and ipsilateral transtympanic electrocochleo graphy. All tumors were histologically confirmed. Main Outcome Measures: The patients were categorized according to ABR resul ts (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, ove r 40 mm). Results: 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 n ormal ABR results (n = 57) caused no hearing loss (n = 12), symmetrical hea ring loss (n = 11), or ipsilateral hearing loss with Short Increment Sensit ivity Index 100% and normal acoustic reflex (cochlear deafness, n = 34). Ca loric response was normal in 59.7% of these tumors. Conclusion: Because validation of ABR as screening for acoustic tumors is b ased on diagnosed tumors, and because MRI allows detection of very small tu mors, the incidence of normal ABR increases and its sensitivity would be ex pected to decrease. ABR is not sufficient for early detection of small CPA tumors.