Auditory brainstem response and magnetic resonance imaging for acoustic neuromas: Costs by prevalence

Objective: To compare hypothetical costs for identification of acoustic tumors when using magnetic resonance imaging with gadolinium Gd 64 (MRI-⁶⁴Gd) as a sole diagnostic test and when using auditory brainstem response (ABR) testing followed by MRI-⁶⁴Gd (ABR+MRI-⁶⁴Gd) for those with positive ABR findings. Patients and Methods: Retrospective review of the medical records of 75 patients having surgically confirmed acoustic neuromas to categorize them into 3 subgroups relative to their risk of having a cerebellopontine angle tumor based on history, symptoms, and routine pure-tone and speech audiometric findings. Hypothetical costs associated with identification of patients with acoustic neuroma in each subgroup were calculated for MRI-⁶⁴Gd alone and ABR+MRI-⁶⁴Gd. Auditory brainstem response sensitivity and specificity data for the 75 patients with acoustic neuroma and 75 patients without a tumor matched for hearing loss were applied to the hypothetical subgroups. Tumor size was considered also. Setting: Tertiary care center. Main Outcome Measure: Comparison of costs for MRI-⁶⁴Gd and ABR+MRI-⁶⁴Gd. Results: Fouteen patients with acoustic neuroma were assigned to the high-risk category (30% probability); 45 were in the intermediate-risk category (5% probability); and 16 were in the low-risk category (1% probability). Auditory brainstem response testing correctly identified 100% of the large tumors (>2.0 cm), 93% of the medium-sized tumors (1.1-2.0 cm), and 82% of the small tumors (< 1.0 cm). The hypothetical costs for identifying 14 patients with acoustic neuroma among 47 patients in the high-risk category using MRI-⁶⁴Gd would be $70500; ABR+MRI-⁶⁴Gd costs for the 13 patients identified by ABR would be $39 600. Hypothetically 900 patients would be tested to identify the 45 acoustic neuromas in the intermediate-risk category. Magnetic resonance imaging with ⁶⁴Gd screening would reach $1.35 million for this sample. Auditory brainstem response testing and MRI-⁶⁴Gd would be $486000, but 4 acoustic neuromas would be missed. For the low-risk subgroup MRI-⁶⁴Gd screening of 1600 patients to identify 16 acoustic neuromas would total $2.4 million; ABR+MRI-⁶⁴Gd to identify 15 of them would be $787500. In this sample of 75 acoustic neuromas, large tumors were more prevalent in the low-risk subgroup than in the high- or intermediate-risk subgroups. Conclusions: Decisions regarding assessment of patients at risk for acoustic neuromas must be made on a case-by-case basis. Use of ABR+MRI-⁶⁴Gd allows considerable savings when patients are in the intermediate- or low-risk subgroups. New MRI and ABR testing techniques offer promise for reducing costs.