The prevalence of acoustic neuroma (AN) in unselected temporal bones was 0.8% in a well-conducted study. Whereas the yearly incidence of AN is reported at 1/100, 000. The prevalence would be calculated at 0.07%, if the ANs presented at a constant rate of 1/100, 000 of the population over a seventy-year life span. Presumably, the value of overly aggressive testing strategies for detection of ANs in asymptomatic individuals must be questioned. The aim of this study is to examine the cost-effectiveness and relative performance of numerical clinical examinations to diagnose the AN.
The auditory brainstem response (ABR), as well as associated audiologic and radiographic studies of 743 suspected of having AN were reviewed. From January 1, 1998 to December 31, 1998, these suspected patients presented with asymmetric hearing loss and/or tinnitus at the Department of Otolaryngology or Neurosurgery. ABRs were examined in 174 cases, the equilibrium tests, including caloric test, were in 300 cases, radiographic examinations were in 219 cases, speech audiometries were 104 cases, CT were in 304 cases and MRI were in 359 cases. Eighteen ANs (2.4% in suspected patients) were identified. Of 18 patients with AN, all eight AN patients examined had abnormal ABRs, i.e. no false negative case was revealed in ABR of the present study. Sensitivity and specificity of ABR were 100% and 88.6%, respectively. The sensitivities of CT and MRI were both 100%, whereas those of equilibrium test and radiographic examination were 66.7% and 85.7%, respectively. In the present study, the cost per AN diagnosed was 104, 700 points in the health insurance. Based on a 2.4% rate of AN identification, the cost of diagnosis would be 98, 244 points per neuroma if all suspected patients undergo only MRIs. If all 743 patients are examined with ABRs first and only those with abnormal ABRs (15.5%) receive MRIs, the cost would be 42, 888 points per AN. These results suggest that ABR is the most efficient and economical screening technique to select the cases for CT and/or MRI examinations to diagnose the AN, though we have to take a false negative in ABR into careful consideration.
