Internal auditory canal involvement of acoustic neuromas: Surgical correlates to magnetic resonance imaging findings

Objective: Factors that play a role in the selection of surgical approach f or acoustic neuromas include patient health and age, size of tumor, hearing status, and location of tumor in the internal auditory canal (IAC) and the cerebellopontine angle. Deep extension into the IAC makes hearing preserva tion extremely difficult when a retrosigmoid craniotomy is used, and the be st approach is a middle fossa subtemporal route. Modern gadolinium-enhanced magnetic resonance imaging (MRI) can be inaccurate in identifying the pres ence of tumor laterally in the IAC. This may affect the selection of a surg ical approach. Study Design: This study was a retrospective case review. Setting: Patients were accrued from a tertiary referral otologic practice. Patients: From 1997 through 2000, the authors identified six patients who h ad undergone acoustic neuroma surgery, had adequate imaging and intraoperat ive data, and demonstrated a lack of correlation between MRI and intraopera tive findings of the lateral IAC. Intervention: The interventions were preoperative MRI of the IAC and surgic al resection of an acoustic neuroma. Main Outcome Measure: Comparison of MRI and intraoperative findings of the lateral IAC were the main outcome measures. Results: Six patients demonstrated a lack of correlation between MRI and in traoperative findings of the lateral IAC. Conclusions: Gadolinium-enhanced TI-weighted MRI findings of the depth of p enetration into the lateral aspect of the IAC do not always correlate with intraoperative findings and thus may have implications in the selection of surgical approaches to acoustic neuromas.