Learning Objectives: MRI IAM is a useful tool for the Neurotologist to clarify related symptoms or reassure the patient. Although the VS pick up rate is low, the potential risks of misdiagnosis justify the wide utilisation, as do the high rates of incidental and abnormal findings.
Introduction: Vestibular schwannomas (VS) account for up to 10% of intracranial neoplasms. Magnetic resonance imaging (MRI) of the internal auditory meatus (IAM) has been established as the gold standard in VS diagnosis. Numerous guidelines (Sunderland, Charing Cross and Oxford) advise when to scan, with reported positive results ranging from 0.5% - 4.3%. We reviewed results of MRI IAM for a catchment area of two million over a three year-period.
Methods: Registration with the Caldicott guardian was made and permission given to obtain audit data from the radiology. The information and statistics team provided the MRI IAM episodes. We entered the report for each episode from the electronic patient record. This was coded to six separate outcomes. Normal, VS, Cholesteatoma, Incidental, Other and Incomplete.
Results: A total of 6978 exams were performed. 96% involved adult ( >16 years) patients; 55% female and 45% male. In total, 66.5% (n = 4640) were reported as normal, a further 15.7% (n = 1097) had incidental findings. The number of new diagnosis of VS was 99 (1.6%), while 3.3% (n = 231) scans were incomplete. Additionally, 1.2% (n = 89) diffusion weighted scans for investigation of cholesteatoma and 10% (n = 726) surveillance of known VS were identified. Twenty-five scans were requested for surveillance of other disease such as facial nerve, external and middle ear lesions. We also noted inappropriate requests for morbidly obese or extremely claustrophobic patients.
Conclusions: This is one of the largest reported databases, demonstrating a VS pick up rate of 1.6%. With 66.5% scans reported as normal, the high incidence of abnormal findings, either incidental or not (33.5%) justifies the usage of MRI IAM.
