Fluid signal in the mastoid is a common incidental finding on MRI of the brain.

Abstract

Incidental findings are common on patients undergoing magnetic resonance imaging (MRI) of the brain. Fluid signal in the mastoid can be such an incidental finding on MRI of the brain. In only a small number of patients, this relates to inflammatory disease of the middle ear or mastoid. In a small retrospective study, the prevalence of this finding has been studied. Fluid signal in the mastoid was found in 21 out of 84 patients (25%). Only in two patients MRI revealed a cause for the mastoid fluid (mastoid osteolysis in a patient with metastatic breast cancer and presumed recurrent cholesteatoma in another patient). Two patients reported about longstanding presbyacusis. At the initial examination, none of the patients reported symptoms of an inflammatory otological disease, and clinical examination was unremarkable in all patients. In conclusion, fluid signal in the mastoid seems to be a frequent incidental finding in asymptomatic patients. A diagnosis of mastoiditis should only be made if there are distinct clinical findings.