Arachnoid granulations and spontaneous cerebrospinal fluid otorrhea: Role of imaging

Arachnoid granulations (AGs) are villous structures that are formed during the development of the cerebrospinal fluid (CSF) system. Their function is to drain the CSF into the dural venous sinuses. A variable number of AGs do not reach a dural venous lumen and are aberrantly embedded in the skull bones, primarily in the tegmen tympani, tegmen mastoidea, petromastoid plate, occipital squama, cribriform plate, and greater wing of the sphenoid bone. It has been shown that when these AGs are adjacent to pneumatized parts of the skull, they are lesions responsible for spontaneous otorrhea or rhinorrhea in adults. This article reviews the role of computed tomography and magnetic resonance imaging in the evaluation of patients with CSF otorrhea caused by AGs.