Arachnoid granulations: Dynamic nature and review.

Arachnoid granulations have been known for centuries yet remain incompletely understood. While traditionally associated with cerebrospinal fluid transport, the precise mechanism remains uncertain. This manuscript reviews the literature on the anatomy, histology, and imaging findings of arachnoid granulations and their mimickers and anomalous variations. We highlight variations in incidence, size, and characteristics of arachnoid granulations on imaging, and hypothesize that these variations may be explained by arachnoid granulations being dynamic secondary to varying functionality. We review the pathophysiologic role of arachnoid granulations in pathologies related to hydrocephalus, neurodegenerative disorders, and intracranial hypertension and hypotension. A further understanding of arachnoid granulations, their mechanism in cerebrospinal fluid transport, and change over time may provide a basis for future imaging markers and therapies.