Arachnoid granulations of the posterior fossa: CT and MR findings.

The radiological appearance of typically located arachnoid granulations on craniograms is well known. Arachnoid granulations of unusual size and location should be distinguished from pathological processes. We analyzed six patients with arachnoid granulations in the posterior fossa. Characteristic findings of arachnoid granulations were disclosed by computed tomography (CT) and magnetic resonance (MR) imaging; a punched out-like bone defect from the inner table into the outer table on CT scans and intensity similar to that of the cerebrospinal fluid in all pulse sequences on MR images.