Abnormalities of the posterior inferior cerebellar artery: MR imaging findings.

The purpose of this essay is to review the normal MR appearance of the posterior inferior cerebellar artery (PICA) and to illustrate the MR findings of representative PICA abnormalities. Because of beam-hardening artifacts, the lower posterior fossa is difficult to evaluate with CT. MR imaging is not hampered by these artifacts. Moreover, the superb sensitivity of MR and its multiplanar imaging capability permit excellent diagnostic accuracy in this region. The PICA is well suited for evaluation on routine MR images, particularly because of the inherent contrast (signal void) of large arteries due to rapid flow. MR imaging has greatly improved our ability to noninvasively diagnose abnormalities of cerebral blood vessels and their resultant manifestations. Some of the diseases that affect the PICA include neoplasms, aneurysms, arteriovenous malformations, and occlusions. The MR images in this essay illustrate the normal appearance of the PICA, as well as these pathologic features. T1-weighted (e.g., 600/15 [TR/TE]), proton density-weighted (e.g., 2000/20), and T2-weighted (e.g., 2400/80) MR images were obtained in axial, sagittal, and coronal planes. The PICA can be evaluated with MR angiography also, although the relatively small size and tortuosity of the artery may preclude adequate visualization.