The vascular territories in the cerebellum and brainstem: CT and MR study.

More than 100 CT and 15 MR studies of infarcts in the cerebellum and brainstem were reviewed to define the most typical distribution of infarcts in the different vascular territories. Posterior inferior cerebellar artery and anterior inferior cerebellar artery territories are variable in size and are in a sort of equilibrium with each other. The posterior inferior cerebellar artery territory in transverse sections reveals a characteristic posterior crescent caused by its cranial posterior extension. The anterior inferior cerebellar artery territory may be limited to the lateral inferior pontine and floccular regions but usually extends over the whole petrosal surface of the cerebellum up to the lateral angle. Superior cerebellar artery territory is the most extensive territory and includes the largest part of the deep white matter. Infarcts in a single-branch distribution, vermian or hemispheric, have a characteristic sagittal or oblique orientation. Watershed cerebellar infarcts can also be recognized. In the brainstem, paramedian, lateral, and dorsal penetrating arteries have characteristic distributions at the medullary, pontine, and mesencephalic levels. With MR, lateral medullary infarcts can be demonstrated. Paramedian penetrating arteries are paired, and symmetric and small infarcts at medullary and pontine levels are sharply delimited on the midline. At the mesencephalic level, infarcts in this distribution usually involve all the arteries originating from the tip of the basilar artery and from the precommunicating segment of the posterior cerebral arteries, resulting in a central mesencephalic infarct with bilateral upward extension in the thalami. The different vascular territories in the cerebellum and in the brainstem are illustrated in schematic drawings in transverse, coronal, and sagittal planes. Knowledge of the vascular territories gained by the multiplanar capabilities of MR, and knowledge of the CT patterns of enhancement and evolution, will improve recognition and definition of infarcts.