Figure 14-36.

Cerebellar Hypoplasia, Cerebellum, Calf.

In the normal neonatal calf, cells of the external granule layer of the cerebellum migrate to form the granule layer (not shown). Bovine viral diarrhea virus infects and kills mitotic cells of the granule layer of the cerebellum. These cells are still dividing during the late gestational and early neonatal periods in the cat and between 100 to 180 days of gestation in the calf. Necrosis of these cells means they are not available to migrate to form the granule layer, and thus the cerebellum does not obtain full size. Depending on the stage of gestation, injury can also alter development of cells in others ways, including altered patterns of migration, resulting in various other lesions termed dysplasia. A, Cerebellar hypoplasia (arrow). In utero infection with bovine viral diarrhea virus (pestivirus) results in cytolysis of dividing germinal cells of the granule layer and vascular impairment secondary to vasculitis of the cerebellum during organogenesis. The severity of the lesion involving the granule cells is at its greatest if dividing cells are infected during the earliest stages of cellular differentiation, and occurs between 100 to 180 days of gestation. B, Note the folia of the cerebellum are hypoplastic and dysplastic with a reduced thickness of the molecular layer (arrows) and haphazardly organized and thinned granule cell layer (arrowheads). H&E stain. C, The molecular layer (M) of the cerebellum is reduced in thickness and lacks the normal number of neuronal nuclei. The Purkinje cell layer (P) has large gaps between adjacent cells as the result of the loss of neuron cell bodies or the failure of neurons to migrate properly to form this layer. Note the retention of Purkinje cells (arrows) in the granule cell layer (G). The granule cell layer has significantly reduced numbers of neurons as shown by the lack of nuclei. H&E stain. W, White matter.

(A courtesy Dr. M.D. McGavin, College of Veterinary Medicine, University of Tennessee. B and C courtesy Dr. J.F. Zachary, College of Veterinary Medicine, University of Illinois.)