Dandy-Walker like malformation in a Fischer-344 rat.

A spontaneous cerebellar malformation was found in a 32-day-old male Fischer 344 rat. The cerebellar malformation was composed of a vermis defect and markedly dilated fourth ventricle. The cerebellar hemispheres were separated, with the left hemisphere being smaller than the right one. Degenerative/inflammatory lesions consisting of macrophage/lymphocyte infiltration, spheroidal calcium depositions, and astrocytic gliosis were seen adjacent to the cerebral aqueduct. Abnormally arranged hyperplastic ependymal cells were observed beneath the fourth ventricle in the medulla oblongata. The gross findings of the present case resemble those of the human Dandy-Walker malformation. While a precise mechanism remains to be elucidated, degenerative/inflammatory lesions in the present rat may be involved in the pathogenesis of this malformation.