Barone G, deLahunta A, Sandler J.
Hydranencephaly has been reported in many domestic 1,2
species and is observed most commonly in the calf. In ruminants, it frequently is associated with in utero viral infections including Akabane, Cache Valley, blue tongue, and, less commonly, bovine viral diarrhea and Border dis- ease virus. It results from in utero destruction of the ger- minal zone of the telencephalon as well as already formed neocortex during a critical period of development, resulting in a reduction of the cerebral hemispheres to membranous sacs filled with cerebrospinal fluid. The tissue encasing the cerebral remnants consists of a thin membrane containing astrocytes, pia, and blood vessels3 and is lined by a discon- tinuous layer of attenuated ependymal cells.2 The most se- verely affected regions tend to be the dorsal, medial, and caudal aspects of the hemispheres.2 Unlike obstructive hy- drocephalus, the cranial cavity in hydranencephalic animals usually is complete and of normal configuration.
The most widely recognized in utero viral infection in small animals that causes brain malformation is the panleu- kopenia virus in cats. The panleukopenia virus generally is associated with cerebellar hypoplasia and has only infre- quently been linked to hydranencephaly.5 To date, canine parvovirus has not been similarly implicated in the dog. In fact, there have been no in utero viral infections linked to the development of brain malformations in the dog. The rarity of this congenital abnormality in the canine species prompted the documentation of the following case reports.