MRI of lobar holoprosencephaly in a cat with hypodipsic hypernatraemia.

Case summary: A 2-year-old neutered female domestic shorthair cat presented with a history of hypodipsia, recurrent hypernatraemia, pelvic limb ataxia and tremor. The serum arginine vasopressin level was low for the serum osmolality. MRI of the brain revealed a failure of separation of the cerebrum, which manifested as absence of the rostral part of the corpus callosum, fornix and septum pellucidum, thus resulting in a single fused ventricle. The diagnosis was lobar holoprosencephaly with hypodipsic hypernatraemia.

Relevance and novel information: To our knowledge, this is the first description of the MRI characteristics of lobar holoprosencephaly in a cat. This report suggests that MRI examination should be considered for precise diagnosis of hypodipsic hypernatraemia in young cats.