Hydrocephalus is enlargement of the ventricular system resulting from increased CSF production, inadequate CSF drainage, obstruction of CSF outflow, or reduced brain parenchyma volume (eg, age-related brain atrophy, infarction).^1,2

Although hydrocephalus can also occur as an acquired disorder, this discussion highlights the congenital form. Congenital hydrocephalus is most often obstructive (ie, noncommunicating). Most cases result from fusion of the rostral colliculi in the midbrain causing obstruction of the mesencephalic aqueduct, with secondary enlargement of the ventricular system rostral to the midbrain.³ Congenital hydrocephalus in cats can be caused by prenatal treatment with griseofulvin⁴ in queens or intrauterine exposure to feline panleukopenia virus.⁵

Signalment

Congenital hydrocephalus is most commonly identified in young (2-3 months of age) toy-breed dogs.^2,6 The condition is much less common in cats.