- Abnormal increase in quantity of cerebrospinal fluid (CSF) in the brain.
- Most commonly seen in neonatal foals (congenital), although may be acquired in the older animal.
- Signs : grossly domed skull (neonate), may be other defects.
- Diagnosis : clinical signs.
- Treatment : none.
- Prognosis : grave.
- Congenital: hopeless - euthanasia is usually indicated.
- Acquired: animals which recover are often mentally deficient ('dummy foals') and unthrifty.