Exencephaly in araucana chickens and silkie bantams.

Exencephaly and hydranencephaly were diagnosed in two 6-week-old araucana chickens (Gallus domesticus) and one adult silkie bantam (Gallus domesticus). The chickens were presented with large, subcutaneous, cranial soft-tissue masses and exhibited neurological signs. There was partial aplasia of the frontal bones, resulting in herniation of the cerebral hemispheres.