A group of 12 dogs, eight of small breeds and four of medium-sized breeds, were used in the study. Prior to the magnetic resonance imaging (MRI) scans, all dogs were subjected to neurological, laboratory, and electroencephalographic examinations, and trans-fontanel ultrasonography was additionally performed in two patients. The acquired obstructive hydrocephalus was diagnosed in two dogs, idiopathic obstructive hydrocephalus - in four patients, obstructive congenital hydrocephalus - in five dogs, and hydrocephalus