Diabetes insipidus may be idiopathic or symptomatic. In the idiopathic type, no gross lesions can be demonstrated and the cause is unknown. The symptomatic group can be caused by any number of pathologic conditions among which are the following: fracture at the base of the skull, encephalitis, cerebral hemorrhage, brain tumors, pituitary tumors, abscesses, or granulomatous diseases. The most common cause of the symptomatic type in the dog is a pituitary tumor.