CHRONIC HYDROCEPHALUS 227 



CHRONIC HYDROCEPHALUS. 



Definition. — Chronic hydrocephalus is a brain disorder 

 common in horses, but rare in other animals, caused by the 

 collection of serous fluid in the lateral ventricles of the brain. 

 It leads through pressure to dilatation of the lateral ventricles, 

 an increase in the size of the brain and an elevation of the 

 intracranial pressure. The condition is rarely congenital, 

 more often acquired. 



Etiology. — Two types of hydrocephalus may be. distin- 

 guished from the standpoint of etiology : (a) Inflammatory 

 hydrocephalus, the result of acute inflammation of the brain 

 of which it is a sequela developing in about one month. In 

 this condition the fluid is an exudate, (b) A primary or 

 idiopathic hydrocephalus is probably of mechanical origin and 

 the fluid a transudate. It may be due to a congenital con- 

 striction or closing of the Sylvian aqueduct. An inherited 

 predisposition to this form of brain hydropsy is probable. 



Symptoms. — Chronic hydrocephalus in the horse is the 

 commonest cause of the so-called "dummy." There is 

 usually more or less disturbance in consciousness which the 

 animal shows by a number of clinical symptoms. The follow- 

 ing are the most characteristic, all of which are made more 

 prominent by vigorous exercise: The attitude of the patient 

 is unphysiological, the head is held low, the limbs are fre- 

 quently misplaced, the legs being crossed, and the patient is 

 apt to stand diagonally in the stall. The patient seems indif- 

 ferent to its surroundings, is sleepy, the eyelids partially 

 closed, little attention is paid to commands, and an effort to 

 back the horse is futile. The heart action is slow, the pulse 

 in some cases dropping to 20 to 30, although it retains its 

 normal softness. The symptoms of depression, appearing 

 from time to time, are due to a rise of intracranial press- 

 ure. Periods of excitement may occur which cause the 

 animal to show symptoms as in the stage of excitement 

 in acute inflammation of the brain. The appetite of the 

 "dummy" is often impaired and the prehension of food 

 unphysiological. Eating is quite frequently interrupted, the 

 animal apparently forgetting for the moment that it is at a 



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