780 THE NERVOUS SYSTEM 



change in the ependyma is an important or even an actual primary 

 factor. 



Hydrocephalus. We may, for convenience of study, consider three 

 classes of cases of hydrocephalus : first, congenital hydrocephalus in young 

 children; second, secondary hydrocephalus in children and adults; third, 

 primary hydrocephalus in adults. 



1. CONGENITAL HYDROCEPHALUS. The lesion may be in an ad- 

 vanced stage at the time of birth, or it may be scarcely evident or but 

 moderately developed. It may progress rapidly and cause the early 

 death of the child, or it may develop gradually or come to a standstill. 

 In the more marked forms of the disease the ventricles are widely dilated 

 (Fig. 513) and filled with serum, which is usually transparent. Not only 

 the lateral ventricles, but also the third and fifth, may be involved ; the 

 fourth is less apt to participate in the lesion, although it is sometimes 

 dilated, as well as the central canal of the cord. 



The disteution, especially of the lateral ventricles, may be so great 

 that the brain tissue over the vertex is crowded up into a thin layer be- 

 neath the dura mater, or it may be entirely destroyed. When the dila- 

 tation of the ventricles is considerable, the convolutions are flattened 

 and may be almost entirely obliterated. The skull bones may be thin 

 and bulging over the forehead and vertex; the fontauels and sutures 

 widely open. The epeudyma in these cases is usually thick and rough, 



FIG. 513. COXGKNITAL HYDROCEPHALUS IN CHILD. About half natural size, 

 o, a, Dilated lateral ventricles ; b, cornua, unequally dilated ; c, third ventricle ; d, middle commissure. 



but it may be softened, and the blood-vessels may be dilated. The basal 

 portions of the brain may be flattened, but are usually much less affected 

 than the upper portions. The brain tissue is usually soft and anaemic. 



2. SECONDARY HYDROCEPHALUS. This may occur in children and 

 adults, and may be a result of epidemic cerebro-spinal meningitis, 01 of 

 acute meningitis, or of chronic meningitis. It sometimes occurs in 

 chronic alcoholic poisoning and in general paralysis of the insane. The 

 amount of dilatation of the ventricles varies greatly in these cases, but 



