The cyst may be simple or loculated, and its contents consist of red dish serum with small clots and flocculent matters. Often the cyst is double, each half corresponding to one of the hemispheres of the brain. Its walls become thin and transparent, and have a serous appearance. Usually arborescent vessels may be seen to ramify on the surface. The fluid contents become increased in quantity after a time;and may vary from a few spoonfuls to half a pint or more.
Morbid Anatomy.—When the hydrocephalus is congenital and the fluid accumulates in the ventricles of the brain, it tends to press outwards the walls of those chambers. As. a consequence the brain-substance is thinned ; the convolutions are flattened, and, as the pressure is equal in all direc tions, the corpora striata and optic thalami are flattened, separated, and pressed aside ; the septum lucidum is softened, stretched, and often torn ; the ventricles communicate freely through the dilated foramen of iNIonro, and the corpora quadrigernina, the cerebellum, and the pops are flattened and compressed. The membrane lining the ventricles is often found thickened and Softened, and may be roughened or even distinctly granu lar. In some cases the foramen of Majendie is closed. If the effusion is large the walls of the skull also feel the effects of pressure. The head becomes distended; the frontal bone is pushed forwards; the roofs of the orbits are depressed so as to flatten the sockets of the eyeballs, and the occipital bone and the squamous portion of the temporal bone are made almost horizontal. The sutures are widened and the enlarged fontanelles communicate by the sagittal suture. The shape of the head is often not quite symmetrical, neither is it globular. The curve is much greater at the sides, and the skull is rather flattened at the vertex. Ossification in the cranial bones is delayed, and is said to be often aided by the conjunc tion of small islets of bone formed in the membranous interspaces. At a later stage the bones become very thick and the skull is remarkably spher ical in shape.
If no great quantity of fluid is present the size of the head is not in creased, but this is comparatively seldom the case ; usually the skull is distended as described. The fluid is clear or slightly turbid, and varies in quantity from a few ounces to several pounds. It is of higher specific gravity than the cerebrospinal fluid ; is alkaline in reaction, and contains a very feeble proportion of albumen, besides chloride of sodium and urea.
Various abnormalities of the cerebrum•may be present from arrests of development, and sometimes traces of old disease can be discovered, such as patches of sclerosis resulting from past hemorrhage or inflammation. The cerebral substance generally may be of normal consistence, or anmnic, or oedematous. Congenital hydrocephalus is often combined with other arrests of development, such as cardiac malformations, spina bifida, hare lip, etc.
In acquired hydrocephalus the changes above described stop short of the extreme degree often reached when the disease is congenital. The ventricles are still dilated, but to a less extent. They contain several ounces of fluid (six, eight, ten, or twelve), usually limpid and clear. The epenclyma of the ventricles is thickened and often dotted over with fine nodules, especially upon the optic thalami, the immix, and the stria cornea. The choroid plexus is congested, and the brain-substance may be denser or tougher than natural.
If the fluid is in the arachnoid space it is spread more or less over the surface of the brain. The brain is often oedematous, and its consistence is reduced. In extreme cases it may be converted into a white pulp (hy drocephalic softening).
Symptoms.—Many cases of congenital hydrocephalus which reach the full period of gestation die during delivery or shortly afterwards. Others survive for a variable period, but they die in the majority of cases before the end of the second year. In rarer instances the patient may live for five or ten years, or longer, and it is said may even.reach extreme old age.
At birth the size of the head is not always remarkable. The appear ance of the new-born infant may be natural, and no cranial enlargement may be observed until after the lapse of some weeks. Most cases of hy drocephalus present both physical and mental peculiarities. The head of the child becomes very large, but his general development - is strikingly backward. The increase in size of the skull is gradual and progressive, and in some cases the volume of the head becomes enormous. The pecu liar shape of the skull and the strange contrast between the dimensions of the cranium and the little pinched and pointed face beneath it is very striking and characteristic. In a well-marked case the large globular head, greatly expanded at the sides and flattened at the crown, combined with the small face, if represented merely in outline upon paper, would give the impression of a large oriental turban placed upon the head of a child of ordinary size. The skin over the cranium is thin and seems stretched ; the veins are full ; the hair is scattered and meagre. On placing the hand upon the head the large fontanelles, the widely opened sutures, and the thin, yielding bones convey almost the impression of a tense bag of fluid. Often fluctuation can be detected, and the soft parts may have a slight pulsation, rhythmical with the breathing, falling in during inspi ration and dilating again as the breath is expired. The face is thin, the cheeks are often hollow, and the chin is small and pointed. The eyeballs are forced forwards by the flattening of the roofs of their sockets, and at the same time the eyebrows and eyelids are drawn upwards by the tension of the skin. Consequently the eyes look promipent. They appear also to be directed downwards, for there is a rim of white above the cornea from uncovering of the sclerotic, while the lower half of the pupil is cov ered by, the lower eyelid. This large head is necessarily a heavy one, so that the child has a difficulty in supporting it. As the general nutrition is imperfect, and the muscular development of the patient far below a normal standard, the difficulty is often great. The child may endeavour to support the head with his hand, but often he has to abandon the attempt to keep himself upright, and is forced to rest his head on a pillow or on his mother's lap. The weight of the head is one reason why these chil dren are slow in learning to walk. Another cause is the imperfect state of nutrition of the body generally. Although the child as a rule takes food greedily and appears to digest it, he does not thrive. His head gets bigger and bigger, but the muscles of the trunk and limbs remain feeble, flabby, and thin, and seem to derive no benefit from his copious meals.