The causes of chronic hydrocephalus in older subjects and in adults are, in addition to the above mentioned, chiefly mechanical. Any lesion which hinders the exit of venous blood from the cranium may be followed by dropsy of the arachnoid cavity or ventricles. The principal ones are tumors of the brain or its membranes, the effusion of lymph in the neighborhood of veins, thrombosis of the cerebral sinuses, compression of numerous small vessels by tubercular granulations, obstructions outside the cranium, including tumors of the neck, aneurisms, obstructive disease of the heart, emphysema and cirrhosis of the lungs, besides diseases giving rise to general dropsy, as the different forms of nephritis, marasmus, the various cachexiæ, etc.
SYMPTOMS.—When the disease is already somewhat advanced before birth, the head is often abnormally large, the cranial bones are separated, the fontanels are distended and fluctuating, and it occasionally happens that delivery of the distended head can only be effected after the fluid has been evacuated by puncture. Even when there is no abnormal increase in the size of the head, indications of cerebral disturbance are sometimes apparent from birth, such as strabismus or convulsions recurring with more or less frequency, along with signs of failure of the general health. In the course of some weeks, or, it may be, months, the attention of the parents is attracted to the prominence of the child's forehead, strongly contrasting with the comparatively diminutive size of the face. Soon an enlargement of the fontanels is perceived, the sutures between the cranial bones become broader, and the head assumes a globular shape from the pressure of the contained fluid. The separation of the bones at the vertex of the skull causes the os frontis to protrude forward, the parietals backward and outward, and the occipital backward and downward. The orbital plates of the frontal bone yield to the pressure of the fluid behind them, and from a horizontal position tend to assume a vertical one, protruding the eyeballs, which have a peculiar downward direction. The sclerotica is visible above the iris, and the latter is partially covered by the lower eyelid. The enlargement of the head is progressive, though not uniformly so, there being pauses of weeks or months during which it is arrested. If it be considerable, the cranial bones are usually thinned, so that the skull becomes translucent when opposite a bright light. When there is a wide separation of the bones there is an unusual development of ossa triquetra in the sutures.
In cases in which the ossification of the cranium is considerably advanced before the beginning of the disease, the enlargement of the head is apt to be correspondingly less. If all the sutures are consolidated, there may be no increase in size, and this is especially true of the mechanical dropsy of adult life. The dropsical effusion, which is then moderate in amount, finds room through compression of the brain-substance, and part of it escapes into the spinal canal.
The size of the hydrocephalic head varies considerably. Where there has been an early arrest of the disease it may be but slightly above the normal. On the other hand, the dimensions are sometimes enormous. In the Warren Museum of Harvard University is a cranium which measures 27½ inches in its greatest circumference, and 20½ inches from one auditory foramen to the other over the top of the head. Its internal capacity is 257 cubic inches. The patient, who died at the age of three years, was never able to sit up and support the head, or even to turn it from the left side, on which she continually lay; she never spoke, and seemed to have no intelligence. The skull of the celebrated James Cardinal measured 32¼ inches in its largest circumference.4 Even more remarkable instances are on record. The dimensions of the fontanels, particularly the anterior, usually correspond with those of the skull in general. During any strong muscular effort on the part of the patient the membrane covering them is seen to be bulged out by pressure from the fluid beneath. The enlargement is not always uniform; it may be in part or wholly confined to one side, owing to consolidation of the sutures of the opposite side, or because only one of the lateral ventricles is affected. The scalp is traversed by numerous distended veins. The hair is very scanty. The head has a soft, fluctuating feel, and the walls sometimes seem to crackle beneath the fingers, like parchment.
4 Reports of Medical Cases, etc., by Richard Bright, M.D., London, 1831, vol. i. p. 431.
In cases of moderate severity there may be few or no symptoms of active cerebral disturbance, such as convulsions or paralysis, but the child does not learn to talk, to walk, or to control the sphincters even at the age of three or four years, and the signs of imperfect mental development are evident. He is apt to be irritable or mischievous, and even when not actually idiotic is very backward in evincing signs of intelligence. There are, however, not a few exceptions to this, and some children with large hydrocephalic heads are intelligent and amiable. The cranium of a girl who died at the age of sixteen years is preserved in the Warren Museum. It measures 24¼ inches in circumference and 17¼ inches from one auditory meatus to the other over the vertex, and the bone is in no place more than one-eighth of an inch in thickness. The child was an inmate of a house of industry, where she was instructed in the usual branches of knowledge taught in our common schools, until at length, such was her capacity, she was entrusted with the teaching of the other pauper children, and she had an excellent character for intelligence and moral worth. She died of phthisis. On post-mortem examination “the brain was found floating, as it were, in a large collection of water.” As in other chronic diseases, there are often pauses, from time to time, of variable duration, in which there is some improvement in the condition of the patient, as well as a temporary arrest in the enlargement of the head. The growth of the child in stature is often retarded, and when life is prolonged the individual is more or less dwarfed. In some cases there is a considerable increase in the amount of adipose tissue, and the appetite is often voracious. L. Fürst reports5 the case of a hydrocephalic girl, sixteen years old, whose height (or, rather, length, for she was unable to stand) was 81 centimeters (nearly 32 inches), corresponding to the stature of a child between three and four years old. The periphery of the head measured 511/5 centimeters (20¼ inches). The anterior fontanel was still open. The age was verified by reference to the registry of birth at the police-office.
5 “Exquisite Wachsthumshemmung bei Hydrocephalus chronicus,” von Dr. Livius Fürst, Virchow's Archiv, June, 1884.
The symptoms of cerebral disturbance in chronic hydrocephalus are much less striking than one would expect, doubtless because the increase of pressure upon the brain is so gradual. Actual paralysis, especially of the limbs, is rare, but convulsions are not infrequent, as is the spasmodic constriction of the glottis known as laryngismus stridulus or spasmodic croup. A general state of uneasiness and restlessness is common. Vision is often impaired and sometimes wholly lost. Strabismus is frequently present, or there may be an involuntary rolling movement of the eyeballs. The pupils are often dilated and insensible to light. In consequence of the increased weight of the head, the child is unable to support it, and in most cases is compelled to keep the bed. Vomiting is common. The digestive functions are disturbed. Constipation is an almost constant symptom, and the sphincters are relaxed in the advanced stages of the disease. Although in some cases, as already stated, the child may grow fat, the reverse of this is the rule; there is usually progressive emaciation, especially of the lower extremities.
The duration of the disease varies much in different cases. The earlier the characteristic symptoms manifest themselves the more rapid is its course. Most children born hydrocephalic survive but a few days or weeks. In cases which are more slow in their development the patient may live some years, and in rare instances attain adult life. But his feeble vitality usually makes him an easy prey to the ordinary complaints of childhood, and a large proportion of cases succumb to inflammation of the lungs or of other organs, to diarrhœa, whooping cough, or the eruptive diseases. Most of those who escape these intercurrent maladies perish from defective nutrition, the result of malassimilation of food, or else are cut off by acute cerebral inflammation, with convulsions, etc.
PATHOLOGICAL ANATOMY.—It is rarely that a large amount of serum is found in the cavity of the arachnoid unless a free communication has been established between it and the ventricles by the destruction of cerebral tissue. In the pia the quantity may be more abundant than normal, filling the subarachnoid spaces, separating the convolutions from each other, and occasionally forming little sac-like elevations on the surface of the membrane; but it should be borne in mind that a certain amount of serous infiltration of the tissue of the pia is by no means rare in cases of death from various diseases, owing to the obstruction to the circulation during the last hours of life, and should not be considered pathological unless it exceed the usual limits. The amount of effusion into the ventricles varies between very wide limits, from some ounces to two or three pints. It may be transparent, or turbid from particles of cerebral tissue or epithelial or pus-cells, and is occasionally slightly tinged with blood. Its specific gravity is nearly identical with that of water, and it contains a trace of albumen. The effusion usually occupies the two lateral and the middle ventricles. Less frequently the dropsy is unilateral, in consequence, apparently, of an obliteration of the foramen of Monro. The tissues composing the walls of the ventricles are compressed and hardened. The ependyma of the walls and of the plexus is thickened and roughened by the formation of minute elevations, which the microscope shows to be composed of proliferated and sclerosed connective tissue. The brain in cases of large effusion is reduced to a membranous sac, flattened, with hardly any trace of its original structure at first sight apparent. In the case of James Cardinal, before alluded to, Bright says, “The brain lay at its base [of the skull] with its hemispheres opened outward like the leaves of a book.” Closer inspection shows that all the parts are present, although atrophied by pressure. The convolutions are flattened and the brain-substance is pale and softened. The cranial nerves are often softened and flattened.