The term hydrocephalus refers to an excessive amount of cerebro spinal fluid with consequent dilatation of the ventricular system usually accompanied by increased intra cranial pressure.

THE CEREBRAL VENTRICULAR SYSTEM
Within the brain there are four irregular shaped cavities. These cavities are called ventricles. The ventricles contain cerebro spinal fluid. The ventricles are: -
Right & left lateral ventricles
Third ventricle
Fourth ventricle

The lateral ventricles: The lateral ventricles lie within the cerebral hemispheres separated by the septum lucidum, one on each side of the median plane just below the corpus callosum. They communicate with the third ventricle through the inter ventricular foramen.

The third ventricle: The third ventricle is situated below the lateral ventricles between the two parts of the thalamus. It is connected with the fourth ventricle by a canal – the cerebral aqueduct or the aqueduct of midbrain.

The fourth ventricle : The fourth ventricle is a lozenge shaped cavity below & behind the third ventricle, between the cerebellum & the pons.
The fourth ventricle is continuous below with the central canal of the spinal cord and communicates with the subarachnoid space by a single median aperture called the foramen of Magendie and two lateral openings on the roof called the foramina of Luschka.

THE CEREBRO SPINAL FLUID
The cerebro spinal fluid is an ultrafiltrate of the plasma, which is a clear fluid and contains water, mineral salts, glucose, plasma proteins, small amounts of albumin and globulin, creatinine, and urea. It is secreted by the choroids plexus which is constituted by a tuft of capillaries covered by the ependyma. These capillaries differ from the normal capillaries in the sense that they lack the blood brain barrier.
The cerebro spinal fluid is secreted into the ventricles. From the roof of the fourth ventricle the cerebro spinal fluid flows into the subarachnoid space and completely surrounds the brain and spinal cord. The movement of the cerebro spinal fluid is aided by the pulsating blood vessels, respiration, and change of position. In certain places especially the base of the brain, the arachnoid mater and dura mater are separated and these result information of pools of cerebro spinal fluid which protects large veins, arteries and cranial nerves.
The cerebro spinal fluid is secreted at a rate of 0.5ml/mnt which accounts to 720 mls/day. Even then the amount of circulating cerebro spinal fluid is kept constant at 120 mls by maintaining the balance between secretion, and absorption.
The normal cerebro spinal fluid pressure is 10 cms of water on lying and 30 cms of water when sitting up. When the cerebro spinal fluid pressure reaches a threshold level, it passes back into the blood by the tiny diverticula named arachnoid villi, which project into the venous sinuses of the brain. When venous pressure is large the arachnoid villi collapse, preventing the flow of blood constituents into the cerebro spinal fluid. Some amount of cerebro spinal fluid is absorbed by the ventricular walls.

Functions of the cerebro spinal fluid :-
1. It supports and protects the brain and spinal cord.
2. Maintains uniform pressure around delicate structures.
3. Acts as a cushion and shock absorber.
4. Maintains moisture and helps inter change of substances between the cerebro spinal fluid and nerve cells

Hydrocephalus

Incidence : Hydrocephalus is found in 2-5 among 10,000 children.
Presence of excessive amounts of the cerebro spinal fluid can be due to:-
a. Increased production of the cerebro spinal fluid.
b. Block in the flow of the cerebro spinal fluid.
c. Impaired absorption of cerebro spinal fluid.

Etiology :
I. Overproduction of the cerebro spinal fluid : Choroid plexus papillomas usually in the fourth ventricle produces the cerebro spinal fluid in large quantities.
II. Impaired absorption of the cerebro spinal fluid : The causes are necessarily acquired as in complications of subarachnoid haemorrhage, meningitis,& spread of a tumour within the subarachnoid space.

III. Block in the flow of the cerebro spinal fluid is observed in:-
1. Meningitis
2. Tumours
3. Congenital cerebral cysts
4. Congenital occlusion of the inter ventricular foramina
5. Abnormalities of the cerebral aqueduct
6. Blood clots following intra cerebral haemorrhage
7. Absence of the foramina of Magendie & Luschka
8. Agenesis of subarachnoid space

Predisposing Factors :
1. Physical injury
2. Irradiation
3. Nutritional deficiencies
4. Chemicals
5. Drugs
6. Intrauterine viral infection- toxoplasmosis

Factors like parental age, parity, previous still births, smoking, Diabetes mellitus, epilepsy, X-rays, hypertension, medications etc. have been found to have no influence on the occurrence of hydrocephalus.

Depending upon the exact etiology, hydrocephalus could be classified into:-
1. Congenital
2. Traumatic
3. Inflammatory
4. Neoplastic
5. Degenerative

Clinical Features :-
The clinical features vary from infants to older children and adults.
Infants :
1. Large size of the head.
2. Fontanelles become large and bulge out : If the rate of enlargement of the head is more than 2cms/ month at any time of life it is suggestive.
3. Scalp becomes shiny and thin.
4. Scalp veins become distended because of communication with intra cranial veins by the emissary veins.
5. Eyes & ears appear low set.
6. Weakness of upward gaze produces the setting sun sign.
7. The eyeballs are rolled downwards with the supracorneal sclera becoming more prominent.
8. Excessive irritability, Apathy, & Stupor.
9. Inability to retain fluids.
10. Retardation of milestones.

O/E – Head circumference increased
Mac Ewan’s Sign is positive. ( Percussion of the head reveals a cracked pot sound).
Papilloedema
Transillumination gives valuable results
Older children :-
1. After closure of the fontanelle, there are symptoms of raised intracranial pressure.
2. Deterioration of visual acuity.
3. Transient or permanent blindness.
4. Optic atrophy & papilloedema.
5. Difficulty in feeding & suckling because of stretching of the cortico bulbar tracts.
6. Hoarse hydrocephalic cry.
7. Quadriparesis – stretching of the pyramidal tracts.
8. Tendon jerks are exaggerated & plantar responses extensor.
9. Failing mental functions, behavioral abnormalities.
10. Endocrine abnormalities due to pressure on the pituitary,including obesity,small stature, precocious puberty,
adiposo genital atrophy, primary amenorrhoea and Diabetes incipidus

Investigations :-
CT Scan
Magnetic Resonance Imaging
Diagnostic ultra sound

Treatment :-
Prophylaxis-Multi vitamin supplementation
Surgical – To remove the cause for obstruction, like benign tumours, cysts, Choroid plexectomy.