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The term “Hydrocephalus” is derived from the two words “Hydro” and “Encephalon”, which means accumulation of excess water (fluid) inside the cranial vault. The “water” inside the cranial vault represents the cerebrospinal fluid (CSF). Increase in the total quantity of the intracranial fluid in the brain substance causes raised intracranial tension but not hydrocephalus as in pseudo motor cerebri or cerebral oedema.
Normally the entire cavity enclosing the brain and the spinal cord has a volume of about 1950 ml, and only about 150 ml of this volume is occupied by the CSF. Actually this 150 ml of fluid is contained in the ventricles of the brain in the cisterns around the brain and in the subarachnoid space around both the cerebral hemispheres and the spinal cord. All these chambers or spaces are interconnected with one another.
The major function of the CSF is to cushion the brain tissue within the solid and bony vault and project it from sudden physical trauma. The brain tissue and the CSF both have almost the same specific gravity and as such the brain floats in the fluid.
Cerebrospinal fluid is formed from three different sources:
(1) The choroid plexuses inside the ventricles of the brain, mainly the lateral ventricles — the bulk portion of the fluid is formed here.
(2) The blood vessels of the meningeal and ependymal linings of the chambers containing the CSF.
(3) The blood vessel of the brain and the spinal cord.
The choroid plexus is a cauliflower-like tuft of blood vessels covered by a thin layer of cuboidal epithelial cells which contain plenty of mitochondria and vacuoles and it projects into the temporal horns of the lateral ventricles, the posterior portions of the third ventricle and the roof of the fourth ventricle.
The CSF is being formed continually and also being reabsorbed continually into the blood through the veins via the arachnoidal villi and through the “perivascular spaces” of the brain.
CSF pressure varies normally between 80 and 150 mm. water with an average of 130 mm. water (equivalent to 10 mm Hg).
In spite of the fact that there is a continuous secretion and absorption of the CSF the pressure of the fluid is regulated at a constant level by:
(1) The rate of fluid formation and
(2) The resistance to circulation and hence absorption through the arachnoid villi.
The CSF pressure rises or decreases with the rise or fall of either of these two factors.
CSF is a clear, colourless, transparent fluid which does not coagulate on standing. Its reaction is alkaline and contains about 0 to 5 lymphocytes per cubic mm. Its specific gravity is between 1.004 and 1.006.
Chemically it represents colloid-free plasma with some variations in its crystalloid composition. Of the important constituents its protein content and sugar content are respectively much less and slightly less than those in plasma whereas the chloride content is much above than that in plasma.
With all these physiological backgrounds, the pathological basis in the development of hydrocephalus can be discussed subsequently as follows.
Hydrocephalus can be discussed under two headings:
1. Congenital Causes:
(a) Arnold-Chiari Malformation:
It is a congenital defect in the posterior fossa where a tongue-like projection of the cerebellum and the choroid plexus extend with an enlarged fourth ventricle into the spinal canal through the foramen magnum thereby stretching and kinking backward the upper cervical spinal cord. This condition is frequently associated with spina bifida and meningomyelocoele and may lead to hydrocephalus.
(b) Dandy-Walker Malformation (also known as atresia of the foramina of Nlagendie and Luschka) – here some congenital septa or membranes block the outlet of the fourth ventricle and as such the fourth ventricle is ballooned out into a large cavity above which lies the cerebellar vermis.
(c) Congenital Atresia or Forking of the Aqueduct of Sylvius:
Here in this condition the upper portion of the aqueduct is grossly narrowed which again may be forked or obstructed by a transverse septum. This leads to the hydrocephalus of the lateral and the third ventricles.
(d) Agenesis of Corpus Callosum:
Partial or complete – this condition is often associated with lipomas and meningiomas at the site of the developmental defect. Pneumoencephalogram is diagnostic.
2. Acquired Causes:
E.g. birth injuries, head injuries, intracranial haemorrhages especially intraventricular haemorrhage leading to secondary stenosis of the aqueduct of Sylvius are the common causes.
Especially of the meninges and the brain (meningitis, encephalitis and meningo-encephalitis) or inflammatory reaction to subarachnoid bleeding at birth or later in lifer may lead to gliosis of the aqueduct or obliteration of the subarachnoid space.
(c) Neoplasms and Space Occupying Lesions:
Like tuberculomas, gliomas, organised subdural haematomas or abscesses — all may produce obstructive hydrocephalus. Again a tumour of the choroid plexus (particularly choroid plexus papilloma which usually occurs in children below 2 years or age) may rarely cause hydrocephalus due to over-production of the CSF.
Other neoplastic conditions which might cause hydrocephalus in the paediatric age group include — colloid cysts attached to the choroid plexus of the third ventricle, chordoma, pituitary adenomas and pinealoma.
Apart from the above conditions there are some conditions commonly grouped under a single heading of “Pseudotumor Cerebri” (also known as benign intracranial hypertension) which embraces different clinical entities all of which cause over-production of the CSF with mild to moderate gradation of hydrocephalus especially among the paediatric age group.
It has been found in association with various infections especially otitis media hyper- and hypo-vitaminosis A, tetracycline – toxicity, sudden withdrawal of steroids, hypothyroidism, hypoparathyroidism and Addison’s disease. It is a self-limiting condition and prognosis is usually good.
From treatment point of view hydrocephalus can be classified with two types:
(1) Communicating type and
(2) Non-communicating type of hydrocephalus whereas from anatomical point of view it can also be classified under two types:
(a) Internal and
(b) External type of hydrocephalus.
(1) Communicating Type:
In this type of hydrocephalus, as the name signifies there is free communication between the cerebral ventricles and the subarachnoid space. It usually is due to abnormally over-production of the fluid by the choroid plexuses of the ventricles in the newborn infants.
This type leads to a huge accumulation of the fluid due to excessive production the amount of which progressively becomes more and more than the amount which can re-enter the venous system through the arachnoidal villi, leading to huge collection of the fluid both inside ventricles and in the subarachnoid space outside the brain.
(2) Non-Communicating Types:
In this type as the name signifies, there is no free communication between the cerebral ventricles and the subarachnoid space, and instead there is a block or obstruction (and hence also called obstructive type) to such a free flow of liquid.
Actually speaking, the terms ‘communicating’ and ‘non-communicating’ are misleading as has been emphasised by some authors as both the types, strictly from pathological point of view, are due to some form of anatomical or physiological obstruction between the points of formation and absorption of the fluid.
Internal & External Types of Hydrocephalus:
These two anatomical types are differentiated depending upon the anatomical site of greatest enlargement of the CSF spaces, whether ventricular or extra-ventricular.
Clinical Features of Hydrocephalus :
In case of congenital hydrocephalus it is present at birth or becomes manifested and apparent within a short time after birth, usually within a few months of life and progresses quite rapidly producing wide range of symptoms and sequelae.
In case of acquired hydrocephalus, it usually develops later in life, in association with or as sequelae to the conditions predisposing to it and the progress is not as rapid as in the case of congenital type.
The progress of the process and the symptoms arising out of it vary widely — may be rapid or slow and steadily progressing, intermittent or even remittent, depending upon the cause, especially in case of obstructive type where the obstruction may be complete or partial or intermittent.
In either type the classical picture, especially among the infants is dominated by enlarged or an enlarging head due to enlargement of the skull in all diameters with bulging and tense fontanels, wide gaping at cranial suture lines, prominent and dilated scalp veins on shiny scalp protruding forehead with bulging eyebrows.
The eye sign is known as the “Sun-set sign” characteristically by a visible sclera above the iris due more to the retraction of the upper eyelid than to the pressure on the orbit. Other eye signs are failure to gaze and strabismus and papilledema ultimately leading to optic atrophy.
The “papilioedema” which means “the swelling of the optic disc which can be seen with the help of an ophthalmoscope” is due to high pressure in the optic sheath (the dura mater in the orbital region of the frontal lobe of the brain extending as a sheath into the orbit around the optic nerve and this is pierced by the retinal artery and the vein a few millimetres behind the eyeball on their way to and from the eye along with the optic nerve) due to raised cerebrospinal fluid-tension which impedes the flow of blood in the retinal veins thereby also raising the retinal capillary pressure, ultimately resulting in retinal oedema.
As the tissues of the optic disc are much more distensible than those of the remainder of the retina, the optic disc becomes more and more odematous than the remainder of the retina and swells into the cavity of the eye. Other manifestations in infants specially include mild to moderate diplegia, hyperactive reflexes with irritability, a high-pitched cry, fretfulness, ear pulling, head rolling convulsive seizures, vomiting and failure to thrive and gradually leading to a lethargic baby with drowsiness.
Investigations form a very important step in the correct diagnosis of the cause of the condition and of the site of obstruction if there be any so that early and definite approach for the treatment can be instituted.
The important investigations are:
(1) Straight X-ray of the skull – PA, AP, basal and lateral views or any other special view in some cases requiring them.
(2) Tomograms in different planes to localise any tumour or growth.
(3) Electro-encephalogram (EEG) — if necessary serial.
(4) Brain scanning (with the isotope RISHA — Radioactive Ionised Human Serum Albumin).
(5) Carotid angiogram
(6) Pneumo-encephalogram (wherein air or helium or oxygen is introduced into the subarachnoid space, usually in the lumbar region, sometimes by cisternal puncture under general anaesthesia) but cisternal puncture should be avoided in patients suspected to be suffering from Arnold-Chiari malformation).
(7) Ventriculogram (wherein gas is put directly into the ventricular system through a patent fontanel of an infant or through a trephine-hole in older children as adults in whom the: fontanel is not patent).
(8) Echoencephalogram and especially CT-scan in localising a tumour.
In Infants and Very Young Children:
Symptoms of irritability, restlessness, vomiting, failure to thrive along with an enlarged or enlarging head is noted by serial measurements plotted on a head chart. Bulging fontanels and separation at cranial suture lines will be evident.
Positive trans illumination test and “Setting-sun” eye-sign associated with features of rise of intracranial tension are noted in established cases. There may be associated congenital malformation.
In Older Children and Adults:
History of onset and progress along with the history of past illness suggesting inflammation of the brain and/or the meninges symptoms of headache, vomiting and dimness of vision may draw attention.
“Crack-pot” sign on percussion of the skull, presence of papilledema on ophthalmoscopy along with features of raised intracranial tension are strongly suggestive.
This should be made in (1) infants and young children with the possible causes of enlargement of head and in (2) older children and young adults with all possible causes of increased intracranial tension with or without enlargement of head.
In Infants and Young Children with Possibilities of Enlarged Head:
Normal Variations of Skull:
It should be borne in mind that slight and simple enlarged appearance of the head is somewhat within normal variations from infant to infant and as such an enlarged or enlarging head should be confirmed only after serial measurement of the head and plotted against a head chart and compared with percentile variations.
In premature babies also the head apparently looks enlarged in comparison to other body measurements and this is normal. Here also the gestational history and the features of prematurity along with serial measurements of the head will not call for detailed investigations.
In certain families the head at birth and even after birth appears to be somewhat bigger than the average as a “family trend” and as such this possibility should be borne in mind before the diagnosis is inferred.
Especially the babies of diabetic mothers are as a whole large in comparison to average and serial head measurements and absence of other features of raised intracranial tension will clinch the clue.
Subdural Effusion and/or Haematoma:
A localised swelling usually conforming to the shape of the underlying cranial bone along with or without the presence of the ecchymosis under the scalp with a history of birth trauma or any other trauma helps to exclude the possibility of hydrocephalus. X-ray of the skull is diagnostic and in doubtful cases subdural tap should be undertaken both for the sake of diagnosis and to release the effect of compression on the underlying brain tissue.
This condition also leads to separation (rather delayed union) of sutures with an enlarged head but should never be mistaken for hydrocephalus.
The following points in favour of rickets will help to recognise ricket:
(1) It is usually common between 4 months and 2 years of age.
(2) There is diffuse round prominence of the parietal regions as well as of the frontal regions (this is also true of congenital syphilis) and as such there are four prominent bony bulges with an antero posterior and a transverse groove between them thus forming the “hot cross bun” shape. Frontal bossing is also prominent.
(3) Craniotabes is the earliest sign of rickets which may appear as early as 3 months of age and is a softening and thinning of an area of the skull — commonly in the occipitoparietal region of the skull, which indents on pressure and rebound often with a crackle. (This may also be found normally in prematures.)
(4) Presence of funnel-shaped or pigeon-shaped chest.
(5) Presence of Harrison’s groove corresponding to the costal insertions of the diaphragm.
(6) Rachitic rosary — enlarged costochondral junctions.
(7) Presence of kyphosis or lordosis of the spine with prominent and protuberant abdomen.
(8) Presence of enlargement of the elbows, knee, ankles and bow legs in older children.
(9) Raised alkaline phosphate concentration in blood with usually a low blood phosphorus level and rarely with a low blood calcium level (causing infantile tetany).
(10) Presence of characteristic X-fay findings most prominent at the lower ends of the Ulna and Radius — showing typical cupping, spreading, fraying, stippling of the ends of the shafts, spurring and decreased density of the shaft with unusually prominent trabeculae.
This condition also leads to hydrocephalus and some enlargement of the head because of the so-called “hot-cross bun” appearance as in rickets, but the usual features of congenital syphilis make this condition unmistakably distinct from all other alike conditions.
The diagnostic features are:
1. Presence of a family history along with —
2. “snuffles” with a mucopurulent discharge occasionally bloody with upper-lip excoriation;
3. Characteristic lesions of skin and mucous membrane including “rhagades” (radiating fissured scars) around the angles of the mouth and “condylomalata” (flat raised plaques in the anogenital area);
4. Parrot’s paralysis (Pseudoparalysis);
5. Characteristic X-ray findings – multifocal osteochondritis at the metaphyses of the elbows, wrists, knees and ankles, symmetrical periostitis and osteomyelitis of the long bones, Wimberger’s sign — bilateral moth-eaten appearance of the medial aspect of the proximal tibia.;
6. Hepatosplenomegaly, lymphadenopathy — particularly epitrochlear. choreoretinitis;
7. Characteristic CSF changes and finally positive anti-treponema antibodies test (TPI test and FTA-ABS test) and other serological tests for syphilis in blood.
This is a rare condition in which a child has an unusually large brain (and as such has large head) of poor quality without hydrocephalus. Diagnosis is easily made by pneumoencephalogram.
This is another rare condition in which the head of the infant is full of CSF, with little brain tissue. The diagnosis is easily established by transillumination in a dark room and also by air studies.
In this condition, apart from hydrocephalus there is a peculiar facies, hepatosplenomegaly, congenital corneal opacities (along with a peculiar sabot-shaped deformity of the second and third lumbar vertebrae with kyphosis, mental retardation, enlargement of the pituitary fossa when the child becomes a little older than the infant stage).
Neoplastic conditions involving the skull and the brain which produce asymmetric enlargement of the head with or without hydrocephalus. All these conditions are diagnosed by clinical examinations and investigations.
Causes of enlarged head:
In Older Children:
The causes mentioned earlier have all to be considered along with the following additional possibilities:
Normal variation among middle-aged males an increasing prominence of the forehead, mostly over the frontal areas due to slow enlargement of air cells of the frontal air sinuses and is not pathological. This prominence of the forehead makes the eyebrows appear overhanging the eye.
This condition also leads to some enlargement of the head but the involvement of the skull bones is much less than the involvement of the lower jaw and the phalanges of the hand and the feet, giving the face a characteristic appearance and the whole skeleton an overall enhanced growth pattern. Besides, this condition often leads to bilateral temporal hemianopia. X-ray of the skull (lateral view) often exposes an enlarged sella turcica due to hypertrophy of the pituitary body to which the disease is due.
Primary and Secondary Neoplastic Conditions Involving Skull Bones:
These mainly lead to asymmetric enlargement of the head and a close clinical examination and the history of the case will clinch the diagnosis and differentiate them from hydrocephalus.
It is to be borne in mind that, among infants, about 40 per cent of all cases do undergo spontaneous arrest. Surgical interventions, as such, should be reserved to cases in which serial measurements of head circumference show progressive and rapid enlargement of the head and clinical effects raise intracranial tension. Among older children and adults, about 100 per cent of them need surgical treatment.
Before any surgical measure is undertaken, all attempts should be made to confirm the cause of hydrocephalus, its nature and whether communicating or non-communicating type and the exact site of obstruction.
Maintenance of nutrition and electrolyte balance of the body fluids either by oral or by intravenous feeding.
Once the patient is being prepared well to bear the stress and strain of surgical intervention, the plan for surgical treatment should be sorted out. The same should be undertaken by an efficient neurosurgeon in a well-equipped neurosurgical unit.
Two types of surgical approaches have been tried:
(1) Reduction in the production of excess CSF by — fluid restriction, blood-letting, choroid plexectomy — all these measures and procedures are not much beneficial and backdated and have been abandoned in favour of the second type of procedure.
(2) Bypass operations comprising of bypassing the point of obstruction by diverting and shunting the CSF to normal or artificial sites for absorption or excretion.
In pure aqueductal obstruction with adequate subarachnoid system, Torkildsen’s operation draining CSF from the lateral ventricle to cisterna magna by using a plastic tube.
Other bypass operations are:
(1) Between the ventricular system and lesser peritoneal sac or the pleural spaces.
(2) Between the ventricular system and the superior venacava or the atrium using the Spitz- Holter or the Pudenz-Heyer valves to prevent reflux of blood—this is the most popular and widely practised procedure at present.
(3) Between the lateral ventricle or in cases of communicating hydrocephalus, between spinal theca and the ureter after nephrectomy. (This operation leads to a negative electrolyte balance because of huge loss of C.S.F. via urine and as such supplementary sodium or ammonium chloride has to be given by mouth daily).
The risks of such bypass operations include:
(1) Obstruction to the passage of CSF because of blockage inside the tubes which sometimes call for a re visional surgery.
(2) Septicaemia and bacteriaemia due to colonization of organisms of the artificial valves,
(3) Multiple pulmonary thrombosis with pulmonary hypertension and heart failure.
The result of surgery is very difficult to assess. Without surgery, the mortality rate is very high, as high as 75 per cent. But with surgery the survival rate is about 75 to 80 per cent and among survivors the I.Q. is more or less retained within normal limits.
Prognosis should be guarded in hydrocephalic patients. The prognosis with and without surgical interventions . Many patients, even after successful surgery, suffer from emotional complexes.
Paraparesis, ataxia, urinary incontinence (if hydrocephalus is associated with meningomyelocele) and defective vision. The chance of a revisional surgery is also pretty high in cases of bypass operations.