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Hydrocephalus for dummies
Hydrocephalus is derived from two Greek words: hydro meaning water; and cephalus meaning head; also known as "water on the brain".
Hydrocephalus is believed to result from imbalance between fluid production
and absorption, with net accumulation of fluid in the head, cavity; characterized by increase in size of the cerebral ventricles. It is further classified as: Communicating hydrocephalus, in which flow is not obstructed, but fluid is inadequately reabsorbed space and the Non-communicating hydrocephalus or the Obstructive type, in which flow of fluid from the ventricles to subarachnoid space is obstructed. This type may also be sub-classified into Congenital and
The overall incidence of hydrocephalus is not known. Approximately 55% of all hydrocephalus are congenital.
Cerebrospinal Fluid Pathways
CSF is mainly formed within the ventricular system. Formation sites include choroid plexus, ependyma and parenchyma. Most of the CSF is formed by the choroids plexus of lateral ventricles. The rate of formation is 0.35-0.40 ml/min equivalent to 500 ml per day, the rate being same in paediatric and adult population.
Pathophysiology
Hypothetically, hydrocephalus can be subdivided into 3 forms:
* Abnormality in cerebrospinal fluid production: This is the rarest form of hydrocephalus. Choroid plexus papillomas and choroid plexus carcinomas can secrete cerebrospinal fluid in excess of its absorption. Or in Simple words, "there is increase in fluid production regardless of its causes.
* Disorders of cerebrospinal fluid circulation: This form of hydrocephalus results from obstruction of the pathways of cerebrospinal fluid circulation. This can occur at the ventricles or arachnoid villi. Tumors, hemorrhages, congenital
malformations, and infections can cause obstruction at either point in the pathways. Or there is an obstruction in fluid pathways..
* Lower cerebrospinal fluid absorption: Conditions, such as the superior vena cava syndrome and sinus thrombosis, can interfere with cerebrospinal fluid absorption.
Some forms of hydrocephalus cannot be classified clearly. This group includes normal pressure hydrocephalus and pseudotumor cerebri.
Etiology of Hydrocephalus
A lot of conditions can lead to increase of water in brain, wether its effects on production, flow pathways or absorption:
- Intrauterine infections, most popularly related to TORCH infection
- Infections of the brain and meninges
- Intracranial tumor
- Vascular abnormality
- Post hemorrhagic condition
Clinical Features
Clinical manifestation of hydrocephalus depends on the onset. If hydrocephalus occurs less than 2 years old, or before the skull unites, there is a potential for expansion of the volume. While after 2 years old, the skulls already unites, so there is no room for volume expansion, leads to intracranial hypertension.
Before 2 years old:
1) Shape of Head: An abnormal head shape may suggest the diagnosis. Occipital prominence is seen in Dandy walker malformation. A disproportionately large forehead is common with aqueductal stenosis. The enlarged cranial size is quite evident and helpful in diagnosis.
2) Anterior Fontanelle: Normally the anterior fontanelle is small, depressed in a relaxed sitting patient but with hydrocephalus, it is enlarged and full even when the infant is quiet and upright.
3) Scalp Veins: The scalp veins are usually prominent, particularly in crying infants. The prominence is caused by compression of basal venous outlets by increased pressure, which results in shunting of blood through the valveless collateral system into easily distended scalp veins.
4) The Eyes: As the hydrocephalus progresses, the eyes are displaced downward by pressure on the thinned orbital roofs. This displacement of eyes causes the sclera to be visible above the iris, termed as the "setting
sun" sign.
5) Cranial Nerves: Optic nerve atrophy is a common finding in advanced hydrocephalus due to the compression of the optic chiasma and the optic nerve by dilated anterior third ventricle and increased intracranial pressure (ICP). Abducent nerve paresis secondary to stretching is common.
Nystagmus and random eye movement may be present.
6) Muscle Tone and Deep Tendon Reflexes: With progressive hydrocephalus, the deep tendon reflexes and muscle
After 2 years old:
The sign of hydrocephalus can't be easily identified. But we should alert the sign of intracranial hypertension such as projectile vomiting, severe headache, seizures, maybe loss of conscioussness.
Because of there is no room for expansion, hydrocephalus after 2 years old can deterioate rapidly, since it will compress the structure of brain.
Diagnostic procedures
1) Head Circumference: The head size should be measured by taking maximal obtainable circumference with measuring tape. The circumference is plotted on a growth chart having head circumference column.
2) Fusion of Sutures: Progressive hydrocephalus beginning before closure of cranial sutures, prevents the fusion of sutures leading to continuous excessive head enlargement.
3) Plain X rays: This modality is of great diagnostic value and will confirm many clinical findings, such as an enlarged head, crainofacial disproportion, wide spread sutures and large anterior fontanelle. In older children elongated interdigitations of suture line indicates increased ICP. There may be evidence of intracranial convolutional markings (silver beaten appearance) and demineralization of dorsum sella.
4) Ultrasonography: It is a non-invasive procedure used only in patients in whom the anterior fontanelle is open or less than 2 years old.
5) Computed Tomography: CT scan superceded other invasive investigations like Ventriculography and Pneumoencephalography. It has a major role in accurate assessment of ventricular size, extracerebral spaces and site
of obstruction.
6) Magnetic Resonance Imaging (MRI): This is also a noninvasive investigation. It may also be used in antenatal diagnosis of Hydrocephalus.
Management
In early days when methods for diagnosis and treatment of hydrocephalus were unsatisfactory, a number of patients died due to inadequate treatment.
Non Surgical Management
Drugs such as manitol which produce hyperosmotic diuresis and those such as acetazolamide which decrease the secretion of CSF may be treated as temporary management of clinical situation. Their brief action and side effects preclude their prolonged use in the definitive treatment of hydrocephalus.
Surgical Management
The era of modern treatment of hydrocephalus began in early sixties, when Spitz, an engineer along with Holter, introduced pressure sensitive flow regulating valve for diversion of CSF from obstructed ventricles into the right
atrium of the heart. These shunts have been subsequently refined and are now universally employed in the management of hydrocephalus.
The indication of surgical intervention are related to intracranial hypertension, neurological dysfunction, evidence and degree of ventricular dilatation, the presence or absence of pathological lesion, the nature and the location
of obstruction. Some surgeons insert the shunt in any patient with large ventricles while others restrict it to those with potentially reversible deficit or progressive deterioration. Progressive ventriculomegally on CT scan combined with observation of developmental deficits in infants or intellectual and motor disability in older children are a few criteria.
Prognosis
Hydrocephalus is usually a lifelong disorder. Prognosis depends on a number of factors, including the underlying condition, its duration and degree, as well as response to treatment. The mortality rate in shunt-treated pediatric patients with hydrocephalus remains high, dependent on the underlying cause for shunt insertion and the subsequent development of infection and other complications related to shunt apparatus.
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