Introduction
The term hydrocephalus is derived from the Greek words “hydro” meaning water and “cephalus” meaning head. It is a condition in which the primary characteristic is excessive accumulation of fluid in the brain (figure1). Hydrocephalus was once known as “water on the brain,” the “water” is actually cerebrospinal fluid (CSF)
CSF is a clear fluid that surrounds the brain and spinal cord. The excessive accumulation of CSF 1 due to impaired flow of CSF, 2, 6 impaired absorption of CSF 3, 6 excessive secretion, 6 or from complications of head injuries or infections,7 results in an abnormal widening of spaces in the brain called ventricles. It typically appears as very large ventricles on imaging studies. In a person without hydrocephalus, CSF continuously circulates through the brain, its ventricles and the spinal cord and is continuously drained away into the circulatory system.

Causes of hydrocephalus
• The most common cause of hydrocephalus is CSF flow obstruction, hindering the free passage of cerebrospinal fluid through the ventricular system and subarachnoid space (e.g., stenosis of the cerebral aqueduct or obstruction of the interventricular foramina – foramina of Monro secondary to tumors, hemorrhages, infections or congenital malformations).
• Hydrocephalus can also be caused by overproduction of cerebrospinal fluid (e.g., papilloma of choroid plexus).

Classifications of hydrocephalus
Hydrocephalus is a neurological disorder that spans all ages. It could be divided into congenital or acquired. Congenital hydrocephalus is present at birth, may be caused by genetic abnormalities, and may be associated with other developmental disorders such as neural tube defects like spina bifida 1, 2 or Dandy-Walker malformation. Often the cause is unknown. Acquired hydrocephalus develops at the time of birth or at some point afterward, and may be secondary to damage to the brain caused by hemorrhage, stroke, infection, tumor, or traumatic injury.1
Compression of the brain by the accumulating fluid eventually may cause convulsions and mental retardation.5 These signs occur sooner in adults, whose skulls no longer are able to expand to accommodate the increasing fluid volume within.
Fetuses, infants, and young children with hydrocephalus typically have an abnormally large head, 1, 3, and 5 excluding the face due to the pressure of the fluid on the individual skull bones, which haven’t fused yet. So it bulges outward at their juncture points. The medical sign, in infants, is a characteristic fixed downward gaze with whites of the eyes showing above the iris, as though the infant were trying to examine its own lower eyelids.8 Dilated veins are prominent over the scalp.1 Children who have had hydrocephalus may have very small ventricles, and presented as the “normal case”.
Hydrocephalus affects one in every 1000 live births, making it one of the most common developmental disabilities, more common than Down syndrome or deafness.9 There are over 180 different causes of the condition, one of the most common being brain hemorrhage associated with premature birth.
1. Internal hydrocephalus and External hydrocephalus
When there is a blockage of forth ventricle or the cerebral aqueduct, CSF accumulates and internal production of CSF continues so the fluid compresses the nervous tissue and forth ventricle dilates, resulting in internal hydrocephalus (figure 2). Irreversible brain damage can occur. The cerebral aqueduct may be blocked at birth or become blocked later in life due to tumor growing in brainstem.
Internal hydrocephalus can be successfully treated by placing a drainage tube (shunt) between the brain ventricles and abdominal cavity to eliminate the high internal pressures. There is some risk of infection being introduced into the brain through these shunts. These shunts must be replaced as the person grows.
If CSF accumulates in the space between the proper and arachnoid, containing CSF, the condition is called external hydrocephalus. In this condition, pressure is applied to the brain externally. This compress neural tissues and causes brain damage. Thus resulting in further damage of the brain tissue and leading to necrotization.

2. Communicating and Non communicating hydrocephalus
Hydrocephalus may also be classified into communicating or non-communicating. Communicating hydrocephalus occurs when the flow of CSF is blocked after it exits the ventricles. This form is called communicating because the CSF can still flow between the ventricles, which remain open. Non-communicating hydrocephalus is also called “obstructive” hydrocephalus – occurs when the flow of CSF is blocked along one or more of the narrow passages connecting the ventricles. One of the most common causes of hydrocephalus is “aqueductal stenosis.” In this case, hydrocephalus results from a narrowing of the aqueduct of Sylvius, a small passage between the third and fourth ventricles in the middle of the brain. Both forms can be either congenital or acquired.

2.1 Communicating hydrocephalus
Communicating hydrocephalus, also known as non-obstructive hydrocephalus, is caused by impaired cerebrospinal fluid resorption in the absence of any CSF-flow obstruction.This is due to functional impairment of the arachnoid granulations, which are located along the superior sagittal sinus and is the site of cerebrospinal fluid resorption back into the venous system. Various neurologic conditions may result in communicating hydrocephalus, including subarachnoid/intraventricular hemorrhage, meningitis, Chiari malformation, and congenital absence of arachnoid granulations (Pacchioni’s granulations).

2.2 Non-communicating hydrocephlus.
Non-communicating hydrocephalus, or obstructive hydrocephalus, is caused by a CSF-flow obstruction (either due to external compression or intraventricular mass lesions).4
2.2.1. Foramen of Monro obstruction may lead to dilation of one or, if large enough (e.g., in colloid cyst), both lateral ventricles.
2.2.2. The aqueduct of Sylvius, may be obstructed by a number of genetically or acquired lesions6 (e.g., atresia, ependymitis, hemorrhage, tumor) and lead to dilation of both lateral ventricles as well as the third ventricle.
2.2.3. Fourth ventricle5 obstruction will lead to dilatation of the aqueduct as well as the lateral and third ventricles.
2.2.4 The foramina of Luschka and foramen of Magendie may be obstructed due to congenital failure of opening (e.g., Dandy-Walker malformation6).
2.2.5. The subarachnoid space surrounding the brainstem may also be obstructed due to inflammatory or hemorrhagic fibrosing meningitis, leading to widespread dilatation, including the fourth ventricle

3. Congenital and Acquired Hydrocephalus.
3.1 Congenital Hydrocephalus
For head enlargement to occur, hydrocephalus must occur before the 3rd year. Because by the end of 3rd year the cranial bones fuse. The causes are usually genetic but can also be acquired and usually occur within the first few months of life, which include
1) intraventricular matrix hemorrhages in premature infants
2) infections
3) type II Arnold-Chiari malformation
4) aqueduct atresia and stenosis
5) Dandy-Walker malformation.
In newborns and toddlers with hydrocephalus, the head circumference is enlarged rapidly and soon surpasses the 97th percentile. Since the skull bones have not yet firmly joined together, bulging, firm anterior and posterior fontanelles may be present even when the patient is in an upright position.
The infant exhibits fretfulness, poor feeding, and frequent vomiting. As the hydrocephalus progresses, torpor sets in, and the infant shows lack of interest in his surroundings. Later on, the upper eyelids become retracted and the eyes are turned downwards (also called “sunsetting”), and seizures.10 Movements become weak and the arms may become tremulous. Papilledema is absent but there may be reduction of vision. The head becomes so enlarged that the child may eventually be confined to bed.
Hydrocephalus is a heterogeneous group of disorders and not a single disease unit.11About 80-90% of fetuses or newborn infants with spina bifida, often associated with meningocele or myelomeningocele, develop hydrocephalus.12
Older children and adults may experience different symptoms because their skulls cannot expand to accommodate the buildup of CSF. Symptoms may include headache followed by vomiting, nausea, papilledema (swelling of the optic disk which is part of the optic nerve),3 blurred or double vision, sunsetting of the eyes, problems with balance, poor coordination, gait disturbance, urinary incontinence, slowing or loss of developmental progress, lethargy, drowsiness, irritability, or other changes in personality or cognition including memory loss.10

3.2 Acquired hydrocephaus
This condition is acquired as a consequence of CNS infections, meningitis, brain tumors, head trauma, intracranial hemorrhage (subarachnoid or intraparenchymal) and is usually extremely painful. Post traumatic hydrocephalus (PTH) is a relatively rare condition.13,15,16,17,18 In PTH due to subarachnoid and intraventricular blockage, the dilated ventricles cause raised intracranial pressure, which has to be relieved at the earliest to prevent further brain damage.13
Even though PTH relatively rare, is a treatable condition.PTH may present with various clinical syndromes like obtundation, failure to improve and a tetrad of symptoms including psychomotor retardation, memory loss, gait ataxia and incontinence.14, 19 Sometimes, the patient may be too injured to demonstrate clinical signs and symptoms of PTH, or may present with atypical symptoms.14 PTH is rare among children. PTH commonly occurs in the 1st year post- trauma, it has been occasionally described as early as within seven hours post-trauma.13,20

4. Other forms of hydrocephalus.
There are two other forms of hydrocephalus which do not fit exactly into the categories mentioned above and primarily affect adults: hydrocephalus ex-vacuo and normal pressure hydrocephalus.
• Hydrocephalus ex vacuo also refers to an enlargement of cerebral ventricles and subarachnoid spaces, and is usually due to brain atrophy (as it occurs in dementias), post-traumatic brain injuries and even in some psychiatric disorders, such as schizophrenia. As opposed to hydrocephalus, this is a compensatory enlargement of the CSF-spaces in response to brain parenchyma loss – it is not the result of increased CSF pressure.

• Normal pressure hydrocephalus (NPH) is an abnormal increase of cerebrospinal fluid (CSF) in the brain’s ventricles, or cavities. It occurs if the normal flow of CSF through the cord is blocked in some way. This causes the ventricles to enlarge without cortical atrophy,2 putting pressure on the brain. Normal pressure hydrocephalus can occur in people of any age, but it is most common in the elderly population. It may result from a subarachnoid hemorrhage, head trauma, infection, tumor or complications of surgery. However, many people develop NPH even when none of these factors are present. In these cases the cause of the disorder is unknown.21
Symptoms of NPH include progressive mental impairment and dementia, problems with walking, and impaired bladder control leading to urinary frequency and/or incontinence. The person also may have a general slowing of movements or may complain that his or her feet feel “stuck.”
Doctors may use a variety of tests, including brain scans (CT and/or MRI), a spinal tap or lumbar catheter, intracranial pressure monitoring, and neuropsychological tests, to help them diagnose NPH and rule out other conditions.10
Treatment for NPH involves surgical placement of a shunt in the brain to drain excess CSF into the abdomen where it can be absorbed. This allows the brain ventricles to return to their normal size. Regular follow-up care by a physician is important in order to identify subtle changes that might indicate problems with the shunt.21

Diagnosis
Hydrocephalus is diagnosed through clinical neurological evaluation and by using cranial imaging techniques such as ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), or pressure-monitoring techniques.23 A physician selects the appropriate diagnostic tool based on an individual’s age, clinical presentation, and the presence of known or suspected abnormalities of the brain or spinal cord.23

Treatments
Hydrocephalus treatment is surgical. It involves inserting a shunt system.21 This system diverts the flow of CSF from the CNS to another area of the body where it can be absorbed as part of the normal circulatory process. A shunt is a flexible but sturdy plastic tube. A shunt system consists of the shunt, a catheter, and a valve. One end of the catheter is placed within a ventricle inside the brain or in the CSF outside the spinal cord. The other end of the catheter is commonly placed within the abdominal cavity, but may also be placed at other sites in the body. A valve located along the catheter maintains one-way flow4 and regulates the rate of CSF flow.
Most shunts drain the fluid into the peritoneal cavity, so known as ventriculo-peritoneal shunt. But alternative sites include the:
1. right atrium -ventriculo-atrial shunt
2. pleural cavity -ventriculo-pleural shunt
3. gallbladder.
4. peritoneal cavity -ventriculo-pleural shunt A shunt system can also be placed in the lumbar space of the spine and have the CSF redirected to the peritoneal cavity.
An alternative treatment for obstructive hydrocephalus in selected patients is the endoscopic third ventriculostomy (ETV), whereby a surgically created opening in the floor of the third ventricle allows the CSF to flow directly to the basal cisterns, thereby shortcutting any obstruction, as in aqueductal stenosis. This may or may not be appropriate based on individual anatomy.
In this procedure, a neuroendoscope is used. Neuroendoscope is a small camera that uses fiber optic technology to visualize small and difficult to reach surgical areas. This allows a doctor to view the ventricular surface. Once the scope is guided into position, a small tool makes a tiny hole in the floor of the third ventricle, which allows the CSF to bypass the obstruction and flow toward the site of resorption around the surface of the brain.

Complications of a shunt system
Shunt systems are not perfect devices. Complications may occur. They include mechanical failure, infections, obstructions, and the need to lengthen or replace the catheter. Generally, shunt systems require monitoring and regular medical follow up. When complications occur, the shunt system usually requires some type of correction.
Some complications can lead to other problems such as over draining or under draining. Over draining occurs when the shunt allows CSF to drain from the ventricles more quickly than it is produced by choroid plexus. Over draining can cause the ventricles to collapse, tearing blood vessels and causing headache, hemorrhage (subdural hematoma), or slit-like ventricles (slit ventricle syndrome).10 Other symptoms are listlessness, irritability, light sensitivity, auditory hyperesthesia (sound sensitivity), nausea, vomiting, dizziness, vertigo, migraines, seizures, a change in personality, weakness in the arms or legs, strabismus, and double vision – to appear when the patient is vertical. If the patient lies down, the symptoms usually vanish in a short period of time.
Under draining occurs when CSF is not removed quickly enough and the symptoms of hydrocephalus recur. In addition to the common symptoms of hydrocephalus, infections from a shunt may also produce symptoms such as a low-grade fever, soreness of the neck or shoulder muscles, and redness or tenderness along the shunt tract. When there is reason to suspect that a shunt system is not functioning properly (for example, if the symptoms of hydrocephalus return), medical attention should be sought immediately.10
Other complications include shunt malfunction. Although a shunt generally works well, it may stop working if it disconnects, becomes blocked (clogged), infected, or it is outgrown. If this happens the cerebrospinal fluid will begin to accumulate again and a number of physical symptoms will develop. Examples are headaches, nausea, vomiting and photophobia/light sensitivity. Some extremely serious, like seizures. The shunt failure rate is also relatively high (of the 40,000 surgeries performed annually to treat hydrocephalus, only 30% are a patient’s first surgery22 and it is not uncommon for patients to have multiple shunt revisions within their lifetime

Other Mechanisms which may lead to insult in hydrocephalus
This includes a number of factors. Grossly, these include compression, stretch, edema, ischemia, breakdown of the blood-brain barrier (BBB), and toxicity due to poorly circulation of CSF. On the cellular level, pathways of cell death (neurons and glia), axonal degeneration and demyelination, neurotransmitter alterations, gliosis, changes in metabolism, and aberrant regeneration are probably important.
Studies in animal models suggest that calcium mediated damage may contribute to the insult in hydrocephalus.11 There are connections between CSF and the lymphatic system. This has been demonstrated in several mammalian systems. Preliminary data suggest that these CSF-lymph connections form around the time that the CSF secretary capacity of the choroids plexus is developed in utero. There may be some relationship between CSF disorders and impaired CSF lymphatic transport.11

Research Resources for Hydrocephalus
A number of animal models are used to research on adult hydrocephalus. Animal hydrocephalus models have been made in hamster, guinea pig, dog, rat, lamb, cat, and monkey. Many of these have histopathological similarities to what has been seen in human hydrocephalus.11 These are needed in order to allow comparisons across models and with human clinical findings. So that features can be interpreted in therapeutically meaningful ways. In order to improve the process of moving from animal models into clinical trials, several suggestions were made which are consistent with recommendations for studies in other fields (such as stroke), including: assuring that animal trials are appropriately randomized and the evaluations are blinded, having both short and long term outcome measures in animals. Then the validating results in separate laboratories prior to human trials, testing any therapy in more than a single non-human species. Animal models of hydrocephalus would be useful for evaluation of prenatal treatments as well as surgeons to develop knowledge in fetal techniques.

Findings of hydrocephalus
The present observations demonstrate uneven distribution of intracranial pulsatility in patients with hydrocephalus, higher pulse pressure amplitudes within the ventricular CSF than within the brain parenchyma. This may be one mechanism behind ventricular enlargement in hydrocephalus.24
Community-acquired Pseudomonas meningitis causes acute obstructive hydrocephalus. Pseudomonas aeruginosa (PS) infection is serious in children and can cause malignant external otitis, endophthalmitis, endocarditis, meningitis, pneumonia, and septicemia. The early stage of obstructive hydrocephalus caused by community-acquired Pseudomonas is rare and should be immediately detected.25
External ventricular drains (EVD) were placed for traumatic brain injury (TBI), ventriculoperitoneal shunt failure and new-onset hydrocephalus. The overall complication rate was 26%. Complication rates were similar in TBI and hydrocephalus patients, and with EVDs inserted in either the pediatric critical care unit or. Prophylactic antibiotics or antimicrobial-impregnated catheters directed against coagulase-negative Staphylococcus may reduce EVD infections.26

Decompressive craniectomy and postoperative complication management in infants and toddlers with severe traumatic brain injuries: Infants with severe traumatic brain injury can safely undergo decompressive craniectomy with reasonable neurological recovery. Due to the high rate of CSF fistulas encountered in most of the infants, it’s better to recommend both the suturing in of a dural augmentation graft and the placement of either a subdural drain or a ventriculostomy catheter to relieve pressure on the healing surgical incision. And also can use a T-shaped incision as opposed to the traditional reverse question mark-shaped incision. Because wound healing may be compromised due to the potential interruption of the circulation to the posterior and inferior limb with this latter incision.27
Although intracranial pressure (ICP) elevation can induce significant structural and functional changes within the central nervous system (CNS), almost complete neuronal recovery is possible. But ICP and associated pathogenic factors should be restored in the acute phase of the disease process. Endothelial cell nitric oxide synthase (ecNOS), an enzyme that plays a protective role in the CNS, is up-regulated in a time-dependent manner after pressure elevation. ecNOS levels increase after axonal and astrocyte injury, suggesting that it might be a compensatory response that is initiated in an effort to preserve CNS function. Changes in ecNOS levels are therefore be important in the development of neuronal tolerance in the early stages of CNS diseases such as hydrocephalus. 28
Visual disturbance in hydrocephalus occurs due to raised intracranial pressure. Patient who presented with marked loss of peripheral visual fields, but without features suggestive of raised intracranial pressure, MR scan showed an enlarged third ventricle and a downward displacement of the optic chiasm, Chiari II malformation. These radiological changes and the visual field deficits reversed after endoscopic third ventriculostomy and foramen magnum decompression. So the treatment of the hydrocephalus in such patients can help to reverse the change in the position of the optic chiasm and the visual field deficits.29
Neonatal ruptured intracranial aneurysms: Neonatal intracranial aneurysms are rare. Clinical presentation of subarachnoid haemorrhage in this age group is often non-specific. First-line investigation should start with transfontanelle cranial ultrasound, followed by MR angiography then CTA if necessary. Posterior circulation aneurysms and large or giant aneurysms are more frequent in neonates and children than in adults. Early diagnosis and treatment are important for improved outcome. Surgery is better tolerated than in adults.30
Exceptional case
One case involved a person with past hydrocephalus. He was a 44-year old French man, whose brain had been reduced to little more than a thin sheet of actual brain tissue. This was due to the buildup of fluid in his skull. The man had a shunt inserted into his head to drain away fluid (which was removed when he was 14), went to a hospital after he had been experiencing mild weakness in his left leg.
In July 2007, Fox News quoted Dr. Lionel Feuillet of Hôpital de la Timone in Marseille as saying: “The images were most unusual… the brain was virtually absent.31
When doctors learned of the man’s medical history, they performed a CT scan (figure 3) and MRI scan, and were astonished to see “massive enlargement” of the lateral ventricles in the skull. Intelligence tests showed the man had an IQ of 75, below the average score of 100 but not considered mentally retarded or disabled, either.
Remarkably, the man was a married father of two children, and worked as a civil servant, leading a normal life, despite having little brain tissue. “What I find amazing to this day is how the brain can deal with something which you think should not be compatible with life,” commented Dr. Max Muenke, a pediatric brain defect specialist at the National Human Genome Research Institute. “If something happens very slowly over quite some time, maybe over decades, the different parts of the brain take up functions that would normally be done by the part that is pushed to the side.”32, 33