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Hydrocephalus was first described by the ancient Greek physicianHippocrates, but it remained an intractable condition until the 20th century, whenshunts and other neuro-surgicaltreatment modalities were developed. Although 1 million Americans suffer from hydrocephalus, it remains a lesser-known medical condition. Hydrocephalus affects both pediatric and adult patients. Pediatric hydrocephalus affects one in every 500 live births,making it one of the most commondevelopmental disabilities, more common than deafnessor Down syndrome. It may also be a heritable condition and runs in certain families mostly affecting boys. It is the leading cause of brain surgery for children in theUnited States.
This paper will include an overview, signs, symptoms, pathophysiology, and treatment of hydrocephalus.
Definition of Hydrocephalus:
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. Although hydrocephalus was once known as "water on the brain," the "water" is actually cerebrospinal fluid (CSF) which is a clear fluid that surrounds the brain and spinal cord. The excessive accumulation of CSF results in an abnormal widening of spaces in the brain called ventricles. This widening creates potentially harmful pressure on the tissues of the brain and cause an increasedintracranial pressureinside theskulland progressive enlargement of the head, convulsion, and mental disability. Hydrocephalus can also cause death.
Hydrocephalus comprises a highly diverse group of disorders that have little in common except an increase in the volume of CSF within the intracranial fluid spaces. The causes of hydrocephalus relating to the altered pathophysiology and the age of the child are summarized in below tables.
Types of Hydrocephalus:
1. Acquired hydrocephalus develops at the time of birth or at some point afterward. This type of hydrocephalus can affect individuals of all ages and may be caused by injury or disease.
2. Communicating hydrocephalus occurs when full communication occurs between the ventricles and subarachnoid space. It is caused by overproduction of CSF (rarely), defective absorption of CSF (most often), or venous drainage insufficiency (occasionally).
• Arachnoid cyst
• Dandy-Walker malformation
• Associated with craniofacial syndromes
• Posthemorrhagic: intraventricular or subarachnoid
• Choroid plexus papilloma or choroid plexus carcinoma
• Venous obstruction as in superior vena cava syndrome
• Aqueductal stenosis
• Congenital lesions
(vein of Galen malformation, congenital tumors)
• Arachnoid cyst
• Chiari malformations either with or without myelomeningocele
• X-linked hydrocephalus
• Dandy-Walker malformation
• Aqueductal gliosis (posthemorrhagic or postinfectious)
• Space-occupying lesions such as tumors or cysts
• Head injuries
3. Non- communicating hydrocephalus occurs when CSF flow is obstructed within the ventricular system or in its outlets to the arachnoid space, resulting in impairment of the CSF from the ventricular to the subarachnoid space. The most common form of non-communicating hydrocephalus is obstructive and is caused by intraventricular or extraventricular mass-occupying lesions that disrupt the ventricular anatomy.
4. Congenital hydrocephalus applies to the ventriculomegaly that develops in the fetal and infancy periods, often associated with macrocephaly.The most common causes of congenital hydrocephalus are obstruction of the cerebral aqueduct flow, Arnold-Chiari malformation ormalformation. These patients may stabilize in later years due to compensatory mechanisms but may decompensate, especially following minor head injuries. During these decompensations, determining the extent to which any new neurological deficits may be due to the new acute event, compared with hydrocephalus that may have gone unnoticed for many years.
5. Internal Hydrocephalus Internal hydrocephalus refers to ventricular dilation and the associated pathophysiology. The term hydrocephalus is used most commonly to refer to internal hydrocephalus.
6. External hydrocephalus External hydrocephalus refers to the accumulation of CSF in either the subarachnoid or subdural spaces. CSF collection in the subarachnoid space may be a benign condition in infancy, which is called benign subdural hygromas of infancy. CSF mixed with blood in the subdural space may not be benign and usually requires further investigation and treatment. It may be related to trauma. If these fluid collections exert pressure on the brain and cause symptoms or cause accelerated head growth, surgical treatment may be necessary.
7. Ex Vacuo Hydrocephalus Ex vacuo hydrocephalus refers to a condition of brain volume loss. The condition may be present at birth. It may be the result of failure of the fetal development of the brain as in schizencephaly or hydranencephaly. The brain may also undergo destruction or atrophy from infections, very poor nutrition, or unknown causes. The ventricles become large to "fill the space" where there is an absence of brain tissue, and may or may not be under increased pressure. There is technically not an imbalance of CSF production and absorption, but rather there is a loss of brain matter.
8. Normal Pressure Hydrocephalus Normal pressure hydrocephalus is a condition that occurs without increased intracranial pressure. There is ventricular dilation with compression of the cerebral tissue, but the intraventricular pressure is normal. Patients develop symptoms slowly over time. The classic symptoms include dementia, gait difficulties, and urinary incontinence. This is primarily a condition of the elderly.
Signs and Symptoms
The signs and symptoms of hydrocephalus vary by age group and disease progression.
In infants, common signs and symptoms of hydrocephalus include:
- An unusually large head.
- A rapid increase in the size of the head.
- A bulging "soft spot" on the top of the head.
- Eyes fixed downward (sun setting of the eyes).
- Developmental delay.
- A high-pitched cry.
- Problems with sucking or feeding.
- Unexplained, recurrent vomiting.
- Exhibiting an unwillingness to bend or move the neck or head.
- Breathing difficulties.
Irritability is the most common sign of hydrocephalus in infants. If this is not treated, it may lead to lethargy. Bulging of the fontanelles, or the soft spots between the skull bones, may also be an early sign. When hydrocephalus occurs in infants, fusion of the skull bones is prevented. This leads to abnormal expansion of the skull.
In older children and adults, common signs and symptoms of hydrocephalus include:
- Headache followed by vomiting.
- Blurred or double vision.
- Eyes fixed downward (sun setting of the eyes).
- Problems with balance, coordination or gait.
- Sluggishness or lack of energy.
- Slowing or regression of development.
- Memory loss.
- Urinary incontinence.
- Changes in personality.
- Impaired performance in school or work.
- Walking difficulties and weakness.
- Impaired thinking.
Pathophysiology of Hydrocephalus
Normal CSF production is 0.20-0.35 ml/min; most CSFis produced by the choroid plexus, which is located within the ventricular system, mainly the lateral and fourth ventricles. The capacity of the lateral and third ventricles in a healthy person is 20 ml. Total volume of CSF in an adult is 120 ml.
Normal route of CSF from production to clearance is the following: From the choroid plexus, the CSF flows to the lateral ventricle, then to the interventricular foramen of Monro, the third ventricle, the cerebral aqueduct of Sylvius, the fourth ventricle, the 2 lateral foramina of Luschka and 1 medial foramen of Magendie, the subarachnoid space, the arachnoid granulations, the dural sinus, and finally into the venous drainage.
ICP rises if production of CSF exceeds absorption. This occurs if CSF is overproduced, resistance to CSF flow is increased, or venous sinus pressure is increased. CSF production falls as ICP rises. Compensation may occur through transventricular absorption of CSF and also by absorption along nerve root sleeves. Temporal and frontal horns dilate first, often asymmetrically. This may result in elevation of the corpus callosum, stretching or perforation of the septum pellucidum, thinning of the cerebral mantle, or enlargement of the third ventricle downward into the pituitary fossa (which may cause pituitary dysfunction).
The mechanism of NPH has not been elucidated completely. Current theories include increased resistance to flow of CSF within the ventricular system or subarachnoid villi; intermittently elevated CSF pressure, usually at night; and ventricular enlargement caused by an initial rise in CSF pressure; the enlargement is maintained despite normal pressure because of the Laplace law. Although pressure is normal, the enlarged ventricular area reflects increased force on the ventricular wall.
Normal pathway of CSF
Pathophysiology of hydrocephalus
What is the current treatment?
There is currently no medical therapy that definitively treats hydrocephalus effectively. Occasionally, in borderline cases of progressive hydrocephalus and in PHH, diuretics may be useful as a temporizing measure to try to avoid the need for a permanent shunt. Acetazolamide, a carbonic anhydrase inhibitor, has been shown to decrease CSF production. The dose may be as high as 100 mg/kg, and in order for it to be effective, more than 99% of carbonic anhydrase must be blocked before CSF production decreases significantly. Furosemide, 1 mg/kg/day, has also been used. The mechanism of action is unknown, but it is thought to decrease brain extracellular fluid.
Hydrocephalus is most often treated by surgically inserting a shunt system. This system diverts the flow of CSF fromthe 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 placedwithin 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 such as a chamber of the heart orareas around the lung where the CSF can drain and be absorbed. A valve located along the catheter maintains one-way flow and regulates the rate of CSF flow.
A limited number of individuals can be treated with an alternative procedure called third ventriculostomy. In this procedure, a neuroendoscope - a small camera that uses fiber optic technology to visualize small and difficult to reach surgical areas - allows a doctor to view the ventricular surface. Once the scope is guided into position, a small tool makes a tiny holein 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.
Possible complications of a shunt system
Shunt systems are not perfect devices. Complications may 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 revision.
Some complications can lead to other problems such as overdraining or underdraining. Overdraining occurs when the shunt allows CSF to drain from the ventricles more quickly than it is produced. Overdraining can cause the ventricles to collapse, tearing blood vessels and causing headache, hemorrhage (subdural hematoma), or slit-like ventricles (slit ventricle syndrome).
Main complications of ventricular shunts
Underdraining 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.
To summarize, hydrocephalus is a condition resulting from an imbalance between the production and absorption of cerebral spinal fluid (CSF). This imbalance results in an increased volume of spinal fluid, dilation of the ventricular system, and often increased intracranial pressure. The prognosis for children with hydrocephalus has markedly improved with modern shunting. The prognosis of an infant or child with hydrocephalus is mostly dependent on the underlying cause of the hydrocephalus. Hydrocephalus is subdivided into several different categories. Communicating and noncommunicating are the most common categories.
The pathophysiology of hydrocephalus is multifactorial. Aqueductal stenosis, occlusion of the foramina of Lushcka and Magendie, hindbrain herniation, obliteration of the subarachnoid spaces at the level of the posterior fossa, compression of the sigmoid sinuses with consequent venous hypertension and fibrosis of the subarachnoid spaces, are the pathophysiological factors thus far described.
The signs and symptoms of hydrocephalus vary depending on age, the degree of hydrocephalus at presentation, the primary etiology, and the time over which the hydrocephalus develops. Because of the plasticity of the infant brain and the ability of the cranium to expand, ventriculomegaly can progress without obvious signs of increased intracranial pressure.
There is currently no medical therapy that definitively treats hydrocephalus effectively. CSF shunting is the most common standard surgical treatment in the long-term management of hydrocephalus. However, most complications arise from malfunction or infection
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