Cranial Anatomy - Hydrocephalus

Hydrocephalus is a condition in which excess cerebrospinal fluid (CSF) builds up within the ventricles (fluid-containing cavities) of the brain and may increase pressure within the head. Although hydrocephalus is often described as "water on the brain," the "water" is actually CSF, a clear fluid surrounding the brain and spinal cord. Cerebrospinal fluid (CSF) is formed in a region of the brain known as the choroid plexus. CSF has three crucial functions:

1) it acts as a "shock absorber" for the brain and spinal cord;
2) it acts as a vehicle for delivering nutrients to the brain and removing waste;
3) it flows between the cranium and spine to regulate changes in pressure within the brain.

The average adult produces about half a litre of CSF daily. When an injury or illness alters the circulation of CSF, one or more of the ventricles becomes enlarged as CSF accumulates. In an adult, the skull is rigid and cannot expand, so the pressure in the brain may increase profoundly. Hydrocephalus is a chronic condition. It can be controlled, but usually not cured. With appropriate early treatment, however, many people with hydrocephalus lead normal lives with few limitations. Hydrocephalus can occur at any age, but is most common in infants and adults age 60 and older. It affects adult males and females, as well as people of different races about equally. Experts believe that normal pressure hydrocephalus accounts for 5 to 6 percent of all cases of dementia.

The incidence is approximately 1 out of 1,000 people. Hydrocephalus most often occurs in children, but may also occur in adults and the elderly.

Hydrocephalus Ex-Vacuo

Hydrocephalus ex-vacuo occurs when a stroke or injury damages the brain and brain matter actually shrinks. The brain may shrink in older patients or those with Alzheimer's disease, and CSF volume increases to fill the extra space. In these instances, the ventricles are enlarged, but the pressure is usually normal.

Normal Pressure Hydrocephalus (NPH)

NPH results from the gradual blockage of the CSF draining pathways in the brain. The ventricles enlarge to handle the increased volume of CSF, and the compression of the brain from within by the fluid-filled ventricles destroys or damages brain tissue. NPH owes its name to the fact that the ventricles inside the brain become enlarged with little or no increase in pressure. However, the name can be misleading, as some patient's CSF pressure does fluctuate from high to normal to low when monitored. NPH can occur as the result of head injury, cranial surgery, haemorrhage, meningitis or tumour. Unfortunately, the cause of the majority of NPH cases is unknown, making it difficult to diagnose and understand. Compounding this difficulty is the fact that some of the symptoms of NPH are similar to the effects of the aging process, as well as diseases such as Alzheimer's and Parkinson's. The majority of the NPH population is older than 60, and many of these people believe their symptoms are just part of the aging process. Unfortunately, many cases go unrecognised, are never properly treated, or are misdiagnosed.

What symptoms can it cause?

Symptoms vary depending on the cause of the obstruction to CSF circulation, the age at which the problem develops, and the extent of damage to brain tissue caused by the swelling.

Symptoms of Adult-Onset Hydrocephalus:

• Headaches
• Nausea
• Difficulty focusing the eyes
• Unsteady walk or gait
• Leg weakness
• Sudden falls
• Irritability
• Drowsiness
• Personality changes
• Seizures

Primary Symptoms of NPH:

• Gait disturbance (difficulty walking)
• Dementia or forgetfulness
• Bladder control problems (as the condition progresses)

The gait in many patients with NPH is very distinctive: wide-based, short, slow and shuffling. People may have trouble picking up their feet, as if their feet are glued to the ground. They may have difficulty going up and down stairs and curbs, and as a result, they are frequently falling. Gait disturbance is often the most obvious first symptom. These disturbances range in severity, from mild imbalance to the inability to stand or walk at all. The symptoms of NPH usually get worse over time if the condition is left untreated. Patients with untreated, advanced NPH may experience seizures, which can get progressively worse. Dementia and/or bladder control problems usually appear after gait disturbances, as the condition progresses. Mild dementia can be described as a loss of interest in daily activities, forgetfulness, difficulty dealing with routine tasks and short-term memory loss. Not everyone with NPH develops an obvious mental impairment. Bladder control problems usually involve urinary frequency and urgency in mild cases. In severe cases, however, a complete loss of bladder control (urinary incontinence) may result. Urinary frequency is the need to urinate more than usual, often as frequently as every one to two hours. Urinary urgency is a strong, immediate physical need to urinate. This urge is sometimes so strong that it cannot be controlled, resulting in incontinence.

Diagnosing Hydrocephalus

Patients presenting the three primary NPH symptoms or a combination of the other symptoms should consult a neurosurgeon as soon as possible. Before your doctor can recommend a course of treatment, he or she will:

• Review your medical history, and perform a physical examination
• Perform a complete neurological examination including diagnostic testing if needed
• Ask specific questions to determine if symptoms are caused by hydrocephalus

The neurological examination will also help to determine the severity of your condition. There are a wide variety of diagnostic tests that can help pinpoint the cause and severity of hydrocephalus.

• Computed tomography scan (CT or CAT scan): A diagnostic image created after a computer reads x-rays; can show if the ventricles are enlarged or if there is an obvious blockage.
• Magnetic resonance imaging (MRI): A diagnostic test that produces three-dimensional images of body structures using magnetic fields and computer technology; can reveal if the ventricles are enlarged and evaluate the CSF flow. The MRI provides more information than the CT scan, so is the preferred test, in most cases.
• Isotopic cisternography: A test that involves injecting a radioactive isotope into the lower back through a spinal tap. This allows the absorption of CSF to be monitored over a period of time (up to 4 days). Isotopic cisternography is considerably more involved than a CT scan or MRI, but can aid in the diagnosis of NPH.
• Lumbar puncture (spinal tap): Under local anesthetic, a thin needle is passed into the spinal fluid space of the low back. Removal of up to 50 cc of CSF is done to see if symptoms are temporarily relieved. This test is used to measure CSF pressure and analyze the fluid. This procedure may help determine whether a shunt, the common treatment for hydrocephalus, will work. If lumbar puncture improves symptoms even temporarily, this can be an indication that a shunt will be successful. There are patients, however, who show no improvement that go on to have a successful shunt procedure.
• Intracranial pressure monitoring: Monitoring may be able to detect an abnormal pressure or pattern of pressure waves. Monitoring requires insertion of a catheter or small fiber optic cable through the skull into the brain. This procedure requires admission to the hospital for 24 hours.

When Surgery is Necessary

Hydrocephalus can be treated in a variety of ways. The problem area may be treated directly (by removing the cause of CSF obstruction), or indirectly (by diverting the fluid to somewhere else; typically to another body cavity). Indirect treatment is performed by implanting a device known as a shunt to divert the excess CSF away from the brain. The body cavity in which the CSF is diverted is usually the peritoneal cavity (the area surrounding the abdominal organs).

In some cases, two procedures are performed, one to divert the CSF, and another at a later stage to remove the cause of obstruction (e.g., a brain tumor). Once inserted, the shunt system usually remains in place for the duration of a patient's life (although additional operations to revise the shunt system are sometimes needed). The shunt system continuously performs its function of diverting the CSF away from the brain, thereby keeping the intracranial pressure within normal limits.

An alternative operation called endoscopic third ventriculostomy may be recommended. In this operation, a tiny burr hole is made in the skull and a neuroendoscope (a small camera which is attached to medical instrument) is utilised to enter the brain. The neurosurgeon will then make a small hole (several millimeters) in the floor of the third ventricle, creating a new pathway through which CSF can flow.

Recovery

Your neurological function will be evaluated post surgery. If any neurological problems persist, rehabilitation may be required to further your improvement. However, recovery may be limited by the extent of the damage already caused by the hydrocephalus and by your brain's ability to heal.

Because hydrocephalus is an ongoing condition, long-term follow-up by a doctor is required. Follow-up diagnostic tests including CT scans, MRIs and x-rays, are helpful in determining if the shunt is working properly. Do not hesitate to contact your physician if you experience any of the following postoperative symptoms:

• Redness, tenderness, pain or swelling of the skin along the length of the tube or incision
• Irritability or drowsiness
• Nausea, vomiting, headache or double vision
• Fever
• Abdominal pain
• Return of preoperative neurological symptoms

Prognosis

The prognosis for hydrocephalus depends on the cause, the extent of symptoms, and the timeliness of diagnosis and treatment. Some patients show a dramatic improvement with treatment while others do not. In some instances of NPH, dementia can be reversed by shunt placement. Other symptoms such as headaches may disappear almost immediately if the symptoms are related to elevated pressure. If the cause of NPH is known, the rate of shunting success can be as high as 80 percent. In cases in which the cause is unknown, the success rate varies from 25 to 74 percent.

In general, the earlier hydrocephalus is diagnosed, the better the chance for successful treatment. The longer the symptoms have been present, the less likely it is that treatment will be successful. Unfortunately, there is no way to accurately predict how successful surgery will be for each individual. Some patients will improve dramatically while others will reach a plateau or decline after a few months.

Shunt malfunction or failure may occur. The valve can become clogged or the pressure in the shunt may not match the needs of the patient, requiring additional surgery. In the event of an infection, antibiotic therapy may be needed. A shunt malfunction may be indicated by headaches, vision problems, irritability, fatigue, personality change, loss of coordination, difficulty in waking up or staying awake, a return of walking difficulties, mild dementia or incontinence. Fortunately, most complications can be dealt with successfully.

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