Normal-pressure hydrocephalus, also called symptomatic hydrocephalus, is a brain disorder caused by decreased absorption of cerebrospinal fluid. Typical symptoms include gait disturbances, urinary incontinence, and dementia or mental decline. It is difficult to diagnose because these symptoms are common to many other diseases. The usual treatment is to place a shunt to drain excess CSF to another part of the body. This treatment may reverse symptoms and restore normal function, may do so partially, or may not. The term normotensive comes from a paper published in 1965 before the development of intracranial pressure measurement techniques, and it is now recognized that the term normotensive in the name of this disease is a misnomer. There are two types of normotensive hydrocephalus: idiopathic and secondary. Secondary hydrocephalus can be the result of subarachnoid hemorrhage, head trauma, tumor, infection of the central nervous system, or complications of skull surgery. Normal pressure hydrocephalus is an increase in intracranial pressure due to the accumulation of cerebrospinal fluid in larger than normal quantities in the ventricles of the brain, causing ventricles to enlarge. The intracranial pressure gradually decreases but remains slightly elevated, with the CSF pressure reaching the upper limits of the normal range of 150 to 200 mm H2O. These patients do not usually have elevated intracranial pressure numbers, so they do not experience the classic symptoms of increased intracranial pressure such as headache, nausea, vomiting, or altered consciousness, although some studies have shown that they do have intermittent pressure increases. However, the enlarged ventricles compress the adjacent cortical tissue, causing myriad effects on the patient. The classic symptomatic triad was first described by Hakim and Adams in 1965. Normative hydrocephalus is often misdiagnosed as Parkinson's, Alzheimer's, or dementia, due to its chronic nature and nonspecific symptoms. Normotonic hydrocephalus presents with the classic triad of clinical findings of urinary incontinence, unsteady gait, and cognitive impairment. Gait disturbance is usually the initial and most prominent symptom of the triad and may be progressive, due to dilatation of the ventricular system, especially at the level of the lateral ventricles. This compresses the motor fibers that descend through the corticospinal tract to the lumbosacral spinal cord, causing them to be pulled upward. Unsteady gait can be classified as mild, characterized by ataxia, or severe in the early stages. This gait disturbance often presents as ataxia and loss of balance, especially when climbing stairs and sidewalks. Muscle weakness and fatigue in the legs may be part of the complaint, although examination shows no paralysis or ataxia. The patient usually uses something to help him walk steadily without ataxia as he moves from mild to marked. A wheeled crutch or quadrupedal crutch is an aid to this. The patient's gait in the marked stage shows a lack of foot clearance when walking or the patient drags the foot on the ground while walking, in addition to a decrease in walking speed. This pattern is commonly referred to as a magnetic gait, where the foot appears to be stuck to the surface on which it is walking, and the gait disturbance is the characteristic symptom of normotonic hydrocephalus. The gait may begin to mimic a parkinsonian gait, with short, shuffling steps, a hunched, forward-bending posture, but no stiffness or tremor. An increased tendency to fall backwards is also seen, and the patient may also use a wide-based gait to increase their base of support and thus their stability. In the very late stages, the patient may deteriorate from the inability to walk to the inability to stand, sit, rise from a chair, or roll over in bed. This advanced stage is referred to as "ataxia of standing and walking due to hydrocephalus." Cognitive dementia: Cognitive dementia usually predominates in the frontal lobe and is a subcortical type of dementia. It manifests as apathy, forgetfulness, rigidity, inattention, and a decrease in the speed of processing complex information. Disorders of processing acquired knowledge, reflecting loss of frontal lobe integrity. Memory disturbances are often a component of the overall problems and are the most prevalent in some cases, which may lead to misdiagnosis as Alzheimer's. However, in normotonic hydrocephalus there may be a marked contrast between memory impairment and intact or less affected cognition. Dementia Dementia is thought to result from traction of the frontal and myelinated fibers that run in the periventricular area. Urinary incontinence: This appears late in the disease and is found to be caused by spastic hyperreflexia, increased urgency associated with decreased inhibition of bladder contractions and detrusor muscle instability. In the most severe cases, bladder hyperreflexia is associated with loss of interest in urination due to severe cognitive damage to the frontal lobe. This is also known as frontal incontinence, where the patient is indifferent to his frequent urinary symptoms. Diagnosis of normotonic hydrocephalus is usually made initially by brain imaging, either CT or MRI, to detect any mass brain injury. This is followed by lumbar puncture and evaluation of the clinical response to removal of CSF. This may be followed by continuous lumbar drainage of CSF over 3-4 days. CT may show dilated ventricles without atrophy of the cerebral convolutions. MRI may show minimal degrees of migration of CSF surrounding the ventricles into the ependymium in the second/Flier time sequence. Radiography may not differentiate between clinically similar pathologies such as Alzheimer's dementia, vascular dementia, or Parkinson's dementia. After radiography, lumbar puncture is the first step in the diagnosis and the CSF opening pressure is carefully measured. In most cases, the pressure is usually above 155 mm H2O. Clinical improvement after removal of CSF has a high predictive value for the success of subsequent shunt placement. This is called a lumbar puncture or Miller Fisher test. Conversely, a negative test has very little diagnostic value, and many patients improve after shunt placement despite no improvement after CSF removal. A leak test is a test that may have higher sensitivity and specificity than a lumbar puncture but is not performed in most centers. Some centers consider the velocity of CSF egress to be a significant predictor of the success of hydrocephalus surgery. The velocity of egress can be determined by a leak test. This is not a test usually performed before shunt placement but may be useful in determining the likelihood of a patient improving after shunt placement. In some centers, an external lumbar puncture has been shown to have high sensitivity and specificity for the expected success of surgery. Patients with dementia who are dependent on home nursing care and whose only diagnosis of hydrocephalus is stress are likely to become independent once treated. To date, only one study has been able to assess the prevalence of normotonic hydrocephalus in both diagnosed and undiagnosed populations and has shown a prevalence of 9-14%. Patients with normotonic hydrocephalus may recover surgically by implanting a ventriculoperitoneal shunt to drain excess CSF into the abdomen where it is absorbed. Once the shunt is in place, the ventricles usually shrink within 3-4 days, regardless of the duration of hydrocephalus. Despite the reduction in ventricular swelling, only 21% of patients show significant improvement in symptoms. Patients most likely to show improvement are those with only mild or no gait disturbance, mild cognitive impairment, or mild cognitive impairment. A more recent study in 2004 found better results, concluding that if patients with normotonic hydrocephalus are correctly identified, shunt implantation will result in beneficial outcomes in 86% of patients, with 81% of patients experiencing gait disturbance, 70% of patients experiencing improvement in grip strength, or both. Note also that measurements in the diagnostic triad, cortical sulcus size, and periventricular flare are all related to outcome. However, other factors such as patient age, duration of symptoms, ventricular dilatation, and degree of dementia before surgery are also related to outcome. Recent population studies have estimated the prevalence of normotonic hydrocephalus to be about 0.5% in people over 65 years of age with an incidence of about 5.5 patients per 100,000 population per year. This is consistent with similar findings that although normotonic hydrocephalus can occur in both men and women of any age, it has been found to occur predominantly in the elderly and peak incidence in the sixth or seventh decade of life.