Normal-Pressure Hydrocephalus

Conditions known to cause scarring of the piaarachnoid membranes, such as meningeal infection, subarachnoid hemorrhage, or bleeding from past trauma, can cause hydrocephalus by decreasing the effectiveness of CSF absorption. In most elderly patients, communicating hydrocephalus has no easily identifiable cause. Although it could possibly result from degeneration of the arachnoid granulations and membranes, there has been little detailed study of the morphologic structure of the arachnoid in either normal persons or patients with hydrocephalus. Because the CSF pressure is usually high in obstructive hydrocephalus due to tumor and, for uncertain reasons, is within normal range in communicating hydrocephalus, the latter disorder has been called normal-pressure hydrocephalus.

Normal-pressure hydrocephalus usually develops over a period of 6 to 12 months but at times progresses insidiously for a few years. Neuroimaging shows markedly enlarged ventricles, often with little or no cortical atrophy.

Clinical Manifestations. Most symptoms relate to enlargement of the anterior (frontal) horns and loss of frontal lobe white matter and can be described as a classic triad of dementia, gait disturbance, and urinary incontinence.

1. Abnormality of gait: Patients with normal pressure hydrocephalus have significant abnormalities in their gait, often described as “magnetic” because the initiation of steps is difficult and the feet appear as if they are stuck to the floor.

2. Dementia: The patient shows decreased interest in the environment and seems apathetic. Speech becomes less spontaneous, and words are mumbled in a voice of lower volume than normal. Later, the patient may become mute. Despite the reduced amount of conversation, vocabulary and memory are preserved, and answers to questions, although terse, are usually correct.

3. Incontinence: The patient loses the ability to retain urine despite normal perception of the urge and need to urinate. The rapid course; prominence of apathy and early motor, gait, and sphincter dysfunction; and slowness of preserved memory function and vocabulary contrast with the findings in Alzheimer disease.

Treatment. Spinal puncture with drainage of fluid can lead to temporary improvement in gait and alertness. Administration of acetazolamide reduces production of CSF and thus may improve the imbalance between production and absorption of CSF.

Cisternography after introduction of a radionuclide by lumbar puncture may be of value in assessing abnormal CSF flow patterns. Unfortunately, however, there is no single definitive test that reliably predicts whether the patient will improve after surgical placement of a ventricular drain.

Ventricular shunts seem to be most effective in patients who have the classic triad of symptoms and in whom the course of the dementia has been short and a cause of the disorder, such as past subarachnoid hemorrhage, can be identified. Complications of ventriculoperitoneal shunts in adults include intracerebral or intraventricular hematoma during insertion of the tube; infection of the shunt and peritoneal space; oversiphoning of CSF, which causes subsequent brain swelling to take up the void; and collapse of the thin cerebral mantle, with tearing of bridging veins and formation of a subdural hematoma. The incidence of subsequent shunt infection is high.

Only gold members can continue reading. Log In or Register to continue