The development of ventricular shunt tubing with one-way valves opened the way to successful treatment of hydrocephalus. CSF is diverted directly into the peritoneal cavity (ventriculoperitoneal shunt), or less often, a ventriculoatrial or ventriculopleural shunt is used. The valve can be selected for a desired fixed opening pressure, or a variable valve can be inserted and adjustments can be made by an external magnetic device. Gratifying success can be obtained, often a complete or nearly complete restoration of mental function and gait after several weeks or months, by the placement of a shunt.
The most consistent improvement has been attained in the minority of patients in whom a cause can be established (subarachnoid hemorrhage, chronic meningitis, or tumor of the third ventricle). As already noted, other predictors of success are considerable enlargement of the ventricles in comparison to the degree of cortical atrophy, CSF pressures above 150 mm H2O, and improvement after spinal puncture, but none of these is entirely dependable.
Deviations from the characteristic syndrome such as the occurrence of dementia without gait disorder or the presence of apraxias, aphasias, and other focal cerebral signs are associated with poorer outcomes after shunting. Fisher, on analyzing successfully shunted cases, noted that almost without exception, gait disturbance was an early and prominent symptom. Uncertainties of diagnosis increase with advancing age owing to the frequent association of degenerative dementia and vascular lesions. However, in Fisher’s experience, age alone did not exclude NPH as a cause of gait disorder, and long duration of gait symptoms did not preclude a salutary outcome from shunting. In patients who are averse to the shunting procedure or who have medical conditions that make the surgery inadvisable, it is sometimes possible to produce a reasonable improvement in gait by repeating the drainage of large amounts of fluid every few weeks. It is usually feasible to discontinue anticoagulants for a brief period to accommodate shunting or lumbar puncture but the small risk of stroke in patients with atrial fibrillation or cardiac valvular diseases must be considered.
Between the many reported series of NPH treated with shunting, outcomes vary greatly—almost certainly in part dependent on the accuracy of the initial diagnosis and the duration of symptoms. For example, 45 patients reported by Shaw and associates, 69 percent improved in speed of gait, 63 percent improved at least 2 points in MMSE (mini-mental status examination), and 69 percent improved in UPDRS, a standard overall score of assessing Parkinson disease (Chap. 38). While only 38 percent improved on multiple measures, only 15 percent improved on none. These are representative or better than other comparable series. Gauging what happens to incontinence after shunting is difficult and there is little information but we have had patients with advanced disease who reported some improvement, contrary to the usual dictum. Not all neurologists agree to such an optimistic assessment of the benefits of shunting and they also point to the limited durability of effect in case series, such as the one from Kahlon and colleagues with long-term follow-up, and high rate of complications, approximately 10 percent in some series (see editorial by Saper in response to AAN Guidelines).
The potential failure of shunting must be anticipated in patients whose clinical features do not conform to the typical syndrome or whose disease has advanced to the stage of long-standing incontinence or dementia. In some in stances, a lack of improvement, or marked improvement followed by subacute deterioration is explained by inadequate decompression, which justifies a revision of the shunt or downward adjustment of a variable pressure valve. Overdrainage causes headaches that may be chronic or orthostatic and may be associated with small subdural collections of fluid. These fluid collections, or hygromas, consisting of CSF and proteinaceous fluid derived from blood products, are generally innocuous and do not require drain age unless they enlarge or cause focal neurologic symptoms or, rarely, seizures.