Normal pressure hydrocephalus (NPH) is a condition that primarily affects the elderly. Symptoms may include difficulty walking (a magnetic gait in which the patient feels his/her feet are stuck to the ground), urinary incontinence, and cognitive difficulties. Patients with normal pressure hydrocephalus may harbor one or more of these signs and symptoms, however, when the full triad is present the chance of relief following cerebrospinal fluid diversion (shunting) is greatest.

With five pressure level settings, the programmable, adjustable Strata® valve (top) can be "fine-tuned" by the physician after shunt surgery for NPH. Adjusting the valve and verifying the setting is done quickly in the physician's office using a simple set of magnetic tools (bottom), eliminating the need for additional surgery.

With five pressure level settings, the programmable, adjustable Strata® valve (top) can be "fine-tuned" by the physician after shunt surgery for NPH. Adjusting the valve and verifying the setting is done quickly in the physician's office using a simple set of magnetic tools (bottom), eliminating the need for additional surgery.

The etiology behind normal pressure hydrocephalus is not known, however, most work points to an alteration in fluid reabsorption and brain tissue compliance. As individuals age, their cerebrums lose tissue water content. This loss increases the brain’s compliance making it more easily distensible. Therefore, even at normal cerebrospinal fluid pressures the ventricles enlarge. Imaging studies, alone, however, cannot make the diagnosis of normal pressure hydrocephalus because as individuals age their brain’s lose volume and the ventricles enlarge (ex vacuo hydrocephalus). With normal pressure hydrocephalus, the ventricular volume gain is often judged to be out of proportion to the degree of tissue shrinkage. In addition, the gyri are often seen to be flattened against the inner surface of the calvarium as opposed to being rounded with enlarged sulci in ex vacuo hydrocephalus. Once the ventricles enlarge in normal pressure hydrocephalus they stretch the surrounding white matter tracts creating the symptoms listed above.

Many elderly patients may present with enlarged ventricles, organic dementia, difficulty ambulating, and incontinence from bladder abnormalities yet not have normal pressure hydrocephalus. To better predict which patients will respond best to ventriculoperiotoneal or lumboperitoneal shunting procedures physicians have employed a variety of tests including spinal fluid taps, cerebral blood flow studies, and cerebrospinal fluid pressure wave analyses. Over the past several years we have chosen to put eligible patients through a trial of continuous spinal fluid drainage so as to temporarily create the conditions of a permanent shunt. By mimicking the effects of VP shunting we feel we can best detect which patients will respond to a surgical procedure.

As per our protocol all patients are seen preoperatively by a urologist to rule out a bladder or sphincter structural abnormality. All are then admitted to the hospital for a four- or five-day evaluation period. Prior to insertion of a lumbar drain individuals have their gaits objectively analyzed by a member of the physical therapy department. Cognitive function is analyzed by a member of the neuropsychiatry department.

Once testing is completed a lumbar drain is inserted into the subarachnoid space and approximately 40-60 cc of spinal fluid is drained from the patient every eight hours. Gait is reanalyzed twice a day by the physical therapist and cognition is evaluated by the treating physician, neuro-psychiatrist, and/or family member. If patients improve subjectively over the four-day drainage period they are offered a permanent spinal fluid diversion procedure. Those that do not improve are felt to be poor surgical candidates.

Once the decision had been made to insert a shunt we generally opt for a ventriculoperitoneal system. A programmable valve (Medtronic Strata Valve or Codman Medos Valve) is used because it allows the surgeon to adjust the degree of CSF drainage after insertion without having to reoperate on the patient to place a new shunt with a new higher or lower pressure valve. Patients are usually discharged the following day and followed periodically with clinical examinations and CT scans to assess the operation’s efficacy.

If you have a patient with symptoms consistent with suspected normal pressure hydrocephalus, please contact Michael Horowitz, MD or Kimberly Lee, at (412) 647-6778.