Since it is communicating hydrocephalus, NPH can be shunted using either a lumboperitoneal (LP) shunt or a ventriculoperitoneal (VP) shunt. Overall, the number of complications seen with an LP shunt is significantly lower than with a VP shunt. However, they introduce a new spectrum of complications, such as, the possibility of radiculopathy (pain resulting from nerve root compression) and myelopathy (nonspecific spinal cord lesions), and the possibility of inducing tonsillar herniation (herniation of lymphoid or soft tissue) and Chiari malformation. Additionally, the incidence of subdural hematoma is the same as with a VP shunt.2

A variety of methods are used to diagnose normal pressure hydrocephalus, as well as pre dicting the prognosis of shunting. However, no method has been found to be entirely reliable or accurate. One of the most commonly used methods for the diagnosis of normal pressure hydrocephalus is a lumbar puncture, where a bolus of CSF is removed via lumbar puncture.

Generally, there is a good correlation between the improvement of the patient, particularly in relation to gait disturbance, following the tap and the patient’s prognosis for shunting.7 Paes states that patients with a preoperative pressure above 100mm H20 generally demonstrate a better outcome than those patients with a pressure below 100mm H20.19

Another method that has just recently been introduced in the literature is the use of brain oxygen extraction fraction (OEF) as an indicator for shunting NPH patients. Global brain OEF can be calculated from the contents of arterial blood (AO2) and jugular venous blood (VjO2) using the formula: OEF=(AO2-VjO2)/AO2. OEF values for non-NPH patients were measured at approximately .33, while NPH patients demonstrated an elevated OEF of .42-.45. This study suggests that patients with higher preoperative OEF values had a better post-shunting prognosis. Although this method is limited to only one study, it does suggest that OEF may be a useful indicator for predicting shunting outcome.17

There have been many studies that suggest a link between NPH and cerebral blood flow. As a result many researchers are looking into the feasibility of using cerebral blood flow as an indicator for the diagnosis and treatment of NPH. In 1987, Mamo et al. demonstrated that the removal of a CSF from NPH patients resulted in a significant increase in cerebral blood flow. This was correlated with a favorable outcome of 88% of the patients shunted. The preliminary results of this study suggest that patients who demonstrated an increase in cerebral blood flow following the lumbar tap will be more likely to have a favorable outcome after shunting.14 Chang et al, measured cerebral blood flow in 48 patients and determined that patients who demonstrated a preoperative CBF of over 35ml.100g-1.min-1 showed favorable post shunt outcome, however patients with a preoperative CBF below 32 ml.100g-1.min-1 showed poor improvement after shunting.6

Although it is an idiopathic disease, there has been much research associating NPH with cerebrovascular disorders. In 1981, Kondo, et al., suggested that the complicated pathophysiology of NPH was related to not only the impairment of CSF circulation but also the disturbance of cerebral blood flow and brain compliance.11 Akai, et al., observed that the pathological changes in the brain that occurs with NPH are often eventuated simultaneously with pathological changes in the white matter, caused by ischemia, hypoxia, and trauma.1 This is supported by Bech, et al., who determined that the various degenerative changes in the