The clinical outcomes of treated NPH patients reported in the literature vary widely and depend on several factors: the type of patients treated (idiopathic versus secondary NPH and the degree of clinical deterioration before shunt placement), symptom duration, comorbidity, the tests used to establish the diagnosis of NPH (all of which are associated with a variable percentage of false negatives), and the type of hardware selected, among others. Significant improvement after shunting ranges from 29 to 96 % [22, 57, 69]. The largest percentages of improvement have usually been reported in small series of patients managed in single centers [50, 51, 57]. However, larger recent studies have consistently shown that a high percentage of patients improve after shunt placement [17, 39, 54] and that improvement persists several years after treatment [39, 56].

In several series of patients with iNPH, we showed that a high percentage of improvement and a low complications rate can be achieved by using a strict protocol for the study and treatment of these fragile patients [50, 54]. In the management protocol for iNPH, outcome was independently assessed by the neurosurgeon and an independent neuropsychologist using the NPH scale (Table 11.1) 6 months after shunting [64]. If discrepancies were found between the neurosurgeon and the neuropsychologist, the patient was reevaluated and the final score was assigned by consensus. Because a small change in the NPH scale score represents a substantial change in the patient’s functional status, we defined moderate improvement as a one-point increase and marked improvement as an increase of at least two points.

In a series of 244 iNPH patients who were shunted, 1 patient died in the postoperative period from an acute respiratory infection and 3 patients died less than 6 months after surgery from causes unrelated to shunting (stroke, chronic respiratory disease, and myocardial infarction). Four patients (1.6 %) were lost to follow-up and therefore the final sample consisted of 236 patients. After shunting, an increase of 1 or more points in the total NPH scale score was found in 212 of the 236 evaluated patients (89.8 %), no improvement was found in 18 patients (7.6 %), while some worsening was observed in 6 patients (2.5 %). In the 212 patients who improved, improvement was moderate in 30 patients (an increase of 1 point in the NPH scale) and was marked in 182 (a median increase in the NPH scale of 4 points, min = 2, max = 11). In agreement with previous literature, greater improvement was observed in gait and sphincter control when compared to cognitive function [54]. Patients with the highest scores on the NPH scale (13 and 14) showed lower percentages of improvement than patients with scores of between 3 and 12 on the NPH scale. These lower percentages of improvement were probably due to the ceiling effect in the NPH scale: in patients with minor clinical symptoms and little functional deterioration, only small improvements are possible. In these patients the aim of surgery is not only to reverse the subtle symptoms they might present but, more importantly, to prevent further clinical and neuropsychological deterioration. Knowledge of these results is essential when discussing the expectations of surgery with patients and their caregivers.

Because of the potential morbidity associated with shunt implantation, many neurosurgeons have been reluctant to operate on iNPH patients. The complication rates reported in literature vary and are sometimes very high. A meta-analysis by Hebb and Cusimano [22] reported a mean complication rate of 38 % (range: 5–100 %), mostly shunt revisions (22 %; range: 0–47 %), and a 6 % mortality or permanent neurological deficit. The Dutch NPH study reported subdural effusions in 53 % of shunted patients, two-thirds of which spontaneously decreased or resolved [7]. In this series, two patients (0.8 %) died due to problems directly related to shunting (one in the early postoperative period and another at 6 months after surgery). This percentage is very low if we consider the age and the frequent comorbidity commonly found in iNPH patients. Rates of shunt revision of as high as 47 % have also been reported [27]. In Hebb and Cusimano’s review, 22 % of patients required additional surgery [22]. The most frequent serious shunt-related complications are cerebral or subdural hematoma, shunt obstruction, and infection. Less serious adverse events include subdural hygromas that do not require evacuation, orthostatic headache, abdominal pain, and transitory hypoacousia or tinnitus, among others.

In our most recently published cohort of patients, mortality related to treatment was 0.4 % (1 of the 244 shunted patients died in the early postoperative period from an acute respiratory infection) [54]. Early (first month after shunting) or late (within 6 months of surgery) complications were found in less than 10 % of shunted iNPH patients. Only one patient had a shunt infection. Asymptomatic subdural collections found immediately after or at 6 months after surgery were not considered complications because they did not require treatment (Fig. 11.2). However, if we include these collections in the complication rate, the total percentage would increase to 13.8 % [54]; this is still a very low percentage when compared with outcomes reported in other series. This low percentage could be due not only to the use of shunts that include a gravitational device but also by our surgical management protocol, which combines several measures before, during, and after shunt placement [50, 51]. Table 11.2 outlines the complications in this cohort of 244 treated patients.

CSF shunt infection remains 1 of the major causes of morbidity in the treatment of both pediatric and adult hydrocephalus and occurs in 3–15 % of patients [8, 9, 39]. Recently published studies of large series of patients, however, reported relatively low infection rates (1–6 %) [11, 17, 54]. The hardware used does not significantly modify the risk of infection [44], although several studies have demonstrated the modest efficacy of antibiotic-impregnated shunt systems in reducing infections in both pediatric and adult patients [18, 19, 48, 60]. In fact, improvements in surgical technique and surgical experience may be the factors that contribute most to reducing the rate of infection and other shunt-related complications.

The low rates of infection and other complications reported in our series could be explained, in part, by the following surgical management protocol used in our department [50, 54].

Using this protocol, the infection rate in NPH-shunted patients is less than 1 % [50, 54]. This percentage does not justify the routine use of antibiotic-impregnated shunt systems.

Complications due to shunt overdrainage still have an unreasonably high prevalence in high-risk patients such as those with iNPH. Overdrainage is directly related to the hydrodynamic profile of shunts and is caused by the negative hydrostatic pressure distal to the valve when the patient assumes the erect position. Orthostatic headache, diplopia, tinnitus, and chronic subdural effusions are the most frequent phenomena related to overdrainage in adults, while ventricular catheter block, slit ventricle syndrome, subdural hematoma, trapped fourth ventricle, and acquired Chiari I malformation have been frequently reported in children [36, 37]. Between 10 and 30 % of shunt revisions have been attributed to overdrainage in NPH patients.

Under normal circumstances, when a supine subject sits or stands up, ICP falls to subatmospheric values [29]. ICP reduction with even slightly negative values is a well-known physiological phenomenon demonstrated in humans in pivotal clinical studies [29–31]. Head elevation physiologically decreases ICP by displacing CSF into the spinal canal and by improving cerebral venous drainage thought the opening of alternative venous channels in the posterior circulation that remain closed when patients are recumbent [29, 31, 68]. In a large series of patients in whom ICP was monitored before shunting, we showed that ICP values are significantly reduced after changing from a supine to a sitting or upright position. However, this ICP reduction is significantly greater in patients with free CSF flow through the craniospinal junction when compared to those with Chiari malformations (Fig. 11.3). This finding reinforces the theory that CSF displacement into the spinal canal is hampered in this latter group of patients [53]. ICP profile after postural changes was very similar in all the patients, showing a maximal decrease immediately after patients assume the sitting position, with a subsequent moderate recovery followed by stabilization (Fig. 11.4). The median of the maximum ICP differences (differences between mean ICP in the supine position and the lowest ICP values recorded after changing body position) was 13 mmHg (interquartile range: 10–17 mmHg), and the median of the mean ICP differences (differences between mean ICP in the supine position and mean ICP recorded while the patient remained in sitting position during 3 h) was 8 mmHg (interquartile range: 5–11 mmHg) [53].

ICP reduction after changes in body position may also occur in patients with high ICP [16]. To prevent or help to improve intracranial hypertension, various degrees of head elevation have been used as a routine maneuver in the management of neurocritical patients. This physiological phenomenon is magnified, however, in patients in whom a classical differential pressure valve has been implanted. In these patients, ICP values of less than −20 mmHg may be observed when the patient changes to a vertical body position (Fig. 11.5), unless a mechanism to compensate or eliminate what has been called the “siphoning effect” is used [3, 10]. This nonphysiological gradient is a direct consequence of the gravitational changes induced by the hydrostatic fluid column between the tips of the ventricular and the distal catheters. In the supine position, the closing pressure of the valve is the main factor that controls flow in shunts. However, when the patient is upright, hydrostatic pressure in the distal catheter keeps the valve open continuously, even when intraventricular pressure becomes negative [63]. Under these circumstances, the hydrodynamics of the shunt (R _shunt) is the main factor controlling CSF flow until the valve is closed again. In the absence of gravitational devices, when the patient is in an upright position the flow can continue as long as the ventricles contain drainable CSF. A common—but mistaken—strategy to avoid problems related to overdrainage has been the use of medium- or high-pressure valves. However, as Aschoff has stated (personal communication), the problems of overdrainage are related to gravity and therefore have to be prevented by gravitational devices, not by upgrading the opening pressure of the valve. The belief that upgrading the opening pressure of a valve avoids overdrainage is not entirely correct because the opening pressure of a valve only controls flow when the patient is recumbent. There is strong evidence that the use of medium- or high-pressure valves does not exclude the possibility of subdural effusions (hygromas or hematomas). Boon et al. reported a 34 % incidence of subdural effusions in a group of patients with medium-pressure valves [7]. The use of adjustable valves can reduce, but not exclude, nonphysiological flow rates while the patient is upright and the possibility of complications related to hyperdrainage [2].