**9. Shunt surgery**

'probable' INPH are employed in each, with diagnostic criteria based on clinical and imaging features. However, the Japanese guidelines use the term 'probable INPH' in those who improve following the removal of CSF. They also label those who respond to shunt surgery as having 'definite' INPH. The international guidelines make no mention of response to CSF removal or shunting in their diagnostic criteria. The neuroimaging criteria also differ. **Table 1** shows a comparison of the diagnostic neuroimaging features used in these guidelines.

Apart from imaging findings and CSF tap test, there are other variables that can influence outcome after shunt surgery. Knowledge of these factors is important, and, when used in conjunction with diagnostic guidelines, can add weight to the decision‐making process. Several factors have been associated with either good or poor outcomes. These are summarised

The presence of white matter changes is of unclear significance in predicting outcome. The absence of white matter and severe periventricular signals on T2‐weighted imaging studies was associated with a good response to shunt placement [71]. The degree of periventricular and deep white matter lesions was shown to be inversely correlated with the degree of clinical improvement in 41 patients [72]. However, as mentioned earlier, Tullberg et al. [51] found that conventional MRI could not reliably differentiate between the causes of white matter changes and that the presence of DWMH or subcortical lacunar infarctions in NPH did not predict a poor outcome from shunt surgery [11]. These patients should not be denied surgery on the

**Clinical** Gait disturbance occurring before cognitive impairment Dementia as the initial neurological

Mild or moderate dementia Severe dementia at presentation Shorter duration of symptoms Dementia for more than 2 years [67,

**Poor outcome**

sign

68]

70]

AD pathology on cortical biopsy [69,

**8. Predictors of shunt efficacy**

basis of these findings alone [11].

**outcome**

**CSF measures** CSF outflow resistance of 18 mm Hg/ml/min or higher

**Table 2.** Factors influencing the outcome of shunt surgery.

during lumbar constant flow infusion (boon 1998) Occurrence of B‐waves during 50% or more of the recording time during continuous ICP monitoring

**Features Favourable**

**Pathological markers**

in **Table 2**.

538 Update on Dementia

Surgical diversion of CSF via a shunt is the standard intervention for INPH. This is based on the presumption that CSF diversion will reduce or normalise the transmantle pres‐ sure, thereby stabilising or improving symptoms. Ventriculoperitoneal shunts are most commonly used [73]. It is important to remember that not every patient with possible or probable INPH will be a candidate for shunt surgery. The risk‐to‐benefit ratio has to be assessed individually. The patient or family should understand that dementia is least likely to improve and that the mean chance of significant improvement is 30–50% [44]. Information about the risks of complications should also be explicit. Initial studies of shunting in INPH reported a low rate of significant long‐term improvement, but a high rate of complications [74]. There is no definite consensus on how to best assess re‐ sponse to shunting. Also, there was no randomised control trial comparing the out‐ comes of shunting until 2011. This was a small study involving 14 patients who were randomised to open or closed shunts [75]. Those who initially had their shunts ligated after surgery had their shunts opened after 3 months. Those with open shunts experi‐ enced an improvement in motor and psychometric scores (30 and 23% increase, respec‐ tively) at 3 months, whereas those with ligated shunts were unchanged. This group, however, improved following opening of the shunts at 3 months, with an increase in motor and psychometric scores of 28 and 18%, respectively. A systematic review conclud‐ ed that long‐term response was 29% [76]. However, results of more recent studies show a significantly higher rate of 80–90% [2, 77]. It is clear that a general consensus is required to standardise the measurement of outcomes following shunting.

#### **9.1. Complications**

In their systematic review, Hebb et al. [76] also found a mean complication rate of 38%. Potential complications include infection, seizures, abdominal problems (peritonitis, perfora‐ tion, volvulus and ascites), shunt failure or blockage, shunt over‐drainage and intracranial haemorrhage. Shunt over‐drainage is the commonest complication in the first year occurring in about one‐third of patients [76, 78]. Complication rates can differ between centres. The Eu‐ iNPH study revealed a complication rate of 28% [2], while Poca et al. [77] found a complication rate of less than 12% in a prospective study involving 236 patients.

#### **9.2. Follow‐up**

Follow‐up after surgery helps to identify patients who are unchanged or worse, and those who can be helped by further adjustments or shunt revision. Repeat brain imaging is routinely undertaken in the immediate aftermath of surgery, but when performed further down the line, it can also identify a subdural haemorrhage in those who are over‐drained. If this is the case, a higher opening pressure should be targeted. Conversely, a retrospective study found that in those with no substantial improvement and in whom under‐drainage is suspected, selecting a lower pressure can improve the outcome [79].
