The majority of untreated cases, or those with a failed shunt, progress with deterioration of dementia, development of akinetic state, and urine and stool incontinence (Toma et al 2011). Progression can be fast, and the follow-up of surgical candidates for shunting showed a significant progression even within a 3 month period, further supporting a timely surgery when indicated (Andren et al 2014). Patients are at risk for fractures and other injuries, including subdural hematoma, from falls. Immobilization can be complicated by pneumonia, pulmonary embolism, decubiti, urinary tract infections, and sepsis.
Prognosis of patients who have had an operation depends on the selection of cases. The proportion of patients with long-term improvement varies from 25% to 80% and depends on indications for operation, experience of neurosurgeons, and preoperative conditions (Vanneste et al 1992b; Poca et al 2004). The clinical benefit from shunting may be sustained for a long-term period (more than 5 years), but these patients still need frequent follow-up visits because shunt complications requiring shunt revisions are relatively common (Pujari at el 2008). However, shunt-related mortality is negligible (Mirzayan et al 2010). Secondary normal-pressure hydrocephalus has a higher rate of beneficial effect from an operation than idiopathic normal-pressure hydrocephalus. Prominent gait impairment preceding cognitive impairment or as an isolated symptom is considered to be a good prognostic sign (Fisher 1982). The presence of widespread white matter lesions may reduce the degree of the gait improvement (Bugalho and Alves 2007). Best reversibility of dementia has been reported in patients whose verbal memory immediate recall impairment was less than 1 standard deviation from controls and who had relatively preserved frontal executive and visuospatial functions (Thomas et al 2005). Raftopoulos and colleagues reported significant cognitive recovery in 67% of patients within 1 year after the surgery (Raftopoulos et al 1994). Significant improvement of cognitive function was seen in patients who had a higher mean value of intracranial pressure before the shunt surgery (Foss et al 2006). However, patients who are traditionally considered poor candidates for shunting surgery, such as those with a longer history of dementia, cortical atrophy, and urinary incontinence, may also benefit from shunting and improvement of cognitive status; gait and sphincter incontinence is not uncommon (Friedland 1989; Poca et al 2005). Patients presenting with cognitive decline have a higher risk of developing Alzheimer disease or multiinfarct dementia, and the cognitive outcome of shunting of these patients is relatively poor (Koivisto et al 2013). Definite gait improvement was present in 75% of shunted patients 3 to 6 months after the operation, but it was sustained in only one third of patients at 3 years; the 3-year benefit for cognitive improvement was noted only in 1 of 8 patients, and for urinary continence, in 1 of 6 patients (Klassen and Ahlskog 2011).
Decreased ventricular size does not predict a favorable outcome of shunting, and patients with no significant change of the ventricular size tend to have more significant clinical improvement than those with a significant reduction of the ventriculomegaly (Meier and Mutze 2004). Three-day external CSF drainage does not noticeably change the ventricular size in spite of observed clinical improvement (Lenfeldt et al 2012). Patients without clinical improvement and persisting ventriculomegaly in spite of patent shunt and low intracranial pressure are considered to have shunt-nonresponsive hydrocephalus. Dramatic improvement after reduction of the ventricular size by external cerebrospinal fluid drainage with negative pressure (shunt siphoning) has been reported in 4 patients with shunt-nonresponsive hydrocephalus (Bergsneider et al 1999).
Complications of CSF-diverting operations are the main concern. Vanneste and colleagues reviewed results from several hospitals and found the total incidence of complications to reach 30%, but only 5% were serious with long-term sequelae (Vanneste et al 1992b). The ratio of substantial benefit to serious harm was approximately 3 to 1, and the strictness of shunt indication did not significantly alter this ratio (Vanneste et al 1992b). Subdural hematomas, intracranial infections, stroke, and shunt failure were among the most common complications. Ventriculoatrial shunts may cause cardiac tamponade or pulmonary embolism, and ventriculoperitoneal shunt may cause ascites or injury to abdominal organs. Prophylactic therapy with aspirin increases the risk of subdural hematoma (Birkeland et al 2015).