In some cases, the late closure may be recognized by a progressive clinical deterioration and symptom recurrence. In others, a rapid clinical deterioration can occur that needs to be promptly diagnosed.

The rapidity of onset of the clinical manifestations in case of closure of a patent stoma might depend according to some authors on the pathogenesis of the hydrocephalus [20]. The rapidity of onset of the clinical manifestations of the hydrocephalus before the ETV was performed would suggest the rapidity of the manifestations at the time of ETV failure [20]. However, because of the paucity of the reported cases, such correlation is difficult to assess and remains speculative.

Cases of delayed sudden death after a functional ETV have also been reported [10, 16, 20]. Patients in whom an autopsy or repeated ETV were performed were found to have an occluded ETV [5, 10, 35] usually by a new membrane or scar (Fig. 24.5) and rarely by a clot or tumoral extension [13, 20, 21].

Because of the potential consequences of the raised hypertension, education of patients and their families about the risk of a late closure is of paramount importance to allow for a rapid management with a timely intervention. In fact, a repeated ETV is generally effective to restore the stoma and allow a symptom resolution.

A similar information that the one is given to the patients having an extrathecal CSF shunt device (i.e., of hardware dysfunction) and his or her family, should be given after an ETV even if there is no hardware implanted, in order to recognize any delayed ETV failure on time.

Similarly, a late closure can occur in other endoscopic procedures: cystostomies may close, with consequent cyst enlargement and symptom recurrence (2/23 in Tamburrini et al. series [32]). Large fenestrations in the cyst wall are often necessary to avoid cyst recurrence [14]. The opening of the cyst in the ventricles and in the cisterns (ventriculo-cysto-cisternostomy) may reduce such risk of secondary closure [8].

Radiological follow-up is recommended in order to monitor the effectiveness of the endoscopic procedure.

A diminished ventricular volume, an increase in pericerebral CSF, a flow void signal through the stoma, as well as a modification of the ventricular shape are the main radiological criteria to assess on postoperative MR [13, 14, 19, 28]. However, the ventricular volume might remain enlarged in the postoperative imaging so that persisting ventriculomegaly should not be considered necessarily a failure of the procedure [14, 19].

Though after a successful ETV even if the ventricular volume might reduce only slightly, other radiological criteria can allow to confirm the patency of the stoma and efficacy of the surgical procedure.

On MR imaging, the CSF motion through the stoma can be assessed. A flow void signal is present at the level of the third ventricle floor that has lost its downward convexity due to the supratentorial/infratentorial pressure gradient.

The presence of the flow void signal is correlated to the patency of the stoma and success of the ETV. Conversely, its disappearance at a control MR may be considered as a marker of the closure of the stoma.

Another main criterion to assess on postoperative MR imaging is the enlargement of the subarachnoid spaces. This enlargement usually occurs in the first postoperative weeks and correlates with the patency of the stoma. In case of occlusion of the ETV, the subarachnoid spaces tend to reduce in size [9].

These radiological criteria should be monitored regularly because, in case of ETV closure, their modification might precede the occurrence of the clinical manifestations allowing an early recognition of the ETV dysfunction and a prompt management.

The recommended duration of such radiological follow-up is still debated, but the occurrence of late closures after several years suggests that more than 8–10 years follow-up should be performed.

Whereas early failure might be prevented by a proper indication and technique, no prevention of late ETV failure is known. In some centers, at the end of the endoscopic procedure, a ventricular reservoir (i.e., Ommaya or Rickheim) is implanted as a routine in order to have the possibility to draw some CSF in case of acute ETV dysfunction [20, 22]. However, the actual utility of such implant has not been proven. Indeed, other centers question its utility. Such system might not be patent or correctly in place when needed, that is, at the time of the ETV failure because of the large delay that might exist between the ETV procedure and its potential failure. Moreover, leaving an implanted device increases significantly the risks of infection.

Some cases of late morbidity such as the occurrence of chronic subdural hematomas or of neuropsychological disturbances have also been reported in the literature [2, 18]. These should be considered in many cases as a delayed recognition of an early complication of the surgical procedure itself more than an actual late complication.