Surgical outcome
Shunt failure can be aseptic (malfunction) or septic (shunt infection). Malfunction includes obstruction, overdrainage, underdrainage, and occult shunt failure (including the need for elective revision for tube lengthening). Its occurrence being duration-dependent, the incidence of malfunction is generally expressed as actuarial survival. Reoperation, although potentially subject to surgeon bias, can be seen as the best criterion to define malfunction, as it is a binary variable and a dated event, allowing survival analysis. However, some cases of malfunction can be dealt with without surgery, e.g., overdrainage that is solved by valve adjustment or one that is simply accepted by the patient as a minor nuisance. On the other hand, occult shunt failure (e.g., a broken shunt in an asymptomatic patient) is sometimes accepted with little scientific evidence, as an indication that the patient has become shunt-independent [
5]. A more rigorous approach to shunt independence is advocated below.
Shunt infection has been defined differently depending on the goal of the study: a positive culture is an adequate criterion for bacteriological studies; clinical symptoms with positive culture and or pleocytosis (Odio’s criteria) [
6] is a criterion more adapted to clinical studies, however cultures can be falsely positive as well as falsely negative. Restrictive definitions excluding cases with negative cultures carry the risk of underestimating the real problem. Studies on surgical outcome should adopt a surgery-based criterion: a medical diagnosis based on clinical findings and/or biology, leading to reoperation or death [
7‐
9]. This definition, based on the assumption that infection cannot be cured without reoperation, generally shunt removal, has the advantage of a binary and dated event allowing actuarial analysis [
8]. More detail on the type of infection can be provided using the classification proposed by the CDC [
10], rating the infection as incisional (skin and dermis), deep-incisional (subcutaneous tissues), and organ/space infection. The definition of infection by the CDC also emphasizes the importance of clinical judgment: “Diagnosis of an organ/space (surgical site infection) by a surgeon or attending physician” [
10]. Although postoperative infection is generally defined as occurring with one month of surgery, the rate of infection should also be evaluated over a longer term, since infection can occasionally occur several years after surgery. Survival analysis should be used in order to take into account the impact of late shunt contamination [
9]. Different types of infection rates can be calculated and should be clearly specified: by operation (number of operations complicated by infection); by patient (number of patients in a series having had at least one septic episode); by surgeon (number of septic complications among the total number of patients operated by a given surgeon) [
11], or by hospital [
12]; and actuarial incidence [
8,
9]. Rates by surgeon or by hospital can be difficult to ascertain because patients are often operated by different surgeons or in different hospitals [
13].
Shunt independence is defined as the successful removal or ligature of all shunts, but it does not always mean that the hydrocephalus is “cured”. It includes patients with successful secondary endoscopic treatment [
14,
15], but who, nevertheless, remain reliant on internal CSF diversion; patients who become shunt independent spontaneously [
16]; and patients who undergo progressive upgrading of an adjustable valve, or planned removal of their shunt, which should be performed with great caution and patience. Some delay after shunt removal is necessary to assert that the patient is truly shunt-independent; how long the follow-up should be is undetermined, but delayed deterioration has been reported several years after apparently successful shunt removal [
17]. It should be emphasized that, whereas symptomatic shunt failure proves shunt-dependence, the reverse is not true. Contrary to some authors who stated that the absence of shunt failure during more than 18 years attests to shunt-independence [
18], some patients can present with their first malfunction more than 20 years after shunt insertion: in a series of 456 patients having reached adulthood, 22 patients presented with their first shunt failure after the age of 20, with a fatal outcome in one case [
4].
Complications of endoscopy include failure (obstruction), infection and surgical morbidity [
19]. Failure of endoscopic third ventriculocisternostomy (ETV) can be defined as primary (failure to achieve an efficient stoma) or secondary (obstruction of a previously patent stoma). In studies comparing endoscopy and shunting, failure of the endoscopic technique has also been defined as the need to implant a shunt, but this definition excludes failed cases that were treated by redo ETV [
20,
21]. Evaluation of the primary failure rate should be based on a clear statement of the intent to treat. The rate of secondary failure is duration dependant, and actuarial survival studies are necessary [
22,
23]. In spite of a growing literature, the long-term actuarial survival of ETV is still poorly documented. For the comparison between ETV and shunting, important confounders, like age and origin of hydrocephalus need to be accounted for with sophisticated statistical methods [
24], although this still falls short of the gold-standard of randomization.
Mortality
It is important to determine whether or not mortality is related to hydrocephalus and its treatment. When death occurs immediately after surgery, or of documented shunt failure, shunt-related mortality is beyond doubt. Shunted patients can also die of associated conditions, e.g., brain tumor or metabolic disease, unrelated intercurrent events, e.g., accidental trauma, or related ailment, e.g., malnutrition or infection in a severely debilitated patient. All of these identified causes of death should be considered as shunt-unrelated. There remain grey areas in which the cause of death can be multiple or be totally unexplained. In a shunted patient, the occasional sudden death can often be retrospectively ascribed to shunt complication [
25]. Based on these data, sudden unexpected death in a shunted patient should be considered as shunt-related by default, similar to the SUDEP in epilepsy (Sudden Unexpected Death of the Epileptic Patient).
Morbidity
This term covers all health-related limitations to living a normal life. It is evaluated quantitatively by outcome and quality of life scales, and by the presence or absence of different sequela (binary variables). Overall functional outcome can be quantified using established generic scales like the Barthel index (10 variables graded 1 to 10) [
26], Karnofsky scale (11 grades), and the Glasgow Outcome Scale (GOS, 5 grades) [
4]; historically, a five-tier grading system precursory of the GOS had already been proposed by Laurence in 1962 [
1], and Resch also used a scale very similar to the GOS [
27]. The GOS following the WFNS (1 = normal, 5 = dead) is relatively crude but can easily be calculated in retrospective studies, is not influenced by age, and allows comparisons with other neurosurgical diseases [
28]. We found no study on pediatric hydrocephalus using the Rankin 7-grades scale, although this is widely used in adult studies. The Barthel index is a highly detailed quantitative outcome measure, but we found it used in no study on pediatric hydrocephalus. Quality of life can be evaluated quantitatively with SF36 scale [
26], which requires a prospective evaluation of patients. Recently, the Hydrocephalus Outcome Questionnaire (HOQ), a disease-specific quality of life scale, has been proposed for pediatric hydrocephalus by Kulkarni
et al.[
29], translated in several languages, and validated by other teams [
30]. The Barthel Index, SF36 and HOQ are highly detailed quantitative scores, which require prospective collection of data and a fairly heavy logistic organization.
In hydrocephalus, the most important specific functional concerns are:
All these variables are often rated dichotomously as present or absent (binary variables) or measured quantitatively, following specific scales. In particular, cognition can be evaluated by different tests, adapted to age: Wechsler preschool, WISC 3, WISC 4 [
31,
41], Gesell, Bayley developmental scale for infants [
33,
34,
39], and Brunet-Lezine test developmental test for infants [
39]. These tests are useful to determine a neuropsychological profile and compare hydrocephalic patients with others. However, many of these tests cannot be performed in severely delayed patients, introducing an important selection bias [
42]. Studies reporting the results of tests are conflicting: classically, Dennis
et al. found a predominant deficiency of performance
versus verbal IQ [
32], while more recent studies did not confirm their results [
31,
41]. Moreover, these tests often underestimate deficits in social competence [
4]. School difficulties can be the result of a range of different deficits, cognitive being the most prominent, as well as frequent absences from school due to repeated hospital stays. Schooling is thus not a faithful reflection of pure cognitive handicap. Schooling is generally grossly rated as normal or delayed [
26] or can be given a little more detail, such as: normal, normal with help, delayed, special school for mentally handicapped, and no schooling at all [
4].
How a pediatric patient functions in society is perhaps the ultimate test of outcome. This includes professional/career achievement, achievement of intimate relationships, and community integration. It should be evaluated by comparison with the expected social outcomes for peers. In many cases the social outcome is poorer than would be expected based on cognitive deficits and school performance, illustrating a “hidden handicap” [
4]. Employment status can be categorized as full employment (on the competitive labor market or independent mothers at home), unemployed, sheltered/assisted employment, and handicapped (at home or in special institution).