Multiple studies have shown that there is insufficient evidence to support the use of plain abdominal X-rays as a diagnostic tool in children with functional defecation disorders [42–46]. There is no clear association between clinical symptoms of constipation and fecal loading on abdominal X-rays [46, 47]. Moreover, the sensitivity and specificity rates for the different scoring systems that are used to evaluate fecal load based on abdominal X-rays are unsatisfactory, and low inter- and intra-observer reliability has been reported [46]. However, some physicians argue that if the presence of a fecal mass is uncertain, for example, in a child who is obese, or when rectal examination is not possible due to resistance of the child or when it is considered distressing (e.g., after sexual abuse), an abdominal X-ray may be useful.

Determining the colonic transit time (CTT ) can be a valuable tool in the workup of a child with FI when it is unclear if the child suffers from FNRFI or constipation-associated FI. Currently, the most widely used technique to determine CTT is the radiopaque marker test, which is cost effective and simple to perform [48]. Several days after ingestion of capsules with radiopaque markers, an abdominal X-ray is obtained and the CTT is calculated based on the amount of remaining intra-abdominal markers. Different protocols are in use, with variance in the amount of markers, the amount of study days, and calculations used [48–52]. Based on CTT data in healthy children by Arhan et al., a total CTT exceeding 62 h (mean +2 SD) is considered delayed [49]. In approximately 50 % of constipated children, the CTT is delayed with the majority of the delay occurring in the rectosigmoid segment [53, 54]. In contrast to constipated children, 90 % of children with FNRFI have a normal CTT [7]. Thus, in children with functional FI who do not fulfill the Rome III criteria for functional constipation based on the history and physical examination and who have a normal CTT, the diagnosis should be FNRFI [7]. Therefore, in inconclusive cases, CTT can help to differentiate between FC and FNRFI [9]. In children and adults, a good correlation is found between colonic transit time and symptoms of constipation such as defecation frequency and fecal incontinence frequency [53]. Patients with a severely prolonged CTT (>100 h) have a less favorable outcome at 1 year follow-up [53].

CTT can also be determined by colonic transit scintigraphy, a technique that visualizes the progression of a radiolabeled marker after intraluminal instillation or ingestion. However, this technique is used less commonly in children [52, 55, 56].

Transabdominal ultrasonography can be used to measure the transverse rectal diameter [57, 58]. An increased rectal diameter (>30 mm) has been suggested to indicate fecal impaction [59–63]. This is a promising technique that may be used as an alternative for digital rectal examination in the future [59, 61]. However, currently there is insufficient evidence to support the use of the transverse diameter as a reliable predictor of constipation and fecal impaction in children [41, 43].

A magnetic resonance imaging (MRI ) of the spine is not necessarily required to assess lumbosacral spine abnormalities in the routine workup of children with FI. A prospective study among children with both FC and FNRFI revealed that lumbosacral abnormalities are rarely present and that lumbosacral abnormalities do not correlate with treatment success [64]. Therefore, MRI of the spinal cord should only be performed when there is a clear indication, e.g., abnormal lower extremity findings, midline lower back skin manifestations during neurologic examination, or a suspected neurologic disorder.

Several techniques can be used to assess anorectal sensorimotor function. Anorectal manometry is especially useful to assess the rectoanal inhibitory reflex (RAIR ), anal sphincter tone, and rectal sensation. Although the routine use of anorectal manometry in children with FI is not recommended [9, 65], it may provide valuable information in specific cases. When tested with anorectal manometry, children with FNRFI show normal sensorimotor function and sphincter tone but abnormal defecation dynamics have been reported to be present in ~50 % of patients [7, 66]. These children are often unable to relax the external anal sphincter during defecation, which is thought to be an acquired control mechanism in which after losing the first stool, contraction of the external anal sphincter occurs to retain the rest of the stool [23]. Anorectal manometry can also provide valuable information in children with intractable constipation, especially to rule out Hirschsprung’s disease and to detect anal achalasia or dyssynergia (see Chaps. 42 and 25).

Rectal barostat is another technique to assess anorectal function; it utilizes a rectally inserted pressure-controlled inflatable balloon to determine rectal compliance and pressure thresholds for rectal sensitivity. Children with functional constipation have higher rectal compliance than children with FNRFI and healthy controls, causing them to require a larger volume of rectal contents to reach the intrarectal pressure to evoke an urge to defecate [25]. Even after FC patients are in remission, rectal compliance remains increased [67]. At this moment, there is no indication for routinely performing rectal barostat in children with FI, as findings have no clinical implications [9].

Colonic manometry is used to assess neuromuscular integrity of the colon; it can identify motility disorders. Colonic manometry may be useful in the workup of children with FI due to severe intractable constipation, especially to guide surgical management, but does not belong in the routine workup of children with functional FI.

Education and demystification are the first steps in the treatment of children with FI. It is important to provide information on prevalence, symptoms, treatment options, and prognosis. When discussing the subject of FI, a nonaccusatory approach is key, since this topic may be accompanied by feelings of guilt, shame, and anger in both children and their parents [8, 23, 68].

The most important step in the non-pharmacological management is instituting a toilet program [23, 68, 69]. A toilet program comprises of daily scheduled toilet sits, which last 5–10 min. Toilet sits are usually scheduled after a meal, to take advantage of the gastrocolic reflex, which increases colonic motility upon gastric distension, thereby facilitating defecation. An extra toilet “sit” right after school can be introduced, since most children experience episodes of fecal incontinence in the afternoon. During these sits, it is important that the child tries to become aware of the feeling of urge to defecate; if the child feels an urge, an attempt at defecation should be made. However, there should be no pressure and defecation is not a prerequisite for a successful toilet sit. Toilet sits need to be conducted in a stress-free, positive, and relaxed environment. The aim of these sits is that the child pays attention to the sensory stimuli in the anorectum and learns how to recognize these sensations and how to act accordingly. This should be explained clearly to children and their parents. Additionally, the importance of a relaxed posture needs to be explained and foot support should be provided for small children in order to achieve correct posture.

Maintaining a toilet program may often prove difficult and noncompliance is a considerable problem, especially in children with behavioral disorders. One technique to improve compliance is to let the child fill out a daily bowel diary and to institute a reward system [65]. Filling out the diary provides the child and the parents better insights into the problem and can help to recognize treatment effect and the effect of noncompliance [70]. By giving the child small rewards for the completion of toilet sits, the child can be motivated to maintain the toilet program. However, rewarding periods without FI should be avoided since this can be discouraging, as most episodes of FI occur involuntarily.

The pharmacological treatment of constipation-associated FI is described in detail in Chap. 42. In summary, pharmacological treatment consists of disimpaction followed by maintenance treatment, preferably with poly-ethylene glycol, an osmotic laxative. For FNRFI, there is no clear pharmacological treatment. In contrast to the treatment of constipation-associated FI, the use of oral laxatives in children with FNRFI is not indicated [27]. Using oral laxatives may even increase the risk of FI by making the stools too soft to retain. There is anecdotal evidence that loperamide and imipramine could have a beneficial role in the treatment of FNRFI [71, 72]. Loperamide is an opiate receptor agonist, which decreases peristalsis and increases the internal anal sphincter tone; it is hypothesized that it improves sphincter function and thereby prevents involuntary loss of stools. Imipramine is an antidepressant; it functions as an anticholinergic, which decreases motility and increases sphincter tone and may be beneficial for similar reasons as loperamide. However, due to cardiovascular side effects, imipramine should not be given routinely and close clinical supervision is warranted.

Regular evacuation of the rectum may decrease the chance of losing stools in the underwear. In a RCT among FNRFI patients, children received conventional therapy alone or combined with daily enemas for 2 weeks. Clinical improvement was shown to be greater in the group receiving enemas compared with controls during the active treatment period [73]. However, this difference in outcome did not persist throughout the follow-up period, possibly due to the short duration of treatment.

Another method to achieve a clean out of the rectum is transanal irrigation; this technique has been proven to be effective and safe in children with constipation-associated FI and FI with organic causes [74, 75]. However, evidence on the effect of transanal irrigation in children with FNRFI is lacking.