A detailed and careful clinical history will reveal important information relating to several key areas: (1) severity of symptoms of constipation, (2) impact of symptoms on quality of life, (3) presence of associated symptoms such as soiling/fecal incontinence, and (4) possible etiology. An assessment of the severity of symptoms may be made by recording details related to the frequency (or, more accurately, the infrequency) of defectation and the effectiveness of evacuatory function. It is important to ascertain the onset and duration of symptoms because those with onset of symptoms during childhood or adolescence invariably experience recurrent fecal impaction with soiling, whereas patients with a “late onset” of symptoms tend not to complain of this symptom [6, 28] Additional relevant information includes the usual stool consistency and the percentage of defecatory attempts that are associated with (1) the need to strain, (2) a sensation of anorectal obstruction or incomplete emptying, and (3) defecation attempts that are ultimately unsuccessful. The usual time required to defaecate and the need for digitation (either vaginally or anally) to facilitate rectal emptying should be noted. Abdominal pain, distension, and regular use of a laxative/suppository/enema are present in the vast ­majority of patients [6, 22, 28], and their extent and specific nature also should be documented.

It is advisable to obtain objective information about a patient’s symptoms and their severity using validated constipation (with or without fecal incontinence; discussed later) scoring systems (such as the Cleveland Clinic constipation score) [29]. In a research setting, the Rome III diagnostic criteria for chronic constipation [30] should be sought and documented. It is also important to gauge the impact of symptoms on the patient’s quality of life by assessing their effect on activities of daily living and sociopsychological status, which can be formalized using the patient assessment of constipation–quality of life questionnaire [31].

For the purposes of this chapter, it is assumed that other possible organic lower gastrointestinal diseases have already been excluded by appropriate assessment. A full enquiry about all lower gastrointestinal symptoms is clearly important in facilitating this. In addition, in the context of megarectum, it is vital to enquire about soiling and fecal incontinence and, when present, to record detailed information relating to the frequency and amount of leakage of solid and liquid stool and flatus. Again, the use of a validated scoring system (such as the Cleveland Clinic score [32]) provides objective information concerning the severity. Symptoms of pelvic organ and rectal prolapse must be sought.

A detailed history also provides the opportunity for the clinician to exclude other causes of megarectum, for example, psychiatric, endocrine, or central nervous system diseases, including possible underlying psychobehavioral issues (e.g., functional fecal retention during childhood, toilet avoidance during adulthood, or both). A detailed interview with the patient also provides the opportunity to ensure that all nonsurgical interventions have been exhausted.

A thorough general and abdominal examination should be performed. In patients with gross dilatation and fecal impaction of the rectum (especially when associated with concomitant colonic dilatation), it may be possible to palpate a large fecaloma during abdominal examination. This can be recognized as a mass arising from the pelvis that “indents” on palpation. Of particular relevance to the assessment of patients with IMR is the examination of the neurological system and the anorectum. With respect to neurological evaluation, attention should be focused on somatic lumbosacral spinal cord function; an assessment of gait and neurological function of the lower limbs should be performed in all cases. If neurological disease is likely, more detailed examination is clearly warranted.

When examining the anorectum, the patient is usually positioned in the left lateral position with the hips flexed, although the jack-knife position also is used. The examination begins with inspection of the anus and perineum. Evidence of congenital anomalies should be noted. The ­perianal skin and surrounding area should be checked for the presence of fecal soiling, mucus or purulent discharge, and excoriation. Any skin tags, external hemorrhoids, fistulae, or other conditions should be noted and clearly documented. These findings are often present in patients with IMR because of chronic evacuatory difficulties and each may need to be addressed separately.

The anal canal is usually closed at rest; a patulous anus may suggest underlying sphincter dysfunction (see the section “Physiological Investigation of Patients with IMR”). The examination proceeds with digital examination of the anorectum. A basic idea of resting tone and strength of voluntary contraction can be gained, although this is not necessarily accurate. The rectum is examined for masses and the presence of impacted feces. A sense of the “capacity” of the rectum also can be appreciated during digital examination. The examination is completed by performing a proctosigmoidoscopy to exclude local organic pathology of the distal bowel and functional anatomical disorders (prolapsing hemorrhoids/rectal mucosa and rectocele). The finding of a solitary rectal ulcer may confirm the presence of an underlying evacuatory disorder. In our experience, rigid sigmoidoscopic examination also provides the surgeon with a useful assessment of the capacity/elongation of the rectum because the scope often “falls in” to its maximum length with significant ease in patients with IMR, provided, of course, the rectum is empty of impacted feces.

Although certain features of the patient’s history and physical examination may suggest the presence of the most extreme cases of megarectum (such as extreme infrequency of defecation or recurrent fecal impaction with soiling, large fecoloma on abdominal palpation, gross fecal impaction of the rectum on digital examination, obvious dilatation/elongation of the rectum during rigid sigmoidoscopic examination), because clinical features alone are unreliable in identifying such patients, it is likely that milder forms of the condition may remain unrecognized and thus untreated in patients presenting with constipation.

Clearly, it would be impossible and inappropriate to investigate all patients presenting with symptoms of chronic constipation, given that its prevalence approaches 10 % in Western populations [33]. Therefore, investigation of such patients needs to be rationalized and selective. In our practice, we recommend further investigation to those patients with severe, intractable, chronic constipation in whom there is a significant impact on quality of life and in whom simple measures to treat the constipation have failed to alleviate symptoms. This is somewhat biased toward patients referred to a tertiary referral center that specializes in the medical and surgical management of such cases. Assuming that underlying organic disease has been excluded, we undertake investigation in accordance with current recommendations [34]. Measurement of serum calcium levels and thyroid function tests are performed, accepting that the diagnostic yield of such tests will be low. Subsequently, constipated patients are subjected to rigorous laboratory assessment of colonic and anorectal function using comprehensive physiological investigation. We routinely perform the following physiological tests in all constipated patients who are referred for specialist investigation:

The term megarectum is often used indiscriminately. Dilatation of the rectum may be so gross that it is evident during clinical examination or laparotomy (Fig. 25.1) or on a plain radiograph of the abdomen (Fig. 25.2), although ­diagnosis on this basis is somewhat subjective because no specific criteria exist. Traditionally, two methods have been employed to make a diagnosis of megarectum.

First, the diagnosis has usually been made when the rectal diameter at the pelvic brim is greater than 6.5 cm on a lateral radiograph obtained during double-contrast barium enema [45]. In recent years, evacuation proctography, which also utilizes radiopaque contrast, has been used in the assessment of constipated patients, and although used, the above definition has not been validated for this technique. It is important to appreciate that contrast studies may not accurately reflect or assess rectal dimensions [46, 47] because they rely on volumetric distension and do not control for the differing rectal volumes or distensibilities seen in constipated patients [48, 49], which, coupled with proximal progression into the sigmoid and possible anal leakage of contrast, may result in incomplete distension and thus an overall underestimation of rectal diameter [8].

Alternatively, a diagnosis of megarectum has been made during anorectal manometry on the basis of an elevated maximum tolerable volume during simple “latex” balloon distension [37, 50], which is assumed to reflect rectal capacity [51–53]. However, an increase in tolerated rectal volume does not necessarily indicate an increased rectal diameter (and thus a diagnosis of megarectum) because it also is influenced by the sensitivity of the afferent nerves supplying the rectum [49] and thus will be elevated when there are nerve signaling problems along this pathway (such as pelvic nerve or spinal cord injury) [44]. In addition, axial expansion and rostral extension of rectal balloons into the sigmoid colon will influence the sensory threshold volumes [54]. Rostral extrusion of rectal balloons and assumptions regarding their intrinsic compliance affect compliance measurements of the rectum, as does the inherent rectal geometry, which is disturbed in megarectum: Newer technologies such as impedance planimetry and the barostat (discussed later) that equate the estimated cross-sectional area of the ­rectum during standardized rectal distension are needed to separate these cases [55, 56].

Given the fundamental methodological limitations of the above techniques, a novel technique for the diagnosis of megarectum has been developed by our group [8]. This technique involves the use of a barostat, which is a computerized device capable of achieving a constant distending pressure in the viscus under evaluation by changing the volume of air insufflated and which is now the method of choice for the evaluation of various components of rectal sensorimotor function [57–59]. Controlled isobaric distension of the rectum using a barostat during fluoroscopic screening allows rectal diameter to be assessed accurately and consistently. A diagnosis of megarectum was made when the maximum rectal diameter was >6.3 cm at the minimum distending pressure of the rectum (the pressure at which sufficient air is insufflated to prevent collapse of the wall but not cause active distension of the rectum) [8]. An example of a patient with megarectum compared with a constipated patient with a normal-caliber rectum is shown in Fig. 25.3a, b. This technique seems to be well tolerated, demonstrates excellent interobserver agreement, and has criteria for diagnosis defined by a normal range established in asymptomatic controls [8]. Furthermore, the use of a barostat to perform controlled distension to a specific, predefined “threshold” ensured standardization of methodology between subjects [8].

On the basis of all available diagnostic techniques, taking their inherent limitations into consideration, a contemporary strategy for the diagnosis of megarectum recently has been proposed (Fig. 25.4) [20]. In summary, the diagnosis of megarectum should be made using one of the following objective criteria [20]:

In terms of planning, the presence or absence of concomitant proximal colonic dilatation (megacolon) is crucial when deciding appropriate surgical strategy (if clinically indicated). Unfortunately, of the three imaging methods mentioned above, only a double-contrast barium enema study will enable exclusion of proximal bowel dilatation and is thus considered mandatory before undertaking surgical intervention. However, it should be noted that this technique is not always sensitive for diagnosing megarectum and can underestimate dilatation [8]. Therefore, if clinical suspicion is high, the other techniques should also be employed. In contrast, a diagnosis based on elevated sensory threshold volumes during anorectal manometry should not be used because it is not sufficiently specific and overdiagnoses the condition [8].

As alluded to previously, other causes for the development of rectal dilatation (see Table 25.1) should be excluded by appropriate assessment. For the most part, the most significant condition to be excluded is adult HSCR.