Anorectal Physiology Testing

Abstract

This chapter aims to outline the basic principles in using anorectal manometry including indications, methods, and result interpretation. The use of defecography, an important adjunct in pelvic floor investigation, will be discussed at the end of the chapter.

Commentary by J. Marcio N. Jorge, Hospital das Clinicas, University of Sao Paulo, Department of Gastroenterology – Colorectal Division, Sao Paulo, Brazil

Commentary

• J. Marcio N. Jorge 

This chapter addresses the main aspects of physiologic testing in complex functional colorectal disorders. Despite affecting both men and women, constipation and incontinence are more prevalent in the latter group. This is probably due to the effects of pregnancy and childbirth on the pelvic floor and the higher prevalence of constipation in this gender group.

Patients with fecal incontinence and rectal prolapse are among those with the worst quality of life seen in our specialty. Embarrassment poses a major difficulty in addressing evaluation and proper treatment. As emphasized by the authors, although history and physical examination are irreplaceable, anorectal physiology testing can be crucial to better understand the mechanisms involved and to uncover the etiology.

The initial therapeutic schema includes dietary assessment, a diary of defecation and symptoms, and, when indicated, psychological evaluation. Patients referred for colorectal physiologic testing often present with refractory and severe idiopathic symptoms, and a combination of anorectal physiology studies is usually indicated due to the complex etiology of these functional disorders.

In practice, anorectal manometry, videodefecography, colonic transit time, and endoanal ultrasound are considered the most useful tests. Through this physiologic investigation, treatable conditions of the colon, rectum, and anus can be diagnosed in 67% and 55% of patients with constipation and fecal incontinence, respectively [41]. In patients with rectal pain, however, these tests permit definite diagnosis in only 18%, and this condition remains poorly understood and refractory to therapy. In addition, these tests can be helpful preoperatively, when anal continence status may be endangered due to the nature of the procedure or a pre-existing disorder that affects the mechanism of continence.

A history and physical examination often dictate additional tests. Electroneuromyography including conventional anal electromyography (EMG) and pudendal nerve terminal motor latency (PNTML) testing can be helpful to uncover neuromuscular disease. However, pudendal neuropathy is a common finding with increasing age and parity and in many comorbidities including chronic constipation and diabetes. Thus, the therapeutic decision is not usually affected by this finding. As discussed by the authors, these tests should be reserved for patients with complex diagnostic dilemmas [42].

Most tests are performed with minimal preparation. A disposable enema is administered 4 hours prior to the test to remove any significant amount of stool and to allow for a more comfortable exam for both the patient and physician.

Anorectal manometry is often indicated to evaluate functional disorders but is also useful in the preoperative assessment of other disorders when there is a risk of postoperative incontinence either due to the preoperative continence status or the procedure itself. More recently, parameters such as the fatigue index to detect earlier external sphincter dysfunction have been incorporated [43]. Accordingly, 3D high-definition anorectal manometry, a more refined technique, has shown significant correlation between the fecal incontinence score and voluntary contraction variables including the mean anal pressure during sustained squeeze – the most discriminant parameter [44]. The sphincter asymmetry index can help to identify sphincter defects; however, anal ultrasound is preferred if available [45].

Videodefecography provides a wide range of information to assist the surgeon in the evaluation and management of patients with evacuatory and other associated pelvic floor disorders [46]. As pointed out in this chapter, wide ranges of normal values for each of these parameters are observed, and the exact value of any of these isolated parameters is of relatively little consequence. Instead, the role of static proctography is to provide a basis for relative comparison among resting, squeezing, and pushing values in a single patient. Causative or associated abnormalities, such as nonrelaxing puborectalis (puborectalis indentation), rectocele, internal rectal prolapse, sigmoidocele, and enterocele can all be diagnosed by defecography. These findings, particularly a small rectocele and an intussusception, may be found in up to 70% of asymptomatic individuals [46]. Failure to recognize these variants of normal can easily lead to overdiagnosis and overtreatment. Therefore, a treatment decision should be made based upon both clinical history and evaluation of rectal emptying during videodefecography. Most individuals evacuate their rectum within 15–20 seconds; factors affecting rectal emptying rate include consistency of contents and patients’ embarrassment. Patients must be reassured and fully informed regarding the importance of the defecographic findings in their therapeutic approach. Dynamic evaluations of defecation using computerized tomography, resonance, and ultrasound are compatible, with the advantage of evaluating extra-rectal structures. However, in order to better evaluate rectal emptying and the clinical relevance of a diagnostic finding, conventional defecography remains the preferred method in many centers [46, 47].

Defecographic criteria of nonrelaxing puborectalis syndrome include failure to open the anorectal angle, persistence of the puborectalis impression during attempted defecation, an overly capacious rectum, a long and persistently closed anal canal, ballooning of the rectum, and the presence of compensatory anterior and posterior rectoceles. These findings can be associated with non-emptying, incomplete emptying, or even total evacuation after prolonged and difficult attempts. However, although useful, both defecography and electromyography have their limitations. Voluntary contraction of the pelvic floor due to embarrassment may simulate a functional disorder on defecography. Likewise, the inability to relax the sphincter may occur during pushing as a response to fear or pain during electromyographic assessment. These factors may cause false-positive findings of nonrelaxing puborectalis syndrome in patients without symptoms of obstructed evacuation. Sensitivity, specificity, and predictive values of both electromyography and defecography are suboptimal, and the combination of these tests may be necessary to permit optimal data accrual [48]. Nevertheless, defecography is likely superior as it can detect associated abnormalities and demonstrate both the dynamics of evacuation and rectal emptying. Although false-positive results may ensue due to the patient’s fear of evacuating in front of others, they can be asked to evacuate in the privacy of a bathroom followed by fluoroscopic reassessment of the evacuated rectum. Finally, the diagnosis of nonrelaxing puborectalis syndrome should be reserved for patients whose clinical symptoms of pelvic outlet obstruction are supported by physiologic confirmation. In order to differentiate an incidental finding from a clinically significant sigmoidocele, a classification system has been proposed [49]. This classification system is based on the degree of descent of the lowest portion of the sigmoid loop during maximum straining in relation to the following pelvic anatomic landmarks: pubis, coccyx, and ischium. First-degree sigmoidocele corresponds to an intrapelvic loop of sigmoid which does not surpass the pubococcygeal line; second-degree sigmoidocele is noted when the sigmoid loop is situated below the pubococcygeal line but remains above the ischiococcygeal line; and third-degree sigmoidocele is considered if the sigmoid loop transcends the ischiococcygeal line. This classification system yielded excellent correlation between the mean level of sigmoidocele, degree of sigmoid redundancy, and clinical symptoms.

Physiologic testing permits objective assessment of subjective and highly prevalent functional colorectal symptoms. A judicious indication and association and interpretation of the tests discussed in this chapter will ensure a better perspective of treating the refractory, at times, incapacitating symptoms. Finally, because the pelvic floor is an integrated functional structure, these disorders should be addressed using a multidisciplinary and integrated approach.