Carlo Ratto, Angelo Parello, Lorenza Donisi and Francesco Litta (eds.)Colon, Rectum and Anus: Anatomic, Physiologic and Diagnostic Bases for Disease ManagementColoproctology110.1007/978-3-319-09807-4_23

19. Anorectal Manometry

Filippo Pucciani¹

(1)

Department of Surgery and Translational Medicine, University of Florence, Largo Brambilla 3, Piazza Brambilla 3, 50134 Florence, Italy

Filippo Pucciani

Email: pucciani@unifi.it

Abstract

At the present time, anorectal manometry is extensively used to identify the pathophysiological mechanisms of obstructed defecation, fecal incontinence, and Hirschsprung disease. Function of anal sphincter complex, rectoanal reflexes, rectal compliance, and rectal sensation is detected. Anorectal manometry generates useful diagnostic data that assist also in the selection of appropriate therapy.

Diagnostic work-up of fecal incontinence and obstructed defecation is based on both imaging techniques, to discover abnormalities of anorectal structural integrity, and on functional instrumental studies, to evaluate the neuromuscular function of anorectum. Anorectal manometry (AM) is used to study function of anal sphincter complex, rectoanal reflexes , rectal compliance, and rectal sensation, but manometric data must be supplementary to those from other anorectal morphological and functional techniques to make a diagnosis. Actually, the clinical utility of anorectal manometry is limited by the relative absence of standardization of test protocols and by the lack of universally accepted normative data from a large number of healthy individuals. Notwithstanding these limitations, anorectal manometry is considered as a useful test for diagnosis and management of fecal disorders.

Routine diagnostic manometry (Azpiroz et al. 2002) explores all continence mechanisms and entails the following:

Exploration of the anal sphincter apparatus, including smooth and striated components. Anal resting pressure (ARP) reflects the tonic activities of both the internal anal sphincter (IAS) and external anal sphincter (EAS); several studies attribute approximately 55 % of ARP to the IAS, 15 % to the vascular anal cushions, and the remaining 30 % to the EAS (Lestar et al. 1989). Maximal voluntary contraction (MVC) is the squeeze pressure obtained by asking the patient to maximally contract the anus; it reflects the contractile activity of the external anal sphincter.
Evaluation of the rectoanal inhibitory reflex (RAIR). RAIR is the reflex inhibition of internal anal sphincter tone that is elicited by distending a rectal balloon with different volumes of air. It is part of the sampling reflex responsible for triggering the impulse to defecate (Martelli et al. 1978; Kumar et al. 1990). Transient relaxation of the internal anal sphincter allows rectal stool contents to come into contact with specialized sensory organs in the upper anal canal; typifying of rectal content alerts the patient to discharge flatus or to defecate.
Detection of rectal sensation . Volumetric perception of fecal mass is reproduced by distending a rectal balloon with increasing volumes (AGA 1999). Conscious rectal sensitivity threshold (CRST) is the lowest volume of air that evokes the first sensation; constant sensation (CS) is the volume that calls to stool; maximum tolerated volume (MTV) measures the threshold volume for urgency to defecate and for pain.
Monitoring of rectal compliance . Rectal compliance, as determined by the pressure/volume ratio at several different distending volumes, reflects tonic adaptation of rectal wall (rectum distensibility) to the incoming fecal load (Madoff et al. 1990).

Traditional anorectal manometry is performed using perfused or solid state catheters, but none of them can measure circumferential pressures simultaneously throughout the anal canal and in the rectum. High-resolution manometry (HRM) catheters can do so and are increasingly used to evaluate anorectal functions in clinical practice (Noelting et al. 2012). A HRM catheter comprises circumferential sensors, usually at 6-mm intervals along the anal canal, and at least two sensors in the rectal balloon. At each level, 36 circumferentially oriented pressure-sensing elements detect pressure using proprietary pressure transduction technology. Pressures are then averaged to obtain a mean pressure measurement at each level and pressures graphic is displayed on a colorimetric scale ranging from blue, for the lowest pressure values, to violet for the highest pressures. A simultaneous comparison between HRM and anorectal perfused manometry showed that HRM is highly correlated with water perfused manometry measurements and provides greater anatomic detail (Jones et al. 2007; Vitton et al. 2013). A few years ago, 3-D high definition anorectal manometry (HDAM) was introduced, studying pressure topography (Cheeney et al. 2011). HDAM can provide knowledge on the puborectalis, internal and external anal sphincters, and can show how they mediate the rectoanal inhibitory reflex, sensorimotor responses, and the spatiotemporal orientation of these muscles. In addition, anal sphincter defects can be mapped and readily detected using 3-D technology (Lee et al. 2013).

Regardless of monitoring typology, anorectal manometry provides objective information about the mechanisms of fecal continence. For this reason, indications for anorectal manometry are fecal incontinence, obstructed defecation and, in pediatric age, Hirschsprung disease (AGA 1999).

For better understanding of these topics, the use of anorectal manometry will be described according to each individual fecal disorder.

1 Fecal Incontinence

Fecal incontinence is defined as failure to control the elimination of stool and/or flatus recurring for >3 months (Miner 2004; Pucciani 2013). Use of anorectal manometry is mandatory in incontinent patients who undergo work-up studies of fecal incontinence after failure of conservative treatment by drugs, high residual diet, and irrigation systems.

An evaluation of anal pressures is little or no useful because resting and squeezing pressures are generally lower in incontinent patients independently of sphincteric status, with or without sphincter defects. Low anal resting pressure refers to internal anal sphincter dysfunction and may be a manometric marker of passive incontinence; low maximal voluntary contraction is related to external anal sphincter dysfunction and often patients have urge incontinence with loss of stool because of the inability to suppress defecation. Unfortunately, manometry has wide variations in normal pressure that can differ with age and sex so manometric results need to be interpreted carefully along with other findings and symptoms. On the contrary, rectal sensation study and rectal compliance evaluation are decisive in identifying a sensorimotor rectal dysfunction that is the functional report in patients, for example, who are affected by fecal incontinence after sphincter-saving operations (Pucciani et al. 2008). A significant decrease or loss of rectal sensation (> CRST, > CS) may contribute to fecal incontinence by impairing the recognition of impending defecation. When stool enters the rectum, the perception of rectal distension gives the conscious stimulus to contract the anal sphincter to preserve continence; if stool is not perceived, the contractive voluntary response is not elicited and fecal incontinence may occur. Patients with diabetes mellitus (Wald and Tunuguntia 1984) and multiple sclerosis (Caruana et al. 1991) may exhibit this pathophysiological mechanism of incontinence. The rectoanal inhibitory reflex, the transient decrease in resting anal pressure in response to rapid inflation of a rectal balloon, often cannot be elicited when anal pressures are very low (<10 mmHg). Therefore, in some incontinent patients with low ARP it is not possible to judge whether the reflex is present or absent, normal or not. However, there are some reports on RAIR modifications in patients affected by fecal incontinence. One ambulatory manometric study showed that abnormal transient internal anal sphincter relaxation might lead to fecal soiling and pruritus ani (Farouk et al. 1994). The duration of RAIR is longer in patients affected by idiopathic fecal incontinence than in controls; a prolonged contraction time, with a slow return to the prestimulation values, is the typical sign (Pucciani et al. 1997). A longer RAIR impairs the fecal continence mechanism. When small amounts of stool elicit RAIR with a prolonged contraction time in patients with a poor external anal sphincter recruitment and in presence of a conscious rectal sensitivity threshold higher than that of RAIR threshold, fecal passive incontinence may occur. A low MTV, often combined with a defective rectal compliance (>0.50 mmHg/ml), suggests the patient has insufficient rectal volumetric capacity with an impaired adaptation of the rectal wall to endoluminal content. It is the pathological and functional substratum of impaired continence after both low anterior rectal resection and coloanal anastomosis (Pucciani et al. 2008).

Anorectal manometry is a diagnostic testing which may provide information that guides the management of fecal incontinence. Rehabilitative treatment is the first-line conservative therapy of incontinence after the failure of medical treatment (Norton and Kamm 2001) and multimodal rehabilitation may be used as rehabilitative protocol (Pucciani et al. 2003). The algorithm for this rehabilitation management is based on manometric reports. Low anal resting pressures or weak maximal voluntary contraction indicate the patient’s need of biofeedback and pelviperineal kinesitherapy . Volumetric rehabilitation (sensory retraining) is indicated for disordered rectal sensation or impaired rectal compliance. Electrostimulation is only a preliminary step when patients need to feel the anoperineal plane. The usual procedural sequence is (1) volumetric rehabilitation, (2) electrostimulation, (3) pelviperineal kinesitherapy, and (4) biofeedback. Their combination is suggested by manometric data. Clinical outcome of multimodal rehabilitation is good: 89 % of patients has significant improvement of Wexner incontinence score. Furthermore, anorectal manometry can help to select candidates who are in need of surgery for fecal incontinence. Low anal resting pressures (<10 mmHg) and low maximal voluntary contraction (<40 mmHg) are considered cut-off values for overlapping sphincteroplasty (Ternent et al. 1997). The same cut-off values identify those patients with rectal prolapse who are at high risk for postoperative incontinence, modifying the surgical strategy of simple correction of prolapse (Yoshioka et al. 1989).

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