Pelvic Floor Disorders: Surgical Approach

7. Functional Assessment of Anorectal Function

Maria Di Lena, Nunzio Ranaldo, Ivana Giannini, Simona Giuratrabocchetta and Donato F. Altomare 

(1)

Department of Emergency and Organ Transplantation, Aldo Moro University, Bari, Italy

Donato F. Altomare

Email: donatofrancesco.altomare@uniba.it

Abstract

Disorders of the posterior compartment of the pelvic floor are essentially represented by disorders of defecation, fecal incontinence, and constipation. Their functional assessment includes the evaluation of their severity, their impact on quality of life (QoL), and their etiology, by means of medical history, and clinical and instrumental examinations of the perineum and the anorectum.

7.1 Introduction

Disorders of the posterior compartment of the pelvic floor are essentially represented by disorders of defecation, fecal incontinence, and constipation. Their functional assessment includes the evaluation of their severity, their impact on quality of life (QoL), and their etiology, by means of medical history, and clinical and instrumental examinations of the perineum and the anorectum.

7.2 Anorectal Function: Definitions

Fecal incontinence (FI) is defined as the loss of control of the passage of gas and/or stools through the anus (passive incontinence) or the inability to defer the call to defecate to a socially acceptable time and place, resulting in the release of gas, liquid, or solid stool (urge incontinence) [1].

Constipation is defined as infrequent defecation, difficult defecation, or both [2]. Two main mechanisms have been hypothesized as causes of constipation: slow transit in the colon and difficulty in expelling feces. Slow transit can be primary (idiopathic) or secondary, which is the result of low fiber intake, use of drugs such as opioids, or endocrine, metabolic, neurological, or behavioral disorders. Obstructed defecation syndrome can result from functional disorders (pelvic floor muscle dyssynergia, rectal hyposensitivity, and hypomotility) or from anatomical abnormalities during defecation (rectocele, intussusception, mucosa prolapse, descending perineum).

7.3 Clinical Features

In patients with FI or constipation, the duration, the nature of the leakage, and the impact on QoL, and also the presence of other conditions such as diabetes mellitus, spinal cord injury, pelvic radiation, vaginal deliveries, and co-existing urinary incontinence should be assessed. The medical history of the patient should be taken to try to establish the most likely cause of FI and constipation. Previous conservative, pharmacological, and surgical therapies should be investigated.

7.4 Scoring Systems

Assessment of the severity of FI and constipation can help to evaluate the effects of therapy and it is essential in the choice of treatment. One of the oldest scoring sytems for FI was designed by Pescatori et al., who assigned different scores according to the type (flatus/mucus, liquid stool, or solid stools), and frequency of FI [3].

Jorge and Wexner [4], from the Cleveland Clinic, Florida, described the most commonly used score, which introduced alteration of lifestyle items, and Vaizey et al. [5], from St Mark’s Hospital, London, UK, further modified this score by adding the evaluation of urgency. Another well-designed score was proposed by Wong: the American Medical System (AMS) score [6], which assigns a score to any clinical severe condition of the problem and considers the impact on the QoL.

The specific impact of FI on QoL can be assessed by the Fecal Incontinence Quality of Life Scale (FIQL), which was designed and validated by Rockwood and colleagues [7]. It is composed of 29 items, comprising four areas: lifestyle, coping/behavior, depression/self-perception, and embarrassment, which are used to evaluate each aspect of the disorder. The use of other generic scores of QoL, such the SF-36 score, is now discouraged because of their low sensitivity for this clinical condition.

Several scoring systems have been developed to quantify the severity of constipation. The most widely adopted for chronic constipation is the Cleveland Clinic Constipation Score by Agachan and colleagues [8]. It is easy to understand and administer and therefore is well accepted, although it has never been formally validated. It consists of eight items scored from 0 to 4, with a maximum score of 30; however, one of the items, “duration of symptoms”, cannot be modified by therapy. Recently the Constipation Severity Instrument (CSI) [9] was developed, and includes 78 items that can identify and quantify different types of constipation (irritable bowel syndrome, slow transit, and obstructed defecation).

The first specifically designed score for obstructed defecation syndrome was published and prospectively validated in 2008. It consists of seven items scored from 0 to 4, with a maximum score of 27 [10].

7.5 Clinical Examination

A thorough physical examination is essential to assess the general state of the patient (body mass index, dexterity, and mobility), abdominal masses, bladder distention, and surgical scars. Examination of the perineum and external genitalia is of great importance in determining the presence of vaginal prolapse, prolapsed hemorrhoids, dermatitis, skin excoriations, perianal greases, or gaping anus. A digital rectal examination allows evaluation of the resting sphincter tone, the length of the anal canal, the strength of the puborectalis sling, the acuteness of the anorectal angle, the strength of the anal sphincter squeeze, and the presence of rectocele and impacted stools. The sensitivity of the perianal skin and the integrity of the anocutaneous reflex can be assessed rubbing a cotton bud on each quadrant of perineal skin, while the presence of descending perineum or rectal prolapse can be demonstrated by asking the patient to attempt defecation. A simple device (the perineometer) was designed at St Mark’s Hospital to quantify the perineal descensus with a clinical evaluation instead of an X-ray examination, but the device has not produced commercially.

A clinical examination in patients with obstructed defecation should also include an anoscopy, which can demonstrate a mucosal intussusception while the patient is pushing.

7.6 Balloon Expulsion Test

This easy and practical test gives qualitative information reagarding the ability of a patient to retain or expel feces, which might be related to FI or constipation caused by pelvic floor dyssynergia. The test lasts a few minutes and consists of the introduction of an inflatable balloon into the rectum, with the patient being asked to expel it while the operator uses moderate traction to remove the balloon. Patients with pelvic floor dyssynergia have difficulty in performing this maneuver because of anismus or the opposing contraction of the anal sphincters, while those with FI cannot retain the balloon during the external traction by the operator because of the damaged anal sphincters.

An attempt to quantify the outcome of this test was produced by Dodi (Fig. 7.1), who designed a solid sphere connected to an external digital dynamometer. Using this device, the resistance offered by the anal sphincter to the removal of the sphere from the rectum is measured in dynes.

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Fig. 7.1

Solid sphere expulsion test device

7.7 Anorectal Manometry and Sensory Tests

Anorectal manometry consists of the measurement of pressure in the anal canal and the rectal ampulla, and it is useful as a diagnostic tool in patients with FI and outlet obstruction due to pelvic floor dyssynergy, to help understand the pathophysiology of the patients’ symptoms. The measurement of the pressures in the anorectal tract can be performed using various techniques that differ in the type of probe used (water-perfused probe, solid-state probe, microtransducer probe) and the mode of detection.

The pressure detectors can be placed longitudinally, helically, or radially on the probe. At the end of the probe there is a latex balloon placed in the rectum, which is inflated with air or water, mimicking the presence of feces in the rectum. This allows the patient to evoke the rectoanal inhibitor reflex, to determine the compliance and sensitivity of the rectum.

Water-perfused probes are connected to a low-compliance water infusion system, and to a water-filled pressure transducer, linked to a digital multichannel recorder. The pressure is converted to mmHg.

Solid-state probes are directly connected to a pressure transducer, linked to multichannel recorder. This method is more practical, fast, and reliable than water-perfused systems, but more expensive; the pressure is expressed in mmHg.

The rectum must be prepared with a hypertonic phosphate enema (130 cm3) 2 h before the manometry examination, and the patient is placed in a left lateral decubitus position, with legs bent at 90° and superimposed on the trunk (Sims’ position). The probe is positioned with all solid state sensors or opentips in the rectal ampulla and retracted with a rapid pull-through technique using an automatic retractor or with a stationary pull-through technique, in which the probe is stopped for 20 s every 5 mm, allowing to the operator to obtain the pressure profile of the anal canal. In the assessment of voluntary functions, the sensors should be placed all along the anal canal. In the study of reflexes, anorectal sensitivity and compliance, the probe is positioned with the end of the balloon 8–10 cm from the anal margin.

The parameters that are usually considered to have clinical utility are described in the following sections [11].

7.7.1 Resting Anal Pressure

This is mainly influenced by the tone of the internal anal sphincter (IAS). High anal pressure has been observed in patients with anal fissures or anal pain. Pressure reduction, occurring as lone symptom, is usually present in patients with incontinence, but measurements have low specificity and sensitivity.

7.7.2 Squeezing Anal Pressure

This is expressed in peak size and duration, and is produced by the contraction of external anal sphincter (EAS), with possible contributions by the accessory muscles of the perineum (puborectalis and gluteus). A decrease in peak pressure is caused by a weak EAS and may be myogenic (usually iatrogenic or obstetric) or neurogenic. A decrease in duration of squeeze (< 45 s) may indicate pudendal nerve damage.

7.7.3 Rectoanal Inhibitory Reflex

The distention of the rectum elicits an intrinsic reflex (i.e., via the myoenteric plexus) that produces a relaxation of the IAS. This reflex can be elicited by inflating a rectal balloon with 20–40 mL of air. Absence of the reflex is pathognomonic of Hirschsprung’s disease, and is also found in patients after low rectal resection and coloanal anastomosis, when it can disappear.

7.7.4 Cough Reflex

An intra-abdominal pressure increment induces a reflex contraction of the EAS. This parameter is particularly useful in cases of damage of the EAS, resulting in muscular weakness. It can be used to evaluate possible damage to the sacral reflex arc. In patients with lesion of the sacral reflex arc, the contraction of EAS has a lower peak size and duration; in subjects with spinal cord injury above the sacral level, the cough reflex is preserved.

7.7.5 Canal Pressure in Response to Defecatory Attempts

This maneuver determines an inhibition of the EAS. The failure to inhibit the tone of EAS or even its paradoxical contraction is typical of pelvic floor dyssynergia.

7.7.6 Compliance of the Rectum and Sensory Thresholds in Response to Balloon Distention

Rectal compliance is expressed by the pressure/volume ratio during continuous rectal distention obtained by using an inflatable low-compliance balloon. It is influenced by the size of the rectum, the tone of the rectal wall muscles, the elastic properties of the rectum, the integrity of parasympathetic innervations, and the mobility of the pelvic organs, which may limit rectal distention. A normal range of value has never been determined; in our laboratory a normal range is said to be between 2 and 15.

During progressive rectal distention, the sensitivity of the rectal ampulla can be evaluated by asking the patient about his first sensation of rectal distention (threshold of rectal sensitivity), his desire to defecate (threshold of the stimulus to defecate), and pain or impending desire to defecate (maximum tolerable volume). Some authors consider that the sensitive threshold measurement is a suitable test for the identification of patients with rectal hyposensitivity in cases of constipation. In contrast, hypersensitivity can be present in cases of fecal urge incontinence.

7.7.7 Vector Anal Manometry

A more sophisticated application of anal manometry is vector anal manometry, which shows the pressure profile in the anal canal in three dimensions. The methodology requires dedicated software, with automatic retraction of a microtip probe. Vector anal manometry can best assess the asymmetry of the anal pressure in cases of anal sphincter damages, in both resting and squeezing states [12].

7.8 Electromyography

Electromyography (EMG) of the anal sphincter is a neurophysiological examination used to identify the presence and the characteristics of myoelectric activity in the anal sphincters and levator ani. This investigation has lost its importance in the functional assessment of anorectal function because mapping the anal sphincters (IAS and EAS) by EMG, which is aimed at identifying sphincter injury (scar), is now performed by endoanal ultrasound, and because the diagnosis of acute or chronic denervation or re-innervation potentials indicating a pudendal neuropathy have been found to have no prognostic implications. EMG can be performed by three different types of electrode: concentric needle electrode, single fiber electrode, or surface electrode. In routine diagnosis, needle electrodes are used (these are more accurate than surface electrodes).

The standard technique applied with a concentric needle electrode consists of introducing the electrode into each quadrant of the EAS. Introducing the electrode at a greater depth enables study of the puborectalis muscle. Use of an intramuscular needle can identify the electrical activity of the membrane potential in the muscle fibers.

EMG enables measurement of motor unit action potentials, both at rest and during voluntary and reflex activity. This provides qualitative and quantitative assessment of muscle fiber innervation, and also highlights states of acute or chronic denervation, total or partial re-innervation, as well as providing an assessment of the functional capacity of the motor unit.

During voluntary contraction there is an increase in the number of motor unit action potentials; however, during straining there is inhibition of the pathway.

Anal EMG is currently less utilized than in the past; in fact it has been replaced by anal endosonography in patients with incontinence. On the other hand, anal EMG can still be useful for identifying a primary or secondary myogenic disease or motor neuron disease in incontinent patients.

Fibrillation potentials and high-frequency spontaneous discharges indicate denervation, as in cases of cauda equine syndrome or pudendal nerve injury. This investigation is now obsolete.

7.9 Pudendal Nerve Terminal Motor Latency

The neurophysiological study of the pelvic floor is completed with determination of pudendal nerve terminal motor latency (PNTML), which is easily performed by the ‘St Mark’s Hospital’ electrode [13]. This is mounted on the finger of the examiner’s glove, and is used to measure the conduction time (terminal motor latency) of the distal part of the pudendal innervation of the EAS, on each side of its circumference (right and left). Electrical stimulation is applied by the tip of the electrode directly on to the pudendal nerve, which is identified in the ischial spine. The EAS contraction induced by the stimulus is recorded by the zone located at the base of the finger, and the latency time from the stimulus to the start of the contraction is calculated, with normal values at approximately 2 ± 0.2 ms.

PNTML is used as a complementary technique in patients with FI, chronic pelvic pain, and rectal prolapse.

7.10 Motor-evoked Potentials

Motor-evoked potentials are produced by an electric current discharged through a conducting coil, with the production of a magnetic flux, which stimulates the neural tissue. The stimulation of the lumbosacral nerve and the measurement of the conduction time through the cauda equina are used to diagnose sacral motor radiculopathy. Tantiphlachiva and colleagues [14] demonstrated that translumbar and transacral motor-evoked potentials could be used to assess anorectal neuropathy in patients with FI.

7.11 Transanal Endosonography

An ultrasound examination of the rectum by a 360° rotating three-dimensional probe is currently the best technique for investigating the integrity of the anal sphincters, the rectal wall, and the puborectalis muscles in patients with FI. The procedure is fast, safe, and painless, with high reliability [15].

7.12 Dynamic Transperineal Ultrasound

This new noninvasive, no-risk procedure is gaining wide acceptance among radiologists and coloproctologists involved in the functional evaluation of the pelvic floor, but it is still rarely used, probably because of the great amount of operator experience that is required.

Sagittal and transverse transperineal ultrasound imaging has been shown to be able to define the infra-elevator viscera, soft tissues, and margins of the puborectalis muscle. Dynamic measurements are also possible of the extent of puborectalis shortening, the anorectal angle, and the movement of the anorectal junction during straining, but, most interestingly this ultrasound technique can also identify the presence of rectoceles, and calculate the posterior urethrovesical angle, and the movement of the urethra-bladder junction [16]. Transverse images of the anal sphincter are comparable with those obtained using endoanal ultrasonography, and sagittal images can be used for measuring puborectalis contraction and anorectal angle; results of these measurements have been shown to be equivalent to those obtained during defecography. Rectoceles, enteroceles, and rectoanal intussusception can be clearly identified and measured during the dynamic part of the examination, although the rectum cannot be emptied and defecation completed.

7.13 Dynamic Defecography

Dynamic defecography, or evacuation proctography, is an X-ray examination that shows the dynamic changes of the rectum and anal canal during defecation of an artificial radiopaque stool. This test is used to evaluate disorders of the lower bowel that are not evident by colonoscopy or sigmoidoscopy, and to confirm and quantify a diagnosis of rectal intussusception, rectal prolapse, rectocele, dyssynergia, or anismus. Used in association with a bladder X-ray contrast agent, this investigation can help in the evaluation of a cystocele and urinary incontinence/retention in women. The oral administration of 50 mL barium sulfate solution about 1 h before the defecography procedure can be used to help recognize an enterocele in women. Alternatively, the contrast medium (usually about 250–350 mL barium sulfate solution mixed with some gelling agents) is introduced through the anus and vagina, and the patient is then invited to evacuate the artificial stools while sitting on a radiotransparent commode. The examination is digitally recorded on a DVD.

A static proctogram usually precedes the dynamic evaluation of the rectal emptying in order to evaluate the width and changes of the anorectal angle, changes in puborectalis length, and descent of the pelvic floor.

7.14 Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a very good method for evaluating the EAS and its abnormalities. Dynamic MRI defecography [17] produces better delineation of the pelvic anatomy and the surrounding organs, compared with traditional defecography; however, the position of the patient during the attempt to defecate is unnatural (standing-like position) and this may prevent full evaluation of the defecatory function. Open MRI can partially overcome this drawback, but its availability is still very limited. Furthermore, the current cost of the procedure prevents widespread use of this procedure.

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