Anorectal Physiology Testing for Prolapse—What Tests are Necessary?

Abstract

Rectal prolapse frequently occurs in conjunction with functional and anatomic abnormalities of the bowel and pelvic floor. Prolapse surgery should have as its goal not only to correct the prolapse, but also to improve function to the greatest extent possible. Careful history-taking and physical exam continue to be the surgeon's best tools to put rectal prolapse in its functional context. Physiologic testing augments this and informs surgical decision-making. Defecography can identify concomitant middle compartment prolapse and pelvic floor hernias, potentially targeting patients for urogynecologic consultation or combined repair. Other tests, including manometry, ultrasound, and electrophysiologic testing, may be of utility in select cases. Here, we provide an overview of available testing options and their individual utility in rectal prolapse.

In most cases, full-thickness rectal prolapse is a straightforward clinical diagnosis made with suggestive symptoms and the classic physical exam finding of prolapsed concentric bowel. Surgical repair of the prolapse is recommended and choice of operation is influenced by surgeon expertise, patient fitness, and patient preference. If one considers elimination of the prolapse the sole goal, the added benefit of physiologic testing is not obvious. However, rectal prolapse often occurs in conjunction with functional and anatomic abnormalities of the bowel and pelvic floor. As stated in the American Society of Colorectal Surgeons clinical practice guidelines, ¹ the goal of the operation is not only to correct the prolapse, but also to improve functional abnormalities to the extent possible, and to avoid creating new pelvic floor dysfunction. In this context, physiologic testing can clarify an uncertain diagnosis, identify concomitant pelvic organ prolapse, and investigate functional disorders of the pelvic floor with the goal of improving the patient's quality of life to the greatest extent possible. Here, we review the critical portions of the history and physical exam, available testing options, and suggest an algorithm for selecting physiologic assessment.

Current Diagnostic Work Up

History

A thorough history is critical to putting the patient's rectal prolapse in context and targeting patients appropriately for advanced testing. The classic multiparous 70-year-old female with rectal prolapse will likely have substantially different functional complaints than a developmentally delayed man or nulliparous young female with a connective tissue disorder. Patients should be thoroughly and systematically questioned for incontinence and constipation with particular attention to the impact of these on quality of life. Stool quality and dietary or medical changes should be recorded. Standardized questionnaires and scores for incontinence and constipation may be useful, particularly for discerning which symptoms have greatest impact on quality of life.

In terms of the patient history, obstetrical history including episiotomies and delivery requiring forcep or vacuum assistive devices should be recorded as well as anorectal surgery, hysterectomy, or colon resection. Patients should be queried for history of sexual assault. To identify patients with potential anterior and middle compartment disorders, patients should be asked about vaginal bulging, difficulty voiding, urinary incontinence, and sexual dysfunction.

Physical Exam

In addition to standard maneuvers to produce the prolapse and confirm the diagnosis, such as administering an enema or having the patient strain on the commode, a thorough physical exam may identify findings targeting patients to testing or suggesting additional pathology. Neurologic function can be ascertained with a pinprick test and eliciting the anal wink reflex by gently touching the perianal skin. In the decubitus position, asking the patient to rest, squeeze, and push while performing a digital rectal exam can determine baseline sphincter tone and bulk and assess both the patient's strength and capacity to appropriately relax the pelvic floor. Performing these same maneuvers in the lithotomy position with a bimanual or divided speculum exam can identify rectoceles, enteroceles, and uterine/vaginal prolapse, and may provoke stress urinary incontinence.

Colonoscopy

Rarely, premalignant or malignant neoplasms may act as a lead point for rectal prolapse. Additionally, coexisting conditions such as solitary rectal ulcers may alter surgical strategy. Therefore, screening endoscopy is warranted in prolapse patients.

Physiologic Tests in Rectal Prolapse

Anorectal Manometry

Anorectal manometry (ARM) is one of the most common and comprehensive tests used to assess anorectal sensorimotor function during rest, squeeze, and simulated defecation. The test provides information such as (1) voluntary and involuntary anal sphincter function including measurement of the resting and squeeze sphincter pressure, and the functional length of the anal canal, (2) rectoanal inhibitory reflex (RAIR) activity during rectal distension, (3) rectal sensation, (4) rectal compliance, and (5) evacuatory function. ^{2 3 4} Definitions of several of these measures along with others commonly used to describe anorectal physiology are provided in Table 1 . ⁵

Table 1. The American Society of Colon and Rectal Surgeons' consensus definitions of common terms used in anal physiology ⁵ .

Measure	Definition
Anal sensation	Sensation in the anal canal reflecting the somatic sensory component of the pudendal nerve
Cough pressure	Pressure increment above resting pressure after a cough
High-pressure zone	Length of the anal canal with resting pressures ≥30% higher than rectal pressure
Maximum resting pressure	Highest resting pressure recorded
Maximum tolerated volume	Volume at which the patient experiences discomfort and an intense desire to defecate
Maximum voluntary pressure	Highest pressure recorded above the baseline (0) at any level of the anal canal during maximum squeeze effort by the patient
Mean resting pressure	Mean of the resting pressures recorded within the high-pressure zone
Rectal pressure	Pressure generated by the rectum with rest, squeeze, and push
Resting pressure	Pressure in the high-pressure zone at rest after a period of stabilization
Sensory threshold	Minimum rectal volume perceived by the patient
Sphincter endurance	Length of time that the patient can maintain a squeeze pressure above the resting pressure
Squeeze pressure	Pressure increment above resting pressure after voluntary squeeze contraction
Urge sensation	Volume associated with the initial urge to defecate

An ARM study requires four main equipment consisting of a probe, pressure recording device, device for displaying the recordings (e.g., monitor or printer), and a device for both data analysis and storage (e.g., computer or chart recorder). Probes are either water perfused or solid state, each having its associated advantages and disadvantages. A balloon is typically tied to the end of the probe and used for assessing rectal pressures and sensation. ⁶ Regardless of which type of probe is used, careful calibration with the recorder is required to ensure accurate output.

In conventional manometry, anal canal pressures are recorded from single points along a catheter. The catheter is typically pulled out slowly, measuring pressures at each 1-cm interval ( Fig. 1 ). ^{2 7} With the advent of high-resolution manometry, however, simultaneous longitudinal pressure measurements from the rectum, anal canal and atmosphere can be obtained, with minimal effect from catheter displacement ( Fig. 2 ). ^{6 8 9}

Fig. 1.

Example of an anorectal manometry probe showing location of sensors ⁷ (Copyright John Wiley & Sons Licensed Content Publisher. All rights reserved. Reproduced by permission).

Fig. 2.

Series of high-resolution and conventional manometry tracings of attempted defecation in healthy individuals (top panel) and in patients exhibiting the four different types of dyssynergic defecation ¹¹ (Copyright Journal of Neurogastroenterology and Motility. All rights reserved. Reproduced by Permission).

An enema preparation is optional but when used, should clearly be documented along with other medications the patient is on that could affect anorectal function. The study is usually performed with the patient in the left lateral decubitus position. There are some data to suggest, however, that patient positioning can influence the study results, with higher pressures seen in seated or squatting positions which simulate more natural human positioning during defecation. ⁴ Anal canal pressures have also been found to vary by sex and age with higher pressures, in general, seen in men and younger populations. ¹⁰

Prior to probe insertion, it is important to perform a digital rectal exam to evaluate for any anorectal or pelvic floor findings that may explain the patient's symptoms or prevent safe intubation of the anal canal. This is also a good time to determine if the patient understands the basic instructions needed during the test such as “squeeze.” The probe is inserted and after a baseline anal pressure is obtained, the patient is asked to voluntarily “squeeze” thereby tightening the external anal sphincters. This is then usually followed by a “rest” then “push” command. In some ARM protocols, a “cough” is also included between the “squeeze” and “push” phases to document the cough pressure. ³

Dyssynergic defecation occurs when a patient is unable to coordinate their abdominal and pelvic floor muscles to successfully evacuate stool ¹¹ ( Fig. 2 ). For normal defecation to occur, there should be an increase in rectal pressure with simultaneous relaxation of the anal sphincter. Patients with type 1 dyssynergia are able to increase the rectal pressure; however, there is a paradoxical increase in anal sphincter contraction. In type 2 dyssynergia, the patient is unable to increase rectal pressure and also shows signs of paradoxical anal contraction. In type 3, patients appropriately increase rectal pressure but either have an absent or decreased degree of relaxation of the anal sphincters. When a patient is unable to increase rectal pressure and relaxation of the anal sphincters is also absent or decreased, this is referred to as type 4 dyssynergia. ¹¹

The final part of the study involves gradually distending the rectal balloon with fluid. This allows assessment of rectal sensation including the sensory threshold and what volume elicits an urge to defecate. It also helps evaluate for the presence of the RAIR, which when absent should raise suspicion for several disorders such as Hirschsprung's disease or a megarectum. ¹²

Defecography

Evaluation of the pelvic floor during rest, squeeze, and defecation is important for accurately diagnosing pelvic floor disorders and choosing appropriate interventions. Many disorders can be missed on physical examination or static imaging. Defecography offers dynamic evaluation of both the pelvic floor structures and function, and is important for detecting disorders such as obstructive defecation, fecal incontinence, and pelvic organ prolapse. ^{13 14} It is important to obtain a complete history including any comorbidities or medications that affect bowel motility and prior abdominal or pelvic surgeries.

Fluoroscopic Defecography

Fluoroscopic defecography (FD) is a simple test that evaluates the anatomic structure and function of the anorectum and pelvic floor with fluoroscopic imaging. ^{14 15} It is also referred to as barium defecography, cinedefecography, or fluoroscopic evacuation proctography. FD is preferred by many physicians since it is performed in a more natural defecation position with the patient sitting on a commode.

Although not necessary, some centers have patients perform an enema prior to starting the test to clear the rectum of any stool that might affect interpretation of results. ¹³ If opacification of the small bowel is desired, patients are asked to remain on clear liquids for 24 hours prior to the study and complete a bowel regimen consisting of a laxative or cathartic agent. Approximately 350 mL of thin barium is drank an hour before the study. The patient is then placed in the left lateral decubitus or lithotomy position. In females, the vagina is filled with up to 60 mL of thick barium paste. ^{13 14} The presence of vaginal contrast allows for assessment of rectovaginal septum defects or weakness during the study. The rectum is subsequently filled with 250 to 300 mL of barium or a similar contrast suspension. The barium can be mixed with potato starch or fiber supplements such as psyllium to provide a thicker consistency that better resembles fecal material. The test table is then tilted upright and the patient lowered down onto a radiolucent commode. A scout image is obtained first, followed by multiple fluoroscopic images of the patient resting, squeezing, and evacuating rectal contents ( Fig. 3 ). The examiner usually will ask the patient how closely the defecatory process mirrors what occurs at home. If positional changes or maneuvers are performed at home to assist with complete rectal evacuation, additional images should be obtained with the patient doing so. ^{14 16}

Fig. 3.

Fluoroscopic defecography in a healthy patient at rest ( A ), squeeze ( B ) with arrow indicating impression created by the puborectal sling, ( C ) strain against closed sphincters, and ( D ) evacuation. Note changes in the anorectal angle during each study phase as indicated by the arrow ¹⁶ (Copyright Journal of Neurogastroenterology and Motility. All rights reserved. Reproduced by Permission).

Magnetic Resonance Defecography

This modality is increasingly being used due to its multiplanar imaging capability, intrinsic soft-tissue contrast, and the absence of ionizing radiation. ¹⁷ Proponents for it argue that it allows for direct visualization of the pelvic organs and associated support structures while also providing more precise evaluation of anterior and middle compartment abnormalities typically missed on other exams. ¹⁸ It can be performed with the patient supine in a closed magnet system or sitting in an open one. The sitting upright position again allows for a more natural process of defecation, enabling evaluation of the effect of gravity on pelvic floor function. However, several studies have shown that there is no difference in the magnetic resonance defecography detection of clinically significant abnormalities in either positions. ^{17 19}

Instructions are reviewed in detail with patients prior to initiating the examination. Ultrasound gel or potato starch mixed with gadolinium-based contrast is inserted into the rectum with patient in the left lateral position. ^{18 20} Vaginal gel is optional and bladder contrast is usually not required. The patient is then placed supine with knees slightly bent. Static images of the pelvic floor anatomy are obtained first, allowing for evaluation of the anal sphincters, endopelvic fascial defects, and evidence of previous surgeries. ¹⁸ This is followed by dynamic imaging during which the patient is asked to strain against a closed sphincter, squeeze, and then push the gel out. At least two to three attempts at each of these stages is required to increase accuracy of the results. If the patient is unable to evacuate all the gel, they are asked to try in the bathroom and then return for a postevacuation valsalva image, looking for pelvic floor hernias that may have been difficult to detect while the rectum was still distended. ¹⁸

Pudendal Nerve Terminal Motor Latency Testing

Pudendal nerve terminal motor latency (PNTML) testing evaluates speed of conduction of the pudendal nerve by measuring the time from nerve stimulation to motor response. The electrode is positioned on the examining finger and stimulation applied at the level of the ischial spines until the nerve is identified. The receiving electrode located 4 cm away measures the motor response and the latency time is recorded for each side. Normal PNTML is 2.0 ± 0.2 ms. ²¹

Electromyography

Electromyography (EMG) can finely map the electrical activity of the external anal sphincters. ²² Needle EMG was the gold standard for evaluation of anal sphincter defects until endoanal ultrasound was found to correlate highly with EMG ²³ and demonstrate improved patient tolerance. Needle EMG is challenging in functional evaluation due to pain, but surface electrodes, widely used in physical therapy, can be used to identify concomitant dyssynergic defecation.

Ultrasound

Transperineal ultrasound can be used in a dynamic fashion to perform defecography without exposure to ionizing radiation or need for magnetic resonance imaging equipment. ²⁴ While this test is attractive compared with the radiation exposure of standard defecography or the supine position of MRD, this technology has not been widely adopted. Alternatively, a two- or three-dimensional endoanal ultrasound can identify sphincter defects in patients suffering incontinence in conjunction with rectal prolapse, which can be put into clinical context using functional status and the American Society of Cataract and Refractive Surgery (ASCRS) clinical practice guidelines for fecal incontinence. ²⁵ In general, the structural findings of ultrasound correlate well to the functional findings of EMG, but ultrasound can be challenging in areas of heavy scarring and EMG may be superior in this context.

Selection of Tests in Rectal Prolapse

In all conditions, diagnostic testing should provide meaningful information which has the potential to alter clinical decision-making on the part of either the provider or the patient. Particularly in rectal prolapse, in which all tests are physically invasive and potentially psychologically traumatizing, it is critical to have a rationale algorithm to evaluate patients. Of all the tests reviewed above, the patient's detailed history and defecography most frequently meet that criterion.

Eliciting a thorough history of constipation or incontinence, regardless of testing results may alter operative steps and planning. For instance, addition of sigmoid resection to abdominal rectopexy decreases constipation postoperatively compared with rectopexy alone, ^{26 27} but is typically avoided in incontinent patients. Conversely, division of the lateral stalks may increase constipation ²⁸ and is therefore advocated in incontinent, nonconstipated patients undergoing transabdominal repair. Perineal operations are frequently chosen based on patient fitness and preference rather than bowel function; however, levatorplasty is an option that can be added or omitted in this approach. Levatorplasty has been proposed to improve continence, but there is not a strong evidence base for this practice, although it does appear to reduce recurrence in comparison to perineal rectosigmoidectomy alone. ²⁹ It is the opinion of these authors that formal testing is not as critical as thorough history-taking when making these surgical/technical decisions.

Defecography is useful in confirming the diagnosis of rectal prolapse if it is unclear from physical exam findings. Additionally, the presence of other types of pelvic organ prolapse, demonstrated on defecography may trigger consultation to a urogynecologist and alter the operative approach. There is little prospective literature on this topic but defecography does appear to alter clinical decision-making and surgical approach in a significant minority of patients, between 28 and 41%. ^{30 31} Therefore, we recommend careful history and physical exam to assess for urinary and genital prolapse and appropriate referral for urogynecology evaluation and defecography based on symptoms and exam. Correction of both posterior and middle compartment defects may be performed at the same operation. Fluoroscopic and MRD are both well-established techniques. MRD has advantages including patient privacy and lack of exposure to ionizing radiation. Fluoroscopy has the advantage of more natural position and higher detection rate of multiple pelvic floor anomalies. One reason for improved detection may be difficulty in replicating behavior in the supine position. Surgeons should be attentive to patient privacy and radiation exposure, balanced against the chance of lower detection rate of several pelvic floor abnormalities on MRD. ³²

Manometry rarely alters surgical decision-making and its ability to predict functional outcomes is mixed, likely secondary to the multifactorial etiology of fecal incontinence. One study found patients with a maximum squeeze pressure of > 60 mm Hg had improved postoperative continence, but there was little correlation between manometry and severity of incontinence was not associated with manometry. ³³ Because continence changes and manometric findings typically improve after prolapse repair, ³⁴ it is reasonable to repair the prolapse and then assess the function. Manometry may therefore be useful when there is contradictory data regarding the patient's pelvic floor function or in the evaluation of postoperative defecatory problems.

Abnormal electrophysiology evaluation is common in patients with rectal prolapse whether as a causative factor or as a consequence of repetitive trauma to the pelvic floor. One study documented abnormal electrophysiologic evaluation in 72% of patients with either external or internal rectal prolapse. ³⁵ Delayed PNTML is associated with postoperative incontinence in one study, ³⁶ but multiple studies have demonstrated the inability of PNTML to predict functional outcomes following either abdominal ³⁵ or perineal ³⁷ prolapse repair. EMG and PNTML have little impact on surgical decision-making or patient counseling in the setting of full-thickness rectal prolapse. These tests are not a standard component of the preoperative evaluation of rectal prolapse, but may be useful in select situations when there is conflicting data on functional status or evaluation of poor postoperative outcome.

Finally, although in experienced centers transperineal ultrasonography may be used to interrogate the pelvic floor, endoanal ultrasound identification of sphincter defects is unlikely to change operative management of prolapse. In general, given the possible improvement of continence following rectal prolapse repair, the prolapse should be repaired first, incontinence symptoms reevaluated, and addressed as per the ASCRS clinical practice guidelines for evaluation and treatment of fecal incontinence. ²⁵ Therefore, endoanal ultrasound is not a standard preoperative test in rectal prolapse.

Summary

Careful history-taking and physical exam performance are necessary to provide functional context to the typically obvious clinical diagnosis of full-thickness rectal prolapse. Incontinence or constipation may alter surgical technique used for operative repair. When symptoms or physical exam suggest multiple compartment prolapse, then defecography can help in guiding multidisciplinary involvement in patient care, surgical planning and decision-making. Other testing, while potentially useful in select cases, is not recommended in the standard preoperative evaluation of full-thickness rectal prolapse.