Fecal Incontinence Workup

Updated: Mar 05, 2021
  • Author: Tanaz R Ferzandi, MD, MA; Chief Editor: Kris Strohbehn, MD  more...
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Laboratory Studies

Surgical repair for fecal incontinence is usually an elective procedure. Evaluation and treatment of anemia, infection, or other abnormalities indicated by findings from a complete blood cell count should be initiated prior to surgical repair.

A pregnancy test should be performed at or near the time of surgery on every female patient who may be pregnant.


Imaging Studies


The standard diagnostic imaging study for the anal sphincters is transanal or endoanal ultrasonography. Much of the early work on endoanal ultrasonography was performed at St. Marks Hospital in the United Kingdom by Law, Burnett, and Sultan et al. Multiple reports have qualified ultrasonography as the criterion standard in the diagnostic evaluation of the anal sphincters. [38, 39, 40, 41]

Ultrasonography allows the provider to perform a real-time, 360-degree evaluation of both the internal and external anal sphincters. Sensitivity and specificity of ultrasonography findings are 98-100% for the external anal sphincter and 95.5% for the internal anal sphincter. Burnett et al have shown that 90% of women presenting with anal incontinence and a history of a vaginal delivery had ultrasonographic evidence of damage to the external anal sphincter, internal anal sphincter, or both. [42]

Endoanal ultrasonography is performed in the left lateral or lithotomy position. The lithotomy position in females allows for the evaluation of other pelvic support defects.

Traditionally, 3 regions of the rectum are evaluated ultrasonographically. The areas of focus are distal, where only the external anal sphincter is observed (first image below); at the level where both the internal and external anal sphincters can be observed in the mid anal canal (second image below); and proximal at the level of the levators (pubococcygeus) (third image below).

Fecal incontinence. External anal sphincter showin Fecal incontinence. External anal sphincter showing normal narrowing anteriorly.
Fecal incontinence. Ultrasound of mid anal canal t Fecal incontinence. Ultrasound of mid anal canal taken with the patient in the low lithotomy position showing intact internal and external anal sphincters.
Fecal incontinence. Internal anal sphincter at the Fecal incontinence. Internal anal sphincter at the level of the levators. The levators are demonstrated by the U-shaped echogenic band posteriorly.

Normal thickness for the external anal sphincter is consistently described as 8.3 mm (95% confidence interval [CI], 7.6-9 mm). Mean internal anal sphincter thickness is described as 6.5 mm (95% CI, 5.8-7.2 mm), although reports vary from 1-3 mm to 10 mm based on modality. Inflammatory disorders can increase the thickness of these sphincters. [43]

The external anal sphincter appears as a hyperechoic ring that is circumferential. It is striated muscle, which is echogenic in nature. The internal anal sphincter is composed of smooth muscle and appears as a hypoechoic or sonolucent ring that is medial to the external anal sphincter. It can be viewed from the level of the levators to just inside the anal verge. The puborectalis muscle appears as a hyperechoic U-shaped muscle approximately 4 cm into the anal canal (third image above).

Tjandra and colleagues evaluated patients with ultrasonography of the anal sphincters and EMG. They found that ultrasonography helped identify both internal and external sphincter defects with 100% accuracy compared to EMG findings, with considerably less discomfort. They state that ultrasonography is preferable to EMG in mapping anal sphincter defects, especially for evaluation of the internal anal sphincter. [44, 45]


Diagnostic Procedures

Anal manometry

Anal manometry is used to evaluate both the resting and squeeze pressures of the rectum. It can also be used to evaluate the rectoanal inhibitory reflex, rectal capacity, and rectal compliance.

Normal values for manometry vary among institutions. Currently, no uniformly accepted standard exists for performing manometry, and what is considered typical pressure is also quite variable. Normal resting pressures are 40-70 mm Hg (55-95 cm water) from Wexner and 60 cm water (standard deviation [SD], 20 cm water) from St. Marks Physiology Unit in London. Normal squeeze pressures are 100-180 mm Hg (136-244 cm water) from Wexner and 100 cm water (SD, 30 cm water) from St. Marks Physiology Unit in London.

Mean resting and mean squeeze pressures are lower in women who have had a vaginal delivery, regardless of sphincter disruption. Low manometric pressures are not predictive of anal sphincter defects. Women with known sphincter defects tend to have lower mean resting pressures; however, mean squeeze pressures may be unaffected. Squeeze pressures are not significantly related to the presence of an external anal sphincter defect. Tetzschner et al found decreased pressures in continent and incontinent women after vaginal delivery. Both groups had low pressures compared to controls. [13]

The majority of studies that evaluate fecal incontinence in women use manometry as part of their assessment. The results of these studies are variable, and no patients have forgone surgical repair based on a finding of low manometric pressures.

Several studies are available that demonstrate that manometry results are not able to help predict surgical outcomes for anal sphincter repairs. Rasmussen and colleagues found that patients with incontinence persisting after surgical repair had lower anal maximum squeeze pressures compared to continent patients. In patients who are continent after surgery, no difference in anal pressures existed before and after surgery. Felt-Bersma et al found that manometry is not valuable when comparing an individual patient's pressure to the reference range because of the large variability in the reference range. They suggest that evaluation of an individual's pressure changes preoperatively and postoperatively makes more sense. [46] Several investigators have found improvement in manometry pressures postoperatively.

Pudendal nerve terminal motor latency

PNTML helps evaluate the length of time required for a fixed electrical stimulus to travel along the pudendal nerve from the ischial spine to the anal verge. Findings reflect the myelin function of the peripheral nerve, and the test allows for the evaluation of pelvic floor neuromuscular integrity. The pudendal nerve is stimulated at the ischial spine transanally. The latency period between stimulation of the nerve and evoked response of the muscle is measured. Any damage to the neuromuscular unit results in the prolongation of the latency. Normal latency has been described as 2 milliseconds (SD, 0.2 ms).

Several studies have found that prolongation of PNTML occurs after uncomplicated vaginal delivery. PNTML approaches the reference range at three months postpartum; however, Tetzschner et al found a significant and persistent prolongation of PNTML between incontinent and continent women three months postpartum. [13] In addition, the only predictor for the development of anal incontinence at 2-4 years postpartum in women who had rupture of the anal sphincter was abnormal PNTML.

Ryhammer and colleagues evaluated the long-term effects of vaginal delivery on anorectal function and found that PNTML increased with parity. [19] They found the greatest change in PNTML between the second and third deliveries; however, the range of values within groups was large. In a separate study, Tetzschner et al also found a wide range of values within incontinent and continent groups. The incontinent group values ranged from 1.35-3 milliseconds, and the continent group values ranged from 1.44-2.47 milliseconds. [14]

Many investigators have suggested that PNTML is the most significant predictor of functional outcome of a sphincteroplasty. Gilliland et al found that prolonged latency was correlated with outcome. In their series, only 16% of patients with pudendal latency greater than 2.2 milliseconds subjectively described their results as successful (excellent or good, based on telephone interview). [47] In a study of patients with unilaterally prolonged latencies (2 ms; SD, 0.2 ms), Sangwan et al found that only 1 of 7 patients who underwent sphincteroplasty had improvement in their incontinence score. Six patients had either (1) no improvement in incontinence score but less frequent incontinent episodes or (2) no improvement at all. [48]

The difficulty with interpreting findings in the literature is that no consensus has been reached for agreed-upon standard and nonstandard values. Also, variability exists in how PNTML correlates with other physiologic findings. All of the studies previously mentioned used the St. Marks electrode produced by Dantec.

Fynes et al considered latency to be prolonged if longer than 2.4 milliseconds in duration. [49] While evaluating the neurophysiologic changes in fecal incontinence, Osterberg et al used a latency period of longer than 2.5 milliseconds duration (based on a mean of 2 ms and 2 SD to reduce their false-positive rate) as an abnormal value. [50] In the same study, they found no differences in resting pressures, incremental pressures, or rectal sensibility in patients with unilaterally or bilaterally prolonged PNTML compared to patients with normal PNTML. They question the routine use of PNTML in the investigation of patients with fecal incontinence.

As with anal manometry, prolonged PNTML values have not been used as a reason to deny surgical repair. Chen et al found that in patients with prolonged latencies, surgical repair of sphincter defects resulted in improvement of incontinence scores. [51] Felt-Bersma et al, when evaluating anorectal function and ultrasonographic images after sphincter repair, found no relationship between preoperative neurologic function (based on EMG and PNTML findings) and clinical outcome. Acknowledging the fact that PNTML has contributed greatly to the understanding of anorectal pathophysiology, Felt-Bersma's group suggests that PNTML has no place in the routine preoperative assessment of patients. They go one step further by suggesting that withholding a sphincter repair from a patient with a prolonged PNTML may be unethical. [46]

Although prolonged PNTML indicates pudendal neuropathy, normal latency does not exclude nerve injury because only the fastest remaining conducting fibers are recorded. Also, overlap has been shown to exist in the innervation of the external sphincter.


EMG helps evaluate the electrical activity generated by muscle fibers during voluntary muscle contraction, rest, and Valsalva-type activities. The motor unit includes the anterior horn cell, its axon with axonal branches, the motor end plates, and the muscle fibers supplied. Information on the innervation and functional status of motor unit potentials is obtained. Results can be used to map normal muscle fibers. Several methods are available. Electrodes that are available for use are the surface anal plug, concentric needle electrodes, single-fiber electrodes, and monopolar wire electrodes. Injured or damaged muscle results in a lack of electrical activity or a polyphasic pattern. Incomplete damage may allow for reinnervation from adjacent undamaged nerves or regrowth of damaged axons. The result is that a greater number of muscle fibers are innervated by a single nerve, leading to an increase in the amplitude and a more prolonged motor unit action.

Abnormal findings after EMG evaluation are present in more than 90% of patients with fecal incontinence. In a study of 72 patients with fecal incontinence, Osterberg and colleagues found that fiber density observed with single-fiber electrodes correlated with clinical and manometric variables; PNTML did not. [50]

Although EMG is able to help quantitate denervation, findings do not alter clinical management. Similar to PNTML, Felt-Bersma et al suggest that EMG as a means to locate the sphincter defect has also lost its place in the preoperative assessment of anal sphincter defects. [46] EMG studies can be uncomfortable, especially the single-fiber technique, and they may result in incomplete studies due to patient refusal to continue.


Evacuation proctography (defecography) involves imaging the rectum with contrast material and observation of the process, rate, and completeness of rectal evacuation using fluoroscopic techniques. A variety of contrast materials have been used, including esophageal contrast barium and barium mixed with oatmeal or other viscous materials. Barium paste may also be inserted into the rectum. Images are obtained by lateral fluoroscopy and taken during attempted defecation. Defecography helps to assess qualitatively the function of the anorectum and the adequacy of rectal emptying; static images measure the length of the anal sphincter, the anorectal angle, and perineal descent. Diagnosis of rectoceles, enteroceles, and internal or occult rectal prolapse is possible. The true benefit in evaluation of patients with fecal incontinence is unclear, because most incontinent patients cannot tolerate the procedure. [52]