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1
Intestinal Imaging Centre, Level 4V, St. Mark's Hospital, Northwick Park,
Watford Rd., Harrow, London, HA1 3UJ, United Kingdom.
2
Physiology Unit, St. Mark's Hospital, London, HA1 3UJ, United Kingdom.
Received November 13, 2000;
accepted after revision March 16, 2001.
Address correspondence to S. Halligan.
Abstract
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SUBJECTS AND METHODS. Thirty-one adults with signs of impaired evacuation (defined as the inability to evacuate two thirds of a 120 mL contrast enema within 30 sec) during evacuation proctography underwent subsequent anorectal physiologic testing for anismus. A physiologic diagnosis of anismus was based on a typical clinical history of the condition combined with impaired rectal balloon expulsion or abnormal surface electromyogram.
RESULTS. Twenty-eight (90%) of the 31 patients with impaired proctographic evacuation were found to have anismus at subsequent physiologic testing. Among the 28 were all 10 patients who evacuated no contrast medium and all 11 patients with inadequate pelvic floor descent, giving evacuation proctography a positive predictive value of 90% for the diagnosis of anismus. A prominent puborectal impression was seen in only three subjects during proctography, one of whom subsequently showed no physiologic sign of anismus.
CONCLUSION. Impaired evacuation during evacuation proctography is highly predictive for diagnosis of anismus.
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Traditionally, physicians who have used protography to diagnose anismus have concentrated on a patient's inappropriate puborectalis contraction during rectal evacuation. Because the puborectalis cradles the anorectal junction, it has been suggested that a prominent muscular impression during evacuation, reflected by an acute anorectal angle, is indicative of anismus [6, 7, 9]. However, retrospective studies have suggested that impaired rectal evacuation during evacuation proctography is present in many of these patients and that this impairment may be more reliably predictive of anismus than measurement of puborectal configuration is. In a study of 24 subjects known to have anismus, anorectal angle measurements were compared with functional measurements of the rate and volume of contrast medium expelled to determine which was more specific for diagnosing anismus [10]. The authors found that when using structural measurements, they were unable to reliably differentiate patients with anismus from control subjects. However, impaired evacuation was highly specific: only four (16.7%) patients were able to evacuate two thirds of the enema within 30 sec, in contrast to all 20 control subjects who were able to do so [10].
This retrospective data suggests that proctography of impaired evacuation is highly specific for the diagnosis of anismus, but, to our knowledge, no attempt to validate this assumption has been made in a prospective study of a group of consecutive (and thus randomly chosen) patients. The proportion of patients with impaired evacuation at proctography who do not have anismus, or even constipation, is unknown. Our study aimed to determine the positive predictive value of impaired evacuation during proctographic examination in diagnosing anismus in a group of randomly chosen patients presenting for evacuation proctography.
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Evacuation proctography was performed using a standard technique. One hundred mL of 100% wgt/vol barium suspension (Baritop; Bioglan Laboratories, Hitchin, United Kingdom) was diluted with 200 mL of water and 10 mL of meglumine diatrizoate (Gastrografin; Schering Health Care, Burgess Hill, United Kingdom) was added. This solution was given to the patients orally 1 hr before the examination to opacify the small bowel [11]. Two glycerine suppositories were then administered rectally. The patients were asked to retain the suppositories for 20 min and then to empty their rectums in the toilet. Each patient was then escorted to the fluoroscopy suite.
With the patient in the left lateral position on the fluoroscopy couch, the rectum was filled with 120 mL of barium paste (E-Z-paste; E-Z-Em, Westbury, NY) instilled via two 60-mL bladder syringes. The fluoroscopy couch was then brought upright, a commode specially designed for evacuation proctography was placed on the couch's footstool, and the patient was seated on the commode. The patient's rectum was centered using screening, and a single lateral spot image of the filled rectum at rest was taken using a digital unit (Display Plus or Sireskop 5; Siemens, Bracknell, United Kingdom). The patient was then asked to empty his or her rectum as rapidly and completely as possible during lateral digital spot filming (exposed at a rate of one frame per sec using a reduced-dose program). Filming was intermittent if evacuation was delayed or prolonged, so that the maximum total screening time was always less than 60 sec.
Examinations were reported in the usual clinical practice. The details of any patient in whom evacuation was judged to be impaired (prolonged or incomplete) was noted by the examining radiologist. Impaired evacuation was defined as inability to void two thirds of the contrast enema within 30 sec. Assessment of the percentage of contrast medium voided was based on a subjective assessment of the lateral cross-sectional area of contrast medium remaining in the rectum at 30 sec, rather than on any specialized planimetric technique, so as to best reflect everyday practice. Evacuation time was measured directly from the second counter on the digital fluoroscopy unit and was taken from the time of first opening of the anal canal. A proctographic diagnosis of anismus was made in those patients whose evacuations were judged, using the described criteria, to be impaired. A diagnosis of anismus was not made on any finding other than impaired evacuation, although a prominent puborectal impression was noted, if present. Other proctographic abnormalities present in these patients, if any, were also recorded at the time of examination.
All patients presenting for evacuation proctography subsequently underwent full anorectal physiologic testing on the same day, as is our usual clinical practice. Physiologic testing was performed with the examiner having no knowledge of the proctographic findings. Physiologic testing was preceded by collection of a full clinical history, which included the presenting complaint and a full bowel-habit history. Constipation was defined as difficult or incomplete evacuation and included difficulty with initiating evacuation and the need for digital maneuvers to assist evacuation [12]. Infrequent bowel habit, defined as two or fewer bowel movements per week, was also defined as constipation [12].
With the patient in the left lateral position, a rectal balloon was lubricated, inserted, and inflated with water to a volume of 50 mL. The patient was then asked to expel the balloon without assistance. Evacuation was scored as normal expulsion, difficult expulsion (defined by prolonged and excessive straining), or failure to expel. Difficult expulsion or failure to expel was judged to be suggestive of anismus [4, 5, 13]. Contraction of striated pelvic floor muscle during attempted evacuation was measured using a surface electrode technique (13L20 silver-silver chloride electrodes; Dantec, Skovlunde, Denmark) and was recorded as normal (relaxation), no relaxation, or paradoxical (contraction). Paradoxical contraction or inability to relax were judged to be suggestive of anismus. A definitive physiologic diagnosis of anismus was made if the patient had positive findings in two or more of the following three categories: appropriate clinical history, balloon expulsion, and electromyography. Physiologic results were subsequently obtained in those patients judged to have anismus by evacuation proctography, and a comparison was made with the final physiologic diagnosis to determine the positive predictive value of proctography for diagnosing anismus.
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By definition, all patients had impaired evacuation on proctography. Ten
subjects evacuated no contrast medium whatsoever, and all received a
subsequent physiologic diagnosis of anismus. Ten patients showed either no or
little (<1 cm) pelvic floor descent during attempted evacuation at
proctography, and the pelvic floor ascended in another patient. All of these
11 patients were judged to have anismus at subsequent physiologic examination.
A prominent puborectal impression was seen in only three subjects, one of whom
was judged to be normal at subsequent physiologic examination. A significant
rectocele (defined as 
3 cm deep)
[14] was present in 11 (36%)
of subjects, four of whom retained contrast medium at the end of evacuation.
An enterocele was present in five subjects, one of whom also developed
complete rectal prolapse.
The clinical histories taken before physiologic testing revealed that constipation was the main clinical complaint in 30 (97%) of the 31 patients; a single individual presented primarily because of anal pain. Twenty-seven patients (87%) were unable to expel the rectal balloon or expelled it with difficulty; 24 of these patients also displayed either a paradoxical contraction of or an inability to relax the puborectalis normally during simultaneous surface electromyography. In addition, one of the four patients judged to have normally evacuated the balloon showed a paradoxical contraction during simultaneous electromyography. A final diagnosis of anismus was based on the clinical history, balloon expulsion, and electromyographic findings in 28 (90%) of the 31 patients believed to have anismus on the basis of functional proctographic criteria (Table 1), giving evacuation proctography a positive predictive value of 90% for this diagnosis.
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We have shown that impaired evacuation during proctography is highly specific for the diagnosis of anismus, supporting the assumptions made from retrospective data. We defined impaired evacuation as inability to evacuate two thirds of a 120 mL contrast enema within 30 sec. We derived the 30-sec time period from a previous study of rectal evacuation, which found only 12 of 23 constipated patients able to void a similar enema, a feat achieved by all 25 controls [15]. Furthermore, patients were selected merely by using a simple subjective assessment of the volume of intrarectal contrast remaining at 30 sec, an assessment likely to be subject to less interobserver variation than more complex measurements of anorectal configuration [16]. The high positive predictive value of this simple assessment suggests that complex planimetric image analyses to determine the exact rectal cross-sectional area are unnecessary in day-to-day clinical practice [17, 18]. All patients in whom there was no contrast medium evacuation whatsoever received a subsequent diagnosis of anismus, as did all individuals in whom there was no or insufficient pelvic floor descent. All of these proctographic features are likely to merely reflect a failure of pelvic floor coordination. To assess evacuation rates reliably and to compare findings in patients, the rectum should be empty and the same volume of contrast medium should be administered to each patient, hence our use of rectal suppositories.
At one time, paradoxical puborectalis contraction was deemed necessary for diagnosing anismus, and so anorectal angle measurement coupled with a prominent puborectal impression formed the basis for proctographic diagnosis. However, although the anorectal angle may sometimes reflect puborectal tone, it is a secondary sign, and impaired emptying provides better evidence of evacuation failure. Supporting this position is the finding in our study that one of the three subjects with a prominent puborectal impression had no subsequent physiologic evidence of anismus. More than a decade ago, Turnbull et al. [19] found that only proctographic measurements of the volume voided and the time taken to do so reliably differentiated constipated patients from asymptomatic controls, suggesting that failure of coordination was the cause of constipation rather than abnormal rectal configuration.
It has subsequently become apparent that anismus is a generalized pelvic floor disorder [8], the end result of which is impaired rectal emptying. Undoubtedly, some patients cannot evacuate because of an inability to raise intrarectal pressure, not because they paradoxically contract their puborectalis [20, 21]. Both relaxation of the pelvic floor and adequate intrarectal pressure are needed for normal evacuation, and the failure to accomplish either (or both) is symptomatic of pelvic floor incoordination, which may be a more preferable term than anismus. To use tests such as balloon expulsion to diagnose anismus is to rely solely on the patient's inability to evacuate without defining the paradoxical contraction. It seems sensible not to localize the diagnosis to any one muscle group but to broaden the definition to encompass any form of pelvic floor incoordination that results in impaired rectal evacuation.
Many of the subjects in our study showed apparent abnormalities of rectal configuration; 36% had rectoceles. It would be easy to ascribe symptoms in these patients to their rectoceles and operate accordingly. Indeed, surgeons frequently decide to operate on the basis of structural proctographic findings alone, unaware that underlying anismus is actually the cause of symptoms. However, it is now recognized that chronic straining by a patient because of an underlying functional disorder may precipitate abnormalities of rectal configuration such as rectocele, pelvic floor descent, and intussusception. For example, in a study of 41 patients with constipation ascribed to a rectocele, 29 (71%) were found to have underlying anismus [22]. Surgery to correct a structural abnormality is unlikely to relieve symptoms if the underlying anismus remains untreated: surgery for intussusception fails to ameliorate symptoms if there is preoperative proctographic evidence of impaired evacuation [23, 24] but succeeds if findings show evacuation to be normal [25]. A patient's impaired evacuation during proctography, with or without the presence of structural abnormality, allows the examining radiologist to alert the surgeon to the possibility of underlying anismus, thereby avoiding an operation that is likely to be fruitless. Instead, the patient may be more appropriately directed to biofeedback retraining.
Diagnosis of anismus is difficult, and it has been suggested that the no single test is specific enough to confirm its diagnosis. In a study of 112 constipated patients with anismus, researchers found proctographic evidence of anismus in 42 (37%) of the patients and electromyographic evidence of anismus in 40 (36%), but the results of both tests yielded positive findings in only 28 patients (25%) [7]. This study suggests that proctography can achieve higher specificity if the vigorous functional criteria that we used for diagnosis are applied and structural findings are ignored. Indeed, diagnosis of anismus remains controversial because it affects patients in various ways—causing constipation, incontinence, or no symptoms at all [26, 27]—leading to suggestions that it may be an epiphenomenon rather than a primary cause of constipation. Nevertheless, a clear association between impaired evacuation and successful biofeedback retraining in a sizable proportion of patients suggests that it is a practical diagnosis to make.
If only the rate and completeness of rectal evacuation are necessary to diagnose anismus, then it could reasonably be argued that proctography should be dispensed with altogether and replaced by a simple rectodynamic measurement [15]. However, although this study suggests that such an approach would miss few patients with anismus, it would not detect those constipated patients with structural rectal abnormalities but normal rectal evacuation. The combination and relative contributions of both structural and functional abnormalities enable physicians to use proctography to place constipated patients in appropriately defined treatment groups.
In summary, our study has confirmed that evidence of impaired rectal evacuation during evacuation proctography is highly predictive of anismus.
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