Does conventional defecography has a role to play in evaluation of evacuatory disorders in Indian population?

Barium studies are one of the best investigations for evaluating submucosal and extrinsic mass lesions. However, barium studies bring less money, are operator dependent and one of the more difficult investigations for radiologists to master. Economic factors have acted as powerful disincentives for performing gastrointestinal (GI) fluoroscopy in most radiology practices. In this pictorial essay, we discuss the role of conventional defecography in evaluating evacuatory disorders in the Indian population.

Introduction

The exact frequency of constipation in Indian population is unknown.[1] Most affected are women. Constipated patients with functional anorectal abnormalities complain of fecal evacuation difficulties in terms of incomplete evacuation, excessive straining, and need for manually assisted evacuation. The first step in management of constipation is to exclude organic and anatomic causes. Only the patients in whom an obstructive and/or malignant lesion such as colorectal carcinoma as well as slow colonic transit has been ruled out should undergo evacuation imaging to assess for functional defecatory disorders.[2]

Defecography, Magnetic resonance defecography (MRD), the balloon expulsion test, anorectal ultrasound, anorectal manometry, defecometry, sphincter electromyography, and pudendal nerve terminal motor latency study may be used to diagnose fecal evacuation disorder. Defecography is the dynamic study of expulsion of radio-opaque material from the rectum, in order to assess changing anatomical relationships of the pelvic floor and associated organs during defecation.[3] Defecography has a substantial diagnostic and therapeutic effect, allows evaluation in supine position, and is of considerable benefit to referring clinicians.[45678] Defecography may provide useful information in incompetent patients with outlet obstruction constipation symptoms, but has little value in incontinent patients without such symptoms.[9] The radiation dose for defecography is approximately 2-3 mSv.[10]

Relevant Anatomy

The pelvic floor in women is divided into three compartments: The anterior compartment (bladder and urethra), middle compartment (vagina and uterus), and posterior or anorectal compartment.[11] Complete survey of the entire pelvis is necessary for optimal patient management because abnormalities of the three pelvic compartments are frequently associated.[12]

The puborectalis muscle forms a sling around the rectum. A tear in the anterior portion of the endopelvic fascia (pubocervical fascia) results in bladder descent or a cystocele, while a tear in the posterior aspect (rectovaginal fascia) results in an anterior rectocele or enterocele.

The anorectum plays an important role in regulation of defecation and in the maintenance of continence.[1314] Normal defecation involves the coordinated relaxation of the internal anal sphincter, puborectalis, and external anal sphincter muscles, together with increased intra-abdominal pressure and colonic motor activity that propels stools toward the rectum.

Technique

Patient is instructed to come after overnight fasting. Patient cooperation is of outmost importance and the entire procedure is explained to the patient during preparatory phase. Informed consent is taken and privacy of patient is maintained. The patient is instructed to drink 400 ml of thin barium 1 h prior to the actual study. Complete bowl cleansing is usually not necessary for preparation. Low lighting helps in relieving patient's anxiety.

Covering the table with a plastic sheet helps overcome the patient's embarrassment and allows easier cleaning after the examination. The patient is positioned in the left lateral decubitus position. A total of approximately 100 ml of semisolid barium sulfate paste is injected into the rectum via two 50 ml syringes with short plastic tubing attached to the syringes [Figure 1]. The anal verge is marked using a small skin marker sticker. A specially constructed radiolucent commode is positioned and fixed to the table. The table is repositioned into the upright vertical position, with the patient seated on the commode.

Figure 1

Image showing materials and things required for defecography – barium sulfate (black arrow), rectal insufflation syringe and tube (black curved arrow), commode on foot end of table (black arrowhead)

The patient is instructed to perform several maneuvers and these are marked on the radiological images: Rest, squeeze, strain, defecate, and post evacuation. The patient is instructed to evacuate the barium paste as completely as possible. A digital fluoroscopy cine clip is obtained of the entire procedure.

The normal radiological appearances during defecation may be summarized as: Rapid initiation, pelvic floor descent, loss of puborectalis impression, increase in anorectal angle (ARA), shortening of the anal canal, and anal canal opening widely.

During the standard defecogram, the rectum and small bowel loops are usually opacified.[15] However, opacification of the bladder or vagina is not routinely performed. Low et al.[16] concluded that vaginal opacification during defecography may aid in diagnosis of pelvic floor pathology.

Relevant terminology, lines, and angles for interpretation of defecatory disorders[1718]

Anorectal junction is defined as the point of taper of the distal part of the rectum as it meets the anal canal

The ARA is defined as the angle between the posterior wall of the distal part of the rectum and the central axis of the anal canal [Figure 2]. ARA change in healthy volunteers between rest and squeezing and between rest and defecation is usually 15-20%.[19] ARA change of 10% or less between pelvic positions is abnormal

Figure 2

Note the change of ano-rectal angle (ARA) between squeezing and straining position (black arrow)

Pubococcygeal line (PCL) should be drawn from the inferior border of the pubic symphysis to the last coccygeal joint. PCL represents the level of the pelvic floor and is the landmark for measuring organ prolapsed. The perpendicular distance from PCL to the bladder neck, vaginal vault, and anorectal junction, respectively, should be measured on images obtained when the patient is at rest and during maximal pelvic strain

In descending perineal syndrome, the pelvic muscles lose tone, resulting in excessive descent of the entire pelvic floor at rest or during evacuation. To show pathologic pelvic floor descent, the measurements are made on the images, which show maximal organ descent, usually during maximal straining or evacuation [Figures 3-5]

Figure 3

Note severe rectal descent (62 mm) (white arrow) in this 54-year-old female with complete emptying on post-evacuation film

Figure 5

Note the presence of sigmoid diverticulae (black arrow) in this 51-year-old male

Enterocoele is defined as herniation of pelvic peritoneal sac into the rectogenital space, the rectovaginal septum in women, passing below the proximal one-third of the vagina. Since a filled rectum does not allow sufficient space for small bowel to descend into the pelvis, enterocele usually occurs at the end of evacuation as a consequence of increased intra-abdominal pressure. The pelvic peritoneal sac may contain fat, called peritoneocele, small bowel, or sigmoid colon

Rectocele is defined as an outward buldge of the rectal wall. Rectoceles are measured as the depth of wall protrusion beyond the expected margin of the normal anorectal wall [Figures 6 and 7]. They usually involve the anterior wall but may rarely occur posteriorly. They are common findings but become clinically relevant when symptoms occur, as they are responsible for obstructed or incomplete evacuation, requiring vaginal or perineal digitations to empty the rectum

Figure 6

Image showing measurement of rectocele as perpendicular distance from anterior anal plane (black curved arrow)

Figure 7

Note moderate rectal descent (34 mm) and severe anterior rectocele (42 mm) (black arrow) in this 45-year-old female. During defecation, rectocele became more prominent with incomplete emptying accompanied by intra-rectal intussusception (white arrow)

Cystocele is diagnosed when bladder base descends more than 1 cm below PCL

Vaginal or cervical prolapse is defined as descent of the vaginal vault or cervix below PCL

Intussusception is defined as circular invagination of the proximal rectal wall involving both the mucosa and muscular layer during defecation [Figure 8]. This causes a mechanical obstruction to the passage of stool. Extra-anal invagination is termed as rectal prolapse [Figure 9]

Figure 8

Note moderate rectal descent (36 mm) and intra-rectal intussusceptions (black arrow) in this 48-year-old male

Figure 9

Note severe rectal descent along with rectal prolapse (white curved arrow) in this 47-year-old female

Dyskinesia is defined as muscular contraction of the pelvic floor muscles, usually the puborectalis, during defecation. The puborectalis muscle is frequently hypertrophic and makes a prominent impression on the rectal wall [Figure 10]

Figure 10

Note persistent puborectalis impression (black arrow) in this 46-year-old female. Also note the presence of moderate rectocele (24 mm)

Anismus is defined as failure to evacuate more than two-third of the barium paste in less than 30 seconds

Incontinence is defined as spillage of barium paste from anal canal, prior to initiation of defecation. Patients can present with either fecal leakage they are unaware of, suggesting an internal sphincter abnormality, or urge incontinence, indicating external sphincter damage.

There is weakness of pelvic floor with sagging of sigmoid colon (black arrow) in this 48-year-old male

Table 1 shows the three-point grading system followed for measuring cystocele, vaginal vault descent, rectocele, rectal descent, and enterocele.

Table 1

The three-point grading system followed for measuring cystocele, vaginal vault descent, enterocele, rectal descent, and rectocele

Defecography using Magnetic Resonance Imaging (also referred to as MRD) is a special method which is suitable for patients with multicompartment involvement and for those who have undergone previous surgical repairs. Hetzer et al.[20] concluded that MRD findings led to change in surgical approach in 67% of patients who underwent surgery for fecal incontinence. Its main advantage is direct visualization of pelvic structure including the bladder, vagina, cervix and rectum. In addition, MRD allows dynamic assessment of the pelvic floor. However, main drawback is that MRI is an expensive imaging modality with limited availability. Thus, conventional defecography despite being an investigation with radiation hazards is being used extensively in many places in India for evaluation of fecal evacuatory disorders. Its main advantages are cost-effectiveness and excellent resolution for submucosal and extrinsic pathology.

So, we conclude that conventional defecography has an important role to play in the Indian population, especially with myriad of findings which can be detected like rectocele, rectal intussusceptions, rectal descent, enterocele, and rarely other findings like sigmoid diverticulae. However, the results of any dynamic pelvic examination, need to be considered in the light of the patient's history and other tests, so that appropriate therapy is administered.