Radiological investigation

Radiologists analyze images produced by various techniques to identify any anomalies, including obstruction (blockages or narrowing in the gastrointestinal tract), structural abnormalities (abnormalities in the colon's shape, size, or position), and pelvic floor dysfunction (dyssynergic defecation).

The colonic transit study is the first medical procedure to evaluate fecal material's movement and transit time through the colon. Typically, the patient ingests 24 radiopaque markers and undergoes abdominal radiographs on days 1, 3, and 5 after the marker ingestion. In the case of normal subjects, 80% will expel 80% of the markers by day 3. An abnormal test, indicating colonic inertia, will reveal the presence of 20 or more markers scattered throughout the colon on day 3 or 5 [1]. The distribution and location of these markers can help determine if the patient has slow-transit constipation or any disorders affecting the outflow pathway of the intestinal tract, as shown in figure 1.

Slow-transit constipation

After identifying slow-transit constipation, it's essential to determine the specific type of disorder. This may include increased colorectal caliber, decreased colorectal caliber, elongation, or redundancy of the colon. Several radiological diagnostic methods are available for abdominal imaging, including plain X-rays, barium enema, abdominal CT scans, and CT colonography with 3D reformation.

A) Chagas disease

Chagas disease, which is caused by the Trypanosoma cruzi protozoan parasite, can lead to the development of megacolon. This disease is endemic in tropical countries in South America, especially in rural areas of Brazil.

 This condition is characterized by the dilation and dysfunction of the colon, as shown in figure 2. Chronic constipation occurs due to changes in the structures of the colonic wall, which disrupt normal peristalsis. Imaging modalities help the radiologist identify complications like toxic megacolon, volvulus, perforation, and obstruction. In general, we can state that a transverse colon diameter greater than 5,0 cm, within an adequate epidemiological context, is consistent with the hypothesis of chagasic megacolon. When this cutoff point is raised to 9,0 cm, the positive predictive value for the diagnosis of chagasic megacolon increases considerably [4].

B) Redundant sigmoid

Excessive loops or redundancy in the sigmoid colon can cause chronic constipation by impeding the smooth flow of stool. This anatomical variation may lead to dilation of the colon caliber, as shown in figure 3.  Although there are no definitive criteria to determine when the sigmoid colon is redundant, qualitative analysis is based on a tortuous and distended configuration, which may also include a higher or anterior location of the segment in question [5].

C) Tumors

Colonic tumors, whether they are benign or malignant, can cause a reduction in the diameter of the colon, as shown in figure 4. This constriction can lead to the obstruction of stool passage, resulting in chronic constipation. Through the interpretation of imaging tests such as CT, MRI, and CT colonography, the radiologist visualizes the primary tumor, identifies metastases, and evaluates the invasion of adjacent structures.

D) Dolichocolon

Dolichocolon, characterized by an abnormally elongated colon, can disrupt the coordinated movement of stool through the colon, as shown in figure 5. The length of the colon ranged from 1,25 to 2,00 meters [5].  A sigmoid loop rising over the line between the iliac crests, or transverse colon below the same line and extra loops at the flexures had been established as the criteria for the diagnosis of dolichocolon. Colon transit time increases significantly with a raised number of redundancies, which increases abdominal pain, bloating, and infrequent defecation.

Outflow pathway disorders

There are two main causes of pelvic floor disorders: congenital and acquired. Congenital causes may include genetic factors and developmental abnormalities, which can lead to structural or functional. Acquired causes are more frequent particularly in women, and may be due to factors such as vaginal childbirth, aging, intense physical exertion, pelvic surgeries, and obesity.

 These factors can weaken or damage, resulting in disorders such as prolapse and incontinence.

Pelvic floor assessment

The most important imaging test for studying the pelvic floor is defecography (by x-ray or MRI). The pelvic floor's anatomy can be divided into three parts [5], as shown in figure 6.

The pelvic floor is covered by the endopelvic fascia, which is the uppermost layer that provides support to the pelvic organs and levator ani muscles, as shown in figure 7.

Imaging examinations can detect alterations using measurements like the pubococcygeal line (PCL), during rest and defecation, as shown in figure 8.

Another parameter is the H-Line (the anteroposterior diameter of the levator hiatus), and the M-Line (the longitudinal extent of the anal levator), which also are important [6]. The measures that are being referred to are illustrated in Figure 9. Figure 10 shows that dynamic assessment of the anorectal angle provides information on pelvic floor dysfunction.

Defecography by X-ray is a diagnostic imaging test that involves introducing a radiopaque contrast medium into the rectum. Patients are given specific instructions to simulate various maneuvers, which aid in assessing muscle coordination and strength. The imaging method has diagnosed various pathologies, and examples of some of these are demonstrated in figures 11 and 12.

MR-defecography can be performed using either 1.5T or 3T equipment. During the procedure, the patient lies in the supine position with the knees elevated. No oral or intravenous contrast and spasmolytic agents are required. A rectal cleansing enema before the exam is helpful, and then the rectum should be filled with 240 ml of rectal gel. Vaginal filling with 5 ml of ultrasound gel is also helpful, as is a moderately full bladder.

Pelvic floor disorders refer to a wide range of conditions that affect the muscles, ligaments, and connective tissues supporting the pelvic organs, primarily the bladder, rectum, and uterus [8]. Several factors contribute to chronic constipation:

A) Anismus or Outlet Obstruction: Also known as pelvic floor dyssynergia, occurs when there is difficulty relaxing the pelvic floor muscles during defecation. An example that demonstrates this issue is presented in figure 13.

B) Pelvic Floor Muscle Weakness or Hypertonicity: Weakness may lead to inadequate support for the rectum, while hypertonicity can cause excessive tightening. Examples of this condition are in figures 14 and 15.

C) Impaired Rectal Sensation and Coordination (intra-anal/intra-rectal intussusception): Dysfunction in the pelvic floor muscles can result in impaired rectal sensation and coordination. To clarify, an example that demonstrates this particular problem can be located in figure 16.

D) Rectocele and Enterocele: Pelvic floor disorders often lead to structural abnormalities such as rectocele (protrusion of the rectum, anterior or posterior) and enterocele (descent of the bowel). Figures 17 to 22 illustrate several examples.

Imaging diagnosis workflow

The interpretation of imaging methods to help detect potential causes of chronic constipation in adults is challenging and requires a systematic approach, as shown in figure 23.