Colonic motility disorders

General findings and transit assessment

The pathological process often manifests as a focal abnormal contraction of the bowel wall, forming a narrowed, funnel-shaped transition zone. Due to impaired passage, the normal proximal bowel segment undergoes compensatory dilatation.

The primary clinical manifestation of delayed colonic transit is constipation. To objectify it, a radiopaque marker study is used:

1. The patient ingests 20 different geometric markers on the 1st, 2nd, and 3rd days of the study.
2. A plain abdominal radiograph is performed on the 5th day.

Pathology criteria (transit delay):

• Retention of more than 4 markers ingested on the 1st day.
• Retention of more than 5 markers ingested on the 2nd day.
• Retention of more than 12 markers ingested on the 3rd day.

Obstructed defecation syndrome

Obstructed defecation is a component of constipation. Evacuation proctography (using barium or MRI) is used to visualize this process. Delayed or incomplete evacuation is considered pathological if less than 66% of the ampullary contents are expelled in more than 30 seconds.

Main causes of obstructed evacuation:

• Anismus (anismus): the functional inability to relax the striated muscles of the pelvic floor during an attempted defecation.
• Rectocele: an anterior protrusion of the rectal wall, particularly common in women. It is considered functionally significant if contrast remains "trapped" inside the rectocele at the end of evacuation while the rectum itself is already empty. Clinically, this condition requires digital assistance (perineal digitation or per vaginam). On sagittal TrueFISP MR defecograms, such a large protrusion is visualized extremely clearly.
• Rectal prolapse: the process begins with intra-anal intussusception (telescoping of the distal rectal wall into the anal canal), which is a typical finding in solitary rectal ulcer syndrome. If the intussusceptum protrudes outward beyond the anal canal, it is diagnosed as external prolapse.

Incontinence and sphincter injuries

Incontinence (incontinence) is a complex symptom that depends on impaired relationships between the colon and the structures of the anorectal zone.

The choice of diagnostic imaging method depends directly on the suspected pathological substrate:

• Endoanal ultrasound is the method of choice for visualizing structural sphincter damage (e.g., identifying an old scar from obstetric trauma affecting the external anal sphincter).
• MRI is best suited for detecting thinning or diffuse atrophy of the striated pelvic floor muscles.

Anal fistula (Anorectal fistula)

Anal fistulae develop secondarily to cryptoglandular infection of the anal glands. During pathogenesis, the rupture of an abscess forms a tract through part of the sphincter to the perianal skin. Discharges from the primary focus to the outside complete the formation of a full fistulous tract connecting the internal opening in the anal canal to the external environment.

To describe fistulae, the Parks classification (Parks classification) is used, based on their relationship to the anal sphincter muscles:

1. Trans-sphincteric (trans-sphincteric)
2. Intersphincteric (intersphincteric)
3. Suprasphincteric (suprasphincteric)
4. Extrasphincteric (extrasphincteric)

MRI is the imaging method of choice for fistulae (although ultrasound also has its role).

MRI semiotics: on T2-weighted fat-suppressed images (e.g., STIR), fistulous tracts are identified as zones of hyperintense (high) signal. They stand out brightly against the low (dark) signal of the surrounding adipose tissue and the sphincter muscle complex. MRI is critically important for detecting clinically "invisible" complications, such as occult abscesses and supralevator collections, which are extremely difficult to diagnose on routine examination.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Technique and interpretation of TrueFISP MR defecography
• Solitary rectal ulcer syndrome and its association with intra-anal intussusception
• The role of endoanal ultrasound in assessing obstetric trauma to the external sphincter
• Differential diagnosis of anal fistula types according to the Parks classification
• MRI diagnosis of supralevator collections and secondary abscesses

Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

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