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Anorectal studies

Discuss the tests for FI?

  • Endoscopic evaluation of the rectosigmoid region is appropriate for detecting mucosal disease or neoplasia that may contribute to FI.
  • Several specific tests are available for defining the underlying mechanisms of FI. These tests are often complementary.
  • The most useful tests are anorectal manometry, anal endosonography and pudendal nerve terminal motor latency

Anorectal physiology studies
It includes functional assessment like rectal compliance, anal manometry, rectal distension sensitivity, pudendal nerve terminal motor latency (PNTML), anal EMG and electro sensitivity testing
Anorectal manometry with rectal sensory testing is the preferred method for defining the functional weakness of the external or internal anal sphincter and for detecting abnormal rectal sensation. The resting anal sphincter pressure predominantly represents the internal anal sphincter function and the voluntary squeeze anal pressure predominantly measures the external anal sphincter function. Patients with incontinence have been shown to have low resting and low squeeze sphincter pressures.
Rectal balloon distention with either air or water can be used for the assessment of both the sensory responses and the compliance of the rectal wall. By distending a balloon in the rectum with incremental volumes, it is possible to assess the thresholds for first perception, a first desire or an urgent desire to defecate. A higher threshold for sensory perception suggests impaired rectal sensation.
PNTML- It measures neuromuscular integrity between the terminal portion of the pudendal nerve and the anal sphincter. It can help to distinguish a weak sphincter muscle due to muscle injury from that due to nerve injury. A prolonged nerve latency time suggests pudendal neuropathy. A normal PNTML does not exclude pudendal neuropathy, because the presence of a few intact nerve fibers can give a normal result, whereas an abnormal latency time is more significant. PNTML is particularly helpful in predicting the outcome of surgery. Patients with pudendal neuropathy generally have a poor surgical outcome when compared to those without neuropathy.

However, there are no accepted standards for performing these tests and no ‘normal ranges’ agreed or validated. Digital examination is a poor predictor of manometric findings.
Anorectal manometry helps to perform biofeedback training and is also useful in assessing objective improvement following drug therapy, biofeedback therapy, or surgery.
Endoanal ultrasound- It is most widely available and least expensive test for defining structural defects of the anal sphincter. MRI is an alternative to endoanal ultrasound.

Defaecating proctogram- is useful in patients with suspected rectal prolapse but it is otherwise of limited value. It is used to assess several parameters such as the anorectal angle, pelvic floor descent, length of anal canal, presence of a rectocele, rectal prolapse, or mucosal intussusception. Approximately 150 ml of contrast material is placed into the rectum and the subject is asked to squeeze, cough, or expel the contrast.  The functional significance of identifying morphological defects has been questioned.
Undoubtedly, the aforementioned tests help to define the underlying mechanisms, but there is only limited information regarding their clinical utility and their impact on management.

Discuss investigation of constipation?

  • Defecography- The most relevant observations are (a) the failure of the anorectal angle to open (i.e., become more obtuse) during defecation and (b) the degree of pelvic floor descent during defecation. Decreased descent is a component of impaired pelvic floor relaxation, and, conversely, excessive descent can also be a pathophysiologic mechanism of constipation.
  • Anorectal manometry- The procedure has greatest value in
    • Excluding Hirschsprung’s disease by the presence of a normal recto anal inhibitory reflex i.e. absence of normal relaxation of the internal sphincter and the reduction in the intraluminal pressure in the anal canal when the rectum is distended with a balloon.
    • Providing supportive data for clinical or physiologic suggestions of pelvic floor dysfunction. For example, high basal sphincter pressures with relatively little voluntary augmentation, suggest spastic pelvic floor/sphincter dysfunction

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