Distal Gastrointestinal Tract Pathology

Core

Anal Fissure

An anal fissure is a linear tear in the anal mucosa, usually following the posterior midline. It occurs due to high internal anal sphincter tone and decreased blood flow to the anal mucosa. Patients typically present with very painful defaecation and a small amount of haematochezia (bright red blood in the stool).

Conservative management involves increasing hydration, regular exercise and increasing fibre intake to reduce constipation alongside taking warm baths to help relax the anal sphincter tone. Medical treatment is analgesia (not opioids as anal fissures are often linked to constipation) and topical medications to relax anal sphincter tone, e.g. diltiazem. Surgery may be recommended if all other treatment options fail, it is very effective but does carry a risk of incontinence.

Image - Posterior Anal Fissure

Public Domain Source by Jonathanlund [Public domain]

Perianal Abscess

Perianal abscesses are common. They occur in different locations - superficial (most common), intersphincteric, ischiorectal and supralevator (rare and often iatrogenic).

Risk factors include male gender (2:1), middle-aged, IBD, smoking, HIV and diabetes mellitus.

They typically present with an erythematous swelling around the anus with or without pain. Deeper abscesses take longer to reveal themselves so may present with sepsis while no visible abscess can be seen.

Management is incision and drainage within 24 hours of presentation. 1/3 of people with a perianal abscess are found to also have a fistula so it is important to treat the fistula if present to prevent abscess recurrence.

Diagram - Locations of perianal abscesses

Creative commons source by McortNGHH [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Haemorrhoids

Haemorrhoids can be divided into internal haemorrhoids and external haemorrhoids depending on their location.

Internal haemorrhoids are the most common. They are enlarged venous anal cushions caused by a loss of connective tissue support. They form above the dentate line so are relatively painless, but they can prolapse through the anal canal and cause haematochezia and pruritus (itching). Conservative management involves increasing hydration, increasing fibre intake and avoiding straining. If conservative measures are insufficient rubber band ligation or another therapy to shrink the haemorrhoids may be used. Surgery to remove the haemorrhoids may be required in severe cases.

External haemorrhoids are less common and are swollen anal cushions that may then thrombose. These haemorrhoids form below the dentate line so are extremely painful and also cause haematochezia. Initial treatment is usually conservative (analgesia, stool softening and topical measures), with surgery reserved for selected severe or thrombosed cases.

Diagram - Internal vs external haemorrhoid locations

Creative commons source by https://www.myupchar.com/en, edited by Dr. Laura Hansell [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Diarrhoea

Diarrhoea is a sign/symptom, not a condition. It is defined as loose, watery stools occurring more than three times per day.

It is either caused by a secretory dysfunction where there is reduced absorption of Na⁺ ions and therefore an increased net secretion of Cl^- ions into the gut lumen, or by an osmotic dysfunction where the gut lumen contains too much osmotic material (e.g. lactose deficiency).

Diarrhoea is often self-limiting, but management focuses on preventing dehydration. Oral rehydration solutions are first-line to replace fluid and electrolyte losses. Medical assessment is advised if symptoms persist or if there are red flags such as dehydration, fever or blood in the stool. Loperamide may reduce stool frequency in selected cases, but it should be avoided where infection is suspected. Treatment should address the underlying cause; antibiotics are only indicated in specific, confirmed bacterial infections.

Constipation

Constipation is a sign/symptom, not a condition. It is defined as hard stools, difficulty passing stools or the complete inability to pass stools.

Risk factors include female gender (3:1), sedentary lifestyle and increasing age (although it is also common in children under 4 years of age).

Conservative management involves increasing fluid intake, increasing fibre intake and regular exercise. Laxatives of varying types can be prescribed depending on the underlying cause.

Image - Abdominal x-ray showing significant constipation

Creative commons source by James Heilman, MD [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]

Edited by: Dr. Maddie Swannack

Reviewed by: Dr. Thomas Burnell

Quiz

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