Interpretation

• This is a cryptoglandular (anal gland) abscess. The anal glands lie in the intersphincteric space and open at the crypts at the dentate line. Blockage of a gland leads to sepsis, and the infection can then track in different directions (Current Surgical Therapy 14e).
• Because the abscess is intersphincteric, it often causes severe, unremitting perianal pain with little to see on external examination. Yamada's Textbook of Gastroenterology makes this point, and it fits the need for MRI here.
• The abscess is small and has not spread to the ischiorectal fossa or supralevator space. That is favourable, and the sphincters are intact.
• The 1 to 5 o'clock span means the abscess crosses the right anterolateral and anterior sectors, depending on patient position. Confirm the actual site on examination under anaesthesia (EUA).
• A plain MRI can miss a small internal opening. A fistula may still be present or may develop later.

Management

• Check the symptoms: perianal pain, fever, discharge, pain on sitting or defecation, and any retention of urine.
• Do a digital rectal examination and proctoscopy. This is a 63-year-old man, so also look for a rectal or anal mass, and check for diabetes, immunosuppression and inflammatory bowel disease.
• Check blood sugar or HbA1c, a complete blood count and CRP.

• The ASCRS 2022 guideline recommends prompt incision and drainage for acute anorectal abscess (ASCRS guideline summary).
• Intersphincteric abscesses are drained internally, not through the skin. The reason is that external drainage risks creating a complex fistula (Yamada's Textbook of Gastroenterology). The internal approach should be done in the operating room to give adequate exposure and avoid injury to the internal sphincter.
• Technique, per Current Surgical Therapy 14e:
  • Divide the mucosa over the bulging area in the anal canal.
  • Divide the internal sphincter over a hemostat to open the abscess. This generally does not compromise continence, but the patient should be told of the small risk.
  • Alternatively, make a stab incision at the anal verge in the intersphincteric groove and place a small mushroom catheter. Remove it or back it out once the sepsis has resolved.
• Fischer's Mastery of Surgery describes a similar approach: examination under anaesthesia, then an incision just inside the anal canal below the dentate line. It leaves a mushroom catheter in place because, without one, pain-induced sphincter spasm impairs drainage and can cause recurrent sepsis.
• The abscess is small, so a trial of conservative treatment is sometimes tried if the patient is mildly symptomatic. Failure to settle, or worsening pain, calls for drainage. Under the German S3 guideline, abscesses lying entirely within the anal canal with a connection to it are treated by transanal drainage, with or without internal sphincterotomy.

• Antibiotics are not routine. The ASCRS guideline reserves them for cellulitis, systemic signs of infection, or immunosuppression (grade 2C).
• Yamada's also lists valvular heart disease and diabetes as indications.
• If needed, use cover for gram-negative and anaerobic organisms, for example amoxicillin-clavulanate, or ciprofloxacin plus metronidazole.

• Give analgesia, stool softeners and a high-fibre diet.
• Advise warm sitz baths two to three times a day.

• At the time of drainage, gently look for an internal opening. Do not probe forcefully, because that can create a false tract.
• Primary fistulotomy is reasonable only for a clearly superficial, simple tract, and only after assessing how much sphincter is involved. It is generally avoided in this setting because of the risk of faecal incontinence. If an internal opening is found, a loose draining seton is safer.

• After simple drainage, the recurrence or fistula rate quoted in Yamada's is 11 to 66%. Discuss this with the patient at consent.
• If a fistula declares itself later, treat it by Parks type. The intersphincteric tract is treated by fistulotomy, while the options for a more complex tract include a seton, LIFT or an advancement flap (ASCRS: LIFT and endoanal advancement flaps are grade 1B).
• Repeat MRI if symptoms recur or persist.
• At age 63, the usual age-appropriate colorectal cancer screening applies. Do a colonoscopy if there is bleeding, a change in bowel habit, or no recent screening.
• Look for a systemic cause if the disease is recurrent or atypical. This means checking for Crohn disease, tuberculosis, diabetes and immunosuppression.

Red flags that need urgent review

Recent evidence check