PANCE Blueprint GI and Nutrition (9%)

Rectal Abscess and Fistula (Lecture)

Patient with a rectal abscess will present as → a 45-year-old man presents to the emergency department with a 3-day history of severe rectal pain, especially during defecation. He also reports fever and malaise. On physical examination, you note a fluctuant, erythematous mass near the anus. The patient is in obvious discomfort.

Patient with an anorectal fistula will present as → a 45-year-old man presents to the clinic with a 3-month history of recurrent perianal abscesses. He reports intermittent drainage of pus and discomfort in the perianal area. On examination, you note a small opening near the anal verge with surrounding erythema. A probe is easily passed through the opening and emerges in the anal canal.

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What disease should be considered with fistula in ano?
Crohn’s disease
What is a sitz bath?
Sitting in a warm bath (usually done after bowel movement and TID)

An anorectal abscess is a collection of pus in the area around the anus and rectum and is the result of infection, whereas an anorectal fistula is an abnormal tunnel that connects the anus or rectum to the skin around the anus and is a chronic complication of an abscess.

  • Abscesses produce painful swelling at the anus as well as painful defecation. Examination reveals localized tenderness, erythema, swelling, and fluctuance; fever is uncommon.
  • Deeper abscesses may produce buttock or coccyx pain and rectal fullness; fever is more likely.

Perianal swelling, erythema, and drainage due to a perianal abscess by the Department of Urology, University Hospital Center, Fez, Morocco. Image - License: CC BY 2.0

An anorectal fistula is an open tract between two epithelium-lined areas and is associated with deeper anorectal abscesses

  • Communication between the rectum and perianal skin
  • Generally located within 3 cm of the anal margin
  • Fistulae will produce anal discharge and pain when the tract becomes occluded

Intraoperative view of the external openings of the fistula in ano (arrowheads) and the upper part of the tract where the foreign material resided (arrow)

Intraoperative view of the external openings of the fistula in ano (arrowheads) and the upper part of the tract where the foreign material resided (arrow) by Department of General Surgery, Cerrahpasa Medical School, Istanbul University, Cerrahpasa, Fatih 34098, Istanbul, Turkey. Image - License: CC BY 3.0

Anorectal fistulas and abscesses are typically diagnosed through a physical examination and medical history

Anal Abscess - Clinical - perirectal tender swollen mass

  • CT scan of pelvis only if recurrent

Fistula in Ano (perianal fistula)

  • Anoscopy

Treatment of an anorectal abscess requires surgical drainage, followed by warm-water cleansing, analgesics, stool softeners, and a high-fiber diet are prescribed for all patients

  • Prompt incision and adequate drainage are required and should not wait until the abscess points. Many abscesses can be drained as an in-office procedure; deeper abscesses may require drainage in the operating room
  • Antibiotics are needed for high-risk patients

Anorectal fistulas must be treated surgically

Fistula Causes


A fistula is a connection or passageway formed abnormally between two epithelium-lined vessels or organs. Causes of enterocutaneous fistulas can be summarized by the mnemonic “FRIEND.” The “FRIENDs” of a fistula include Foreign body, Radiation, Infection, Epithelialization, Neoplasm, and Distal obstruction.

Play Video + Quiz

Question 1
A 40-year-old male presents with a history of recurrent perianal discomfort and purulent drainage. He has no significant past medical history and takes no medications. On examination, an external opening near the anus with surrounding erythema and tenderness is noted. Which of the following factors is most likely to contribute to the development of his condition?
Chronic constipation
While it can cause anorectal problems, it is less likely to directly cause abscesses or fistulas.
Crohn's disease
Hemorrhoidal disease
Primarily involves the venous structures and does not typically lead to fistula formation.
Anal fissure
These are superficial tears and do not typically lead to abscesses or fistulas unless they become chronically infected.
Diabetes mellitus
While diabetes can predispose to infections due to impaired immunity, it is not a direct cause of rectal abscesses or fistulas.
Question 1 Explanation: 
Rectal abscesses and fistulas are commonly associated with inflammatory bowel diseases, particularly Crohn's disease. Crohn's disease can cause deep ulcers that penetrate the intestinal wall, leading to fistula formation. These fistulas can connect the intestine to the skin or other organs, creating pathways for infection and abscess formation.
Question 2
A 35-year-old female presents with a painful swelling near her anus for the past week. She also complains of fever and malaise. On physical examination, there is a tender, fluctuant mass near the anal verge. Which of the following is the most appropriate next step in the management of this patient?
Initiate broad-spectrum antibiotics
Antibiotics are adjunctive to surgical drainage but not a primary treatment.
Perform a colonoscopy
This is not indicated acutely in the setting of a suspected abscess.
Order an MRI of the pelvis
MRI may be useful in complex cases or to evaluate fistulas but is not the initial step in management.
Incision and drainage
High-fiber diet and sitz baths
These measures may help in relieving symptoms of hemorrhoids and anal fissures but are not appropriate for an abscess.
Question 2 Explanation: 
The patient presents with signs and symptoms suggestive of a perianal abscess, which is typically diagnosed based on clinical examination. The most appropriate next step is incision and drainage to release the purulent material, alleviate pain, and prevent further complications.
Question 3
A patient with a history of rectal abscesses now presents with a chronic perianal fistula. Which of the following is the most appropriate management for this condition?
Topical nitroglycerin
Used for anal fissures, not fistulas.
Systemic steroids
These are used in inflammatory bowel disease but not specifically for fistula management.
High-dose antibiotics
While antibiotics may be used to treat acute infections, they do not address the underlying fistula tract.
Dietary modifications
Helpful in general bowel health but do not treat a fistula.
Question 3 Explanation: 
Chronic perianal fistulas often require surgical intervention for definitive treatment. A fistulotomy, which involves surgically opening the fistula tract, is a common and effective treatment for most simple perianal fistulas.
There are 3 questions to complete.
Shaded items are complete.

References: Merck Manual · UpToDate

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