Enteric Fistulas and Sinus Tracts

Enteric fistula : Abnormal connection between bowel and another epithelial-lined surface (e.g., bladder, vagina, skin)

Enteric sinus tract : Blind-ending tract originating from bowel

Fluoroscopy

• Fistulogram: Best modality for enterocutaneous fistulas

• Small bowel follow-through : Complementary to CT or MR enterography for Crohn's disease

• Contrast enema : Often definitive for colonic fistulas (to bladder, vagina, etc.)

CT: Primary or complementary role

• Definitive or suggestive signs are present with most enteric & colonic fistulas

• e.g., fistulous tract filled with ectopic gas or contrast medium; tethered bowel adherent to abdominal wall, other bowel or viscera

MR is best modality for perianal fistulas

• Perianal fistula in active setting usually T2 hyperintense, T1 hypointense and enhancing on T1 C+ MR

• Old healed fibrotic fistulas usually hypointense on T1/T2WI and non-enhancing

• Parks classification of perianal fistulas

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    Intersphincteric fistula : Fistula traverses internal anal sphincter and extends downwards to skin surface

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    Transsphincteric fistula : Fistula traverses both internal and external anal sphincters

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    Extrasphincteric fistula : Fistula extends from supralevator space into ischioanal fossa without involving sphincter complex

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    Suprasphincteric fistula : Fistula crosses internal sphincter, rises into supralevator space, and then crosses into ischioanal fossa

Symptoms dependent on type of fistula

• Perianal fistulas most commonly present with purulent discharge or local pain and inflammation

• Enterocutaneous fistulas often result in infected wound with purulent drainage

Enteric fistula: Abnormal connection between bowel and another epithelial-lined surface (e.g., bladder, vagina, skin)

Enteric sinus tract: Blind-ending tract originating from bowel

Perianal fistula: Abnormal communication between anal canal and surrounding soft tissues or skin surface

Best diagnostic clue

• Presence of discrete enhancing tract connecting bowel and another epithelial-lined surface

• Presence of unexpected gas, debris, or enteric contrast medium within bladder, vagina, etc.

Morphology

• Fistula tracts are usually linear, sometimes multiple

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    Walls of tract are often hyperemic on CECT