9.1 Fistula Types & Anatomic Classification
Key Takeaways
- Fistulae are named origin-to-destination, so an enterocutaneous fistula runs from small bowel to skin, a colocutaneous from colon to skin, and a vesicocutaneous from bladder to skin.
- An enteroatmospheric fistula opens directly into an open wound with no overlying skin or tract, has no possibility of spontaneous closure, and is the most difficult containment problem in the specialty.
- Pneumaturia and fecaluria are the hallmark symptoms of a colovesical fistula, most commonly caused by diverticular disease.
- The named etiologic categories in the blueprint are radiation, infection, surgery, immune compromise, and inflammatory bowel disease — and roughly 75 to 85 percent of enterocutaneous fistulae are postoperative.
- Anatomy must be defined by imaging — CT with enteral contrast or a fistulogram — before any decision about definitive surgery, because the origin, tract length, and presence of distal obstruction determine whether closure is possible.
Fistula Types & Anatomic Classification
Quick Summary: A fistula is an abnormal communication between two epithelialized surfaces. Everything about its management — whether it can close, how it is contained, what the patient eats, whether surgery is possible — follows from where it starts, where it ends, and how much comes out. This section handles the first two.
The Naming Convention
Fistulae are named origin first, destination second. Learn the convention and you never need to memorize a list.
| Name | From | To | Clinical signature |
|---|---|---|---|
| Enterocutaneous | Small bowel | Skin | Green-brown, enzyme-rich, highly caustic effluent; rapid skin breakdown |
| Colocutaneous | Colon | Skin | Thicker, more formed, feculent; less enzymatic damage than small bowel |
| Enteroatmospheric (EAF) | Bowel | Open wound / atmosphere | No tract, no overlying skin; will not close spontaneously |
| Vesicocutaneous | Bladder | Skin | Continuous urine drainage through the abdominal wall |
| Rectovaginal | Rectum | Vagina | Passage of stool or flatus per vagina |
| Colovaginal | Colon | Vagina | Same presentation; often post-hysterectomy diverticular disease |
| Colovesical / enterovesical | Colon or small bowel | Bladder | Pneumaturia and fecaluria; recurrent polymicrobial urinary infection |
| Enteroenteric / enterocolic | Bowel | Bowel | Internal; malabsorption and diarrhoea from bypassed segment |
| Perianal / anorectal | Anal canal | Perianal skin | Crohn's disease; recurrent abscess and drainage |
Important: Internal fistulae — enteroenteric, colovesical, rectovaginal — drain into another hollow organ rather than onto skin, so the ostomy nurse's containment skills do not apply directly. They still matter because the symptoms are diagnostic. Pneumaturia, air bubbling in the urine, and fecaluria are near-pathognomonic for a colovesical fistula, most often from diverticular disease. Stool or flatus per vagina indicates a rectovaginal or colovaginal fistula.
The Enteroatmospheric Fistula Is a Separate Category
An EAF is not simply an enterocutaneous fistula in a wound. The distinction matters clinically and is heavily tested.
| Feature | Enterocutaneous fistula | Enteroatmospheric fistula |
|---|---|---|
| Tract | A defined tract through soft tissue | No tract — the bowel wall opens directly at the wound surface |
| Overlying skin | Present | Absent |
| Spontaneous closure | Possible, especially low output, short tract, no distal obstruction | Impossible — there is nothing to close over |
| Context | Any abdominal surgery | Open abdomen, "frozen abdomen", laparostomy, damage-control surgery |
| Management goal | Support spontaneous closure; contain | Contain, protect the wound bed, nourish, and plan reconstruction |
Because an EAF sits in the middle of a granulating wound, effluent must be isolated from the wound bed to allow the surrounding tissue to heal. That isolation problem is the subject of the containment section later in this chapter and of the "stoma-in-a-wound" protocol.
Etiologic Factors
The blueprint names five categories under fistula etiology. Anchor them.
| Category | Mechanism and examples |
|---|---|
| Surgery | The dominant cause. Roughly 75 to 85 percent of enterocutaneous fistulae are postoperative — anastomotic disruption, inadvertent enterotomy, mesh erosion, or injury during adhesiolysis |
| Inflammatory bowel disease | Crohn's disease is transmural, so it fistulizes; ulcerative colitis is mucosal and generally does not. A spontaneous enterocutaneous fistula in a young adult is Crohn's until proven otherwise |
| Radiation | Endarteritis obliterans causes chronic ischaemia; radiation fistulae appear months to years after treatment and heal poorly |
| Infection | Diverticulitis, appendiceal or tubo-ovarian abscess, tuberculosis, actinomycosis; an abscess that decompresses through a hollow viscus and the skin |
| Immune compromise | Corticosteroids, biologics, chemotherapy, malnutrition, and uncontrolled diabetes impair healing and permit breakdown |
Malignancy is a sixth cause worth knowing: a fistula arising in an irradiated or previously resected field may represent recurrent tumour, and a fistula that will not close in a cancer patient should prompt that question.
Defining the Anatomy
You cannot plan care for a fistula whose anatomy is unknown. Definition of anatomy is the A in the S-N-A-P-P framework, and it precedes any conversation about definitive surgery.
- CT of the abdomen and pelvis with enteral and IV contrast — the first-line study. Identifies the origin, associated abscess, distal obstruction, and the state of the abdominal wall.
- Fistulogram — water-soluble contrast injected into the external opening under fluoroscopy, mapping the tract, its length, and the segment of bowel involved.
- Small bowel follow-through or CT enterography — defines the length of bowel proximal and distal to the fistula, which predicts nutritional consequences.
- Endoscopy and cystoscopy — for internal fistulae involving the bladder, vagina, or colon.
Three anatomic findings dominate the prognosis for spontaneous closure:
- Origin. Gastric, lateral duodenal, and ileal fistulae close less readily than jejunal or colonic ones.
- Tract length. A tract shorter than about 2 cm closes poorly; a long, well-formed tract does better.
- Distal obstruction. Any obstruction distal to the fistula makes spontaneous closure impossible, because flow follows the path of least resistance straight out the fistula.
Exam Tip: The FRIEND mnemonic lists the factors preventing spontaneous closure — Foreign body, Radiation, Inflammation or Inflammatory bowel disease, Epithelialization of the tract, Neoplasm, Distal obstruction. An item that describes any one of these and asks about the likelihood of spontaneous closure is asking you to recognize that the answer is low, and that surgical planning is required.
What the Ostomy Nurse Contributes at the Classification Stage
The COCN is often the clinician who first characterizes the fistula precisely, and that documentation drives everything downstream:
- Location relative to the wound, incision, bony landmarks, and any stoma.
- Number of openings — multiple openings may be one tract or several.
- Whether the opening is flush, retracted, or protruding above the surrounding surface, which determines the containment strategy.
- Whether it sits in intact skin or in an open wound — the enterocutaneous versus enteroatmospheric distinction.
- Effluent character — colour, consistency, odour, and pH give a strong clue to the level of origin. Bilious green-brown liquid suggests proximal small bowel; thick, formed, feculent output suggests colon.
- Surrounding tissue condition — intact, macerated, denuded, or already showing candidiasis.
- Photographic documentation at a 90-degree angle with a measurement scale in frame.
That description, recorded consistently at each assessment, is what allows the team to tell whether output is falling, whether a tract is maturing, and whether the plan is working.
A 62-year-old with a long history of diverticular disease reports passing air bubbles during urination and recurrent urinary infections growing multiple organisms. What type of fistula does this presentation indicate?
What most fundamentally distinguishes an enteroatmospheric fistula from an enterocutaneous fistula?
Which of the following findings makes spontaneous closure of an enterocutaneous fistula least likely?
Which etiology should be suspected first in a 26-year-old with no surgical history who develops a spontaneous enterocutaneous fistula?