Laboratory Studies
Although laboratory tests do not help diagnose or confirm the presence of intestinal fistulas, they are important for defining the patient’s clinical condition and guiding treatment.
A complete blood count (CBC) should be obtained. An elevated white blood cell (WBC) count suggests associated infection. Abscesses, soft-tissue infection adjacent to an enterocutaneous fistula, bacteremia, or bloodstream infection may be present. Elderly patients or those who are severely nutritionally depleted may not manifest an elevated WBC count as an indicator of infection.
An electrolyte panel is helpful. Electrolyte imbalances and dehydration are common in patients with high-output enterocutaneous fistulas because of intestinal fluid loss. Hypokalemia, hypochloremia, and metabolic alkalosis are observed in patients with high-output gastric fistulas. Patients with pancreatic and small-bowel fistulas have associated hyponatremia, hypokalemia, and metabolic acidosis. Nephroenteric fistulas are often associated with decreased renal function, which manifests as elevated creatinine and blood urea nitrogen (BUN) and a reduced glomerular filtration rate (GFR).
Serum albumin levels are used to predict fistula closure and mortality. In one study, a serum albumin level higher than 3.5 mg/dL was associated with no mortality, whereas a level below 2.5 mg/dL was associated with a mortality of 42%. Higher levels of short-turnover proteins (eg, serum transferrin, prealbumin, retinol-binding protein) are used to predict fistula closure. A serum transferrin level higher than 200 mg/dL is associated with a higher rate of fistula closure and a lower mortality and vice versa.
Patients who are bacteremic or septic have positive blood culture findings. Results of blood culture are used to direct antibiotic therapy to the appropriate organisms.
In a patient with an enterovesical fistula, urine analysis and culture are both are useful for initial confirmation of the diagnosis, as well as for directing antibiotic therapy to the appropriate organisms.
Imaging Studies
Computed tomography (CT) allows identification as well as guided drainage of associated abscesses or fluid collection. CT with oral contrast can also identify the site of the fistula.
Gastric, duodenal, and proximal small-bowel fistulas can be readily identified. The presence or absence of distal bowel obstruction can be revealed; if intraluminal contrast passes distal to the fistula site, then distal obstruction is unlikely. Passage of the oral contrast, as well as the early presence of contrast within the colonic lumen, can demonstrate the gastrocolic fistula tract. The presence of periaortic inflammation, air collection, or fluid collection characterizes aortoenteric fistulas.
Fistulography is performed to confirm and define the location of an enterocutaneous fistula. Closed-suction drainage catheters are placed under radiologic guidance to drain abscesses or fluid collections. If the drainage contents are clearly enteric, the area is allowed to drain adequately for 7-10 days. This period allows a tract to form.
The patient is stabilized with correction of electrolyte imbalances and administration of antibiotics. Water-soluble contrast is injected via the drainage catheter under fluoroscopy or during CT. Intraluminal passage of contrast confirms the presence and defines the origin of the fistula. A complete contrast study of the gastrointestinal (GI) tract should follow fistulography.
Small-bowel follow-through contrast radiography often identifies enteroenteric fistulas in patients with Crohn disease and chronic radiation enteritis. The study is obtained to evaluate nonspecific complaints of abdominal pain, cramping, diarrhea, and anorexia. All of these symptoms and signs are attributable both to the primary disease and to internal fistulas.
Other Tests
After oral administration of activated charcoal, the presence of charcoal granules in the discharge fluid also confirms the presence of an enterocutaneous fistula. The appearance of charcoal particles in urine or vaginal discharge after oral administration confirms an enterovesical fistula or an enterovaginal fistula, respectively.
After oral administration of methylene blue, emergence of the dye thorough an incision, a drain, or a skin defect confirms the presence of an enterocutaneous fistula. Similarly, this test has been used to confirm the presence of an enterovesical fistula or an enterovaginal fistula.
Although the use of methylene blue has been described in the surgical literature as a method for detecting intraoperative and postoperative anastomotic leaks, it has been curtailed because of reports of associated patient deaths. For this reason, methylene blue is not recommended as a means of detecting or confirming the presence of a fistula in situations where other investigative modalities can be used.
Procedures
Diagnostic procedures may include the following:
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Upper GI endoscopy - The presence of bleeding and inflammatory thickening of the wall of the distal duodenum in a patient with an aortic prosthetic graft indicates an aortoenteric fistula
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Cystoscopy - Enterovesical fistulas are often identified on cystoscopic examination; the presence of an area of inflammation and active purulent or intestinal content drainage confirms the diagnosis
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Classification of fistulas.
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Management algorithm for intestinal fistulas.
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Predictive factors for spontaneous closure and mortality associated with fistulas.
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Postoperative enterocutaneous fistula. Fistula forms as a result of partial or complete intestinal anastomotic disruption and associated resultant abscess.
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Congenital patent omphalomesenteric duct resulting in an enterocutaneous fistula.
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Enterovesical fistula.
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Nephroenteric fistula.
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Enterovaginal fistula.
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Aortoenteric fistula demonstrating a direct connection between the intestinal lumen (typically the duodenum) and the prosthetic graft.
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Aortoenteric fistula that forms through erosion of a periprosthetic graft infection into the intestinal lumen.
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Enterocutaneous fistula output is controlled through placement of a soft-sump drain into the cutaneous opening of the fistula tract. The sump drain is connected to low suction, and the fistula opening and drain are contained within an ileostomy bag. An additional drain is placed within the bag and to continuous suction to keep the bag empty and to minimize the contact of surrounding skin with enteric contents.
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Bypass of fistulous bowel loops that are densely adherent within the pelvic cavity by creation of an anastomosis between the divided afferent limb and the transverse colon.
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Bypass of a densely adherent fistula by anastomosis of afferent and efferent limbs of intestine in continuity. This is an ineffective method of bypass, since the enteric contents continue to flow into the fistula tract.
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A densely adherent or unresectable fistula is bypassed by dividing both afferent and efferent intestinal loops and reanastomosing the divided ends to restore intestinal continuity. The fistula tract is essentially isolated from the enteric stream. If a longer loop of bowel is bypassed, the divided ends can be exteriorized.
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Enterocutaneous fistula.
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Enterocutaneous fistula.
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Resected enterocutaneous fistula, embedded in surrounding inflammatory tissue and skin.
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Stapled closure of intestinal lumen to restore intestinal continuity following resection of enterocutaneous fistula.
