Intestinal Fistulas Workup

Updated: Mar 08, 2018
  • Author: David E Stein, MD, MHCM; Chief Editor: Burt Cagir, MD, FACS  more...
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Approach Considerations

Serum tests

Albumin and prealbumin levels should be obtained, as well as blood urea nitrogen (BUN), creatinine, and electrolyte concentrations. These are used to determine the patient's nutritional status and whether fluid or metabolic disturbances are present (more of a concern for high-output fistulas).

Although complete blood cell (CBC) count results may be within the reference range, leukocytosis may be present if an undrained abscess or a continued inflammatory process has developed within a segment of the bowel. Anemia may be present with chronic disease or if a malignant process is involved.


Abscess culture findings may be helpful, especially in the presence of sepsis or ongoing infection (the predominant organism involved being Escherichia coli). Cultures of enterocutaneous fistula output may not be of much clinical use, as normal bowel flora often predominates.

Urinalysis or urine culture

For colovesical fistulas, urinalysis usually reveals increased white blood cell (WBC) count and bacteria levels. Urine culture findings may help to direct antibiotic therapy.


Histologic findings of fistula site biopsy are usually consistent with chronic inflammation. In patients with Crohn disease as the causative factor, transmural involvement with noncaseating granulomas and lymphoid aggregates throughout the bowel wall may be observed. In patients with carcinoma, inflammation adjacent to the tumor remains a typical finding. The clinical scenario and test results are usually helpful in determining the diagnosis.


Staging is appropriate when the etiology of the fistula is carcinoma.

Oral administration of nonabsorbable markers

Patients can be given charcoal or Congo red dye orally to verify the presence of an enterocutaneous fistula. However, this is not helpful in determining which portion of bowel is involved. This test is often used in postoperative patients with persistent drainage from a wound in whom an enterocutaneous fistula is suspected or in women with persistent vaginal drainage in whom a rectovaginal fistula is suspected.



Endoscopy or colonoscopy

This can be helpful in determining the origin of the bowel disease that caused the fistula, but it is not a particularly helpful or necessary study to reveal a fistula. Biopsy samples may be obtained during the procedure and are useful in diagnosing inflammatory bowel disease (IBD) or Crohn disease and malignancy.

Endoscopy is also under consideration in the management of gastrointestinal transmural defects, such as fistulas. [14, 15]


Although it has been reported and described, fistuloscopy is not a widely used modality for diagnostic and therapeutic use with enteric fistulas. A small-caliber endoscope is passed into the lumen of the fistula in an attempt to identify the source of the fistula. Fistuloscopy may identify abscesses and visualize the bowel involved. Therapeutically, a drain can be placed or fibrin glue sealant may be applied to close the fistula. [16]


Useful in the evaluation of suspected enterovesical fistula, cystoscopy may allow visualization of fistulas from within the bladder.

Dye injection

Instilling methylene blue into the rectum and examining a vaginal tampon 15 minutes after placement can often establish the presence of a rectovaginal fistula.


Imaging Studies

In patients with an occult anorectal abscess, complex anal fistula, or perianal Crohn disease, the American Society of Colon and Rectal Surgeons notes computed tomography (CT) scanning, magnetic resonance imaging (MRI), or fistulography should be considered. [13]

CT scanning

Abdominal and pelvic CT scanning is the imaging method of choice to evaluate Crohn disease and possible fistulas. While identification of the fistula is not always possible, CT scanning often reveals perifistular inflammation. This provides additional information regarding the possible etiology of the fistula and the extraluminal involvement of disease.

Revealing abscess cavities or excluding possible sources of sepsis is an important step in the evaluation of patients with suspected fistulas. This information may also prove helpful if surgical intervention is planned. CT angiography (CTA) may be used in the diagnosis of suspected aortoenteric fistulas if the patient is stable.


Although MRI is reported as an imaging modality that can help identify and characterize enteric fistulas, motion artifact may limit its usefulness, and MRI is not considered a routine adjunctive study in the evaluation of patients with enteric fistulas. T1-weighted images provide information relative to the inflammation in fat planes and possible extension of the fistula relative to the surrounding visceral structures. T2-weighted images can demonstrate fluid collections along the fistula tract and inflammatory changes within the surrounding muscle.


Radiographic study with contrast medium (usually given at the site of fistula output) may be performed to help delineate the extent of the fistula and its communication with the underlying bowel.


Ultrasonography can be used in conjunction with physical examination to identify abscesses and fluid collections along the fistula tract. Notably, endoanal ultrasonography has been shown to be superior to digital rectal examination (DRE) for classification of anal fistulae prior to operative intervention. [17]

Barium enema and small bowel series

Contrast studies to evaluate the stomach, small intestine, and colon may reveal a fistula and may also be helpful in determining the cause of fistula formation by identifying diverticular disease, Crohn disease (characteristic string sign), or evidence of malignancy.

Cystography and CT cystography

This procedure can help to evaluate for the presence of a possible enterovesical fistula. [12]


Angiography may assist in preoperative planning and evaluation of aortoenteric fistulas in a stable patient or determine the arterial source of bleeding in those with a less common arterioenteric fistula.