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Intestinal Fistulas Workup

  • Author: David E Stein, MD; Chief Editor: Julian Katz, MD  more...
Updated: Dec 16, 2014

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 count (CBC) 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 IBD or Crohn disease and malignancy.


Although it has been reported and described, this procedure 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.[10]


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

CT scanning

Abdominal and pelvic computed tomography (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 may be used in the diagnosis of suspected aortoenteric fistulas if the patient is stable.


Although magnetic resonance imaging (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.

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.[9]


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.

Contributor Information and Disclosures

David E Stein, MD Chief, Division of Colorectal Surgery, Associate Professor, Department of Surgery, Director, Mini-Medical School Program, Drexel University College of Medicine; Chief, Division of Colorectal Surgery, Department of Surgery, Hahneman University Hospital; Consultant, Merck; Consultant, Ethicon Endo-Surgery; Consultant, Health Partners; Consultant, Cook Surgical

David E Stein, MD is a member of the following medical societies: American College of Surgeons, American Society of Colon and Rectal Surgeons, Association for Surgical Education, Pennsylvania Medical Society, Society for Surgery of the Alimentary Tract, Crohn's and Colitis Foundation of America

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Merck<br/>Serve(d) as a speaker or a member of a speakers bureau for: Merck.


Asyia S Ahmad, MD Assistant Professor of Medicine, Division of Gastroenterology and Hepatology, Associate Program Director, Gastroenterology and Hepatology Fellowship Training Program, Drexel University College of Medicine

Asyia S Ahmad, MD is a member of the following medical societies: American Gastroenterological Association, American Neurogastroenterology and Motility Society, American Society for Gastrointestinal Endoscopy, Pennsylvania Medical Society

Disclosure: Nothing to disclose.

Radha V Menon, MD Resident Physician, Department of Internal Medicine, Drexel University College of Medicine

Disclosure: Nothing to disclose.

Chief Editor

Julian Katz, MD Clinical Professor of Medicine, Drexel University College of Medicine

Julian Katz, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, American Geriatrics Society, American Medical Association, American Society for Gastrointestinal Endoscopy, American Society of Law, Medicine & Ethics, American Trauma Society, Association of American Medical Colleges, Physicians for Social Responsibility

Disclosure: Nothing to disclose.


Christopher K Chiu, MD Staff Physician, Department of General Surgery, Drexel University College of Medicine

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

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Enterocutaneous fistula after bowel injury from an incisional hernia repair, 6 weeks postinjury.
Status post-pancreatic debridement for necrotizing pancreatitis. The patient had a colonic injury with attempted closure using a skin graft. The patient later underwent definitive repair.
Psoas abscess from Crohn disease that later fistulized to the skin.
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