A fistula is an abnormal connection between 2 epithelial surfaces that usually involves the intestine and another hollow organ, such as the bladder, urethra, vagina, or other regions of the gastrointestinal tract.
Fistulas may also form between the gut and the skin or between the gut and an abscess cavity, and can arise between a blood vessel and the gut.
75-85% of intestinal fistulas occur as a complication of abdominal surgery.
15-25% of fistulas occur spontaneously and are usually the result of intra-abdominal inflammation or infection.
Fistulas associated with mortality rate to approximately 20%.
Frequency of fistula formation has not decreased, because of advanced and complicated disease, complex surgeries, and an aging population.
Classification systems commonly used are based on anatomic, physiologic, and etiologic characteristics.
Anatomically fistulas are named according to their participating anatomic components.
Fistulas can be divided into internal and external fistulas.
Internal fistulas connect the GI tract with another internal organ, the peritoneal space, the retroperitoneal space, the thorax, or a blood vessel.
External fistulas, which commonly occur postoperatively.
External fistulas are abnormal connections between the GI tract and the skin.
Risk factors for intestinal fistulas include: Cancer surgery, inflammatory bowel disease (IBD), adhesions, perforated peptic ulcer disease, diverticular disease, prior radiation exposure, cancer, appendicitis, trauma, gunshot wounds, stab wounds, blunt trauma, abdominal aortic surgery, infected aortic graft, and aortic aneurysm.
Gastric fistulas are related to iatrogenic causes in about 85% of cases.
Gastric fistulas may rarely be a consequence of radiation, malignancy, inflammation, and ischemia.
The development of an anastomotic leak after a gastric resection or after bariatric surgery can lead to leakage of intestinal or gastric juices causing infection, abscess formation, and fistula formation.
Small bowel fistulas are due primarily as a result from complications of abdominal surgery.
These small intestine fistulas occur from disruption of an anastomoses, or small bowel injury/perforation.
Approximately 10 – 15 % of small bowel fistulas or related spontaneously to Crohn’s disease, peptic ulcer disease, pancreatitis, and malignancies.
Crohn fistulas are most often internal.
Ileosigmoid fistulas are the most common type of fistula between two loops of bowel.
Enteroenteric, gastrocolic, duodenocolic, enterovesical, rectovaginal, and perianal fistulas may be complications of Crohn disease.
Perianal fistulas are the most common external fistulas seen with patients with Crohn disease.
Colonic fistulas are primarily due to intra-abdominal inflammation but can also occur after surgical intervention for an inflammatory condition.
Aortoenteric fistulas most commonly occur after the surgical placement of a graft.