Background
Fistulas are abnormal communications between two epithelialized surfaces. An intestinal fistula is an abnormal anatomic connection between a part (or multiple parts) of the intestinal lumen and the lumen of another epithelialized structure or the skin. Intestinal fistula includes many clinical entities. Because fistulas are widely defined, they are generally classified by anatomic, physiologic, and etiologic methods, all of which have treatment implications.[1] Note the images below.
Postoperative enterocutaneous fistula. Fistula forms as a result of partial or complete intestinal anastomotic disruption and associated resultant abscess. 
Congenital patent omphalomesenteric duct resulting in an enterocutaneous fistula. 
Enterovesical fistula. 
Nephroenteric fistula. In general, medical treatment and stabilization precede attempts at surgical intervention. In patients with all forms of enteric fistulas, sepsis is a major cause of mortality and must be treated aggressively. Surgical treatment is reserved for patients whose fistulas do not resolve with medical and nonsurgical therapy. Aortoenteric fistulas, which mandate emergent surgery when diagnosed, are an exception.
The aim of surgical intervention is to restore GI tract continuity as well as to repair and restore function to the other involved structures. One surgical procedure may not suffice; staged surgical procedures may be required. Individualize treatment based on the patient's overall medical condition and radiologic and intraoperative findings.
History of the Procedure
In 450 BC, Sushruta, the renowned surgeon of ancient India, wrote his treatise known as Sushruta Samhita. These writings were devoted to descriptions of surgical procedures and the care of the surgical patient. Sushruta described major abdominal operative procedures, including resection and reanastomosis of intestinal segment for repair of external intestinal perforations or enterocutaneous fistulas. An ingenious method for suturing the severed ends of intestine was described, in which the cut ends of the intestine were apposed to each other and a type of black ant, collected specifically for this purpose, was made to bite the apposed ends. The heads of the ants were then severed when the pincers had closed. Thus, the pincers remained in place due to rigor mortis, retaining the cut ends of the intestine in apposition. The heads and the pincers of the ants, being organic matter, were digested in due course, not unlike the catgut used in present-day surgery.
In 350 BC, the ancient Greek surgeon Praxagoras created an enterocutaneous fistula to relieve intestinal obstruction. This technique was referenced in Western medical literature in 1899 by Werth, who advocated creation of an enterostomy to treat intestinal obstruction. In 1906, at a surgical society meeting in Chicago, John Finney mentioned enterostomy as a surgical option to treat severe postoperative ileus recalcitrant to other management.
In 1597, Fabricius Hildanus, a German surgeon, reported a patient with a Richter hernia who developed intestinal gangrene and formed an enterocutaneous fistula. The fistula continued to discharge intestinal contents for a period of approximately 2 months, then spontaneously healed. Hildanus was so amazed by this that he quoted several prominent townspeople as witnesses to this "miraculous cure" of an intestinal wound.
As recently as the early 20th century, the mortality rate associated with enterocutaneous fistulas was quoted to be as high as 70-100%. This was attributable primarily to sepsis, severe electrolyte and fluid imbalances, and malnourishment. With the advent of parenteral nutritional support and aggressive treatment of sepsis, the mortality and morbidity rates of fistulas decreased to 30-50%. In the current treatment of intestinal fistulas, a multidisciplinary approach has helped decrease the mortality rate to 15-30%.
Epidemiology
Frequency
Approximately 80-90% of all small intestinal fistulas occur because of operative intervention. Approximately 50% of small intestinal fistulas form because of inadvertent enterotomies in patients in which no intestinal anastomoses were performed. The remaining 50% are related to complete or partial disruption of intestinal anastomotic suture lines.
Approximately 10-20% of all small bowel fistulas arise spontaneously in association with inflammatory processes, malignancy, radiation therapy, and infectious diseases. Of that 10-20%, Crohn disease accounts for 5-50%, cancer for 2-15%, peptic ulcer disease for 3-5%, pancreatitis for 3-10%, radiation-related for 2-5%, and infections for 2-5%.
Surgical procedures that are commonly associated with postoperative fistula formation include reoperative procedures that require extensive lysis of adhesions, trauma surgery, mesh repair of ventral hernias, laparoscopic procedures, and surgery for cancer.
Crohn disease is the leading cause of spontaneous small intestinal fistulas, accounting for more than 50% of cases. Small intestinal fistulas develop in 20-40% of all patients with Crohn enteritis; half of these are enterocutaneous, and the remainder are internal fistulas to other abdominal viscus or organs.
Etiology
The etiology of small intestinal fistulas is important to determine the subsequent treatment. The common mechanisms of intestinal fistula formation are outlined below.
Trauma
Operative trauma is the most common cause of enterocutaneous fistula formation. Inadvertent enterotomies and leak from intestinal anastomosis result in leak of intestinal contents with abscess formation. The abscess erodes through the abdominal wall, commonly at the surgical incision site or drainage site. This results in communication of the intestinal lumen with the skin surface, forming an enterocutaneous fistula depicted in the image below. Note the image below.
Postoperative enterocutaneous fistula. Fistula forms as a result of partial or complete intestinal anastomotic disruption and associated resultant abscess. Intestinal anastomoses are susceptible to partial or complete dehiscence in the presence of impaired blood supply to the area, systemic hypotension, anastomotic suture line tension, perianastomotic infection, and diseased bowel segment anastomosis.
Exposure of the bowel to prosthetic mesh or a large abdominal defect can lead to wall erosion, resulting in enterocutaneous fistula. Intraperitoneal drainage tubes can erode into the intestinal lumen, leading to enterocutaneous fistula formation.
Penetration of the intestinal wall from a foreign body (eg, ingested metallic objects, fish bone) can lead to enteroenteric fistula formation because of erosion into adjacent bowel loops. Fistulas do not commonly form this way. Similarly, penetrating trauma (ie, stab wound) rarely results in enterocutaneous or enteroenteric fistula formation. Nephroenteric fistula formation because of penetrating flank trauma is slightly more common.
Infection
Intestinal infections that erode through the wall cause an abscess and may lead to fistula formation between adjacent viscus, solid organs, or externally. Amebiasis, actinomycosis, tuberculosis, Salmonella, coccidiomycosis, and cryptosporidiosis can all result in periluminal abscesses and fistulas.
A solid organ abscess, such as an amebic hepatic abscess, can erode into small bowel loops. Similarly, rupture of a perinephric abscess can lead to nephroenteric fistula formation. Diverticular and appendiceal abscesses can also lead to enteroenteric or enterocutaneous fistula formation. Appendicocutaneous fistulas are uncommon and occur most often after percutaneous drainage of an appendiceal abscess. In patients with Crohn enteritis, fistulas that occur in the right lower quadrant after an appendectomy usually arise because of the involved terminal ileum adhering to the healing abdominal incision. In these instances, the fistula rarely arises from the appendiceal stump.
Inflammation
Crohn disease leads to ulceration and chronic transmural inflammation of the intestinal wall. The serosa of healthy viscus adheres to the diseased intestine. Adjacent bowel loops, bladder, colon, and vagina are commonly involved. Inflammation gradually progresses to microabscess formation and internal perforation in the ulcerated areas. The ulcerated areas penetrate through the bowel wall into the adjacent involved structure, leading to fistula formation. Enteroenteric, enterovesical, enterovaginal, and perineal fistulas develop frequently in patients with Crohn disease. Ulcerated bowel wall perforation may also lead to interloop abscess formation. The abscess may erode into adjacent bowel loops, resulting in fistula formation.
Radiation injury and malignancy
Long-term radiation injury to the intestine leads to ischemic changes in the intestinal wall. Erosions and dense adhesions between bowel loops develop, which can result in enteroenteric fistula formation. Similarly, degeneration of malignant tumors of the intestine or solid abdominal structures can lead to erosion into adjacent bowel loops, leading to fistulas.
Congenital
Complete failure of the omphalomesenteric duct to obliterate results in an enterocutaneous fistula at the umbilicus as depicted in the image below. This is a rare congenital form of enterocutaneous fistula. The appearance of feculent material at the umbilicus suggests the diagnosis, and surgical resection of the patent duct is performed. Note the image below.
Congenital patent omphalomesenteric duct resulting in an enterocutaneous fistula. Pathophysiology
The pathophysiology of all forms of small bowel fistulas is related to the exposure of nonintestinal tissue to intestinal contents because of the fistula. The intestinal bacterial flora leads to contamination and eventual development of sepsis. The local effect of intestinal fluid can be damaging or corrosive to the nonintestinal tissue, leading to breakdown, erosions, and loss of normal organ or organ system function.
A small intestinal fistula can be classified according to the anatomic structures involved, the etiology of the disease process leading to its formation, and its physiologic output (primarily for enterocutaneous fistulas). Anatomic classifications define the sites of fistula origin, drainage point, and whether the fistula is internal or external. Physiologic classifications rely on fistula output in a 24-hour period. Etiologic classifications (eg, malignancy, inflammatory bowel disease, radiation) define the associated disease entity leading to the development of the fistula.
Each type of classification system carries specific implications regarding the likelihood of spontaneous closure, prognosis, operative timing, and nonoperative care planning. These classification schemes are not exclusive; if possible, all 3 methods should be used to classify each fistula.
Presentation
The clinical presentation of the various forms of intestinal fistulas depends on the organs involved. The predominant signs and symptoms are those of infection from intestinal bacterial contamination.
Enterocutaneous fistulas
Excessive drainage via the abdominal incision or via operatively placed drainage catheters is often the first indicator of a postoperative enterocutaneous fistula. The drainage is typically obvious intestinal contents or fluid with bile staining as seen in the image below. The presence of purulent fluid may disguise the character of the intestinal fluids, leading to an initial misdiagnosis of a wound infection. The presence of gas bubbles in the wound or drain output also indicates an intestinal connection. If differentiation proves difficult, the patient may be given oral methylene blue, indigo carmine, or activated charcoal. The presence of these substances in the drainage confirms the presence of an intestinal leak. Note the image below.
Enterocutaneous fistula. The skin surrounding the area of the fistula is erythematous and indurated and may be fluctuant if an underlying collection is present.
Clinical signs of sepsis (eg, fever, tachycardia, chills) are common when the fistula is associated with undrained intraperitoneal abscesses and infection of the soft tissue of the abdominal wall.
Enteroenteric fistula
Radiologic studies are often used to initially diagnose enteroenteric fistulas. The studies are obtained to evaluate intestinal symptoms or abdominal pain. Diarrhea, abdominal pain, weight loss, and fever are common symptoms associated with enteroenteric fistulas of all etiologies.
Enteroenteric fistula symptoms are nonspecific and may be due to the underlying disease process (eg, Crohn enteritis, radiation enteritis) or the presence of the fistula. Abdominal tenderness may be present on physical examination. Occasionally, a palpable abdominal mass representing densely adherent bowel loops is present.
Enterovesical fistula
Urinary tract contamination with intestinal organisms leads to the development of urinary symptoms in more than 80-90% of patients with enterovesical fistulas. The common presenting urinary symptoms include bladder irritability, dysuria, pyuria, fecaluria, and pneumaturia. Fulminant urosepsis may develop, especially in patients who are immunocompromised from underlying disease or immunosuppressant medications. Note the image below.
Enterovesical fistula. Nephroenteric fistulas
Typically, nephroenteric fistulas (depicted in the image below) develop slowly because of chronic renal disease; thus, the most common initial symptom is chronic urinary tract infection. In contrast, nephroenteric fistulas that occur from penetrating trauma often present early with symptoms of urinary tract infection. Note the image below.
Nephroenteric fistula. Patients may have flank pain, tenderness, and a mass. As the fistula becomes established, fecaluria, pneumaturia, fever, chills, and fulminant sepsis develop. A watery diarrhea can occur, and, in the late stages, severe dehydration, uremia, and acidosis develop. Function of the affected kidney is rarely normal. Perinephric abscesses are common and may cause a mass effect, leading to further deterioration of function.
Enterovaginal fistulas
Purulent or feculent vaginal discharge is the most common presentation of enterovaginal fistula (depicted in the image below). Sepsis from associated intraperitoneal abscesses is common, and these patients experience abdominal pain, fever, and chills. Patients may develop a urinary tract infection because of bacterial contamination ascending the urethra. Note the image below.
Enterovaginal fistula. Aortoenteric fistula
Aortoenteric fistulas (depicted in the image below) present with GI bleeding because of a direct communication between enteric lumen (commonly duodenum and the arterial lumen). Initial herald or sentinel bleeding (eg, hematemesis, hematochezia, melena) is commonly mild and self-limited. Often weeks to months later, the patient has an episode of massive GI hemorrhage. Note the image below.
Aortoenteric fistula demonstrating a direct connection between the intestinal lumen (typically the duodenum) and the prosthetic graft. Patients with a paraprosthetic-enteric fistula (depicted in the image below) have a perigraft abscess or an aneurysm that communicates with the intestinal lumen. Sepsis and abdominal pain are observed on initial presentation. If the infection remains untreated, eventually a communication develops between the arterial and intestinal lumen and GI hemorrhage occurs. Note the image below.
Aortoenteric fistula that forms through erosion of a periprosthetic graft infection into the intestinal lumen. Subclinical ongoing bleeding leads to chronic anemia. A patient with an aortic prosthetic graft and evidence of either acute or chronic GI hemorrhage must have an aortoenteric fistula unless definitively proved otherwise.
Indications
Indications for surgery for intestinal fistula depend on anatomic, physiologic, and etiologic classification. Once appropriately classified, one can predict the likelihood of fistula closure with nonsurgical treatment.
Many enterocutaneous fistulas close spontaneously if infection is controlled, nutrition is adequate, and distal obstruction is not present. Definitive operative correction remains the final step in the treatment of nonhealing small intestinal fistulas. Such procedures should be undertaken only after the patient has been stabilized and is in positive nitrogen balance, with normal protein indices. Usually, a minimum of 3-6 weeks is required. During this time, if the fistula appears unlikely to respond to conservative treatment, radiologic evaluation and surgical planning can be undertaken.
Based on the above discussion, indications for surgery for intestinal fistulas can be classified into early and delayed surgical intervention.
Early surgery is infrequently required but may be necessary in the following circumstances:
- Sepsis or abscess formation not amenable to percutaneous drainage
- Complete distal intestinal obstruction
- Uncontrolled bleeding from fistula
- Removal of mesh or other foreign bodies
- Inability to control the fistula without surgical drainage
- Aortoenteric fistulas (definitively managed by emergent surgery as soon as diagnosis is made)
Delayed surgery is most commonly indicated in patients whose fistulas have not healed after several weeks (typically 4-8 wk) of comprehensive conservative treatment. Specific indications include the following:
- Continued high output from fistula after patient has been given nothing by mouth and started on parenteral nutrition
- Continued signs of infection after institution of adequate antibiotic therapy and drainage of associated abscesses
- Uncontrolled bleeding
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