Rectocutaneous Fistula Presenting as an Insect Bite at the Distal Posterior Thigh: A Multidisciplinary Approach

Introduction

A fistula is an abnormal passage between two hollow/tubular organs or between a hollow/tubular organ and the body surface. Fistula formation is an uncommon medical condition. The most common causes of fistula formation include foreign bodies, history of radiation therapy, persistent infection (anastomotic leak), ischemia or inflammation, poor wound epithelization usually secondary to malnutrition, neoplasm, distal obstruction, and sepsis. Radiation therapy, in the context of the multimodal treatment of rectal cancer, can contribute to the formation of enterocutaneous fistulae. These fistulas may track from the rectum to distal sites, but distant eruption through the skin is exceedingly rare. Colocutaneous or rectocutaneous fistulae, where the passage created involves the skin, are even more rare. Oftentimes they are a complication of sigmoid diverticulitis. ^1–3 In rare cases, a thigh abscess may be the only symptom, with complete absence of gastrointestinal symptoms. However, gas in the thigh should raise the index of suspicion for bowel pathology, as would decreased movement of the lower extremity, deformity of the extremity, and presence of crepitus. ^1–3 Mortality from an enterocutaneous fistula can range from 10% to 30%. ⁴

Although many of the reported fistulae result from diverticular disease, there are also some cases of fistulization concurrent with tumor formation and post cancer treatment. One study reported that the most common primary tumor site was the colon/rectum in males and the ovary in females, with most patients having metastatic disease at diagnosis. The fistulae were usually solitary, mostly developed from the jejunum/ileum or colon/rectum. ⁵ Most fistulae developed early in the postoperative period, between the 4th and 6th postoperative days. ⁶ The most common reasons were anastomotic failure, a leak from primary closure, or from unnoticed missed perforations.

Transanal total mesorectal excision (TaTME) has been proven to be a safe and equivalent means of achieving curative therapy for rectal cancer. Short-term data demonstrate acceptable outcomes in comparison to laparoscopic total mesorectal excision (TME). ⁷ TaTME with transabdominal laparoscopic assistance is both feasible and safe. Pathologic analysis has proven that TME specimens are of acceptable macroscopic quality, which is the most important prognostic factor in rectal cancer. Intraoperative outcomes regarding conversion, surgical times, and intraoperative complications are also satisfactory, with short-term morbidity and oncologic outcomes as good as those in other laparoscopic TME series. ⁸ Independent risk factors of anastomotic failure in TaTME patients include male sex, obesity, smoking, diabetes mellitus, tumors < 25 mm in diameter, excessive intraoperative blood loss, manual anastomosis, and prolonged perineal operative time. A scoring system for preoperative risk factors is associated with observed rates of anastomotic failure of between 6.3% and 50% based on cumulative score. ⁹ Large tumors in obese, male patients with diabetes who smoke have the highest risk of anastomotic failure.

Favorable short-term oncologic results have been reported where TaTME is associated with mesorectal specimen of a better quality and a longer distal resection margin that is established at the beginning of the procedure under direct view. ¹⁰ Long-term follow-up and ongoing randomized control trial data are pending regarding functional results, local recurrence, and survival, as well as to facilitate the comparison with standard laparoscopic or robotic rectal resections. ¹⁰ Many patients with these fistulae either present with sepsis or develop sepsis during their hospitalization. ¹ Pathogens that have been cultured from these fistulae include Streptococcus milleri and coliforms.

Fistula treatment entails adoption of various methods aimed at the control of sepsis, protection of surrounding skin and soft tissue, control of fistula output, and maintenance of nutrition, with eventual spontaneous or surgical closure of the fistula. In some cases, especially with involvement of the colon, elective sigmoid resection with primary colorectal anastomosis, partial fistulectomy, and injection of a fibrin sealant in the residual tract has been described. ¹¹ Cases of metastatic anal cancer from colorectal cancer have been treated by abdominoperineal resection, where local excision can also be employed if the anal tumor has not invaded the surrounding tissue. Radical resection of the primary tumor combined with the metastatic tumor has a crucial role in the treatment of metastatic anal cancer. ¹²

Case Presentation

A 61-year-old female presented to an outside emergency department complaining of pain and swelling in her left popliteal fossa. She had a history of rectal cancer, had a status of post TaTME with neoadjuvant chemoradiation therapy, and had been lost to follow-up for 1 year by her treating surgeon. At the time of her index operation, her lesion was noted at 4 cm from the anal verge and her post neoadjuvant staging was T0. Her pathology showed complete pathological response.

Upon new presentation, the patient complained of pain with ambulation and swelling over the past 3 months in her posterior thigh. She also complained of intermittent fevers and fatigue over the past 3 months. The patient thought she had been bitten by a spider and attributed her symptoms to an insect bite. She was diagnosed with an abscess, thought to represent an infected papular urticaria from “an insect bite.” However, the abscess had ruptured and started draining what appeared to be stool combined with undigested food.

Physical examination of the involved thigh revealed a larger posterior compartment than the contralateral leg, with thigh circumference being approximately 60 cm, whereas the uninvolved thigh circumference measured 40 cm. The posterior compartment of the thigh appeared erythematous and felt tense, with tenderness to deep palpation. Approximately 3 cm proximal to the popliteal fossa, a 1 cm × 2 cm ulcerated lesion was identified with surrounding erythema and induration, with both feculent and purulent drainage, as well as undigested food matter, such as corn (Figure 1). The patient was unable to ambulate due to pain. No adenopathy or other lesions were identified. On digital rectal examination a severe anastomotic stricture was noted.

Figure 1:

Patient at initial presentation with fistula visualized in distal posterior thigh.

Laboratory studies revealed an elevated C-reactive protein level of 85 mg/L and erythrocyte sedimentation rate of 141 mm/h, with a markedly elevated white blood cell count of 32,000. The patient, however, was afebrile, normotensive, and had a normal resting heart rate. Radiographs of the thigh were unremarkable. Computed tomography revealed presacral fat infiltration and a 1.9 cm × 1.6 cm × 6.3 cm enhancing focus along the anterior aspect of the right sacrum and coccyx. There was a 3.6-cm rim-enhancing collection in the posterior left perirectal region, suspicious for an abscess. The lesion extended inferolaterally from this collection into the left gluteus maximus muscle. Gas and inflammatory changes in the distal left gluteus maximus muscle and in the posterior compartment of the left thigh, consistent with myositis and cellulitis, were also described. There were multiple intramuscular abscesses within the distal biceps femoris measuring up to 2.2 cm as well (Figure 2).

Figure 2:

CT scan images showing (A) the origin of the fistula and (B) the left posterior thigh fistula, as CT proceeds distally. CT = computed tomography.

Given her history of rectal cancer and radiation, her clinical picture created suspicion for a rectocutaneous fistula and infection of the posterior compartment of her thigh. A multidisciplinary approach to care was utilized for this patient’s case: Colorectal surgery, infectious disease, radiation oncology, plastic surgery, and orthopedic surgery were consulted and met to coordinate plans for the patient’s care. A three-part plan was created: 1) colostomy with concomitant incision and debridement to decompress the abscess and excise the fistula tract, 2) serial washouts and debridement of the thigh wound with eventual closure, and 3) eventual robotic abdominoperineal resection with gluteal V-Y advancement flap and excision of the fistula, as with the presence of the rectum, the patient would likely refistulize.

As a result, the patient underwent colostomy with incision and debridement of the thigh to decompress the abscess and excise the fistula (Figure 3). She remained stable during her colorectal procedure, but upon decompression of the abscess, became suddenly hypotensive and tachycardic. The patient returned to the operating room for multiple debridement procedures before eventual delayed primary closure. Soft tissue biopsies were taken from the rectum and fistula, both negative for malignancy. Cultures taken from the fistula grew Enterococcus faecalis, Proteus mirabilis, and Candida albicans, and she was treated with ampicillin–sulbactam with fluconazole for a course of 6 weeks under infectious disease recommendations. The radiation oncology team determined that no further treatment was needed in the absence of malignancy.

Figure 3:

intraoperative images locating origin of fistula (encircled in green).

The patient recovered well, but 4 months later she refistulized, this time to her upper thigh as predicted, approximately 15 cm distal to her anus and 25 cm proximal to the original fistula. Her drainage was limited to mucus isolated from the rectum. Due to concern for future infections, her nutritional status was optimized with the support of a hospital nutrition team, and she ultimately underwent a robotic abdominoperineal resection with gluteal V-Y advancement flap and excision of the fistula. Pathology results of the resection specimen were again negative for malignancy and cultures grew Proteus mirabilis, so she was treated with amoxicillin–clavulanate for 14 days, per infectious disease specialist recommendation. The patient recovered without incident or further fistula and at 2 years follow-up remained in good health.

The patient was informed that data concerning the case would be submitted for publication. The patient agreed to presentation of their case and informed consent was obtained. The CAse REport (CARE) Statement and Checklist guidelines for case reports were followed for reduction of bias and reporting of accurate clinical information.

Conclusion

Enterocutaneous fistulae occur for numerous reasons, most commonly associated with foreign bodies, history of radiation therapy, persistent infection (anastomotic leak), ischemia or inflammation, and poor wound epithelization usually secondary to malnutrition, neoplasm, distal obstruction, and sepsis. ⁶ The patient described in this case had a previous history of rectal cancer and a status of post TaTME with prior neoadjuvant therapy. This is a rare presentation of rectocutaneous fistula involving the posterior thigh, with fistula opening in the most distal region of the thigh.

TaTME is associated with mesorectal specimens of better quality and a longer distal resection margins that are established at the beginning of the procedure under direct view. ¹⁰ Robotics, when available, will probably overcome the steep learning curve related to the complexity of TaTME. ¹⁰ Despite this technological advance, there are reports of anastomotic leaks resulting in reoperation. ¹³ Other long-term complications include conduit ischemia, anastomotic stricture, and fecal incontinence. However, long-term oncologic outcomes of TaTME have not been reported.

This case study is unique in that the patient’s fistula developed likely due to conduit ischemia (low grade), as it was noted that the patient had some severe stricturing at the anastomosis. Had this been an anastomotic leak, the patient would have most likely presented with a posterior sacral abscess, ¹⁴ which would have been readily noticeable within the first few months of surgery. Anastomotic leakage and presacral abscess after rectal cancer surgery are a major concern for the colorectal surgeon; there is an incidence of 9.7% Presacral abscess in patient populations following surgery. The presentation of anastomotic leak is widely variable and ranges from florid sepsis and peritonitis, to a more insidious course with fevers, leukocytosis, and abdominal pain. ⁵ On the other hand, metastasis from colorectal cancer to a fistula is very rare. The mechanism is thought to involve the adherence of free cancer cells to the tract of the fistula, followed by tumor proliferation and invasive growth. ¹² This patient also had the fistula track through the posterior thigh, rather than through the surrounding gluteus, as is customary for fistulae associated with TaTME.

It is also remarkable that the patient did not show symptoms earlier or become septic prior to presentation. She presented with a skin lesion in the popliteal fossa, thought to be an insect bite that had become infected, which was only diagnosed as fistula once feculent drainage was discovered. This means that the fistula tract had tunneled throughout the posterior thigh. She never developed compartment syndrome or intramuscular abscess, which is the mostly likely rationale for lack of sepsis initially at presentation. The incidence of sepsis has been steadily increasing in the past decade. Sepsis was ranked in the top four most costly conditions, costing an aggregate of $20,298,000 million yearly. ⁵ Musculoskeletal infection incidence has had a steep increase in recent years, one study estimates an annual increase of 34.2%. Reports of posterior thigh abscess are rare, but those reported typically involve intramuscular abscess and even sciatic nerve involvement in some cases. ^15,16 Our patient thankfully had no intramuscular involvement or neurologic damage despite her abscess.

This patient’s presentation of lower limb infection leading to sepsis adds to her unique presentation of fistula formation. Chou et al reported a similar finding with right-sided lower limb sepsis tracking distally from the medial aspect of the psoas muscle to give rise to a multiloculated abscess in the adductor compartment. ¹⁷ Their study underlined the significance of perforated colonic carcinoma as a leading differential for lower limb abscesses. ¹⁷ Additionally, Mascolino et al presented abscess formation and infection with involvement of the lower extremities in the context of Crohn’s disease. They reported a case of a large abscess of the right iliac fossa reaching the spaces between the anterior lateral muscles of the right thigh as far as the anterior lateral pre-tibial region, leading to infection and sepsis. ⁹ They conjectured that one possible cause of sepsis and poor prognosis was bacterial translocation. This may be a similar process by which the patient in our case became septic once the posterior compartment of her thigh was incised and the abscess decompressed.

This case was also unique in that, due to the complexity of the patient’s condition, a multidisciplinary approach was vital to a good patient outcome. It is rare and challenging to connect multiple specialists together, especially in a private practice setting, but the colorectal surgery team in this case coordinated multiple meetings and check-ins with the various specialists involved. The index surgical procedure was completed by both the colorectal and orthopedic surgeons, with subsequent washouts and eventual closure by orthopedics and plastic surgery. The infectious disease specialist even observed the index surgical procedure and subsequent washouts and reviewed the cultures with the surgical teams. The final procedure, robotic abdominoperineal resection with V-Y advancement and fistula excision, was performed by all three surgeons (plastic, orthopedic, and colorectal surgery) together. In decision making for this case, the colorectal surgeon’s knowledge of fistula formation habits was vital in recognizing that the patient would likely refistulize with the presence of a rectum at the time of index procedure, as the rectum will still produce mucus. The orthopedic surgeon and plastic surgeon thus recommended a staged approach, hoping to close the patient’s thigh incision primarily together and clear her initial infection before proceeding to a flap reconstruction, as infection would risk flap viability. The nutritionist was key in optimizing the patient’s presurgical nutritional status, which was important for preventing wound healing issues. The infectious disease specialist’s expertise was also key in identifying the optimal antibiotic and antifungal regimen for the patient. This team approach to care, focusing on communication and coordinated care, resulted in a good prognosis for this patient.

The present case emphasizes the possibility of varied presentations of fistula formation following treatment of rectal cancer. It also underscores the importance of a team approach to complex surgical problems and ongoing follow-up with patients. The unique presentation and the rare location of the fistula make this an important case to consider, especially in the context of the TaTME procedure. More data are needed about the long-term findings and oncological outcomes of TaTME, with future directions including surveillance for incidence of fistula formation following cancer treatment in postoperative patients following TaTME.