A case report of colouterine fistula due to colonic diverticulitis: a rare complication

Colouterine fistula is a very rare entity because of the sturdy and muscular nature of the uterus. Due to the rarity of this condition and nonspecific clinical findings, it poses a diagnostic challenge to treating physicians. Here, we report a case of a 64-year-old female, who presented with lower abdominal pain. Clinically, there was suspicion of a recto-vaginal fistula. However, on imaging, she was found to have a colouterine fistula secondary to sigmoid diverticulitis. It is essential to be aware of this rare complication of sigmoid diverticulitis. The imaging plays a cardinal role in the diagnosis and guiding the management of this disease.


Background
Diverticular disease of the colon is a commonly seen entity in the developed countries. The prevalence of this disease among Asian countries is comparatively quite low. Consumption of a diet having a low fiber content has been attributed to have a major role in the development of diverticular disease. There has been an increase in its incidence in Asian countries due to the adoption of western dietary habits. The incidence of colonic diverticulosis also increases with aging [1].
Diverticulitis due to infection and inflammation of the diverticula is a common complication of diverticular diseases with a complication rate of around 20%. Diverticulitis itself can result in various secondary complications like stricture formation, perforation, bleeding, and formation of a fistula. Fistula formation, which is communication between two surfaces lined by epithelium, accounts for~2% of total cases of complicated diverticulitis [1].
The thick musculature of the uterus is generally resistant to involvement by benign or malignant disease.
Hence, a colouterine fistula is a rare occurrence, particularly as a complication of diverticulitis [2]. We report a case of sigmoid diverticulitis with the formation of colouterine fistula in a 64-year-old female.

Case presentation
A 64-year-old female presented with complaints of lower abdominal pain in the region of left iliac fossa and supra-pubic region of 1-month duration. She was evaluated for urinary tract infection, and a gynecological consult was also taken. On per speculum examination, fecal matter was seen in the vagina and a provisional diagnosis of the rectovaginal fistula was made. She did not have prior history of similar symptoms. Her medical history and family history were unremarkable.
A contrast-enhanced computed tomography was performed on a 16 slice CT scanner. Positive oral and rectal iodinated contrast was administered followed by intravenous administration of 60 ml of non-ioniciodinated water-soluble contrast at a rate of 2.5 ml/s. CECT images of the pelvis showed multiple small outpouchings arising from the sigmoid colon with contrast filled in them, which was consistent with diverticulosis. An air-and contrast-filled outpouching was seen arising from the anterior wall of the sigmoid colon and projecting between the urinary bladder and uterus. There was uniform wall thickening of this segment of bowel with surrounding fat stranding and heterogeneous post-contrast enhancement (Fig. 1). Contrast along with air locules was noted in the endometrial cavity and cervix. However, a definite fistulous track was not well delineated on CT images. There was thickening of the subjacent posterior wall of the urinary bladder. No contrast was seen in the lumen of the urinary bladder.
Magnetic resonance imaging (MRI) of the pelvis was performed with the acquisition of multiplanar T1weighted images (T1WI), T2-weighted images (T2WI), diffusion-weighted images (DWI), and dynamic postgadolinium T1-weighted fat-saturated images. The findings seen on CECT were confirmed, and the fistulous tract between the inflamed diverticula and the uterine cavity was well delineated (Fig. 2). Hence, a final diagnosis of colouterine fistula secondary to sigmoid diverticulitis was made.
Our patient is planned for management in two stages. In the first stage, an end-colostomy has been created to allow healing of inflamed diverticulum. The second stage of resection and anastomosis will be performed in the future. Presently, patient is asymptomatic and tolerating the end-colostomy well.

Ethics approval and consent to participate
The present study was approved by the ethical board of the hospital in which the study was performed. The patient reported in this article had signed a written informed consent form. This case report was a reporting of a case in a medical educational center, in which all patients are informed that they may be subjects of scientific experiments and are informed of the ethical codes of conducts. This study was in compliance to the latest version of the Helsinki Declaration.

Discussion
Diverticular diseases of the colon are prevalent in Western countries and are one of the leading causes for outpatient visits and hospitalizations [3]. Its prevalence shows wide geographic and ethnic variability. It is considered to be low in the Asian population, mostly due to the higher fiber content in the diet [4].
Diverticulitis is inflammation or infection in diverticula and is one of the most common complications of diverticulosis. Approximately 20% of patients with colonic diverticula develop this complication. Diverticulitis can further complicate to give rise to conditions like obstruction, hemorrhage, abscess, and fistula formation. Fistula formation is a relatively rare complication of diverticulitis. It accounts for approximately 20% of surgeries for complicated diverticulitis [4].
Among fistulous complications of diverticulitis, a colovesical fistula is the most common type, followed by a colovaginal fistula. As the uterus is a thick and muscular organ, it resists invasion and the spread of inflammation. Hence, colovesical fistula is also a more common occurrence in males as compared to females. The females who have undergone hysterectomy show an equal incidence of colovesical fistula as in men, due to loss of this protective barrier [5].
The first case of colouterine fistula was reported by Lejemtel in 1909 [6]. According to his paper, the main causative etiologies identified for this condition were uterine trauma, rupture of abscess into the bowel, and carcinoma of the uterus and sigmoid colon. Later studies added radiotherapy as one of the etiological factors. Iatrogenic causes like invasive procedures and surgeries can also lead to this condition. Infectious causes remain the key etiological factors. Infection of the bowel can lead to severe inflammation and abscess formation which can decompress by perforating into subjacent pelvic organs like the uterus, vagina, and urinary bladder or through the body surface [5].
The fistulous communication between the colon and the urinary bladder (colovesical fistula) can be seen in up to 65% of the cases whereas between the colon and the vagina (colovaginal) in about 25% of the patients. Colouterine fistula is a rare complication of diverticulitis of the colon. Clinical presentation of the colouterine fistula can be varied. As the colon communicates with the uterus through a fistula tract, these patients generally present with foul-smelling fecal or purulent vaginal discharge [7].
Various radiological imaging modalities have been used for diagnosing colouterine fistula. Ultrasound is a commonly available, inexpensive, and safe imaging modality for gynecologic diseases. It is a common first-line imaging modality that is used to analyze the uterine cavity and endometrium. Although it has limited diagnostic value in the diagnosis of colouterine fistula, it plays a major role in guiding further diagnostic work-up in these patients. Sonohysterography with contrast medium can be used to demonstrate the fistula track for diagnosis of colouterine fistula [8].
There has been an increase in the use of computed tomography nowadays in the setting of an acute abdomen, and it has also been used increasingly in the evaluation of fistulous diseases of the abdomen and pelvis. In colouterine fistula, computed tomography can demonstrate the joining of walls of the uterine cavity and colon. The presence of air bubbles in the uterine cavity further strengthens the diagnosis. However, failure of the demonstration of the exact fistulous tract in all cases remains a primary limitation of this modality. Multiplanar reconstructions on multidetector CT allows improved visualization of pathology along with faster acquisition time of images [9]. Positron emission tomography is an infrequently used modality for the diagnosis. Increased activity in the endometrium is seen in cases of colouterine fistula secondary to carcinoma. However, infection and the inflammatory change associated with diverticulitis can also result in increased standardized uptake values (SUV) [10].
MRI is a non-invasive, detailed, and accurate diagnostic modality with better soft tissue resolution as compared to computed tomography. MRI can delineate the fistulous tract. T1-weighted images are useful in assessing the extension of fistula relative to the adjacent organ and associated inflammatory changes in the surrounding fat planes. Abscesses and collections are better depicted on T2-weighted images and diffusion-weighted image [11].
Surgery is the definitive management of colouterine fistula in most of the cases. In cases with underlying malignancy as the etiological factor of colouterine fistula, en bloc resection is mandatory. For underlying benign conditions, the need for a hysterectomy has not been established. In these cases, resection of the colon and drainage of the purulent uterine lesion is generally adequate as definitive treatment [7].
In cases of colouterine fistula secondary to diverticulitis, a two-stage operative procedure is generally preferred. The first stage involves resection and formation of an end colostomy. This is followed by bowel restoration by reanastomosis of the colon. Percutaneous drainage of intraabdominal abscesses is useful in pre-operative confirmation of diagnosis. It is used for stabilization of the patients and also provides definitive therapy [12].

Conclusion
Colouterine fistula secondary to sigmoid diverticulitis is a rare complication. CT and magnetic resonance imaging (MRI) play a key role in its diagnosis, preoperative surgical planning, and also in follow-up of these patients. The surgical approach is selected depending on the imaging findings and the condition of the patient.