Colo-Ovarian Fistula With a Background of Endometriosis: A Report of Three Cases

Our first patient was a 36‐year‐old woman (gravida 0, para 0) who presented with abdominal pain. She had undergone a right salpingo‐oophorectomy 16 years earlier for an ovarian endometrioma. Five years prior to presentation, she underwent laparoscopic surgery for recurrence of a left ovarian endometrioma; however, the procedure was aborted because of severe adhesions. The cyst continued to grow and reached 7 cm in size. A laparotomy with left ovarian cystectomy was performed. However, postoperative abdominal pain persisted; thus, gonadotropin‐releasing hormone (GnRH) antagonist was administered for 3 months. Two months prior to presentation, she was hospitalized with lower abdominal pain and fever. There were no symptoms suggestive of bowel involvement, such as defecation pain, tenesmus, hematochezia, or localized rectal tenderness. She was diagnosed with PID and left ovarian endometrioma with an abscess, and was treated with antibiotics. Magnetic resonance imaging (MRI) revealed a left ovarian endometrioma adherent to the sigmoid colon; T2‐weighted fat‐suppressed (T2FS) imaging revealed a tear‐drop‐shaped high‐intensity lesion, the narrow portion of which extended into the colon lumen, suggesting the possibility of a colo‐ovarian fistulous connection (Figure  1a ). No fatty component was observed; therefore, teratoma was ruled out. Computed tomography (CT) performed around the same time showed a 6‐cm cystic mass in the left adnexa containing intralesional air (Figure  1b ), suggesting a possible communication between the intestine and the ovary, further supporting the presence of a fistula. (a) An axial image of T2‐weighted fat‐suppressed (T2FS) magnetic resonance imaging (MRI) of Case 1. MRI revealed a tear‐drop‐shaped high‐intensity lesion, the narrow portion of which extended into the colon lumen, suggesting the possibility of a colo‐ovarian fistulous connection. The left image shows the original scan, and the right image shows the annotated structures: The colon (pink outline), ovarian cyst (yellow outline), and the fistulous tract (red arrow). (b) Computed tomography (CT) performed around the same time as (a). CT showed a 6‐cm cystic mass in the left adnexa containing intralesional air (yellow arrow). Given the potential risks of surgical castration and bowel perforation associated with the removal of an ovarian endometrioma, a gonadotropin‐releasing hormone (GnRH) antagonist (relugolix 40 mg/day) was administered for 6 months, followed by dienogest 2 mg/day. The patient's symptoms remained stable for a period of 9 months. The second patient was a 42‐year‐old woman (gravida 1, para 1) who presented with dysmenorrhea, pelvic pain, and a one‐week history of fever. She also did not complain of any bowel‐related symptoms. On T2‐weighted images, a high‐intensity area, similar in signal characteristics to the ovarian endometrioma content, appeared to extend from within the cyst toward the colo‐rectal lumen, suggesting a possible fistulous tract (Figure  2a,b ). MRI also demonstrated the presence of free air within the left ovarian endometrioma, further supporting a possible communication between the intestine and the ovarian endometrioma and suggesting the presence of a fistula. (a) An axial image of T2‐weighted magnetic resonance imaging (MRI) of Case 2. A high‐intensity area, similar in signal characteristics to the ovarian endometrioma content, appeared to extend from within the cyst toward the colo‐rectal lumen, suggesting a possible fistulous tract (red arrow). Yellow arrow indicates free air. (b) A sagittal image of T2‐weighted magnetic resonance imaging (MRI) of Case 2. A sagittal image also demonstrates the presence of free air (yellow arrow) and findings suggestive of a fistulous connection between the recto‐sigmoid colon and the ovarian endometrioma (red arrow). Antibiotic treatment was administered, and her symptoms improved. A follow‐up MRI performed 1 month later revealed that the free air had resolved. Consequently, the patient was managed expectantly without any medication for 9 months. During this period, there was no recurrence of PID symptoms. The third patient was a 42‐year‐old woman (gravida 2, para 0) with no significant medical history. Nine years prior to presentation, she developed dysmenorrhea and severe anemia and was diagnosed with adenomyosis. Four years prior to presentation, her dysmenorrhea worsened, and she was admitted to our hospital. At that time, she also wished to undergo infertility treatment; however, this was not feasible due to severe anemia. A GnRH agonist was administered. She eventually discontinued infertility treatment and underwent a hysterectomy. Preoperative MRI revealed diffuse adenomyosis but no ovarian cysts. A hysterectomy with bilateral salpingectomy was performed to relieve symptoms. Intraoperatively, the uterus was found to be enlarged with diffuse adenomyosis and multiple myomas, and dense adhesions were observed around the left ovary. The adhesions surrounding the left ovary were partially dissected; however, the adhesions involving the recto‐sigmoid colon were left untouched. The uterus with bilateral fallopian tubes was removed. Pathological examination confirmed adenomyosis and uterine leiomyoma, with no evidence of malignancy. The postoperative course was initially uneventful; however, on postoperative Day 2, following the resumption of oral water intake, the patient developed fever and abdominal pain and was diagnosed with peritonitis. Although antibiotics were initiated, her symptoms worsened the following day. A CT scan revealed a low‐density area without contrast enhancement, raising suspicion for rectal perforation. An emergent laparotomy was performed, and the left ovary was found to be densely adherent to the recto‐sigmoid colon, as observed in the previous surgery. An intraoperative leak test was performed by insufflating air through the rectum. No direct leakage from the intestinal tract into the abdominal cavity was observed. Instead, air leakage was observed from the surface of the ovary opposite the side that was densely adherent to the intestinal tract. Based on these findings, we concluded that there was a fistula between the intestinal tract and the ovary and that the leakage from the intestinal tract was reaching the abdominal cavity via the ovary, and we decided to perform the en bloc resection of both the affected part of the sigmoid colon and the left ovary followed by colostomy. Macroscopic examination of the resected specimen clearly revealed a fistulous tract extending from the mucosal surface of the intestine into the ovary (Figure  3a ), which was adherent to the intestinal wall. The ruptured segment of the intestine was covered by the ovary and did not exhibit features consistent with mechanical injury. Pathological examination revealed a diverticulum in the subserosal layer and endometriosis in the mucosa surrounding the fistula. From a retrospective viewpoint, the following scenario is assumed. A fistulous connection between the recto‐sigmoid colon and the ovary existed prior to the initial surgery; however, the dense adhesions around the left ovary effectively “sealed” the surface of the ovary. When adhesions surrounding the ovary were partially dissected in the initial surgery, the “seal” on the ovarian surface was “disrupted”, allowing intestinal contents—previously trapped within the ovary—to begin leaking into the abdominal cavity (Figure  3b ). The colostomy was closed within 3 months. (a) Macroscopic appearance of the resected specimen in Case 3. Macroscopic examination of the resected specimen clearly revealed a fistulous tract extending from the mucosal surface of the intestine into the ovary, which was adherent to the intestinal wall. (b) Schematic scenario in Case 3. A fistulous connection between the recto‐sigmoid colon and the ovary existed prior to the initial surgery (the top figure). When adhesions surrounding the ovary were partially dissected in the initial surgery, the “seal” on the ovarian surface was “disrupted”, allowing intestinal contents to begin leaking into the abdominal cavity (the bottom figure).

Sayuri Fukaya: conceptualization, data curation, formal analysis, methodology, project administration, resources, validation, visualization, writing – original draft. Gentaro Izumi: conceptualization, data curation, investigation, project administration, resources, validation, writing – original draft. Kaori Koga: data curation, resources, supervision, writing – original draft, writing – review and editing. Yuko Sanada: supervision. Yasushi Hirota: conceptualization, investigation, supervision. Yutaka Osuga: supervision.

The authors have nothing to report.

Here we report three cases of colo‐ovarian fistulas with different courses. In Cases 1 and 2, the patients with ovarian endometriomas exhibited imaging findings suggestive of communication between the intestine and the ovary. In both cases, the fistulas resolved after conservative treatment. In Case 3, the fistula was not identified preoperatively; however, a colo‐ovarian fistula became evident after surgery and was managed surgically. All three cases of colo‐ovarian fistulas were associated with endometriosis, although only a few similar cases have been reported in the literature. Cases 1 and 2 involved fistulas associated with ovarian endometrioma. Case 3, the fistula associated with endometriosis of the sigmoid colon, had no evidence of ovarian involvement, making this the first reported case of its kind. We suspected that, in this case, a colonic diverticulum and endometriotic lesion overlapped, contributing to the formation of the fistula. Diverticula are known to be associated with fistula development [ 5 , 6 , 7 ], and in this case, the inflammation caused by endometriotic lesions may also have played a role in its formation. In two of the three cases presented, conservative management was chosen. In the existing literature, colo‐ovarian fistulas associated with endometriosis have predominantly been treated surgically, and to our knowledge, no reports have documented successful conservative management. Although surgical intervention is often considered the first‐line approach, it carries significant risks, including colostomy and bowel perforation. These risks highlight the potential value of conservative treatment strategies, which may offer a safer alternative and improve patient quality of life. In our two conservatively managed cases, symptoms were successfully controlled without surgical intervention, suggesting that nonsurgical approaches may be a viable option in selected patients with endometriosis‐associated colo‐ovarian fistulas. Imaging diagnosis of colo‐ovarian fistulas remains challenging. In Cases 1 and 2, MRI revealed a contiguous luminal structure between the intestinal tract and the ovarian endometrioma adhesions. Notably, in both cases, MRI and CT demonstrated the presence of free air within the ovary. Although the possibility of gas‐producing bacterial infection cannot be entirely excluded, the clinical presentation and imaging findings in these two cases suggest that the intralesional gas was more likely the result of intestinal gas leakage through a fistulous connection. Based on our experience with the present cases, we would like to propose that the presence of air within the ovary may serve as a warning sign of a possible fistulous connection with the intestinal tract. In Case 3, it was suggested that the fistula between the intestine and ovary may have been effectively “sealed” by dense adhesions surrounding the ovary. This case highlights the important lesson that unintentional disruption of such a “seal” during adhesiolysis for endometriosis can result in the reopening of a previously closed lumen and the subsequent manifestation of symptoms. It should be noted that such a scenario may occur during extensive adhesion dissection in endometriosis, even in the absence of direct intraoperative bowel injury.

The authors have nothing to report.

Endometriosis is defined as the presence of endometrial tissue outside the uterus. Although the exact cause remains unknown, the most widely accepted theory is retrograde menstruation, in which endometrial tissue within menstrual blood flows back through the fallopian tubes during menstruation. These cells then implant on the pelvic peritoneum and ovarian surfaces, where they proliferate, invade, and spread to the uterus. Endometriosis, which affects an estimated 1 in 10 women, causes chronic pelvic pain during menstruation and infertility; however, the actual prevalence may be much higher, as many cases remain undiagnosed. Endometriosis is also associated with pelvic inflammatory diseases (PID). Patients with PID have been reported to have a higher frequency of endometriosis [ 1 , 2 ]. Various immunological abnormalities observed in endometriosis are thought to be associated with PID [ 3 ]. Most patients with endometriosis‐related PID present with tubo‐ovarian abscesses [ 4 ]; however, PID may also manifest as a colo‐ovarian fistula [ 5 , 6 ]. Previous studies have identified colo‐ovarian abscesses during surgery for intestinal complications. Therefore, the epidemiology of colo‐ovarian fistulas, their potential nonsurgical management, and patient outcomes remain poorly understood. Here we report three cases of colo‐ovarian fistulas, all of which were associated with endometriosis. Two of the cases were successfully managed without surgical intervention. All patients provided written informed consent for the publication of this case report and accompanying images.

The authors declare no conflicts of interest.