Case Report
A 52 years old woman with a large pelvic cyst was admitted to our hospital. There was no history of other gastrointestinal conditions, cardiovascular conditions, infection, trauma, or family history. She had undergone right breast cancer resection 2 years ago, and the pelvic cyst was detected by positive emission tomography in the preoperative examination for the breast cancer. There were no symptoms and findings of malignancy, so she was kept under observation. However, a follow-up CT showed an increasing tendency of cystic mass in size, and she was referred to our hospital. Her laboratory studies were unremarkable except for CA19-9. The level of CA19-9 was 142.4U/ml. CT of the pelvis with contrast revealed a 4.5 cm well-defined, homogenous cystic mass in the right para-rectal area (Fig.1). The inside has a poor contrast effect, and there are no findings suggestive of a solid component. Pelvic MRI with contrast demonstrated a 4.4cm retroperitoneal cystic tumor with high signal intensity on T1-weighted images in the right para-rectal area (Fig.2). The cyst appeared continuous with the rectal wall.
The patient underwent robot-assisted low anterior resection without a preoperative definitive diagnosis. Epidermoid cyst, duplication cyst, and tailgut cyst were mentioned as differential diagnoses based on the radiological findings. Access was gained with a 8-mm supraumbilical metallic robot port followed by four same-size ports (Fig.3). The abdomen was insufflated to an abdominal pressure of 10 mm Hg with CO2 gas supplied by AIR SEAL® intelligent flow system. The mesorectal dissection from the sacral promontory was continued up to the level of puborectalis sling and the levator ani muscles. After cystic tumor-specific mesorectal excision was performed, the clip for the bowel clamp was applied to the distal side of the cystic tumor for transanal bowel irrigation. The patient-side cart was rolled out after transection of the rectum with the cyst. The umbilical wound was then extended to retrieve the specimen and closed. For subsequent anastomosis, the double stapling technique was performed by using a circular stapler. The excisions of cysts were complete with macroscopically negative margins. There was no intraoperative event and the operative time was 356 minutes.
The surgical specimens consisted of a cystic lesion from the posterior wall of the rectal to the right side, with no continuity with the rectal lumen (Fig.4). Histologically, most of the cyst lumen has epithelial shedding, granulation tissue and histiocyte clusters, and numerous cholesterin fissures and hemosiderin deposits in the thickened fibrous connective tissue. The remaining epithelium shows morphology similar to anal canal epithelium, which is a mixture of goblet cells in a cubic to columnar epithelium of about five layers, and squamous epithelium-like. The epithelium is surrounded by developed smooth muscle tissue and transitions to skeletal muscle tissue, which is thought to be the levator ani muscle. It is a tissue image that distinguishes between a duplication cyst and a tailgut cyst. Although the nerve plexus is not clear and the epithelium is not a glandular epithelium, which is not typical as a duplication cyst, the above diagnosis was made because the thickening of the muscular layer is conspicuous to make it a tailgut cyst.
The postoperative course was uneventful. The patient was discharged 27 days after surgery, and she has remained in excellent health so far for a year and 5 months.