OP09.03: Tailgut cyst mistaken for pelvic endometriotic nodule: a case report

Tailgut cysts (or rectal cyst hamartomas) are retrorectal developmental cysts. They originate from the tailgut and embryological remnants of neuroenteric canal in the presacral-retrorectal space. At macroscopy, they are usually multilocular with mucoid and gelatinous cystic content. At histology, the epithelium is squamous, transitional, columnar and mucinous and contain disorganised smooth muscle bundles. Malignancy infrequently occurs, at a rate of less than 8%, and it may be adenocarcinoma or carcinoid. We present a 30-year-old patient with pelvic pain, dyschezia, dyspareunia, in estrogen-progestin therapy. A Transvaginal ultrasound examination showed a unilocular cyst of 63 mm with regular walls, with mixed cystic content and hyperechogenic spots, between the posterior wall of the rectum and the sacrum. The mass was not vascularised at Colour Doppler examination and no acoustic shadows were seen. Our primary hypothesis was a Tailgut cyst. The MRI confirmed the unilocular cyst hyperintense in T2 and hypointense in T1, suggesting a cyst with liquid content and thin walls. At LPS, the mass was seen in the retroperitoneum, adjacent to the levator ani, infiltrating the sacri periostium, the levator ani and the piriformis muscle. Due to the adhesions to the posterior wall of the rectum, it was necessary to stitch the rectus muscle tunic. No sign of endometriosis was detected during surgery. Final histology was Tailgut cyst. In conclusion, Tailgut cyst is a rare disease presenting typical ultrasound features, it should be suspected when a retroperitoneal mass is detected at imaging. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.