EP243 - Retrorectal Tailgut Cyst: A Case Report

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Purpose/Background: Retrorectal tailgut cysts, or cystic hamartomas, are rare congenital cystic lesions found in the presacral region. They form when the embryologic tailgut fails to involute and are typically asymptomatic but can grow and become symptomatic secondary to mass effect. These cysts are frequently misdiagnosed due to rarity and varied presentation, and biopsy can lead to infection or hemorrhage. We present a case of retrorectal tailgut cyst in a woman in her 50’s with a family history of Lynch syndrome.

Methods/Interventions: The patient initially presented with flank pain secondary to urinary tract infection and was incidentally found to have a presacral cystic mass measuring 7 cm x 6 cm x 6 cm. She achieved symptomatic relief of her UTI with antibiotics and followed up with her primary care physician for follow up. Pelvic ultrasound demonstrated similar findings of a retrorectal cyst measuring 7 cm in diameter. An MRI with and without contrast further characterized the mass, revealing a midline/left paramedian lobular cystic retrorectal mass measuring 7.3 cm, containing a few internal incomplete septations. The mass appeared non-enhancing on T2-weighted imaging and exhibited a few T1 hyperintense foci. The mass was located entirely below S3. The patient notably was asymptomatic and had no changes in bowel or bladder function. She had an extensive family history of Lynch syndrome and colorectal cancer, but otherwise no other history and had minimal health problems. She underwent colonoscopy demonstrating fullness of the presacral space on digital rectal examination and on scope retroflexion, but no intraluminal masses were appreciated, and the rest of the colon and rectum cleared. Due to the family history of Lynch, genetic testing was performed, which was negative.

Results/Outcomes: Given size, location, and reports of malignant degeneration of presacral cysts, the patient elected to undergo posterior approach presacral cyst excision. Pathological examination of the fluid and histological examination of the cyst lining revealed a congenital tailgut cyst. The patient made a full recovery following surgery. She had postoperative right lateral femoral cutaneous nerve palsy that likely was due to patient positioning and improved with time and physical therapy.

Conclusion/Discussion: The retrorectal, or presacral, space is a potential space that becomes clinically evident in the setting of mass growth in the area, such as a tailgut cyst. Clinical presentation of tailgut cysts is nonspecific with half of patients presenting asymptomatically with incidental findings on imaging and the other half with mass effect symptoms such as constipation, diarrhea, rectal pain and/or bleeding, changes in stool, compression neuropathies, and symptoms of urinary obstruction. For cystic structures, biopsy can introduce infection and increase recurrence rates after resection. Malignant degeneration of tailgut cysts is described in isolated reports with rates ranging from 13%- 40% in some case studies to include adenocarcinoma, carcinoid, and sarcoma, thus surgical resection is preferred to prevent transformation or infection.