Malignant recurrence of a tailgut cyst resected 50 years ago.

Abstract

A 55 year old female presented to clinic with lower back and right sided sciatic nerve pain. She reported no recent trauma, neurological deficits or constitutional symptoms. There were no associated bowel or urinary symptoms or PR bleeding. Her medical history was significant for a previous resection of a benign coccygeal cyst at the age of 5, with no further symptoms since surgical removal. On examination, there were no focal neurological deficits. Her PR examination was significant for a palpable mass posteriorly beginning 2 cm and extending up to 7 cm from the anal verge. A transverse scar was also noted posterior to the anus. She underwent further investigations with a colonoscopy and MRI rectum. Her MRI demonstrated a complex cystic presacral lesion which was multiloculated with septations measuring 68 × 59 × 70 mm craniocaudal (See Fig. 1). Nodular enhancing components along the cyst wall were concerning for potential malignant changes. Her colonoscopy did not demonstrate any luminal involvement from the presacral lesion. The patient underwent excision of the presacral tumour via the posterior perineal approach. Macroscopically, the resected specimen measured 130 × 50 × 50 mm, consisting of fibroadipose tissue with an overlying skin ellipse (See Fig. 2). Microscopically, there was a multi-cystic mass lined by a mixture of respiratory, squamous and intestinalised epithelium in keeping with a tailgut cyst. The wall of the cyst demonstrated invasive adenocarcinoma with mucinous features and a signet ring cell component with positive margins. These histological features were diagnostic of an invasive adenocarcinoma arising from a tailgut cyst. She had a subsequent staging CT chest-abdomen-pelvis and PET scan which did not demonstrate any distant metastatic disease. The patient's case was reviewed at our institution's multidisciplinary team meeting and she was recommended to commence adjuvant chemoradiotherapy. Tailgut cysts are benign congenital cystic lesions derived from the incomplete regression of the embryonic hindgut.1, 2 Due to their location in the presacral space, they often present with non-specific symptoms and therefore a high degree of clinical suspicion is required for diagnosis and treatment. All tailgut cysts carry the potential for malignant transformation into adenocarcinoma, neuroendocrine tumours, squamous carcinoma, carcinoid tumours or sarcoma. The incidence of malignant transformation of tailgut cysts have been reported to be 2%–13%,3 with the most common being adenocarcinoma.4 Due to their potential for malignant transformation, early identification and complete surgical resection is imperative. The mainstay of treatment for tailgut cysts is complete surgical resection of all the epithelial lining with a negative margin of excision.2, 5, 6 Incomplete surgical resection can lead to significant morbidity associated with complications including abscess formation, fistulisation, malignant spread and recurrence of the presacral lesion.6, 7 The recurrence and malignant transformation observed in our patient may be attributed to previous incomplete resection of the tailgut cyst as a child. Our case demonstrates a retrorectal adenocarcinoma arising from a previously excised tailgut cyst. This case highlights the risk of malignant transformation in any residual tissue after excision and highlights the rationale behind complete excision of tailgut cysts.