Neuroendocrine tumour developing within a long-standing tailgut cyst: case report and review of the literature.

A tailgut cyst is a rare congenital lesion that can develop in the presacral space from the remnants of an embryonic hindgut. It is unusual for malignant change to occur in a tailgut cyst. We report a case of a large long-standing tailgut cyst, which was removed during a laparotomy. Histopathology showed a well-differentiated neuroendocrine tumour (primary carcinoid tumour) arising in a tailgut cyst. We reviewed the English literature for all adult cases with this condition. All original articles were reviewed, and data were compiled and tabulated. Including this report, 29 cases of NET developing in a tailgut cyst were found in the English literature. Tailgut cysts have been reported as more common in females, with a mean age of presentation in the fifth decade (Devine, in: Zbar A, Wexner S (eds) Coloproctology. Springer specialist surgery series, Springer, London, 2010; Hjermstad and Helwig in Am J Clin Pathol 89:139-147, 1988). Tailgut cysts may undergo malignant change including adenocarcinoma, sarcoma, and NET (Mathis et al. Br J Surg 97:575-579, 2010; Messick in Dis Colon Rectum 61:151-153, 2018; Patsouras et al. in Colorectal Dis 17:724-729, 2015; Chereau et al in Colorectal Dis 15:e476-e482, 2013). It is difficult to estimate the true incidence of malignant change in a tailgut cyst, with the literature reports only limited to case reports and small-case series. Although rare, our case confirms need to consider the possibility of a malignant component, even in a benign process such as a tailgut cyst. This prompts consideration for upfront definitive management.