A neuroendocrine tumor arising in a tailgut cyst: Case report and literature review

Introduction and importance: Cystic lesions in the retrorectal space include developmental abnormality, inflammatory process, and tumor-relevant cysts. Among them, the tailgut cyst is the most common lesion which is featured by the complex epithelium lining the wall. It is generally accepted that tailgut cysts are embryonic residues and are mostly benign, but there are also reports about malignant transformation and even metastasis. Case presentation: A 44-year-old female complained a sacrococcygeal discomfort more than one year. The imaging diagnosis was an infectious cyst. After surgery, a solid region was defined in a cyst. Morphologically, the region was composed of bland epithelia forming glandular or ribbon-like structure, with round nuclei and fine chromatin. Immunohistochemically, the cells were positive for CK7, CD56 and synaptophysin. The Ki-67-positive cells were about 1 %. The final diagnosis is a low-grade neuroendocrine tumor arising in a tailgut cyst. The patient was living without recurrence by the follow-up of 20 months after surgery. Clinical discussion: By reviewing the previously reported NET arising from tailgut cysts, we summarized 29 cases of neuroendocrine neoplasms that reported detailed information, and the majority are women. We found that the higher-grade tumor presented a higher tendency of distant metastasis or recurrence after surgery. Complete resection and full evaluation by pathologists are necessary to get a correct diagnosis and avoid disease progression. Conclusion: We reported the rare case of NET G1 arising from a tailgut cyst and reviewed relevant reports, in order to broaden differential diagnoses when an isolated mass is identified in the retrorectal space.