Adenocarcinoma with Lymph Node Metastases of a Recurrent Tailgut Cyst: A Report of a Rare Case

Tailgut cyst (TGC) is a rare congenital lesion noted in the retrorectal space and occurs due to failure of regression of tailgut appendage derived from the embryonic hindgut. Herein, a 46-year-old female presented with a painful cystic swelling in the sacral region for 3 months. Past history of swelling in the sacral region, noted since birth was excised in 2020 and diagnosed as TGC. The swelling recurred and was aspirated four times between 2021 and 2023. Examination showed a diffuse, soft, fluctuant swelling with ill-defined borders of size 10 × 8 cm along with right inguinal lymphadenopathy. PET-CT showed a well-defined, multiloculated, heterointense, solid cystic lesion measuring 11 × 9.2 × 11.7 cm in the presacral region infiltrating the S3-S5 vertebral body and gluteus medius muscle. Bilateral iliac, right inguinal and right inferior gluteal lymph nodes showed metastatic deposits. Differential diagnoses of malignant transformation of TGC with metastases and chordoma with metastases were considered. A biopsy of the right inguinal lymph node showed tumour cells arranged in clusters and acini indicating features of metastatic adenocarcinoma. Tumour cells were immunopositive for pan CK, CK 20 and CDX 2 and negative for CK 7 and S-100. Painful sacral swelling with a significant past history of TGC with recurrences, infiltration of the vertebral body, metastatic deposits in the lymph node and positivity for pan CK, CK 20 and CDX 2 helped us diagnose adenocarcinoma with lymph node metastases of a recurrent TGC. The patient is currently receiving chemotherapy and is on follow-up.