Tailgut cyst with adenocarcinoma transition: A rare case report

RATIONALE: Tailgut cyst (TGC) is a rare congenital disease that originates from residues of the tail intestine during the embryonic period. Most TGCs are benign lesions and the malignant transition is very rare. PATIENT CONCERNS: A 50-year-old woman attended our department complaining of defecation difficulty for more than 2 months. She reported irregular defecation with a small amount of liquid stool, 3 to 4 times per day. DIAGNOSIS: Biochemical analysis showed high levels of carcinoembryonic antigen (79.89 ng/mL; normal, 0–3 ng/mL) and carbohydrate antigen 199 (57.60 U/mL; normal, 0–35 U/mL). Abdominal computer tomography and magnetic resonance imaging showed a large cystic mass with enhanced signals. Post-surgical histopathology indicated that the mass was a TGC with adenocarcinoma transition. INTERVENTIONS: The cyst was completely resected. Symptomatic treatment was further performed, and the patient recovered well. LESSONS: We reported a rare case of a large TGC with adenocarcinoma transition. CT, MRI, and histopathology are important to diagnose TGC. Complete surgical resection is the first choice to treat TGC.