• Zekai Zhang, Ling Zhang, Hua Zhang, Xiaoguang Huo, Wenzhe Xu, and Yongting Zhang.
• Department of Ultrasound, Zibo Central Hospital, Zibo, China.
• Medicine (Baltimore). 2025 Jan 17; 104 (3): e41284e41284.

RationaleA case of retroperitoneal cystic mature teratoma in an adult male. Retroperitoneal cystic mature teratoma is a type of teratoma. The disease has occult onset, does not have the typical characteristics of teratoma, and is difficult to distinguish from cystadenoma and other diseases. Cystic mature teratoma is benign, but it has a certain risk of malignant transformation. The purpose of this case report is to highlight the specificity of the case, collect and analyze the imaging features of the disease, and provide assistance for daily clinical diagnosis.Patient ConcernsAdult extraglandular abdominopelvic teratoma is extremely rare, especially in men. These masses are most commonly found by chance and require surgical resection for diagnostic confirmation after a thorough examination.DiagnosesWe report a case of retroperitoneal cystic mature teratoma in an 86-year-old man. Abdominal ultrasound revealed a cystic mass in the abdominal cavity (possibly from the pancreas). Enhanced abdominal computed tomography showed a space-occupying lesion with a lack of blood supply in the hepatogastric space (above the pancreas), and the local boundary with the pancreas was unclear. The tumor was considered first, but pancreatic cystadenoma was not excluded.InterventionsSurgical resection is the most important treatment for retroperitoneal cystic teratoma, and the best adjuvant treatment needs further study.OutcomesPostoperative pathological findings showed (retroperitoneal) mature cystic teratoma with lymphoid hyperplasia, lymphoid follicle formation, and mild to moderate atypical hyperplasia of squamous epithelium.LessonsIn conclusion, adult retroperitoneal cystic mature teratoma is a rare disease. This disease should be taken into account when we find a retroperitoneal cystic mass on our routine imaging. The shortcomings of this case report are mainly single case, small sample size, need to collect more cases, and long-term follow-up to summarize the characteristics of retroperitoneal cystic mature teratoma, in addition, this case did not undergo magnetic resonance imaging examination, magnetic resonance images cannot be analyzed.Copyright © 2025 the Author(s). Published by Wolters Kluwer Health, Inc.

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