Incidentally Detected Ovarian Teratoma on Fluorodeoxyglucose (FDG) PET/CT Scanning in a Patient With Gastric Cancer

This report aims to present the imaging findings of an ovarian teratoma incidentally detected during fluorodeoxyglucose (FDG) positron emission tomography combined with computed tomography (PET/CT) examination performed for the staging of gastric carcinoma, and to discuss these findings in the context of the current literature. A 53-year-old woman with a recently confirmed diagnosis of gastric carcinoma via endoscopic biopsy was referred for PET/CT staging. Imaging revealed pathological FDG uptake along the gastric wall from the cardia to the lesser curvature, consistent with the primary tumor. Additionally, a well-circumscribed, smoothly marginated pelvic mass with no appreciable FDG uptake was identified, demonstrating tooth-like calcifications and fatty fluid components on CT. Given its mixed-density composition, ovarian teratoma was considered the primary differential diagnosis, which was subsequently confirmed on targeted ultrasonography. Mature cystic teratoma typically presents as a metabolically inactive lesion on PET/CT; however, its characteristic CT morphology allows for reliable incidental identification. Awareness of incidental ovarian pathologies encountered during PET/CT examinations performed for unrelated malignancies is of considerable clinical importance.