Organized urachal abscess mimicking urachal carcinoma on FDG PET/CT

Urachal inflammation is rarely seen in adults. Two patients with suspected abdominal tumor underwent FDG PET/CT. One patient showed an irregular hypermetabolic mass anterosuperior to the bladder. The other patient showed a thick-walled cystic mass with strong FDG uptake extending from the bladder dome to the anterior abdominal wall. Urachal carcinomas were suspected based on imaging findings. Both patients underwent complete resection of the masses. However, both masses were organized urachal abscesses confirmed by pathological examination. These two cases highlight that differentiation between organized urachal abscess and carcinoma is difficult on the basis of imaging.