Delayed ¹⁸F-FDG PET/CT Appearance of Urachal Adenocarcinomas

Background. Urachal carcinoma is a rare urological malignancy. Use of 18F-FDG PET/CT in urological oncology has developed slowly because of the urinary elimination of 18F-FDG. We investigated whether delayed postdiuretic 18F-FDG PET/CT could be used for diagnosing urachal carcinoma. Methods. This retrospective study included 6 patients who underwent delayed postdiuretic 18F-FDG PET/CT for the evaluation of urachal carcinoma. The delayed postdiuretic PET/CT parameters and clinical characteristics of urachal carcinoma were investigated. Results. There was no significant difference in the SUVmax between the primary tumors and the urine in the bladder before delayed diuresis (25.4 ± 19.5 vs. 42.9 ± 31.1, P=0.18). However, the SUVmax of the primary tumors was significantly higher than the SUVmax of urine after delayed diuresis (25.4 ± 19.5 vs. 3.5 ± 1.6, P=0.002). Diuretic 18F-FDG PET/CT was positive in all patients when compared with normal liver tissues or urine after delayed diuresis. The SUVmax, TLR, and TUR of the primary tumors were 25.4 (range: 7.2–58.9), 7.0 (range: 1.8–14.7), and 6.8 (range: 3.8–11.3), respectively. Delayed postdiuretic 18F-FDG PET/CT had a negative predictive value of 100% (5/5) for predicting lymph node metastasis. One patient received chemotherapy after radical resection of urachal carcinoma because 18F-FDG PET/CT found lung metastases, and one patient only received chemotherapy because PET/CT found peritoneal and skeletal metastases. Conclusions. Delayed postdiuretic 18F-FDG PET/CT is a useful tool for the preoperative evaluation of urachal carcinoma. 18F-FDG PET/CT may improve clinical decision making and management of urachal carcinomas.