Comparable Diagnostic Performance of 99m Tc-FAPI Scintigraphy and Contrast-enhanced CT in Restaging a Rare Case of Metastatic Colon Adenocarcinoma to the Urachus.

We present a case of a 33-year-old man with gross hematuria and dysuria, leading to the discovery of a bladder and urachal mass. Imaging revealed significant bladder wall thickening and regional lymph node metastases. Following transurethral resection, histopathologic and immunohistochemical analyses were consistent with the urachal metastatic adenocarcinoma with colon origin. After chemotherapy, a 99m Tc-FAPI-46 scintigraphy was performed, revealing favorable FAPI uptake in all tumoral lesions detected in the contrast-enhanced CT scan. This case highlights the diagnostic utility of FAPI-46, as a novel radiotracer, in evaluating urachal neoplasms and its potential for theranostic approaches.