THE DIAGNOSTIC VALUE OF FDG-PET/CT FOR URACHAL CANCER

ABSTRACT Introduction Urachal carcinoma (UrC) is a rare malignancy, which often presents at advanced stage with metastases in up to a quarter of patients. There is no consensus on the optimal form of staging for patients with UrC. In the present study, we evaluated the diagnostic value of 18F-fluorodeoxyglucose-positron emitted tomography/computed tomography (FDG-PET/CT) for UrC. Patients and methods We evaluated 40 consecutive patients who were staged for urachal cancer between 2010 and 2020. They underwent a total of 62 FDG-PET/CTs; 40 for primary staging; 22 during follow-up, next to standard-of-care contrast-enhanced CT (CECT). The metabolic detection of the primary tumor, lymph node metastases (LNM), peritoneal metastases (PM), distant metastases (DM) and local recurrence by FDG-PET/CT were evaluated. Sensitivity and specificity were calculated compared to CECT. Histopathology or follow-up imaging was the reference standard. Results Of all 40 patients, 33 (83%) had urachal adenocarcinoma; 26/40 (65%) with a mucinous component and 7 (17%) had invasive urothelial carcinoma. All local UrC tumors could be visualized on CT, whereas 80% showed increased FDG uptake. At initial staging, FDG-PET/CT detected FDG-avid LN, PM and DM in respectively 50%, 17% and 25% of patients. These metastases were also visualized on CECT. During follow up, FDG-PET/CT revealed FDG-avid local recurrences which were not seen on CT in two out of eight patients (25%). Conclusion The present study demonstrates that most of the UrC can be visualized on FDG- PET/CT. At initial diagnosis, FDG-PET/CT does not seem to yield additional information over CECT, whereas FDG-PET/CT may be helpful during follow-up. This is a small study and the findings need to be corroborated with larger series. MICROABSTRACT Urachal cancer is a very rare malignancy. There is no consensus on the optimal form of staging for this disease. In this study, we evaluated FDG-PET/CT for staging urachal cancer in forty patients. We found that most of the urachal tumours can be visualized on FDG-PET/CT, but that it seems to add little additional staging information, next to standard CT.