Diagnostic role of 18F-FDG PET/CT in upper urinary tract urothelial carcinoma – a rare clinicopathological entity

Introduction: Urothelial carcinoma (UC) involves the urinary bladder in ~90-95% of the cases. Upper urinary tract urothelial carcinoma (UTUC) is a rare entity accounting for ~5-10% of all UCs. UTUCs involve primary sites such as the pelvicalyceal system or the ureters. In this retrospective study, we aimed to assess the role of ¹⁸F-FDG PET/CT in the evaluation of UTUCs.

Methods: Medical records of 42 patients (mean age 58.6 ± 11.5 years, range 15-77 years, M: F = 29:13) with either suspected or histologically proven UTUC who underwent ¹⁸F-FDG PET/CT from January 2015 to December 2021 were reviewed. Two certified nuclear medicine physicians independently reviewed all the PET/CT studies. Anatomical lesions with non‐physiologic, abnormal tracer uptake, higher than the background tracer uptake consistent with the disease process (primary in the urinary tract or metastatic lesions) after ruling out common pitfalls associated with ¹⁸F-FDG PET/CT were taken as positive disease foci. The number and characteristics of the primary lesion, number of the loco‐regional and distant metastatic lesion(s) and intensity of tracer uptake (SUVmax) were measured.

Results: Of the 42 patients, 36 (85.7%) had histologically proven UTUC. UTUC was suspected based on clinical symptoms and anatomical imaging in 5/42 patients. In 1/42 patients, UTUC was incidentally detected on ¹⁸F-FDG PET/CT done for response assessment of multiple myeloma. The sites of primary tumor included renal pelvis (22/42; left -11, right - 10 and bilateral - 1), upper ureter (9/42), mid ureter (4/42), lower ureter (7/42). PET/CT was done for diagnosis or initial staging in 14/42 patients and in all of them, primary tumor site was localized on PET with the mean SUVmax value being 15.4 ± 13.8 (range 2.8-43.4). Of these, 2/14 (14.3%) patients had co-existing urinary bladder involvement and 1/14 (7.1%) patients had metachronous UTUC with past history of urinary bladder UC. PET/CT was done for restaging post-surgery in 18/42 patients, for response assessment/restaging post-surgery & adjuvant chemotherapy in 7/42 patients and for surveillance in 2/42 patients. Of the patients who underwent PET/CT for restaging post-surgery and/or chemotherapy (25/42), residual primary or local recurrence was detected in 3/25 (12%) patients, recurrence in the urinary bladder was detected in 3/25 (12%) patients and no abnormality was detected on PET/CT in 5/25 (20%) patients. Of the patients who underwent PET for surveillance (2/42), one patient had regional lymph nodal recurrence and the other patient had no abnormality on PET/CT. Overall, regional lymph nodal metastases were detected on PET/CT in 22/42 (52.4%) patients, with mean SUVmax of the most tracer avid lymph node being 10.8 ± 7.8 (range 2.3-29.4). Extra-regional lymph nodal metastases were detected in 9/42 (21.4%) patients, with mean SUVmax of the most tracer avid lymph node being 8.7 ± 4.1 (range 2.7-13.3). Skeletal metastases were detected in 3/42 (7.1%) patients and visceral metastases in 13/42 (30.9%) patients (lung – 8, liver – 5 and adrenal – 2). Other significant findings on PET/CT were peritoneal/omental/serosal/muscular deposits in 6/42 (14.3%) patients and the presence of renal vein/IVC thrombus in 3/42 (7.1%) patients. Overall, ¹⁸F-FDG PET/CT changed management protocol in 16/42 (38.1%) patients.

Conclusions: ¹⁸F-FDG PET/CT imaging has the potential to accurately assess disease extent in UTUCs for diagnosis, initial staging, restaging post-surgery and response evaluation and can potentially alter the management.