The role of 18F-FDG-PET/CT in evaluating retroperitoneal masses -Keeping your eye on the ball!

Abstract

Background Testicular germ cell tumour is the commonest malignancy affecting males aged between 15 and 35, with an increased relative risk amongst those with a history of cryptorchidism. In patients presenting with locoregional metastatic disease, retroperitoneal and pelvic soft tissue masses are common findings on ultrasound and computed tomography, which has several differential diagnoses within this demographic cohort. On staging 18 F-FDG-PET/CT, understanding the typical testicular lymphatic drainage pathway facilitates prompt recognition of the pathognomonic constellation of unilateral absence of testicular scrotal activity, and FDG-avid nodal masses along the drainage pathway. We describe the cases of three young males presenting with abdominopelvic masses, in whom FDG-PET/CT was helpful in formulating a unifying diagnosis of metastatic seminoma, retrospectively corroborated by a history of testicular maldescent. Case presentations In all three cases, the patients were males aged in their 30s and 40s who were brought to medical attention for back and lower abdominal pain of varying duration. Initial imaging evaluation with computed tomography and/or ultrasound revealed large abdominopelvic soft tissue masses, with lymphoproliferative disorders or soft tissue sarcomas being high on the list of differential diagnoses. As such, they were referred for staging FDG-PET/CT, all of whom demonstrated the pathognomonic constellation of, 1) unilateral absence of scrotal testicular activity, and 2) FDG-avid nodal masses along the typical testicular lymphatic drainage pathway. These characteristic patterns were corroborated by a targeted clinical history and examination which revealed a history of cryptorchidism, and elevated β-hCG in two of three patients. All were subsequently confirmed as metastatic seminoma on biopsy and open resection. Conclusion These cases highlight the importance of clinical history and examination for the clinician, as well as a sound knowledge of the typical testicular lymphatic drainage pathway for the PET physician, which would assist with prompt recognition of the characteristic imaging patterns on FDG-PET/CT. It further anecdotally supports the utility of FDG-PET/CT in evaluating undiagnosed abdominopelvic masses, as well as a potential role in the initial staging of germ cell tumours in appropriately selected patients.

Imaging of pediatric testicular tumors: A COG Diagnostic Imaging Committee/SPR Oncology Committee White Paper

“…Instead, its use is reserved to identify occult disease in patients with rising tumor markers and a negative CT or MR, or to evaluate equivocal findings that could affect surgical planning or therapy (Grade C, SOR 1.78). 46 There is an emerging role for FDG PET/CT in problem-solving equivocal findings and also in patients with rising tumor markers in the context of negative CT or MR. 46 Although PET offers excellent negative predictive value in the setting of seminomas, The International Global Germ Cell Cancer Group Registry cautions against clinical decisions based on PET positivity alone due to risk of false positives. 7,47 Currently, there is little evidence to support its routine use in staging or follow-up surveillance in nonseminomatous GCT in the pediatric population; however, it should be considered in equivocal cases.…”

“…Routine use of 18 F‐fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT for staging or surveillance of nonseminomatous GCT is not recommended. Instead, its use is reserved to identify occult disease in patients with rising tumor markers and a negative CT or MR, or to evaluate equivocal findings that could affect surgical planning or therapy (Grade C, SOR 1.78) 46 . There is an emerging role for FDG PET/CT in problem‐solving equivocal findings and also in patients with rising tumor markers in the context of negative CT or MR 46 .…”