Testicular relapse of non-Hodgkin Lymphoma noted on FDG-PET

Testicular relapse of leukemia and lymphoma is a well-recognized phenomenon, with testicular relapse of lymphoma being more common in the adult population and leukemia relapse being more common in the pediatric population. With the advent of F-18 fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) in the evaluation of lymphoma it is possible to evaluate testicular uptake of FDG and to detect primary testicular lymphoma or testicular relapse on the FDG-PET examination. Testicular relapse of non-Hodgkin lymphoma (NHL) detected on FDG-PET has been reported previously. We report an additional case in which there was testicular activity at presentation, a response to therapy (orchiectomy not performed) and then testicular relapse followed by orchiectomy. We review the literature with regard to testicular recurrence and testicular uptake of FDG-PET. There have been studies that have examined normal standardized uptake value maximum (SUVmax) values in the testicle, with normal values ranging from 2.81 (30-39 years) to 2.18 (80-89 years), depending upon age. However, it should be noted that there could be considerable variability in SUVmax values depending upon the units used (e.g. normalized to lean body mass vs. body weight) and depending upon examination variables such as dietary conditions, muscle uptake or extravasation of FDG. Elevated activity or lateralizing activity should be viewed with suspicion, with etiologies including primary testicular tumor, primary or secondary testicular lymphoma and metastatic disease with other etiologies less likely.