Establishing Normal Testicular 18F-FDG PET/CT SUVs

Leydig cell tumor of the testis: an incidental finding at 18F-FDG PET/CT imaging

Background

Leydig cell tumors (LCTs) represent the most common form of stromal tumors. We reported the 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) findings of a patient with testicular LCT.

Case presentation

A 50-year-old man with a history of end-stage renal disease and renal transplantation 19 years ago. One year earlier, he started to have a chronic rejection. During the investigation to determine the cause of chronic rejection, a suspicious lesion in the graft with a collection around it was seen on ultrasound (US) images, raising the possibility of post-transplant lymphoproliferative disorder (PTLD). The patient was referred for further evaluation by whole body 18F-FDG PET/CT imaging. The image finding revealed an incidental hypermetabolic focal lesion in the right testicle—no other specific findings in the remaining parts of the body nor definitive FDG avid lymphadenopathy to suggest PTLD. Testicular US was requested and showed a well-defined right-sided heterogeneous hypoechoic intratesticular focal mass at the upper pole of the right testis with significant internal vascularity on the color Doppler imaging. The patient underwent a right radical orchidectomy, and the tumor was pathologically confirmed as an LCT.

Conclusion

In our case, 18F-FDG-PET/CT has been helpful in incidentally detecting this rare testicular tumor in a patient with suspected PTLD.

Testicular FDG Uptake on PET/CT in Patients with Lymphoma: Correlation with Age

The purpose of this observational study was to investigate whether the standard uptake value (SUV) measurement has practical utility in distinguishing secondary testicular involvement from physiologic uptake in patients with lymphoma. A Radiology Information System (RIS) search was conducted for all PET/CT studies performed from 2010-2016 on adult male patients with a diagnosis of lymphoma. Patients with clinical or pathologic diagnosis of testicular lymphoma were excluded to undergo a separate analysis. PET/CT images of 606 patients with 1087 scans, in which 2045 testes were included in the field of view, were reviewed and measurements were performed for standardized uptake values of both testicles (SUV_max) as well as of the liver (SUV_max and SUV_mean). The mean SUV_max of the testicles was 3.75 ± 0.90 (range 1.16-8.38). The mean ratio of testis SUV_max / liver SUV_mean (T/L) was 1.78 ± 0.43. Trends in SUV_max and age were significant for a negative correlation by a small magnitude of 0.066 per 10 years (P < 0.001). T/L had similar changes with significant low magnitude decrease with increasing age (0.059 per 10-year increase, P < 0.001). In our separate analysis of 3 patients with clinical or pathology proven testicular lymphoma, the average pathologic SUV_max was 13.47 (range 11.39-15.97). This study has the largest known sample size for quantifying physiologic uptake in the testes. SUV measurements to quantify F-18 Fluorodeoxyglucose (FDG) uptake on PET/CT likely have practical utility in discriminating between physiologic and pathologic uptake of FDG in cases of secondary testicular lymphoma.