Testicular Metastasis from Urothelial Carcinoma of the Renal Pelvis Detected on ¹⁸F-FDG PET/CT: A Rare Case

INTRODUCTION

Upper tract urothelial carcinoma (UTUC), arising from the renal pelvis and ureter, is an uncommon but aggressive malignancy, accounting for approximately 5–10% of all urothelial tumours.^[1] At presentation, a significant proportion of patients have locally advanced or metastatic diseases. The most frequent sites of metastasis include the lungs, liver, bones, and lymph nodes.^[2] Testicular metastases from solid tumours are rare, constituting less than 1% of all testicular neoplasms, with prostate, lung, and gastrointestinal primaries being the most common sources.^[3] Metastasis to the testicles from renal malignancies, including renal cell carcinoma and renal pelvis carcinoma, is exceptionally uncommon, with only isolated case reports and small series documented in the literature.^[4,5] Proposed mechanisms include retrograde venous spread via the renal and gonadal veins, lymphatic dissemination, and arterial embolisation.^{[4] 18}F-FDG PET/CT is increasingly used in advanced genitourinary malignancies for whole-body staging and detection of metastatic disease, particularly at atypical sites not routinely evaluated on conventional imaging.^[6,7]We report a rare case of carcinoma of the renal pelvis with extensive multi-organ metastases, including testicular involvement, detected on ¹⁸F-FDG PET/CT.

CASE REPORT

A 61-year-old male presented with painless intermittent haematuria with passage of clots for one week. There was no associated fever, abdominal pain, or urinary retention. Past history was significant for right inguinal hernia repair performed 8–10 years earlier, with no available medical records. The patient reported chronic pan chewing with betel nut for approximately five years. There were no known comorbidities. He complained of disturbed sleep due to chronic back pain.

On examination, the patient was conscious, oriented, and hemodynamically stable. Abdominal examination was unremarkable. External genitalia appeared normal, and both testes were firm on palpation. Digital rectal examination revealed normal anal tone, intact bulbocavernosus reflex, and a Grade II firm prostate. Laboratory investigations revealed persistent microscopic and gross haematuria (up to 677 red blood cells per high-power field), pyuria, and elevated erythrocyte sedimentation rate (65 mm/hr). Renal and liver function tests were within normal limits. Echocardiography showed normal left ventricular systolic function with mild valvular regurgitation.

Ultrasonography of the kidneys, ureters, and bladder demonstrated a well-defined endophytic heteroechoic lesion measuring approximately 4.9 × 4.5 cm in the upper pole of the left kidney, suspicious for neoplasm. CT urography revealed a 6.0 × 6.5 × 6.4 cm ill-defined mass in the upper pole of the left kidney with enhancing septations and central hypo enhancement. Partial extension into the left renal vein with tumour thrombus was noted. Extensive retroperitoneal and pelvic lymphadenopathy with vascular encasement was present. Additional suspicious lesions were identified in the left adrenal gland and liver. MRI of the dorsal lumbar spine demonstrated L4–L5 disc bulge with canal stenosis and enlarged retroperitoneal lymph nodes.

The patient was referred to nuclear medicine for a whole body ¹⁸F-FDG PET/CT for staging workup. ¹⁸F-FDG PET/CT showed an FDG-avid, ill-defined mass with central necrosis in the left renal pelvis and extension into the left renal vein. It also showed retroperitoneal lymph nodes, bilateral lung nodules, a left adrenal lesion, liver, and L1 vertebral lesion, along with a right testicular mass [Fig 1].

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Fig 1: (A) MIP image showing intense FDG uptake in the left renal mass, bilateral lungs, liver, abdominal lymph nodes, and right testes (arrow); (B and C) Coronal CT and fused PET/CT images of the left renal mass and L1 vertebral metastasis; (D and E) Coronal CT and fused PET/CT images showing FDG-avid right testicular lesion (arrows); (F and G) Axial CT and fused PET/CT images of the right testicular lesion (arrows). MIP- Maximum intensity projection; PET/CT- Positron emission tomography/ computed tomography.

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Ultrasound-guided biopsy from a liver lesion revealed a malignant neoplasm arranged in nests and lobules, composed of tumour cells with clear-to-eosinophilic cytoplasm, moderate nuclear pleomorphism, and areas of necrosis. Mitotic activity was 16–18 per 10 high-power fields. On immunohistochemistry, tumour cells were positive for GATA3, p63, CK7, CK20, and moderately positive for AMACR, while negative for CD10 and CD117. PAX8 was non-contributory. The overall findings were consistent with metastatic carcinoma, favouring a urothelial origin in correlation with clinical and imaging findings [Figs 2 and 3]. A final diagnosis of metastatic carcinoma of the left renal pelvis with multi-organ involvement, including lungs, liver, adrenal gland, lymph nodes, vertebrae, and right testis was established.

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Fig 2: (A) Cores of liver (arrow) and tumour tissue (H&E, 40X); (B) Tumour is arranged in nests and sheets (H&E, 200X); (C) Tumour cells have moderate eosinophilic cytoplasm, moderate nuclear pleomorphism, and show brisk mitosis (H&E, 400X); (D) Desmoplastic stroma and necrosis (H&E, 100X) H&E: Haematoxylin and Eosin

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Fig 3: (A) Tumour cells are positive for CK7 (IHC, 100X); (B) Tumour cells are positive for CK20 (IHC, 100X); (C) Tumour cells are positive for GATA3 (IHC, 100X); (D) Tumour cells are positive for p63 (IHC, 100X) (IHC: Immunohistochemistry)

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DISCUSSION

UTUC and renal cell carcinoma differ in histogenesis but share overlapping metastatic patterns, most commonly involving lungs, liver, bones, and lymph nodes.^[2] Testicular metastasis from renal malignancies is exceedingly rare, with only isolated case reports and small reviews described in the literature.^[4,5] Several mechanisms have been proposed to explain testicular involvement, including retrograde venous spread through the renal and gonadal veins, lymphatic dissemination and arterial tumour embolisation.^[4] The presence of renal vein tumour thrombus in the present case may have facilitated retrograde venous dissemination to the testis. FDG PET/CT plays a valuable role in the evaluation of advanced renal malignancies by enabling whole-body assessment and detection of metastatic disease at unusual sites.^[6,7] Previous studies have demonstrated its usefulness in identifying atypical metastatic deposits that may not be suspected clinically or detected on conventional imaging.^[6,7] In the present case, FDG PET/CT accurately delineated the full extent of disease, including rare testicular involvement, thereby providing crucial information for staging and therapeutic planning.

CONCLUSION

This case illustrates a rare presentation of carcinoma of the renal pelvis with extensive metastatic disease, including testicular involvement. ¹⁸F-FDG PET/CT proved invaluable in delineating the full extent of disease and identifying unusual metastatic sites that may be overlooked on conventional imaging. Awareness of such atypical metastatic patterns is essential for accurate staging, prognostication, and optimal treatment planning in advanced renal malignancies.