Primary Germ Cell Tumor of Testes with Extensive Lymph Nodal and Splenic Metastases Masquerading Lymphoma on ^18-F-FDG PET/CT

A 40-year-old male presented with chief complaints of back pain, intermittent fever, dyspnea, pain abdomen, flank pain, and swelling of neck for 3 months. On physical examination, there were painful palpable cervical lymph nodes and splenomegaly. For further evaluation, the patient was referred for FDG PET-CT. ¹⁸F-FDG PET/CT revealed multiple hypermetabolic lymph nodes involving both sides of diaphragm with multiple hypermetabolic hypodense lesions involving spleen [Figure 1a–Figure 1d]. Along with that, heterogenous FDG uptake and calcification noted in enlarged left testis [Figure 1e, Figure 1f]. Based on the FDG PET-CT findings, provisional diagnosis of lymphoproliferative disorder with secondary testicular involvement was made [Figure 1g MIP image]. So for further confirmation, biopsy from the left supraclavicular lymph node was performed, which revealed predominantly fibrocollagenous tissue with chronic inflammatory infiltrate. Tumor cells showed hyperchromatic nuclei with prominent nucleoli and moderate amount of clear cytoplasm [Figure 2a]. Tumor cells are immunopositive for SALL4 [Figure 2b] and CD117 [Figure 2c], whereas negative for pancytokeratin [Figure 2d], CD20 [Figure 2e] and CD3 [Figure 2f], which suggested seminomatous germ cell tumor.

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Figure 1 (a-d) 18F-FDG PET/CT revealed multiple hypermetabolic lymph nodes involving both sides of diaphragm with multiple hypermetabolic hypodense lesions involving spleen. (e,f) Along with that heterogenous FDG uptake and calcification noted in enlarged left testis.

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Figure 2 Microphotograph shows atypical calls with scant cytoplasm and hyper chromatic nuclei and mild nuclear pleomorphism. Few lymphoid cells are present in the background. [H and E ×200] Immunohistochemistry shows positive for (b) SAL4 [×200], (c) CD117 [×200], whereas it negative for (d) Cytokeratin [×200], (e) CD20, and (f) CD3 [×200]

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The testes have shown to demonstrate normal physiological ¹⁸F-FDG uptake, which is moderate in intensity and symmetrical in pattern, and the level of uptake declines with advancing age.[1] There are currently no standard interpretative criteria to evaluate 18F-FDG testicular uptake. The interpretation generally relies on visual analysis, and the presence of focal or asymmetrical uptake on PET would be regarded as pathological. Secondary involvement of the testes as an extranodal site is rare and occurs in 1% of all NHL and more common in males >60 years.[23] Furthermore, there is a paucity of literature, limited to several case reports, evaluating the pattern, prevalence, and clinical significance of abnormal testicular 18F-FDG uptake on PET in patients with lymphoma.[456] So for further confirmation, histopathological evaluation was suggested which was consistent with metastatic seminoma. Seminoma is a malignant germ cell tumor of the testis or, more rarely, of extragonadal locations which originates in the germinal epithelium of the seminiferous tubules. About half of germ cell tumors of the testis are seminomas. Metastatic seminoma is the paradigm of a curable cancer and the cure rate has now attained 95%, with extrapulmonary visceral metastases being the main identified prognostic factor.[78] So, we hereby discussed FDG PET-CT findings of seminoma involving left testis with extensive lymph nodal, splenic, and liver metastasis masquerading lymphoma. This case further illustrates the fact that heterogeneous uptake in testes should be interpreted with caution and should be confirmed with histopathological diagnosis.