Primary neuroectodermal tumour of the testis

A 51-year-old male presented with metastasis of a small cell carcinoma of unknown origin in a right inguinal lymph node. Clinical and laboratory studies failed to locate the primary tumour. After three years, a swelling appeared in the right testis, which was removed. Histological examination revealed a proliferation of small tumour cells forming irregular masses or nests that occupied most of the testicular parenchyma. At the periphery of the testicular parenchyma a few seminiferous tubules could be observed, showing a low and incomplete seminiferous epithelium and numerous tumour cells in the lumen. Most of the tumour cells showed a euchromatic nucleus with small nucleoli and scanty cytoplasm. Among these cells, larger binucleate or trinucleate cells as well as small cells with pyknotic nuclei were also observed. Mitoses were numerous. Electron microscopy revealed some tumour cells with 80 to 100 nm vesicles containing electron-dense granules. Some cells displayed dendrite-like prolongations with numerous intermediate filaments and electron-dense vesicles. This tumour is compatible with a primary neuroectodermal tumour of the testis.