Juvenile granulosa cell tumor of the infantile testis. Evidence of a dual epithelial-smooth muscle differentiation.

We report the ultrastructure and immunohistochemical profile of seven juvenile granulosa cell tumors of the infantile testis. The infants' ages ranged from 1 day to 11 months. All tumors had characteristics ultrastructure with a mixture of spindle smooth-muscle and theca cells and polygonal granulosa cells. Clusters of polygonal granulosa cells were invested by a continuous basal lamina and contained bundles of distinct cytoplasmic filaments with evenly distributed dense bodies resembling smooth muscle. These filaments were occasionally attached to well-developed, prominent desmosomes. Tumor cells had a conspicuous rough endoplasmic reticulum and Golgi complex and occasional neutral fat droplets. In all tumors, mitochondria had laminated cristae and only rarely were there cristae with a tubulovesicular pattern characteristic of steroid secreting cells. Tumor cells stained focally with low-molecular-weight cytokeratins (8,18, and 19), smooth-muscle-specific actin, desmin, and more noticeably with vimentin. These ultrastructural and immunohistochemical features of dual epithelial-mesenchymal differentiation and distinct muscle-like filaments with dense bodies are characteristic of the juvenile granulosa cell tumor of the infantile testis.