Yolk Sac Tumor : Solid Pattern
Yolk sac tumor shows a variety of architectural patterns that are admixed in varying proportions. Solid pattern consists of polygonal tumor cells with abundant pale eosinophilic or clear cytoplasm arranged in solid nodules. The tumor cells have distinct cytoplasmic membranes and pleomorphic nuclei. Blastema-like foci composed of small round blue cells may be present. Solid pattern can mimic seminoma; however, the fibrous septa and lymphocytes of seminoma are absent. In addition, the cells are more pleomorphic than those of seminoma. In difficult cases, immunostains can help in differentiating between the two entities.