The neoplastic cells contain basophilic cytoplasm with large pleomorphic nuclei and solitary prominent nucleoli. Cell borders are usually indistinct. Mitoses are common. Yolk sac tumors are the most common testicular tumor in children under the age of three years. Grossly, these tumors are yellow-white and multinodular.
Most tumors also contain intra- and extracellular hyaline globules.
Teratomas are divided into mature and immature subtypes based on the degree of histologic differentiation. Tissues derived from all three germ cell layers may be seen. The gross appearance is heterogeneous, composed of solid, cartilaginous, and cystic areas. Hemorrhage and necrosis are common. They tend to be larger than other germ cell tumors.