Definition : a primitive germ cell tumor, similar to testicular seminoma.

Synopsis :

 90% are apparently unilateral, but occult foci of dysgerminoma can be detected by biopsy of the contralateral ovary in 10% of cases
 monotonous proliferation of primitive germ cells
 connective tissue septa containing variable amounts of chronic inflammatory cells

Immunohistochemistry :

 most are vimentin + and PLAP + (placental-like alkaline phosphatase)
 CD117 (c-kit) +
 inconstant + to : cytokeratins, desmin, GFAP, CEA and S-100 protein

Etiology and evolution :

 the vast majority have no precursor lesion
 may arise from gonadoblastoma
 may be a precursor to other primitive germ cell tumors