Teratoma is a tumor derived from germ cells with 2-3 germ layers of differentiation, most of them (about 90-95%) are benign and a few are malignant. In order of origin, they are sacrococcygeal, gonadal (ovarian and testicular), retroperitoneal and mediastinal; benign cystic teratoma, also known as mature teratoma, is one of the most common tumors of the ovary. (To the naked eye, they are mostly single large sacs filled with sebaceous material, mixed with varying amounts of hair, and often have one or several nodular projections on the wall of the sac, with hair on the surface of the nodule.) The skin, fat, cartilage, bone and other structures are visible in the section, and about 1/3 of the teeth are visible. Microscopically, it consists of differentiated mature tissue or organ-like structures of two or three germ layers origin. The most common ones are differentiated mature skin tissue and its appendages, adipose tissue and smooth muscle, less common ones are respiratory mucosa, bone, cartilage, nerve tissue, gastrointestinal tract and thyroid tissue, etc. A few benign teratomas may also be solid, but are composed entirely of mature tissue. Immature teratoma occurs mostly in young women, children and adolescents under 25 years of age. To the naked eye, the tumor is usually large and predominantly solid, in which sacs of varying sizes are seen, often with hemorrhagic necrosis. Microscopically, the tumor contains both mature and immature 2-3 germ layer differentiated components. It is common to find immature neural tissue forming chrysalis clusters neural tube like or diffuse patches of neuroepithelium, immature cartilage or embryonic mesenchymal tissue. The more immature tissues contained in malignant teratoma tumor, the higher the malignancy, and the more prone to recurrence or pelvic or abdominal implantation and metastasis after surgery, with poor prognosis. If immature teratoma cannot be completely removed surgically, some of them may need chemotherapy. Very few teratomas may turn malignant and become malignant germ cell tumors or other malignant tumors later. Yolk sac tumor, known as mesonephrosis until 1959, is now recognized as a tumor of extraembryonic yolk sac differentiation of germ cell origin, unrelated to the mesonephrosis and endodermal sinus, with basic histologic features similar to those of the developing yolk sac. The most common site is the sacral spine, followed by the testes and ovaries, and the majority of patients have elevated α-FP in the serum. The tumor is a fast growing, cystic structure with extensive hemorrhage and necrosis, and has a variety of microscopic structures, including the following 10 structures: 1. 5. polycystic yolk sac-like structures; 6. mesenchymal lax mucinous-like; 7. papillary; 8. macrocapsular; 9. hepatic-like structures, resembling hepatocellular carcinoma; 10. primitive endoderm, resembling intestinal-type epithelial differentiation. A mixture of these 10 structures exists, often with 2-3 structures as the main components. Microscopically, there is also a more specific component, namely the proteinous vesicles that show droplet-like red staining and PAS positivity in conventional HE sections. Immunohistochemistry shows positive vesicles and intraepithelial α-FP. Immunohistochemistry is important in the diagnosis and differential diagnosis. In addition to positive α-FP, immunohistochemistry may also be positive for EMA and α-1 chymotrypsin (α-l-ACT). Endodermal sinus tumors are common in adolescents and have a poor prognosis, with a 3-year survival rate of only 13%. Patients with testicular yolk cysts who are younger than 1 year of age and have not metastasized usually have their testicles surgically removed; children older than 1 year of age have a poorer prognosis and must be treated with chemotherapy and radiation. Ovarian yolk cysts are usually fast-growing and metastatic, so in addition to removal of the affected fallopian tubes and ovaries, chemotherapy or radiation is required. Germ cell tumors Germ cell tumors, also known as anaplastic cell tumors or seminoma, are the most common malignant germ cell tumors that occur in children with ovarian and central nervous system tumors, and are derived from multipotent, undifferentiated germ cells. It is a solid, spherical gyrus-shaped tumor. The cut surface is soft, homogeneous, and grayish-yellow in color. Microscopically, the histology of asexual cell tumors is similar to that of testicular spermatocytes. The tumors consist of morphologically uniform tumor cells that resemble primitive germ cells. The nuclei are large and round with prominent nucleoli. The tumor cell mass is separated into lobules by a thin layer of mesenchyme. The interstitium is often infiltrated with lymphocytes. A tuberculosis-like granulomatous reaction may also be present, which helps in the diagnosis.