Teratomas originate from potentially multifunctional primordial germ cells and are mostly benign, although the malignant tendency tends to increase with age. The site of occurrence is related to the midline anterior axis or paramedian area of the embryological body cavity, mostly in the sacrococcygeal, mediastinal, retroperitoneal, and gonadal areas. It occurs in newborns and infants, and is more common in women. 1. Etiology and pathology: During human embryonic development, there is a kind of pluripotent cell with pluripotent development potential, which develops and differentiates into mature cells of each germ layer under normal embryonic development. Embryonic anomalies can occur if, at different times in the embryo, certain pluripotent cells detach or fall off from the whole, causing mutations in the cell genes and abnormal differentiation. It is generally believed that such separation or shedding occurs in the early embryonic stage, then a teratoma is formed, while if it occurs in the late embryonic stage, then an abnormally differentiated tissue with three embryonic layers, endoderm, mesoderm and ectoderm, is formed, i.e., a teratoma is formed. The pathological features of teratoma are that the tumor tissue consists of ectodermal, mesodermal and endodermal tissues, and often contains mature or immature skin, teeth, bone, cartilage, nerves, muscle, fat, epithelium and other tissues, and in a few cases, gastric mucosa, pancreas, liver, kidney, lung, thyroid and thymus. Malignant teratoma is often manifested as immature tissue that cannot be easily determined and distinguished. The malignant transformation of teratoma is mostly manifested as abnormal proliferation of neural tissue or epithelial tissue to form malignant teratoma. The pathological classification of teratoma is as follows: (1) mature teratoma: benign teratoma, consisting of differentiated and mature tissues, is the most common benign ovarian tumor; (2) immature teratoma: malignant teratoma, consisting of immature tissue structures during embryogenesis, mostly glial or neural tube like structures, often with undifferentiated and increased mitotic malignant pathological manifestations. In the past, some germ cell malignancies such as seminoma, asexual cell tumor, embryonal carcinoma and endodermal sinus tumor were collectively called malignant teratoma, but in fact, they are the result of abnormal differentiation in various areas of embryological germ cell tumor and migration from yolk sac to gonads, which often have no trichoblast structure in pathology and should not be classified as teratoma. (1) Painless mass: This is the most common symptom of teratoma, mostly round and cystic, with clear boundary, hard and soft texture, and even bony nodules can be found. Among the exophytic tumors, sacrococcygeal, occipital, frontal, nasal and other midline sites are common. Sacrococcygeal teratoma can often be divided into three clinical types: dominant, cryptic and mixed according to its location. (2) Compression and cavity obstruction symptoms: mediastinal teratoma can often compress the respiratory tract and cause choking, dyspnea and jugular vein anger; retroperitoneal teratoma mostly has abdominal pain and can cause intestinal obstruction. The pelvic and sacrococcygeal occult teratomas are often seen for constipation, difficulty in defecation and urinary retention. (3) Acute symptoms of abnormal changes of tumor: ovarian and testicular teratoma may cause ovarian or testicular torsion and necrosis, which manifests as severe pain and corresponding local symptoms; when secondary infection and intracapsular hemorrhage occur in teratoma, the mass may increase rapidly, with obvious local pressure pain, and accompanied by fever, anemia, shock and other symptoms of systemic infection or blood loss; tumor in retroperitoneum, ovary, pelvis and sacrococcygeal area may also Tumors in retroperitoneum, ovary, pelvis, sacrococcygeal area, etc. may also rupture suddenly and cause hemorrhage, bloody abdomen, shock and other dangerous manifestations. (4) Symptoms of tumor malignancy: When malignant teratoma and benign teratoma are malignant, they often show rapid growth of tumor, loss of original elasticity, exophytic tumor, superficial venous anger, congestion, local skin infiltration and increase in skin temperature. It may have lymph node enlargement and lung and bone metastasis symptoms through lymphatic and hematogenous metastasis, as well as systemic symptoms such as emaciation, anemia and tumor fever. 3.Diagnosis: Most teratomas are exophytic or have obvious masses that can be retrieved, and early diagnosis can often be made according to clinical manifestations. Careful abdominal physical examination and rectal examination are very necessary for the examination of abdomen, pelvis and cryptic sacrococcygeal teratoma; X-ray plain film of tumor site can find abnormal calcification shadow of bone and teeth in the tumor and clarify teratoma, and most of them are mature teratoma; barium meal of gastrointestinal tract, barium enema and intravenous pyelogram can understand the pressure pushing of gastrointestinal tract or kidney, ureter, bladder and other organs in the corresponding area. CT and MRI should be performed in cases of rapid growth and extensive infiltration of teratoma to clarify the extent of tumor infiltration and the adjacent relationship with important blood vessels and spinal nerves. If malignant teratoma is considered, AFP and HCG levels should be measured to guide the diagnosis and prognosis. It is found that 92% of malignant teratoma have increased AFP, while 4% of benign teratoma also have abnormal AFP, and the recurrence rate of benign teratoma with increased AFP is significantly higher after surgery. 4.Treatment: Once the teratoma is diagnosed, early surgery is necessary to avoid malignancy of benign teratoma due to delayed surgery, and to prevent tumor infection, rupture, bleeding and complications. The main point of surgery for teratoma is to remove the tumor completely, both ovarian and testicular tumors should be removed from one side of the ovary or testicle, and the sacrococcygeal teratoma should be removed together with the tailbone to avoid recurrence of the tumor due to residual pluripotent cells. The principle of treatment for malignant teratoma is combined adjuvant therapy, and conventional chemotherapy is used for 1.5 to 2 years after surgical resection, and cisplatin, vincristine or vincristine and bleomycin are commonly used. In recent years, the application of chemotherapy drugs such as cisplatin, adriamycin and isocyclophosphamide is recommended for combination chemotherapy. Radiotherapy is only used for malignant teratoma cases with clear microscopic or sarcoid residuals. 25 Gy is appropriate for microscopic residuals and up to 35 Gy for sarcoid residuals. For those with complete surgical resection, chemotherapy is advocated as the main treatment in recent years and radiotherapy is used cautiously to avoid delayed damage to reproductive organs and bone development during radiotherapy. For malignant teratoma with huge or extensive infiltration, which cannot be resected by clinical judgment, preoperative chemotherapy or radiotherapy can be applied to shrink the tumor before postponing the radical surgery, which has positive significance to improve the surgical resection rate and preserve the important organs. For advanced cases, preoperative chemotherapy or radiotherapy can also achieve the treatment purpose of relieving tumor compression, controlling metastases and fighting for re-operation. 5.Prognosis: The prognosis of teratoma is closely related to the age of initial diagnosis, tumor site, malignancy rate and treatment outcome. The younger the age of initial diagnosis, the lower the incidence of malignancy, among which the highest malignancy rate is 71.4% for cryptic teratoma, 46.7% for mixed type and only 9.4% for dominant type. Complete resection of the tumor and reduction of postoperative recurrence and malignancy is another major prognostic factor for teratoma, and even for malignant teratoma, completion of surgical resection is still the basic guarantee for long-term survival. At present, the survival rate of malignant teratoma can reach 50% in three years and 35% in five years after complete resection of comprehensive treatment, while the survival rate of those with intraoperative residual or recurrence is only 3%. The survival rate of malignant teratoma in the testes and ovaries, which are easily resected, is significantly higher than that of retroperitoneal and sacrococcygeal malignant teratoma, among which the prognosis of cryptic sacrococcygeal malignant teratoma is the worst, with a survival rate of only 8%.