1. How does teratoma occur? Teratoma is an ovarian tumor that originates from ovarian germ cells. It does not evolve after a woman has conceived a strange child, but comes from the abnormal proliferation of germ cells, and is a tumor that grows in the ovarian tissue formed by the abnormal proliferation and aggregation of germ cells. Because germ cells contain three types of tissue: ectodermal, mesodermal and endodermal, with ectodermal tissue being the most common, the tumor may contain ectodermal tissue such as hair, oil, skin, teeth and bone fragments, and may also contain mesodermal or endodermal tissue such as muscle, gastrointestinal and thyroid tissue. The etiology of ovarian teratoma is not yet clear. Background knowledge: Johann Sculteus first published a detailed description of an ovarian teratoma in 1658, reporting the history of a German woman with lower abdominal pain prior to death. An autopsy revealed a mass containing hair and “putrefied” material in the ovary. “The term “dermatomatous cyst” was first coined by Lebert in 1857 to describe a cyst with “tissue resembling skin”. Virchow first used the term “teratoma” to describe the various types of tissue seen in these tumors. After the 19th century, most reports proposed abnormal fertilization as the most likely origin of these tumors; the concept of a “fetus within a fetus” became quite popular. The occurrence of a teratoma in a prepubertal girl with an “intact hymen” disproves this notion. The lack of human tissue in mature teratomas often supports the idea that these tumors occur in the ovary. It is now believed that 2/3 of mature teratomas arise from a single germ cell that has failed to divide at second maturity or from an intranuclear replication of a mature egg. The remaining mature teratomas and most immature teratomas arise from abnormal mitotic divisions of germ cells prior to maturation, or due to failure of the first maturation division. Some immature teratomas can also occur from the fusion of two eggs. Most teratomas have a karyotype of 46, XX: a few have an abnormal karyotype. Abnormal karyotypes are most common in higher grade immature teratomas. 2. Is teratoma a benign tumor? Ovarian teratomas are divided into mature teratomas (benign) and immature teratomas (malignant), 97% of which are cystic mature teratomas, also known as dermatomal cysts. Cortical cysts are the most common ovarian tumors, accounting for 10%-20% of all ovarian tumors, 85%-97% of germ cell tumors, and over 95% of teratomas. Because it is not related to pregnancy, ovarian teratoma can occur at any age, including newborns, adolescents, middle-aged or elderly people, but 80%-90% are women of reproductive age between 20-40 years old, accounting for about 1/4-1/3 of ovarian tumors. Most of them are unilateral, and about 10%-17% are bilateral. ～The majority of these tumors are unilateral and about 10% to 17% are bilateral. Immature teratoma is a malignant tumor containing 2 to 3 germ layers. The tumor consists of immature embryonic tissues with different degrees of differentiation, mainly primitive neural tissue. They are prevalent in adolescents. The tumors are mostly solid, in which cystic areas may be present. The malignancy of the tumor depends on the proportion of immature tissue, the degree of differentiation and the neuroepithelial content. Recurrence and metastasis rates are high. However, after the surgery again after recurrence, it can be seen that the tumor tissue has the characteristic of transformation from immature to mature, that is, the phenomenon of reversal of malignancy degree. 3.What are the symptoms of teratoma? Most of them are asymptomatic, but when the teratoma is too large, there will be abdominal distension, mild abdominal pain and pressure symptoms. When the teratoma is twisted, there will be cramps in the lower abdomen, nausea, vomiting and other symptoms. Infertility can result when compression of the fallopian tubes occurs. Most of the patients are found during health checkups or wedding and pregnancy tests with ultrasound. 4.What tests should be done for teratoma? Ultrasound examination is the most economical, simple and specific method. The ultrasound image of teratoma is very specific. The typical image of teratoma is a cystic mass in the adnexal area on one side, with dough and lipid separation signs, which is a good diagnosis of teratoma. X-ray, CT examination and MRI of the pelvis may reveal calcified spots within the pelvic mass. Blood sampling to determine tumor markers such as CA-125, AFP, CEA, hCG, etc. are meaningful for diagnosis and differential diagnosis. 5.How should teratoma be treated? Once ovarian teratoma is formed, it is impossible to disappear. It cannot be eliminated even by medication or injection, but it does not mean that surgery is needed immediately. When the diameter of the teratoma is less than 3cm, we recommend dynamic observation and regular ultrasound examination. Because the teratoma is too small, one is afraid of wrong diagnosis, and the other is that the tumor is too small, making it difficult to find the tumor during surgical treatment and damaging the normal ovarian tissue too much. If it is larger than 3cm, early surgery should be performed. 6.What is the best surgical method to be used? Laparoscopic treatment is the best way to treat teratoma, which is not only complete, but also minimally invasive and will not leave any surgical scars on the abdomen. Laparoscopic teratoma removal is not a major operation, but it is technically demanding. The level of proficiency and delicacy of the operation is closely related to the subsequent pregnancy. The general laparoscopic surgeon’s surgery has only a 50% complete microscopic debridement rate (tumor unrupture rate), while our hospital has a complete microscopic debridement rate of about 99%, with few cases of microscopic rupture. If the microscopic debridement ruptures, there is a possibility of peritoneal implantation and chemical peritonitis, so patients are advised to choose the hospital and surgeon carefully in a responsible manner. In most cases, ovarian teratoma surgery can preserve the normal ovarian tissue on the affected side (resection of the affected adnexa is recommended in menopausal patients), and the contralateral ovary is not dissected in principle if no abnormality is seen on preoperative ultrasound and intraoperative probing. For teratoma in perimenopausal women, resection of the affected adnexa or the uterus plus bilateral adnexa is recommended. The youngest patient treated by laparoscopic surgery in our medical group was 7 years old, and the largest number of patients with bilateral ovarian teratomas peeled laparoscopically was 11. Some patients with very large teratomas, larger than 13 cm in diameter and with a very high solid component, may be better treated with open surgery. 7.Can ovarian teratomas become malignant? Can they recur? What are the consequences of untimely treatment? Benign ovarian mature teratoma has the possibility of malignancy, and the malignancy rate is about 2-3%. In a very small percentage of patients, teratomas reappear on the same or opposite side after surgery. Ovarian teratoma is prone to tumor reversal because of the heterogeneity of the tumor. Once reversed, emergency surgical treatment is necessary, in most cases requiring removal of the adnexa on the reversed side, causing irreversible damage to the body. Most of the clinical cases of ovarian cyst torsion are caused by teratoma. 8. How to manage teratoma in pregnancy? If ovarian teratoma is found during pregnancy, it should be temporarily observed during the first 3 months of pregnancy and then treated with laparoscopic surgery after 12 weeks. Teratoma is most prone to torsion and acute abdomen, so it should be treated laparoscopically in principle. Teratoma found in mid to late pregnancy can wait to be treated together at the end of delivery. Teratoma found before pregnancy is best treated surgically first to avoid tumor growth during pregnancy and the need for surgery. Contraception is not required after teratoma surgery.