1.Clinical manifestations Smaller masses usually do not produce symptoms, and occasionally there is a feeling of sinking or drawing pain in the lower abdomen on the affected side. The abdominal mass can be clearly palpated, with smooth surface, no pressure pain and cystic feeling. Most benign tumors form a long stalk with the fallopian tube. Since the tumor is not adherent to the surrounding tissues, it is more mobile and can often push the mass from one side of the lower abdomen to the upper abdomen. Malignant tumors grow rapidly, the masses are irregular and immobile, and may be accompanied by ascites and systemic symptoms such as weakness, fever and loss of appetite within a short period of time. Functional ovarian tumors, such as granulosa cell tumors, can cause symptoms of precocious puberty due to the production of large amounts of estrogen. Female features such as physical, breast and external genitalia develop rapidly and menstruation occurs, but ovulation does not occur. Skeletal development may exceed the normal range. Urinary estrogen is elevated, as well as urinary gonadotropins, which exceed the normal and adult levels. Reversal of the tumor and tip may occur in moderately sized ovarian masses with long tips (including retained ovarian cysts). Once torsion occurs, hemorrhage and necrosis can occur, which clinically manifests as an acute abdomen. Children may have abdominal pain, nausea or vomiting, and on examination, abdominal muscle tension and pressure pain at the tumor site are evident, and children may have elevated body temperature and leukocytosis. When the tumor is large, it may cause difficulty in urination and defecation due to compression of adjacent organs. (1) Dysgerminoma: Also known as germ cell carcinoma, it is the most common malignant germ cell tumor in children and adolescents. It is morphologically and biologically equivalent to testicular germ cell carcinoma and extragonadal germ cell carcinoma of the pineal region, anterior mediastinum, and retroperitoneum. Signs and symptoms of abdominal masses develop relatively rapidly and abdominal pain is infrequent except for tumor torsion. 75% of cases are stage I at diagnosis and may have local spread, regional lymph node metastasis and distant metastasis to lung, liver or supra-diaphragmatic lymph nodes. Asexual cell tumors are large nodular tumors, up to 20 cm in diameter, most often occurring on the right side, with 5% to 10% occurring bilaterally. 14% to 25% of cases are mixed asexual cell tumors, which include other germ cell tumor components, such as gonadoblastoma, immature teratoma, endodermal sinus tumor, mature teratoma, and choriocarcinoma. If the tumor is confined to the ovary, only the affected ovary and fallopian tube can be removed with or without radiotherapy, the survival rate is similar and can be over 80%. If the tumor is stage II-IV, comprehensive treatment is required. According to FIGO (international federation of gynaecology and obstetrics) ovarian tumor staging: Stage I: tumor is confined to ovary. Stage II: Tumor invades unilateral or bilateral ovaries with pelvic spread. Stage III: tumor invades unilateral or bilateral ovaries with intra-abdominal metastasis and spread to extra-pelvic and/or retroperitoneal lymph nodes. Stage IV: distant metastasis. (2) Endodermal sinus tumor: It represents almost all highly malignant embryonal epithelial tumors and is characterized by embryonal cells with a lax reticular structure resembling the peculiar perivascular structure of the endodermal sinus of the murine placenta and the presence of PAS-reactive hyaline corpuscle both inside and outside the cells. This tumor was also known as yolk sac tumor and contains many small vesicles resembling yolk sac vacuoles. The tumor is highly malignant and spreads rapidly to the lymphatic tract and abdominal tissues, so the course of the disease is short. It is more often associated with abdominal pain and is mostly stage III at the time of diagnosis, with an average age of 18 to 19 years at diagnosis. Increased serum AFP can be detected, and it should be noted that infants (<6 months) may also have increased AFP in normal cases. Surgery plus multiple drug combinations such as VAC regimen (vincristine, actinomycin D, cyclophosphamide) or PVB (cisplatin, vincristine sulfate and bleomycin) can improve the survival rate up to 45%-72%. (3) Embryonal carcinoma: It accounts for about 4% of ovarian malignant tumors, and the average age at diagnosis is 14 years. In addition to the abdominal mass, half of the patients have abdominal pain. Although microscopically resembling an endodermal sinus tumor, the cells are undifferentiated, with more pronounced nuclear schizophrenia, hemorrhage and necrosis, and no Schiller-Duval vesicles. There is a higher incidence of clinical endocrine manifestations, including a positive pregnancy response and elevated HCG. At diagnosis, 60% are stage I lesions, occasionally bilateral. Stage I lesions have a 50% survival rate with resection of the affected ovary and fallopian tube only. Radiotherapy is not effective and chemotherapy can be referred to endodermal sinus tumors. (4) Teratoma: It is the most common germ cell tumor and can be divided into mature type (99%) and immature type (1%). The mature type includes: (1) typical cystic and solid teratomas, often including three germ layers; (2) monodermal lesions containing thyroid tissue, carcinoid tumors, neuroectodermal tumors or thyroid carcinoid tumors. With the exception of neuroectodermal lesions, these tumors are benign in pediatric and adolescent patients, although malignant changes have been reported. The immature type accounts for 7.4% of pediatric malignant ovarian tumors. The mean age at diagnosis is 11-14 years, and half occur before menarche. In addition to abdominal masses, abdominal pain is often present. Because of rapid growth and infiltration of the peritoneum, the tumor has already extended beyond the ovary in 50% of patients at the time of surgery. The tumor may extend to the peritoneum, regional lymph nodes, lungs and liver. The prognosis is poor if the tumor ruptures. The typical tumor has an envelope, with a maximum diameter of 15-20 cm, and a cystic and parenchymal portion in the cut surface. Ovarian tumors are divided into different grades according to their neuroepithelial content: Grade 0: mature tissue only. Grade 1: mainly mature tissue with some immature components. Only neuroepithelium is seen in 1 low magnification view on all slices. Grade 2: Moderate amount of immature components, with neuroepithelium visible in 1 to 3 low magnification fields in all slices. Grade 3: A large amount of immature components, with 4 low magnification neuroepithelium in all slices. In summary, i.e., the grade of immaturity was judged according to the amount of neuroepithelium, and grade 0 or above was judged as malignant. If the lesion is below stage II grade II, only resection of the affected ovary and fallopian tube can be done, otherwise chemotherapy must be added with VAC and cisplatin to control local recurrence and metastasis. (5) Malignant mixed germ cell tumor: 20% of pediatric and adolescent ovarian germ cell tumors and 8% of malignant ovarian germ cell tumors. The average age at diagnosis is 16 years, and 40% are premenstrual girls. Preoperative AFP and HCG testing is required because the tumor may contain endodermal sinus tumor and embryonal carcinoma components. Bilateral lesions can be as high as 20%, so the contralateral ovary must be examined at the time of surgery. The prognosis is determined by the histology and the survival rate is about 50%. Chemotherapy such as vincristine, actinomycin D, cyclophosphamide, and cisplatin, vincristine sulfate, bleomycin may improve the prognosis. (6) Granulosa-theca cell tumor: It accounts for 3% of pediatric ovarian tumors and the average age at diagnosis is 8 years. 60% of children have precocious puberty and the lesions are mostly unilateral. It has a low malignant tendency and is treated by resection of the affected ovary and fallopian tube. Radiotherapy and chemotherapy are only used for advanced and recurrent cases. (7) Epithelial tumors: rare in prepubertal girls, pathologically they can be classified as plasmacytosis, mucinous, endometriosis (endometriosis) or clear cell tumors, showing different degrees of cell morphology can be benign or malignant margins up to malignancy. The diagnosis of ovarian tumor is usually made based on the medical history, the growth site of the mass and the greater mobility. However, a few masses fixed in the pelvic cavity cannot be excluded from ovarian tumors. Ovarian teratoma may show calcifications, bone and tooth shadows on abdominal plain radiographs. To examine the lower abdominal mass, it is emphasized that the child should first be instructed to urinate or catheterize to empty the bladder and the abdominal examination should be done in conjunction with a rectal finger examination to do a double colectomy to exclude a full bladder. At the same time, the mass is pushed, and any pulling on the uterus is noted to determine the relationship to the uterus. Ultrasound and CT examinations can assist in localization and characterization. Chest radiography for the presence of lung field and thoracic lymph node metastases and determination of tumor markers - AFP, HCG and LDH are also important to determine treatment planning and monitor tumor behavior.