Fetal primary cardiac tumors are a rare group of congenital cardiac disorders, the exact incidence of which is unknown to date, ranging between 0.0017% and 0.028% in live births. The majority of fetal primary cardiac tumors are benign, the most common being rhabdomyosarcoma, and others include teratoma, fibroma, mucinous tumor, hemangioma, etc. Malignant fetal cardiac tumors are very rare. Although most fetal primary cardiac tumors are histologically benign, they can cause obstructive hemodynamic disorders, cardiac arrhythmias, fetal edema/heart failure, and even fetal death depending on the growth site, so they are potentially fatal. Therefore, accurate prenatal diagnosis, timely clinical decision and effective intervention are of great clinical significance. The clinical characteristics and prognosis of primary fetal heart tumors The clinical manifestation and prognosis of primary fetal heart tumors not only depend on the type of tumor itself, but also on the location, size, number and complications of the tumor, so fetal heart tumors can be asymptomatic, but can also show obvious hemodynamic changes, malignant arrhythmias, severe cardiac dysfunction and progressive fetal edema. Therefore, the prognosis and clinical decision making of fetal cardiac tumors need to be based on etiology, tumor size, location, and the presence of serious complications. (1) Rhabdomyosarcoma Rhabdomyosarcoma accounts for more than 60% of fetal cardiac tumors and is the most common of the primary fetal cardiac tumors, often multiple, originating from the free wall of the ventricle and the ventricular septum, mostly involving the left atrium of the heart. Fetal arrhythmias are one of the most common manifestations of cardiac rhabdomyosarcoma, most often presenting as ventricular tachycardia on postnatal electrocardiogram. Cardiac rhabdomyosarcoma is often associated with certain genetic disorders, particularly tuberous sclerosis. Studies have shown that more than half of patients with tuberous sclerosis also have cardiac rhabdomyosarcoma. Transverse myxoma can coexist with genetic disorders (e.g., Down syndrome) and congenital heart disease (e.g., atrial septal defect, tetralogy of Fallot, hypoplastic left heart syndrome), adding to the complexity of its diagnosis and treatment. However, because cardiac rhabdomyosarcoma is the most likely cause of fatal fetal arrhythmia and is often associated with tuberous sclerosis, the latter causing fetal neurological damage is the most important risk factor for disability and death after birth, so its prognosis ranks second to that of hemangioma and benign teratoma, both prenatally and postnatally. The prognosis of rhabdomyosarcoma is not optimistic after hemangioma and benign teratoma, especially if the fetus cannot be identified prenatally for other concomitant diseases. (2) Benign teratoma Benign teratoma is the second most common primary fetal cardiac tumor, accounting for approximately 15% of primary fetal cardiac tumors. Most benign cardiac teratomas originate from the pericardium, while a few originate directly from the myocardium itself. Almost all fetuses with this disease develop pericardial effusion, which may lead to fatal cardiac tamponade. Both pericardial and intracardiac teratomas are essentially identical in histology to teratomas elsewhere in the fetus, containing three germ layers composed of benign, mature tissue. In the postnatal population, the success rate of surgery and long-term postoperative survival of benign cardiac teratomas is high, second only to hemangiomas, and thus primary fetal cardiac teratomas should be closely monitored. The prognosis after birth is good for those with no complications, while the outcome and prognosis after birth is relatively poor for those with prenatal complications, and fetal death may occur if fetal edema develops in utero. (3) Fibromas Primary cardiac fibromas have a similar incidence to cardiac teratomas and are connective tissue tumors of fibroblastic origin, most commonly seen in the ventricular septum, and often cause cardiac block and arrhythmias such as ventricular tachycardia and ventricular fibrillation [8]. Children with fibroids often die suddenly after birth due to malignant arrhythmias and have little chance of survival without timely surgery, so the overall survival rate of cardiac fibroids is significantly lower than that of the above-mentioned types of cardiac tumors. Fetal cardiac fibromas may occasionally be combined with other malformations or syndromes, such as cleft lip and palate, BeckwithCWiedemann syndrome, nevus-like basal cell carcinoma syndrome, etc. The prognosis of fetal cardiac fibromas with combined syndromes is even worse. (4) Mucinous tumor Mucinous tumor is the most common primary cardiac tumor in adult life, but it is very rare in fetus, and only a few cases have been reported. Mucinous tumors are benign tumors that originate from multipotent mesenchymal cells in the heart and cause mitral valve stenosis in the left atrium and tricuspid or pulmonary valve structural abnormalities in the right atrium. Cyanosis, systolic murmur, and congestive heart failure are the most common clinical manifestations of mucinous tumors. Isaacs H reported six cases of postnatal diagnosis of cardiac mucinous tumor, only one of which was treated surgically and survived. (5) Hemangioma Fetal cardiac hemangioma is also very rare and only a few cases have been reported. Histologically, there are three types of hemangiomas: cavernous hemangioma, capillary hemangioma, and mixed hemangioma. Pericardial effusion is the most common manifestation of hemangioma. Similar to rhabdomyosarcoma, hemangiomas have a tendency to degenerate on their own and are rarely associated with other syndromes, making them the type with the highest survival rate and best prognosis of all fetal cardiac tumors. (6) Primary fetal cardiac malignancies The most common type of cardiac malignancies in the postnatal population is rhabdomyosarcoma, followed by fibrosarcoma, whose clinical symptoms are related to the location and extent of tumor accumulation, and often have extensive metastases to the lungs, thymus, and focal lymph nodes at the time of diagnosis. Lazarus et al. reported a case of fibrosarcoma of pericardial origin in which the fetus presented postnatally with tachypnea, lethargy, diastolic gallop rhythm, and a large mediastinal mass and pericardial effusion on imaging, and was treated with chemotherapy after birth, but the child died at 3 months of age. 2. Imaging features and diagnosis of various types of primary cardiac tumors in fetal life The classification of fetal cardiac tumors is mainly based on the clinical manifestations and imaging features of the tumor, rather than on histopathological examinations. Fetal echocardiography can detect cardiac tumors early and accurately. It can evaluate the location, size, hemodynamic changes, cardiac function changes and arrhythmias of fetal cardiac tumors at any time, and can be followed up and monitored, which is safe, non-invasive and accurate. In recent years, real-time echocardiography can display tumors using “instantaneous volume reconstruction”, which is superior to traditional two-dimensional echocardiography in terms of continuous visualization, intracardiac tumor localization, and observation of cardiac dynamic changes. The first diagnosis of fetal primary cardiac tumors is made at about 20-30 weeks of gestational age, with an average of 22 weeks. The most significant manifestations of echocardiography are cardiac enlargement, ventricular outflow tract obstruction, pericardial effusion, arrhythmia and cardiac hypoperfusion. Due to the peculiarities of the fetal period, CT and MRI, which may be of great help in the diagnosis of fetal cardiac tumors, are rarely used, and 2D and 3D fetal echocardiography become the main diagnostic tools. Ultrasonography of fetal cardiac rhabdomyosarcoma may reveal an enlarged heart. Tumors are often multiple and may be located in any part of the myocardial layer, typically presenting as nodular strongly echogenic masses within the myocardium with well-defined borders and uniform echogenicity, and the masses may have a certain range of motion with the diastolic motion of the heart. Most teratomas originate from the pericardium, and the tumor is located in the pericardial cavity, containing cystic and calcified tissue. Fibromas appear as well-defined solitary masses, usually in the left ventricular free wall or septum, with heterogeneous echogenicity due to areas of calcification and cystic degeneration. Mucinous tumors are most often located in the right atrium. The ultrasound presentation of hemangioma is a mixed echogenic mass, but this rare tumor is usually located in the right atrium and is often associated with pericardial effusion. Because of the 2 mm resolution of ultrasound, some authors suggest that when diagnosing fetal cardiac tumors, if the heart tumor is too small, it may not be distinguished by ultrasound, especially in small tumors of the ventricular wall, and hypertrophic papillary muscle in the ventricle may be mistaken for transverse myxoma. Clinical decision making and management of all types of primary cardiac tumors in the fetus: Clinical decision making and management of fetal cardiac tumors should be based on the safety of the pregnant woman and her future fertility, which is the highest principle of prenatal intervention for fetal disease. In primary fetal malignant cardiac tumors, pregnancy should be terminated immediately upon detection to prevent the potential harm to the mother. In the case of primary benign fetal cardiac tumors, the overall survival rate of primary benign fetal cardiac tumors is 66%, and the survival rate of children treated with surgery after birth is 72%. The survival rate of children who received surgery after birth was 72%, and the survival rate of children who did not receive surgical treatment was 55%. In recent years, with the development of imaging technology, improved cardiac surgery techniques, prenatal interventions and fetal monitoring, the level of prenatal diagnosis, intervention and postnatal treatment of cardiac tumors has improved significantly, and the overall survival rate has shown an increasing trend. Asymptomatic fetal benign cardiac tumors with normal cardiac function do not require prenatal treatment, but only regular ultrasound follow-up of the fetus, and if there are no serious complications, the intrauterine growth of the fetus should be prolonged as long as possible. For fetuses without severe compression or obstruction symptoms but with cardiac insufficiency and/or arrhythmia, comprehensive therapeutic measures such as transplacental transfer medication or intrauterine pericardiocentesis for cardiac decompression should be given promptly to try to control the arrhythmia and cardiac function status of the affected fetus and prolong the gestation time. For fetuses with severe compression or obstruction symptoms, arrhythmia and heart failure that are difficult to control with medications, if the fetus has sufficient lung maturity, timely delivery can be considered and cardiac surgery and postoperative comprehensive treatment can be given after birth; if the fetus is diagnosed with the above-mentioned severe symptoms and is still at an early gestational age and cannot survive after timely delivery, termination of pregnancy can be considered to ensure the safety of the mother. In addition, the type of tumor should be considered. In addition, the type of tumor and its prognosis need to be considered. For rhabdomyosarcomas and hemangiomas with the possibility of spontaneous regression, the observation and treatment of complications can take slightly longer than for other types of cardiac tumors. Prenatal interventions for these diseases must take into account the individualized nature of the disease and its developmental changes, requiring close monitoring and dynamic evaluation of the evolution of the disease in the affected fetus, with joint judgment and risk assessment by pediatric, cardiology, obstetrics and ultrasound specialists, and timely clinical decisions for the patient’s family. Specifically, rhabdomyosarcoma has the highest incidence and relatively good clinical prognosis, and rhabdomyosarcoma has a tendency to regress spontaneously, so most fetal cardiac rhabdomyosarcoma is treated conservatively without early delivery or cardiac surgery unless necessary; teratoma and large hemangioma can produce pericardial effusion and cause pericardial tamponade leading to fetal death, so treatment usually requires prenatal intervention such as pericardial puncture for decompression, or prenatal Fetal cardiac fibrous tumors are often in a quiescent state and have no possibility of spontaneous regression, and may continue to grow after birth. If the surgical resection is incomplete, the tumor is likely to recur. The principle of surgical treatment for primary benign cardiac tumors in the postnatal population is to maximize the restoration of myocardial function rather than complete removal of the tumor. While complete resection of the tumor is desirable, partial resection of most benign cardiac tumors to preserve important structures and myocardial tissue within the heart chambers is also effective. For some large cardiac tumors, surgical resection is not easy to achieve and is more likely to result in obstructive hemodynamic disorders, for which the only treatment option is heart transplantation. The increasing sophistication of prenatal interventions has allowed some fetuses with primary cardiac tumors to grow, develop, and mature in utero until delivery, and to have a relatively good prognosis after birth with cardiac surgery. Although it is controversial [19], it is believed that fetal surgery will be accepted by more and more families with the disease as the society develops and the level of human disease awareness increases. After the completion of basic experimental studies, fetal cardiac surgery will also make great clinical progress. The maturity of infant cardiac surgery, the increasing success rate and postoperative survival rate, and the improving long-term quality of life of patients after surgery give us reason to believe that the prognosis of fetal cardiac tumors will continue to improve.