According to the World Health Organization classification in 2020, GTN includes invasive hydatidiform mole, choriocarcinoma (hereafter referred to as choriocarcinoma), PSTT, and epithelioid trophoblastic tumor . Invasive hydatidiform mole and choriocarcinoma comprise the majority of GTN cases. The principles of diagnosis and treatment of the two diseases are generally the same and involve referring to the FIGO stage and prognosis score [4, 5]. The two diseases were analyzed together as the GTN group during this study. PSTT and epithelioid trophoblastic tumor are rare but important forms of GTN with unique pathologies, natural histories, and treatment paradigms [6, 7]. They were analyzed together as the other GTN group during this study.
The statistics of this study suggest that the formation of UAVM is related to the prognosis score. The higher the prognosis score, the greater the possibility of UAVM.
Gestational trophoblastic tumors usually have a rich blood supply. Tumor cells have an erosive and reconstructive effect on blood vessels, forming masses that expand and distort vascular lesions. AVM is an abnormal connection between arteries and veins bypassing capillaries. UAVM is rare and can be caused by curettage, cesarean delivery, GTN, maternal diethylstilbestrol exposure, or endometrial and cervical tumors. The most common cause is GTN . Studies have indicated that cesarean delivery increases the risk of GTN after hydatidiform mole . Another study  suggested that the formation of vascular lesions in the uterus is associated with placental tissue invasion in the myometrium and trauma. β-hCG may have a key regulatory role in angiogenesis and vascular function. High levels of β-hCG and unorganized trophoblast lead to destructive changes in the vascular structure and the likelihood of causing the arterial vessels to flow directly to venous vessels at the scar site to form UAVM . The β-hCG value, as the first biomarker in the diagnosis, treatment, and follow-up of GTN, is high with an invasive hydatidiform mole and choriocarcinoma, but it is low with PSTT and epithelioid trophoblastic tumor . During this study, the β-hCG value and prognosis score of the two groups were analyzed. The results suggested that when β-hCG was ≥ 10,000 mIU/mL, the probability of UAVM increased, and that the formation of UAVM is related to the prognosis score.
Two GTN cases with UAVM were also found in the PSTT group. The high β-hCG value may explain the cause of UAVM in these cases. However, β-hCG values were < 10,000 mIU/mL in the GTN group and PSTT group, and they may have been related to the complete angiogenesis between tumor cells in PSTT lesions and the infiltration of intermediate trophoblasts in the vessels. Touhami et al.  summarized 50 patients with GTN combined with UAVM in 14 works. The median hCG level at the time of AVM diagnosis was 2864.9 mIU/mL (range, 0–32,000), and three patients had undetectable hCG levels at the time of AVM diagnosis. During our study, β-hCG values during the early stage of treatment would have had greater reference value.
There were 25 cases of UAVM in this study; two of these UAVM cases included PSTT and 23 of these UAVM cases included GTN. The uterine arteries of all cases had different degrees of tortuous expansion, suggesting that the main blood supply of the focus came from the uterine artery. Ovarian artery imaging of two cases of GTN showed that the blood supply of the tumors was partly from the ovarian arteries. Uterine veins in all cases were dilated. Two cases of PSTT and 20 cases of GTN were complicated with unilateral or bilateral ovarian vein dilation, suggesting that the draining veins of the lesions were uterine veins and ovarian veins. Dilated ovarian veins may cause the formation of local UAVM, which leads to the expansion of the pelvic vein volume and an increase in the total pelvic vessel pressure along with the reflux mode of ovarian vein resistance and the lack of venous valve, resulting in the expansion of the ovarian vein and early observation of the arterial phase with CE-MRA .
Approximately 10–15% of patients experience GTN combined with UAVM. However, it appears that only 2% of uterine AVMs are symptomatic and cause chronic or heavy bleeding . Some patients also experience pelvic pain. Some studies have shown that even after GTN is completely cured, UAVM still exists and poses the risk of massive hemorrhage. UAVM will cause bleeding and influence the effects of intravenous chemotherapy because the arterial blood carrying a large number of chemotherapy drugs does not enter the focus tissue and flows directly back into the vein, leading to ineffective circulation of chemotherapy drugs. During this study, drug resistance occurred in two cases in the group without UAVM and in three cases in the group with UAVM. Considering the small number of cases, whether UVAM will cause drug resistance requires follow-up research. The most effective treatment for UAVM complicated with massive hemorrhage is interventional therapy. The success rate of interventional therapy is 78.6–90% [13–16]. Interventional therapy can control the bleeding caused by UAVM and treat the bleeding caused by the primary focus and metastasis. During this study, six patients underwent interventional embolization because of vaginal bleeding; of these patients, five had UAVM. All six patients underwent CE-MRA before interventional therapy, and hemorrhage was effectively controlled in every patient.
The gold standard for the diagnosis of UAVM is interventional angiography. However, this technique is invasive and exposes the patient to a certain amount of ionizing radiation. MRI has advantages in the diagnosis of GTN combined with UAVM [14, 17, 18]; for example, it can obtain the vascular characteristics of the feeding arteries and drainage veins, provide a reference for the design of the interventional treatment scheme, shorten the interventional time, and reduce the radiation dose experienced by physicians and patients during interventional surgery. The time-resolved CE-MRA sequence can be used to observe UAVM combined with ovarian venous dilatation reflux and the whole process of blood circulation, to clarify the circulation characteristics of the tumor vessels, and to provide a reference for subsequent treatment .
The formation of UVAM is related to the prognosis score. The higher the prognosis score, the greater the possibility of UVAM. CE-MRA is helpful for diagnosing UVAM in a timely manner, thereby preventing life-threatening massive bleeding and providing a better reference for follow-up treatment.