A reclassification and comprehensive examination of uterine arteriovenous malformation: insights derived from a case series.

This project is a retrospective study. Initially, cases of patients diagnosed with UAVM via ultrasound imaging will be reviewed within the case management system. Subsequently, clinical data for these patients will be further retrieved to verify those with a confirmed clinical diagnosis of UAVM, and the medical histories of these clinically confirmed cases will be collected. By integrating the aforementioned case data with findings from existing literature, patients diagnosed with UAVM through ultrasound and clinical evaluation will be reclassified according to distinct etiologies. This reclassification will facilitate an in-depth investigation of the ultrasound imaging characteristics, pathological features, diagnostic criteria, and treatment strategies associated with each category, thereby providing more comprehensive case data and evidence to inform clinical practice. We used the keywords “arteriovenous fistula” and “arteriovenous spectrum” to query the ultrasound diagnosis of female obstetric and gynecological disease patients in the medical record system of Tongji Hospital of Huazhong University of Science and Technology from January 1, 2010, to March 31, 2025. The standard for ultrasound diagnosis is: abundant abnormal blood flow signals are observed within the uterine myometrium, presenting a spectrum of arteriovenous fistula. All procedures involving human participants in this study were approved by the Ethics Committee of Huazhong University of Science and Technology (Ethical Number: TJ-IRB202506027). We retrieved a total of 121 cases of ultrasound-diagnosed UAVM patients, and then we further searched the medical records of all the aforementioned patients using their ID numbers, finding that 19 cases were clinically diagnosed as UAVM. The clinical diagnosis is established based on the pathological findings derived from hysteroscopic or laparoscopic examination, or confirmed through interventional surgical procedures. Subsequently, we collected the clinical data of the confirmed patients, which includes the following: ① age; ② number of pregnancies; ③ number of deliveries; ④ history of surgery and other triggers; ⑤ clinical manifestations; ⑥ location and size of lesions; ⑦ basis for diagnosis; ⑧ treatment process and methods; ⑨ prognosis. Finally, in conjunction with the published literature, we summarized, analyzed, and discussed the confirmed cases. The flowchart for retrieval is shown in Fig.  1 . Fig. 1 Flowchart for Clinical Case Retrieval of UAVM Flowchart for Clinical Case Retrieval of UAVM The data analysis in this study was conducted using descriptive statistical techniques. Descriptive statistics were utilized to characterize the case attributes of the study population, and the overall incidence rate of UAVM was determined for each classification method. Specifically, the incidence rate was computed by dividing the number of cases within each classification by the total number of cases across all classifications, with the resulting quotient expressed as a percentage through multiplication by 100%.

Among the 121 patients with UAVM diagnosed by ultrasound, 2 cases were primary UAVM (2/121, 1.7%), while the remaining 191 cases were secondary UAVM (191/121, 98.3%). Due to the significant differences in treatment goals and plans for UAVM patients caused by miscarriage, postpartum, trophoblastic disease, and other non-pregnancy-related reasons. We reclassified secondary UAVM into non-pregnancy-related UAVM (16/121, 13.2%) and pregnancy-related UAVM (103/121, 85.1%). Pregnancy-related UAVM was further classified into post-abortion UAVM (77/121, 63.7%), postpartum UAVM (13/121, 10.7%), and UAVM after chemotherapy for trophoblastic disease (13/121, 10.7%). According to the search of 121 cases of ultrasound-diagnosed UAVM patients, 19 cases were clinically diagnosed, resulting in a clinical diagnosis rate of 15.7% (19/121). Among the 19 confirmed UAVM patients, 2 cases were primary UAVM (2/19, 10.5%), and 17 cases were secondary UAVM (15/19, 89.5%). Within the category of secondary UAVM, non-pregnancy-related UAVM constitutes 11.8% (2/17), whereas pregnancy-related UAVM represents 88.2% (15/17). Then, Pregnancy-associated UAVM were also categorized into three distinct types: post-abortion UAVM, which accounted for 58.8% (10/17); postpartum UAVM, comprising 23.5% (4/17); and UAVM occurring subsequent to chemotherapy for trophoblastic disease, representing 5.9% (1/17). Therefore, the ultrasound-diagnosed incidence of UAVM in our study is significantly higher than the incidence in previous reports. This suggests that clinicians should pay close attention to the UAVM results reported by ultrasound and provide timely intervention and follow-up for patients to avoid serious complications. All confirmed cases were women of childbearing age (20–40 years old), with most being patients after pregnancy or miscarriage, which is highly consistent with previous reports. The early clinical manifestations of the patient mainly include recurrent heavy vaginal bleeding and abundant blood flow signals detected by ultrasound. Due to the large amount of bleeding and the urgency of the condition, all patients underwent surgical treatment based on their fertility wishes, the location of the lesions, and clinical characteristics. Postoperative follow-up showed that bleeding had stopped in all patients, and ultrasound re-examination indicated that the UAVM lesions gradually disappeared. Accurate classification and treatment plans are essential for patients. Therefore, we will combine the clinical cases in this cohort to provide a detailed classification and description of the patients. In our case series, two patients were diagnosed with primary UAVM. One patient exhibited vascular lesions characterized by full-length dilation of the uterine myometrial vessels, along with significant dilation of bilateral paracervical vessels. This patient has completed her reproductive needs and underwent a hysterectomy, along with bilateral internal iliac artery ligation. On the other hand, another patient presented with recurrent “switch-type” vaginal bleeding without obvious triggers. The patient underwent a curettage procedure in the outpatient setting for the first treatment, and there was a significant reduction in vaginal bleeding post-operation. However, two days after the surgery, there was another episode of heavy vaginal bleeding, and an emergency balloon tamponade was performed in the uterine cavity, but the effect was poor. Subsequently, bilateral uterine artery embolization was performed, and there was no significant bleeding afterward. Three months post-surgery, the patient experienced heavy vaginal bleeding again during menstruation, and bilateral uterine artery embolization was performed, which stopped the bleeding. During the first menstrual period after that, the patient experienced heavy vaginal bleeding again, leading to a left uterine artery branch embolization, which successfully stopped the bleeding. Therefore, it can be seen that the symptoms of primary UAVM are often more severe and have a tendency to recur, making clinical treatment relatively difficult (Fig.  2 ). Accurate diagnosis of primary UAVM and proper assessment of recurrence risk are of great significance. Fig. 2 Doppler ultrasound image of the primary UAVM patient. Abnormal blood flow in the uterus and surrounding areas, arteriovenous fistula. The uterine myometrial vessels are fully dilated, measuring approximately 4.9 × 3.3 cm, and the paracervical vessels on both sides of the uterus are significantly enlarged Doppler ultrasound image of the primary UAVM patient. Abnormal blood flow in the uterus and surrounding areas, arteriovenous fistula. The uterine myometrial vessels are fully dilated, measuring approximately 4.9 × 3.3 cm, and the paracervical vessels on both sides of the uterus are significantly enlarged Next, we will classify secondary UAVM based on its relationship with pregnancy. Non-pregnancy-related UAVM diagnosed by ultrasound are mainly caused by uterine fibroids, trophoblastic diseases, endometrial cancer, cervical cancer, and postoperative conditions. Most patients often see the arteriovenous fistula disappear after treating the primary disease. However, In our cases, two patients encountered complications that were not associated with pregnancy; these complications arose as a consequence of LEEP surgery and uterine leiomyoma, respectively. One experienced significant vaginal bleeding after cervical LEEP surgery, and ultrasound revealed turbulent blood flow signals in the cervical canal, leading to a diagnosis of cervical arteriovenous fistula. The patient underwent urgent iliac artery interventional embolization due to hemorrhagic shock, and the bleeding stopped afterward. Another patient had a history of heavy menstrual bleeding due to uterine fibroids and suddenly experienced massive vaginal bleeding during her menstrual period. Balloon compression hemostasis was ineffective, and ultrasound showed the formation of an arteriovenous fistula within the uterine myometrium. She subsequently underwent laparoscopic myomectomy combined with uterine artery ligation, and the bleeding stopped postoperatively. Therefore, the clinical treatment of non-pregnancy-related UAVM primarily focuses on controlling severe hemorrhage, with comprehensive treatment based on the patient’s underlying disease being the main therapeutic approach (Fig.  3 ). Fig. 3 Doppler ultrasound images of non-pregnancy related UAVM. Abnormal echoes in the endometrium and myometrium of the anterior wall of the uterus, uterine arteriovenous fistula. The uterine morphology is abnormal, with a 6.9 × 5.6 × 5.7 cm hypoechoic mass observed in the lower segment of the left posterior wall. A 0.5 × 1.1 × 0.6 cm tortuous tubular anechoic structure is seen within the anterior wall endometrium and myometrium, showing blood flow signals with a PSV of 56 cm/s and an RI of 0.39 Doppler ultrasound images of non-pregnancy related UAVM. Abnormal echoes in the endometrium and myometrium of the anterior wall of the uterus, uterine arteriovenous fistula. The uterine morphology is abnormal, with a 6.9 × 5.6 × 5.7 cm hypoechoic mass observed in the lower segment of the left posterior wall. A 0.5 × 1.1 × 0.6 cm tortuous tubular anechoic structure is seen within the anterior wall endometrium and myometrium, showing blood flow signals with a PSV of 56 cm/s and an RI of 0.39 After a patient experiences a miscarriage, if there is abnormal tissue remaining in the uterine cavity or placental implantation, ultrasound diagnosis often shows abundant blood flow signals, presenting a spectrum of arteriovenous fistula. Most patients see the arteriovenous fistula disappear after follow-up observation, medication treatment, or curettage. However, some patients may ultimately be clinically diagnosed with UAVM. In our case series, there are 10 patients diagnosed with post-abortion UAVM. Their main clinical presentation was persistent irregular vaginal bleeding accompanied by sudden heavy vaginal bleeding after abortion. Ultrasound examination may show abnormal tissue remnants in the uterine cavity, along with rich blood flow signals from arteriovenous fistulas (Fig.  4 ). Most of them underwent arterial embolization or arterial ligation for hemostasis. Those with tissue remnants underwent curettage or hysteroscopic to remove the remaining pregnancy tissue, and postoperative care included anti-infection treatment and symptomatic support. Fig. 4 Doppler ultrasound images of post-abortion UAVM. In the uterine cavity, there is a mixed echo strip measuring 1.8 cm in the anteroposterior diameter and 4.9 cm in the longitudinal diameter. The blood vessels in the anterior wall of the myometrium are significantly thickened and appear honeycomb-like, with abundant blood flow signals, measuring 4.1 × 2.0 cm, and some blood flow penetrates the serosal layer Doppler ultrasound images of post-abortion UAVM. In the uterine cavity, there is a mixed echo strip measuring 1.8 cm in the anteroposterior diameter and 4.9 cm in the longitudinal diameter. The blood vessels in the anterior wall of the myometrium are significantly thickened and appear honeycomb-like, with abundant blood flow signals, measuring 4.1 × 2.0 cm, and some blood flow penetrates the serosal layer Next, we will classify secondary UAVM as postpartum UAVM. On one hand, postpartum UAVM can also be accompanied by retained pregnancy tissue, similar to UAVM after abortion mentioned above. More importantly, the formation of UAVM at the incision diverticulum after cesarean section is a unique type of postpartum UAVM. In our cases, two out of four postpartum UAVM patients developed uterine incision diverticula and formed arteriovenous fistulas. Ultrasound showed abnormal rich blood flow signals and mass formation at the lower segment cesarean section incision of the uterus, accompanied by abnormal vaginal bleeding (Fig.  5 ). The main procedures performed on the patients included uterine artery embolization or ligation, along with repair of the incisional diverticula. Postpartum hemorrhage caused by incision diverticula is often misdiagnosed or overlooked, and clinicians should pay attention to this issue. Fig. 5 Doppler ultrasound images of postpartum UAVM. An irregular mass is observed at the site of the cesarean section incision, indicating a uterine arteriovenous fistula. At the lower segment of the anterior wall of the uterus, a 2.9 × 2.1 × 2.6 cm heterogeneous echo mass is visible at the cesarean section incision, with clear boundaries. Inside, there is a 2.3 × 1.6 × 1.9 cm anechoic area, partially bulging outward, with the anechoic outer boundary closely adhering to the serosa. Vortex-like blood flow is observed inside, along with the spectrum of the arteriovenous fistula Doppler ultrasound images of postpartum UAVM. An irregular mass is observed at the site of the cesarean section incision, indicating a uterine arteriovenous fistula. At the lower segment of the anterior wall of the uterus, a 2.9 × 2.1 × 2.6 cm heterogeneous echo mass is visible at the cesarean section incision, with clear boundaries. Inside, there is a 2.3 × 1.6 × 1.9 cm anechoic area, partially bulging outward, with the anechoic outer boundary closely adhering to the serosa. Vortex-like blood flow is observed inside, along with the spectrum of the arteriovenous fistula Finally, we classify secondary UAVM as trophoblastic disease-related UAVM. Trophoblastic diseases can lead to the formation of UAVM due to their high invasiveness and rich vascularization. In our case, one patient experienced three episodes of abnormal heavy vaginal bleeding one year after active chemotherapy for hydatidiform mole. Ultimately, an ultrasound revealed the formation of a uterine myometrial arteriovenous fistula (Fig.  6 ). The patient underwent hysteroscopic examination, followed by suturing of the uterine lesions and bilateral uterine artery ligation. Postoperatively, the bleeding stopped. Therefore, the treatment of trophoblastic disease-related UAVM should be based on a comprehensive assessment of the patient’s bleeding situation, disease type, chemotherapy cycle, and pathological characteristics, providing a personalized treatment plan for the patient. Fig. 6 Doppler ultrasound images of trophoblastic disease-related UAVM. Abnormal blood flow signals in the uterine myometrium, possible uterine arteriovenous fistula. A 1.9 × 1.2 cm tortuous anechoic area is observed on the posterior wall of the uterine fundus, with a maximum internal diameter of 0.46 cm, showing rich blood flow signals, RI 0.41 Doppler ultrasound images of trophoblastic disease-related UAVM. Abnormal blood flow signals in the uterine myometrium, possible uterine arteriovenous fistula. A 1.9 × 1.2 cm tortuous anechoic area is observed on the posterior wall of the uterine fundus, with a maximum internal diameter of 0.46 cm, showing rich blood flow signals, RI 0.41

This study possesses considerable clinical significance and originality. Through a systematic review of ultrasound diagnostic cases collected over a 15-year period, it represents the first effort to integrate 19 authentic clinical cases to deliver a comprehensive clinical classification and methodological elucidation of UAVM. This research not only enhances the current understanding of UAVM but also innovatively develops a diagnostic and therapeutic strategy framework customized to diverse clinical contexts, thereby providing essential and pragmatic theoretical foundations and guidance for clinical application. However, this study is subject to several limitations. First, the sample size of clinically confirmed UAVM cases was relatively limited, necessitating the expansion of the clinical cohort in future investigations. Second, the reliance on retrospectively collected medical records introduces potential issues related to incomplete data and information bias. Finally, as the data were obtained from a single center, the study population may not be representative of a wider demographic. To address these limitations, future research should incorporate multi-center studies to more comprehensively evaluate the accuracy of the novel classification method and to develop more precise diagnostic and therapeutic strategies for clinical application.

Currently, with the increasing rates of cesarean sections and induced abortions, combined with the actual clinical incidence of UAVM diagnosed by ultrasound mentioned above, UAVM may be severely overlooked in clinical practice. Therefore, UAVM ought to be considered in the differential diagnosis of abnormal or excessive vaginal bleeding. Our aforementioned aetiology-based classification method for UAVM will offer new perspectives and insights for early identification, multidisciplinary collaboration, and personalised treatment, providing important clinical references for UAVM in various clinical scenarios.

Drawing from the classification and analysis of the aforementioned cases, we then systematically synthesized and examined the pathological mechanisms, clinical presentations, imaging characteristics, differential diagnoses, and treatment of UAVM. The purpose is to remind clinicians to pay more attention for this rare disease and provide clearer clinical references. The characteristic of UAVM is the abnormal direct connection between the uterine arteries and veins, bypassing the normal capillary network, which leads to the formation and expansion of atypical vascular clusters. At this point, the “short circuit” of blood flow between the high-pressure arterial system and the low-pressure venous system can cause severe complications such as acute massive hemorrhage [ 9 , 10 ]. Although the final pathological features of primary and secondary UAVM are the expansion and formation of capillary clusters, their initial pathogenesis is different. Primary UAVM is caused by abnormal formation of the original vascular structure during embryonic development, leading to the creation of numerous vascular connections between the supplying arteries and draining veins. These vascular branches often extend from the edge of the uterus into the pelvis, resulting in more extensive vascular lesions that can affect other organs within the pelvic cavity [ 6 , 11 ]. From a histological perspective, due to the absence of external pathological stimuli, the vascular network formed by primary UAVM does not exhibit significant proliferation of endothelial cells and stroma, resulting in a spiral network of vascular dilation [ 12 ]. However, secondary UAVM is caused by factors such as trauma and infection that lead to the blockage of small veins in the uterus. From the perspective of the classification we mentioned above, non-pregnancy-related UAVM is often caused by abnormal arteriovenous connections formed from primary diseases, occurring relatively rarely, and the pathological mechanisms vary depending on the primary disease. However, most pregnancy-related UAVM mainly occur after induced abortion. During pregnancy, the increased blood flow to the uterus and the thinning of blood vessels due to vasodilation make it easier for surgical procedures like curettage to damage the blood vessels in the endometrium and myometrium, leading to the formation of abnormal connections between arteries and veins. Additionally, retained pregnancy tissue may trigger inflammatory infections, further increasing vascular fragility and promoting the proliferation of abnormal blood vessels and the formation of arteriovenous fistulas [ 13 ]. Trophoblastic diseases are highly invasive; the invasion of tumor cells into the endometrium and myometrium can disrupt normal arterial and venous structures, making it easier to form arteriovenous shunts. Additionally, trophoblastic lesions have an extremely rich blood supply, with high blood flow velocity and pressure, which can also easily lead to the formation of UAVM. The continuous influx of arterial blood causes compensatory hyperplasia and dilation of the capillary network, resulting in changes in vascular structure [ 14 , 15 ]. Histologically, secondary UAVM leads to the excessive activation of endothelial cells, fibroblasts, and smooth muscle cells, resulting in the formation of numerous fistulas between arteries and veins [ 12 , 16 ]. Therefore, based on the aforementioned pathogenesis, the symptoms of primary UAVM are relatively severe, and the treatment outcomes are poor. Figure 7 shows the pathogenesis and pathological characteristics of primary and secondary UAVM. Fig. 7 Causes and pathological mechanisms of primary and secondary UAVM Causes and pathological mechanisms of primary and secondary UAVM The clinical features of UAVM vary greatly. Mild UAVM shows no obvious clinical symptoms and is only identified through ultrasound characteristics. Whereas severe UAVM often leads to serious complications in patients within a short period. Therefore, based on our case series, we summarized the clinical manifestations of UAVM in Fig.  8 . The main clinical manifestation of UAVM is irregular vaginal bleeding, which can vary in severity, presenting as “switch-like” heavy bleeding or a large amount of bleeding occurring within a short period. Some studies have defined vaginal bleeding in UAVM patients as major or minor bleeding based on the amount of blood loss, categorizing it as major bleeding if the loss exceeds 500mL within 24 h or if a single episode exceeds 100mL [ 17 ]. In the 19 patients we clinically diagnosed, the main reason for seeking medical attention was vaginal bleeding. Therefore, vaginal bleeding is often the initial symptom of UAVM. In our case, Patient 18 presented with menorrhagia. Excessive menstruation is one of the serious complications of UAVM. During menstruation, the shedding of the endometrium exposes and ruptures the abnormal blood vessels of UAVM, leading to acute and significant bleeding in a short period, which presents as excessive menstrual bleeding for patients [ 18 ]. At this time, clinicians need to carefully differentiate between menorrhagia caused by UAVM and other conditions such as uterine fibroids, endometrial polyps, and dysfunctional uterine bleeding. Pelvic pain may be one of the clinical manifestations of UAVM [ 19 ]. In UAVM patients, local vascular congestion and dilation in the pelvic area can obstruct venous return and increase pelvic pressure, which may stimulate surrounding nerves and lead to chronic pelvic pain. Additionally, arteriovenous fistulas that shunt arterial blood may cause ischemic pain in the pelvic organs. More seriously, the rupture of an arteriovenous fistula can lead to bleeding that irritates the peritoneum or causes thrombosis, potentially resulting in acute pelvic pain. Therefore, it is necessary to rule out other causes of pelvic pain, such as endometriosis, pelvic inflammatory disease, and ruptured ovarian cysts. Due to the main clinical manifestation of UAVM being abnormal uterine bleeding, long-term chronic blood loss or sudden massive bleeding can lead to hemodynamic-related symptoms. High-output heart failure caused by large/high-flow UAVM can result in symptoms such as palpitations, shortness of breath, and fatigue, while continuous “machinelike” murmurs may be heard upon pelvic auscultation [ 20 ]. At this time, timely management of the patient’s hemorrhagic shock symptoms to save the patient’s life is the top priority in clinical treatment. In addition, the localized pressure caused by UAVM can compress the bladder, leading to symptoms such as frequent urination and difficulty urinating [ 21 ]. Compression of the rectum can cause a feeling of urgency and heaviness, as well as constipation. At the same time, the mass formed by UAVM may lead to symptoms such as dyspareunia, infertility, and miscarriage [ 2 ]. When a patient presents with pregnancy-related UAVM, there may also be an elevation in HCG levels. The severity of these symptoms varies depending on the location and extent of the lesions caused by UAVM. Fig. 8 The clinical manifestations of UAVM The clinical manifestations of UAVM Rapid imaging diagnosis and differentiation from other hemorrhagic diseases are crucial for confirming the diagnosis of UAVM, avoiding misdiagnosis, and guiding treatment. Subsequently, we will elucidate the five main imaging characteristics associated with UAVM (Fig.  9 ). Ultrasound is the fastest and most convenient imaging method for diagnosing UAVM. The grayscale ultrasound images of UAVM may show an enlarged uterus with an irregular shape, and there may be cystic or honeycomb-like anechoic or hypoechoic areas within the myometrium. If the lesions involve the endometrium, a mixed mass may appear in the uterine cavity, accompanied by a disruption of the endometrial line. The grayscale ultrasound imaging characteristics of UAVM are not significantly specific, but color Doppler ultrasound can present typical UAVM images. Typical UAVM color Doppler ultrasound can observe an abnormal increase in high-speed blood flow signals, revealing a convoluted and chaotic vascular mass that appears “like a blood lake.” At the same time, pulse Doppler analysis shows a typical high-speed, low-resistance blood flow pattern, characterized by a significant increase in peak systolic velocity (PSV) and a decrease in pulsatility index (PI) [ 17 , 22 – 24 ]. CT is another important imaging method for diagnosing UAVM. It plays a crucial role in identifying the location of the fistula, as well as the supplying arteries and draining veins, and can guide interventional embolization treatment. Similar to the grayscale ultrasound findings, a plain CT scan may reveal an irregularly shaped enlarged uterus, with slightly low-density or isodense foci visible within the myometrium. If there is associated bleeding, a high-density hematoma may be seen within the uterine cavity or myometrium, but the above findings are not specific. The most important thing is that enhanced CT shows significant enhancement of the uterine myometrium during the arterial phase, presenting as nodular, convoluted vascular clusters or patchy high-density shadows. And the dilated vascular channels may also lead to the formation of flow-related aneurysms [ 25 – 27 ]. MRI has advantages such as no radiation, high soft tissue resolution, and multi-parameter imaging. It can clearly display the anatomical structure and hemodynamic characteristics of fistulas, making it an important imaging method for diagnosing UAVM. MRI can show serpentine, dilated high-velocity blood flow within the myometrium or pericervical tissue, with tortuous blood vessels appearing as linear or tubular low signals, which may protrude into the uterine cavity. At the same time, magnetic resonance angiography (MRA), as a non-invasive and valuable vascular imaging technique, may reveal significant pulsatile mass formation, clearly displaying abnormal vascular clusters, blood supply arteries, and drainage venous blood flow. Through three-dimensional reconstruction, it is also possible to visually observe the location of the fistula and the course of the blood vessels [ 24 , 26 , 28 – 30 ]. DSA is the gold standard for diagnostic UAVM with an invasive and therapeutic purpose. DSA shows significant thickening and tortuosity of the supplying arteries, as well as rapid early filling of enlarged veins within the vascular mass. When a patient experiences a severe hemorrhage, interventional embolization for diagnostic and therapeutic purposes can quickly stop the bleeding. If a follow-up DSA is needed postoperatively, it can assess the effectiveness of the DSA interventional embolization treatment and help prevent the recurrence of UAVM. Hysteroscopic examination is not the primary imaging method for diagnosing UAVM; its diagnostic capability is limited. However, it holds significant value for submucosal or endometrial-involved UAVM. In the case of superficial UAVM during hysteroscopy, abnormal blood vessels with irregular diameters and disordered pathways can be observed in the endometrium, appearing as purplish-blue or dark red. When there is pulsatile bleeding at the arteriovenous fistula, jet-like bleeding can be seen [ 31 – 34 ]. Fig. 9 Five imaging methods for diagnosing UAVM Five imaging methods for diagnosing UAVM Symptoms of UAVM often have similar imaging manifestations to those of retained tissue after abortion, trophoblastic diseases, and uterine artery pseudoaneurysm, making clinical diagnosis quite challenging and prone to confusion. Accurate diagnosis and the selection of appropriate treatment methods are very important. Subsequently, we will delineate the distinct characteristics of each entity to facilitate their differentiation from UAVM (Table  1 ). In our case series, most of the secondary UAVM is caused by pregnancy, so RPOC is the first condition that needs to be differentiated in diagnosis. Clinically, RPOC often presents as persistent or intermittent vaginal bleeding post -abortion or postpartum, which can vary in volume and is frequently accompanied by abdominal pain. Ultrasound examinations typically reveal irregular, abnormal echo masses within the uterine cavity, with unclear boundaries. Color Doppler ultrasound may show few or focal abundant blood flow signals, usually characterized by low-velocity blood flow spectra. The level of serum β-human chorionic gonadotropin (β-hCG) generally shows a slow declining trend or may rise again. In contrast, the clinical symptoms of a UAVM primarily include significant vaginal bleeding, which can be sudden and severe. Ultrasound findings are as described above, and the serum β-hCG levels are often within the normal range. In uterine artery angiography, retained products of conception may show filling defects in the uterine cavity, while a uterine arteriovenous fistula is characterized by thickening and twisting of the uterine artery, significantly shortened arteriovenous circulation time, and early visualization of veins. A comprehensive assessment can be made based on the history of abortion, blood HCG levels, hemodynamic characteristics, and bleeding patterns, but it is also important to be vigilant for the possibility of both conditions coexisting [ 35 – 37 ]. GTD and UAVM can both present as abnormal uterine bleeding, but their causes, pathological mechanisms, and treatment strategies are quite different. GTD (such as hydatidiform mole, invasive mole, and choriocarcinoma) is characterized by abnormal trophoblastic proliferation after pregnancy, clinically presenting as irregular vaginal bleeding after amenorrhea, with the uterus often larger than expected for the gestational age, significantly elevated blood β-hCG levels, accompanied by pregnancy-related nausea and abdominal pain. Invasive moles and choriocarcinoma may also present with symptoms such as pulmonary metastasis. Ultrasound findings for GTD show a “snowstorm” or “honeycomb” appearance in the uterine cavity, with poorly defined low echogenic or mixed echogenic areas in the myometrium, and space-occupying lesions in the cavity or myometrium with focal hypervascularity. In contrast, UAVM is mostly asymptomatic, typically presenting as sudden, painless massive bleeding, with normal blood β-hCG levels, and ultrasound findings as described above. Clinically, it is essential to comprehensively assess the medical history, clinical symptoms, imaging, and laboratory test results to accurately differentiate between gestational trophoblastic disease and UAVM [ 38 – 40 ]. UAP often occurs as a result of iatrogenic injuries such as after cesarean sections, uterine surgeries, or interventional procedures, leading to the rupture of arterial vessel walls and the formation of a localized hematoma wrapped in fibrous tissue. Patients may experience irregular vaginal bleeding unrelated to the menstrual cycle and may palpate a pulsatile mass in the pelvic area. At the same time, UAP shows characteristic unidirectional arterial waveform blood flow spectra on color Doppler, and on DSA, it presents as localized contrast agent extravasation and localized aneurysmal dilation of the uterine artery branches. In contrast, UAVM is a true vascular malformation composed of an abnormally proliferating network of blood vessels, characterized by excessive menstrual bleeding, prolonged menstrual periods, or irregular bleeding related to the menstrual cycle. Color Doppler shows a relatively diffuse vascular cluster with mixed arterial and venous blood flow, and DSA reveals an abnormal vascular cluster with early venous opacification [ 41 – 44 ]. Table 1 Differential diagnosis of UAVM with RPOC, GTD, and UAP Feature UAVM RPOC GTD UAP Medical history History of multiple uterine cavity procedures, trophoblastic disease, or spontaneous formation Recent history of abortions, curettage or pregnancy Recent pregnancy (especially molar pregnancy) Iatrogenic injuries (cesarean sections, uterine surgeries, or interventional procedures) Bleeding time Sudden heavy vaginal bleeding Postoperative persistent or intermittent bleeding Continuous, moderate in amount, with the possibility of sudden severe bleeding Vaginal bleeding unrelated to the menstrual cycle Abdominal pain Painless or sudden severe pain (when ruptured) Mild intermittent pain (caused by contractions) Mild intermittent pain Painless or sudden severe pain (when ruptured) Ultrasonic manifestations High-speed blood flow signals, convoluted and chaotic vascular mass, high-speed and low-resistance blood flow pattern Irregular abnormal echo masses within the uterine cavity, few or focal abundant blood flow signals “Snowstorm” or “honeycomb” appearance Unidirectional arterial waveform blood flow spectra β-hCG - +, slow declining trend or may rise again +++ -/+ Other symptoms Shock, no expulsion of pregnancy tissue Occasionally see the expulsion of pregnancy tissue Distant transfer Extravasation and localized aneurysmal dilation of the uterine artery branches on DSA Differential diagnosis of UAVM with RPOC, GTD, and UAP The UAVM treatment approach typically necessitates a thorough evaluation of various factors, including hemodynamic stability, age, reproductive requirements, comorbid conditions, and underlying diseases of the patients. Next, we will reorganize the treatment methods for patients based on our new classification system, providing precise treatment plans based on accurate classification and diagnosis (Table  2 ). Among the patients diagnosed with UAVM through ultrasound, most have shown complete regression of the lesions during conservative treatment. Therefore, patients who are asymptomatic or have only mild symptoms with minimal vaginal bleeding, when they are hemodynamically stable and have reproductive needs, conservative treatment can be adopted, including follow-up observation or medication. For medication treatment, oral contraceptives or progestin therapy can be used to effectively manage bleeding. During the conservative treatment period, patients should undergo regular ultrasound examinations to determine the regression of the UAVM lesions, and attention should be paid to the vaginal bleeding situation [ 2 , 45 ]. Uterine artery embolization is suitable for most patients, especially as a primary treatment for acute massive hemorrhage, hemodynamic instability, and young patients who wish to preserve their fertility. Studies have shown that the live birth rate after uterine artery embolization is not significantly different from that of the general population, making uterine artery embolization a relatively safe treatment option [ 46 , 47 ]. However, there is a risk of embolization failure, which may require repeat embolization. There is also the potential for extensive necrosis and infarction of the uterus, amenorrhea, and radiation exposure, necessitating different treatment measures based on the specific circumstances [ 8 , 48 ]. Additionally, primary UAVM may involve lesions that extend into the pelvis or beyond, making uterine artery embolization potentially ineffective as a treatment option [ 8 ]. When interventional treatment fails, the lesions are extensive, severe bleeding threatens life, or there is no desire for fertility, surgical treatment for UAVM can be considered. For young women with fertility needs, if conditions permit, UAVM lesion resection or uterine artery ligation can be performed. If the above conditions are not met, a subtotal or total hysterectomy may be performed. Additionally, if symptoms persist after uterine artery embolization and the lesions are superficial, hysteroscopic surgery can be chosen, but caution should be exercised with procedures like electrosurgery to prevent uncontrollable bleeding, and thorough preoperative preparation and intraoperative hemostatic measures should be ensured [ 12 , 49 , 50 ]. The primary principle for the treatment of non-pregnancy-related UAVM is to control major bleeding, followed by the treatment of the underlying disease. In patients diagnosed with uterine smooth muscle tumors in conjunction with UAVM, arterial embolization may be indicated in instances of acute massive hemorrhage. If the patient does not wish to maintain reproductive capabilities, a hysterectomy is a viable surgical option. Conversely, if the patient expresses a desire to preserve fertility, a myomectomy may be considered [ 51 , 52 ]. Uterine endometrial cancer or cervical cancer with vascular invasion can lead to the formation of UAVM, requiring a comprehensive approach to manage both the tumor and the risk of bleeding. In cases of acute bleeding, timely arterial embolization should be performed to achieve hemostasis. The final treatment depends on the stage of the tumor: early-stage disease often requires radical tumor resection to treat the primary disease, and preoperative embolization can reduce intraoperative bleeding. During surgery, the tumor and affected blood vessels should be thoroughly removed to avoid residual fistulas. For early-stage patients who wish to preserve their fertility, hormonal treatment (progesterone therapy for endometrial cancer) or cervical conization (treatment for cervical cancer) may be considered. However, due to the risk of rupture of pregnancy-related UAVM, close monitoring of the UAVM lesions is necessary. In cases of metastasis, palliative embolization combined with systemic tumor treatment is the main therapeutic strategy. The treatment strategy for UAVM after miscarriage should be individualized based on the presence of retained products of conception. For UAVM with retained products, the treatment principle is to prioritize the removal of residual tissue and control bleeding from the fistula. This can be achieved through the use of mifepristone combined with misoprostol or methotrexate, or by performing a curettage or hysteroscopic surgery to remove the residual tissue. If there is significant bleeding during the procedure, uterine artery embolization should be performed in conjunction, and emergency surgery may be necessary if required. For UAVM without retained products, asymptomatic patients with a small fistula can be conservatively observed, while symptomatic patients or those with a larger fistula should primarily undergo uterine artery embolization to block blood flow to the fistula. Medications such as oxytocin and tranexamic acid can be used for hemostasis. In cases of intervention failure or severe conditions, uterine suturing or resection may be performed [ 53 , 54 ]. Specifically, for patients with ectopic pregnancy combined with UAVM, the main treatment method is arterial embolization to occlude the blood supply artery of the gestational sac. After this, ectopic focus resection or chemotherapy to kill the embryo can be performed, achieving the dual purpose of eliminating ectopic pregnancy tissue and occluding the abnormal vascular network [ 55 – 57 ]. Treatment options should comprehensively consider the patient’s fertility needs, hemodynamic stability, and the risk of complications to achieve the goals of hemostasis and closure of the fistula. The treatment of postpartum UAVM caused by residual pregnancy material is similar to that of UAVM after miscarriage, with a particular focus on the arteriovenous fistula formed at the site of the cesarean section uterine incision diverticulum. The treatment of uterine incision diverticulum combined with UAVM after cesarean section should be based on the anatomy of the diverticulum, blood flow at the fistula site, and fertility needs to develop an individualized plan. For asymptomatic patients or those with mild bleeding, conservative treatment with medications such as tranexamic acid and oxytocin can be administered, along with oral contraceptives to regulate the endometrium. For moderate to severe bleeding, uterine artery embolization is the first choice, which blocks abnormal blood flow by embolizing the supplying arteries, with a success rate of 85% to 90%. Hysteroscopic electrocautery of the fistula vessel and adjustment of the diverticulum edge are suitable for localized fistulas, while open or laparoscopic diverticulum repair and vessel ligation are used for cases where interventional or hysteroscopic treatment has failed, or in cases of severe scar defects. In patients with no fertility needs and uncontrolled bleeding, hysterectomy may be performed. Treatment options should comprehensively consider fertility needs, scar repair status, and the risk of complications. For those planning to conceive again, uterine artery embolization or hysteroscopic treatment should be prioritized. Postoperative assessment of the myometrial thickness and monitoring of placental implantation risk are necessary. For complex cases, a multidisciplinary collaboration to develop a stepwise strategy is recommended [ 58 – 61 ]. The treatment of trophoblastic disease combined with UAVM requires multidisciplinary collaboration, with individualized plans based on the malignancy of the disease, the degree of lesion invasion, and the patient’s fertility needs. For patients with acute massive bleeding, priority is given to anti-shock treatment, and intervention is performed after controlling inflammation in cases of infection. Low-risk patients are treated with single-agent chemotherapy using methotrexate or dactinomycin to suppress trophoblastic activity, while high-risk patients are treated with combination chemotherapy regimens such as EMA-CO. Uterine artery embolization is suitable for emergency hemostasis or to prevent bleeding during chemotherapy, achieving a hemostasis success rate of over 85% by selectively embolizing the fistula’s blood flow. Hysteroscopic surgery is appropriate for localized lesions with small fistulas, while open or laparoscopic resection of lesions or hysterectomy is performed for patients with ineffective conservative treatment, no fertility needs, or extensive malignant infiltration. Throughout the treatment process, it is essential to balance hemostasis, tumor control, and the protection of reproductive function. For malignant cases, consolidation treatment is required after chemotherapy, and those with fertility needs should avoid pregnancy for one-year post-surgery and assess the thickness of the uterine myometrium. Strategies should be adjusted based on imaging and dynamic monitoring of blood β-hCG levels to reduce the risk of recurrence and metastasis [ 40 , 62 – 64 ]. Table 2 Treatment options for UAVM Treatment Indications Advantages Disadvantages Key Consideration Observation Asymptomatic/minor bleeding, small and stable lesions Non-invasive, fertility preserved Risk of progression to severe hemorrhage Regular surveillance Medical Therapy Adjuvant for bleeding Non-invasive, symptom relief Limited efficacy Regular surveillance Uterine artery embolisation Acute hemorrhage, fertility preservation desired Fast recovery, minimally invasive Recurrence, post-embolization syndrome Post-procedure monitoring for recurrence Lesion resection Focal lesions, failed UAE or recurrence, uterine preservation desired Complete lesion removal, fertility sparing Invasive Intraoperative imaging guidance Hysterectomy Diffuse lesions, no fertility desire, refractory bleeding Curative, no recurrence Loss of fertility, surgical complications Surgical operation with caution Hysteroscopy Persist after uterine artery embolization and superficial lesions Direct visualization High-risk for catastrophic bleeding Interventional team on standby Treatment options for UAVM

Uterine arteriovenous malformation (UAVM) is an abnormal direct connection between the uterine artery and vein, leading to the twisting and dilation of atypical blood vessels, which can result in a pressure difference between the arterial and venous systems that may cause acute massive bleeding, threatening women’s health and life [ 1 ]. UAVM accounts for approximately 1% to 2% of all cases of genital and intraperitoneal hemorrhages [ 2 ]. In 1926, Dubreuil and Loubat made the initial record of a uterine arteriovenous fistula, which they referred to as “aneurysme cirsoide de l’uterus” [ 3 ]. According to the source of its initiation, UAVM is currently classified into two categories in clinical practice: congenital and secondary [ 4 ]. Due to the extreme rarity of congenital UAVM, its true incidence is still unclear. Secondary UAVM is mainly caused by various iatrogenic traumas, such as infection, abortion, dilation and curettage, cesarean section, trophoblastic diseases, and exposure to diethylstilbestrol [ 5 ]. Literature reports that the incidence of UAVM after induced abortion is 5.2%, the incidence postpartum is 0.22%, and the incidence in outpatient settings is 0.24%, with an average onset age of 30 years [ 6 ]. In recent years, due to the increase in abortion and cesarean section rates, the incidence of UAVM may also gradually rise [ 2 ]. The clinical manifestations of UAVM are diverse, ranging from asymptomatic cases to potentially fatal massive hemorrhage. Acute bleeding can lead to symptoms such as anemia, hypovolemic shock, and congestive heart failure, often requiring large amounts of blood transfusion to save the patient’s life. Given its sudden and critical clinical characteristics, it is essential to quickly and accurately diagnose UAVM and provide timely intervention measures [ 7 ]. Currently, imaging methods such as ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), and angiography can all diagnose UAVM. Each option possesses distinct advantages and disadvantages. Among them, ultrasound is the simplest and most efficient diagnostic method, and angiography is the gold standard for diagnosis [ 8 ]. However, the exact incidence of UAVM diagnosed by ultrasound is still unclear, there is currently no literature exploring this issue. This study aims to establish, for the first time, the true incidence of UAVM in clinical settings as determined through ultrasound diagnostics. Meanwhile, in clinical practice, it is difficult to differentiate patients diagnosed with UAVM by ultrasound from those with retained tissue after abortion or childbirth, gestational trophoblastic disease, and uterine artery pseudoaneurysm. Previous literature often describes these diseases individually; our study will delve into distinguishing and differentiating these similar clinical presentations to better guide clinical differential diagnosis. Previous literature has only roughly classified UAVMs into primary and secondary types, which is not conducive to precise clinical diagnosis and guidance. Therefore, we will further subdivide UAVMs and provide corresponding treatment plans for each category to better guide clinical practice. Therefore, this article reports on a search for clinical cases of UAVM diagnosed by ultrasound at Tongji Hospital of Huazhong University of Science and Technology over the past 15 years, finding that 19 cases were clinically diagnosed. This study aims to provide an in-depth analysis of the clinical classification of UAVM in conjunction with the above clinical cases. It will also seek to give a systematic description of UAVM tailored to various clinical scenarios. This may help us better understand UAVM and provide important reference for clinical practice.