An Unsuspected Case of Uterine Arteriovenous Malformation with Nidus Aneurysm Following Vaginal Delivery: Diagnostic Challenges and Management

Uterine arteriovenous malformations (AVMs) are rare but potentially life-threatening cause of postpartum hemorrhage (PPH). Accurate differentiation from other PPH causes, such as retained products of conception (RPOC) and gestational trophoblastic disease (GTD), is imperative, as inadvertent improper management such as uterine curettage may cause catastrophic bleeding with high mortality rates. We present the case of 35-year-old woman who presented with excessive vaginal bleeding two months post-normal vaginal delivery. Initial ultrasound findings raised suspicion of uterine AVM with a differential diagnosis of type 3 RPOC. Further imaging with CT angiography and digital subtraction angiography (DSA) confirmed an underlying uterine AVM with a nidus aneurysm. The patient subsequently was treated with successful embolization and was discharged in stable condition.

Uterine artery AVM is rare but potentially life-threatening condition. AVMs can be defined as a vascular structural anomaly involving abnormal communication between arteries and veins that bypass the capillary system [1]. Recognition of the condition as the cause of hemorrhage is important, as it can be treated safely and effectively with transcatheter arterial embolization but may be worsened by uterine curettage, precipitating massive uterine bleeding [2]. This case report presents a unique instance of a uterine AVM with a nidus aneurysm in a young woman following vaginal delivery. The case highlights the importance of distinguishing uterine AVM from RPOC and GTD, which present with similar symptoms and overlapping imaging findings, but require distinct treatment strategies.

A 35-year-old woman, gravida 1, para 1, arrived at the emergency department with heavy vaginal bleeding and lower abdominal pain two months after giving birth. She had a normal vaginal delivery and a history of one previous abortion, which was treated medically. There was no history of dilation and curettage (D&C), cesarean section, or any other uterine surgeries. Patient was further referred for diagnostic imaging. 

Imaging Findings 

Transabdominal and transvaginal ultrasound examination revealed cystic areas in the upper endometrial cavity (fig 1) showing turbulent swirling intraluminal flow on color doppler study, with few tortuous feeding vessels in anterior myometrium (fig 2 a and b).  Doppler measurements indicated high peak systolic velocity (PSV) of 46.5 cm/s and low resistance (resistance index, RI: 0.71) (fig 2c and 2d). The findings raised a differential diagnosis of uterine AVM versus type 3 RPOC.

Figure 1: Transvaginal Gray scale USG image showing uterus in a retroverted position. Anechoic cystic areas are visible in the upper endometrial cavity (indicated by solid black arrow), with tortuous, serpiginous structures noted in the anterior myometrium (indicated by solid white arrow).

Figure 2(a - d): 2a and 2b) Gray scale and colour doppler ultrasound image of the uterus showing anechoic cystic spaces in the upper endometrial cavity, exhibiting internal swirling colour flow suggestive of turbulent blood flow.

2c) Colour doppler imaging highlights a tortuous feeder vessel in the anterior myometrium (indicated by hollow black arrow) a characteristic feature of AVM.

2d) Pulse wave Doppler shows high peak systolic velocity (PSV) with low resistance flow, reinforcing the diagnosis of AVM.

The patient’s negative beta-hCG result ruled out gestational trophoblastic disease and type 3 RPOC. To further clarify the diagnosis and plan the management, CT angiography was performed, which demonstrated an arterially enhancing lesion within the endometrial cavity with an enhancement pattern following the blood pool dynamics. (Fig 3a-3e). Tortuous enhancing feeder vessels were seen in the anterior myometrium along with early filling of the draining vein, confirming the preliminary diagnosis of uterine AVM with a nidus aneurysm. (Fig 4a-4c).

Figure 3 (a-e): CT angiography images in multiple planes demonstrating vascular characteristics of uterine AVM with nidus aneurysm.
3a) Non-contrast axial CT image showing no hyperdensity or calcification in the uterus or endometrial cavity.
3b) Axial arterial phase image illustrating a bulbous, arterially enhancing lesion within the endometrial cavity that follows the blood pool (indicated by solid black arrow).
3c) Tortuous feeding vessels seen in the anterior myometrium (indicated by hollow black arrow).
3d and 3e) Sagittal and coronal reformatted images showing multiple tortuous vessels in the anterior myometrium (indicated by  hollow black arrow).and a prominent arterially enhancing lesion in the endometrial cavity, indicating nidus aneurysm (indicated by solid black arrow).

Figure 4 (a-c): Coronal Maximum Intensity Projection (MIP) images demonstrating aneurysmal characteristics in uterine AVM
4a and 4b) MIP images show an enhancing aneurysmal lesion within the endometrial cavity (indicated by solid black arrow) with associated feeder vessels and an early draining vein (indicated by solid white arrow), consistent with high-flow AVM.
4c) 3D reformatting further delineates the aneurysmal focus and adjacent tortuous vessels, aiding in surgical planning.

Digital subtraction angiography (DSA) was performed under local anesthesia in the Interventional Radiology suite. Right common femoral artery puncture was performed and the right uterine artery was identified angiographically which was selectively catheterised using a microcatheter.  Selective angiography of the right uterine artery demonstrated tortuous myometrial vessels feeding an aneurysmal nidus in the endometrial cavity, with early venous drainage. (Fig 5a and 5b). Embolization of the right uterine artery was achieved using 500-700 µ polyvinyl alcohol (PVA) particles and gelatin sponge, effectively obliterating the aneurysmal nidus. Post-procedure angiography confirmed successful occlusion of the AVM with no remaining vascular blush. (Fig 6a and 6b). The left uterine artery was also evaluated and showed no evidence of feeder vessels to the AVM. Patient had regular follow ups in the clinic with no sign of recurrence. 

Uterine arteriovenous malformation (AVM) is a rare condition characterised by direct communication between uterine arteries and veins, bypassing the capillary system [1]. The true incidence is not yet known. AVMs may be congenital or acquired [3,4]. The congenital form is relatively uncommon and occurs due to a defect in the development of blood vessels during embryonic growth or an early interruption in the formation of the capillary network, resulting in multiple abnormal connections between arteries and veins [5,6]. These congenital AVMs often penetrate the surrounding tissue and can cause an elaborate collateral vascular network. Furthermore, these congenital lesions can grow as pregnancy progresses [3,7]. However, most of the acquired AVMs occur after uterine tissue damage. Spontaneous miscarriage, dilation and curettage (D&C), Cesarean section, carcinoma of the cervix or endometrium, uterine infection, trophoblastic disease, myomata, endometriosis or exposure to diethylstilbestrol are among the reported causes of AVM [8]. Historically, the diagnosis of AVM was made following laparotomy. Subsequently angiography became the ‘gold standard’ technique [8]. On angiography true AVMs are recognized by early venous contrast filling of vascular plexus in the endometrium or myometrium. These appear as heterogeneous lesion with arterial phase enhancement following the blood pool. Arterial feeders may be visible, typically arising from one or both uterine arteries, with disruption of the endo-myometrial junction, serpentine vessels within the myometrium, and increased vascularity in the parametrial region [4,8]. CTA helps in better determining the extent of the lesion in the pelvis and subsequent vascular supply. 

More recently, transvaginal ultrasonography with color doppler imaging has been proposed [4,8]. While ultrasound (USG) is the preferred initial diagnostic tool, it has its limitations. Angiography is now typically reserved for cases where surgical intervention or therapeutic embolization is necessary [8].  The ultrasonographic characteristics are nonspecific and include the presence of hypoechoic tubular structures within the myometrium [9,10]. Color Doppler ultrasound offers a more detailed image, displaying a color mosaic with thickened vessels and reversed blood flow. Pulsed Doppler reveals low-resistance vessels with high pulsatility indices and elevated peak systolic velocity (PSV). In normal myometrium, vessels have a peak systolic velocity ranging from 9–40 cm/s and a resistance index between 0.6 and 0.8. In cases of uterine arteriovenous malformation, both systolic and diastolic velocities are four to six times higher [11,12].

Depending on the PSV of the lesions, they can be classified as follows [13,14]: 

Mild: PSV less than 40 cm/s, where expectant management is recommended.

Moderate: PSV of 40–60 cm/s, where medical treatment is recommended.

Severe: PSV grater than  60–70 cm/s, where arterial embolization or surgical treatment is recommended.

Computed tomography scan with contrast, nuclear magnetic resonance imaging, hysterosalpingography and hysteroscopy have also been described for diagnosing AVM. 

The differential diagnosis of AVM includes several conditions including RPOC and gestational trophoblastic disease.

Gestational trophoblastic disease and RPOC can have similar presentations with menorrhagia[15]. On imaging, both conditions appear as heterogeneous areas, with the abnormality typically located in the endometrial cavity, while AVMs are centered in the myometrium [16]. GTD may exhibit the loss of the junctional zone with invasion into the surrounding myometrium or parametrium. Beta hCG levels are useful in distinguishing between pregnancy-related and non-pregnancy-related postpartum hemorrhage (PPH). GTD typically presents with elevated beta hCG levels, whereas retained products of conception (RPOC) show a slower decline in beta hCG levels [10]. If beta hCG levels are negative, the possibility of the uterine AVM should be considered [15]. Color doppler US demonstrates a hyper vascular mass having flow from the endometrium extending into myometrium in RPOC. In AVM, blood flow is mainly concentrated in the myometrium [16], characterized by intense flow and color aliasing, with high peak systolic velocity (PSV) and low resistance index (RI) ranging from 0.2 to 0.5. However, differentiation between the two can sometimes be challenging. In such cases, vascular grading of RPOC assists in properly triaging patients to determine the most appropriate management approach [17,18].

On color and duplex Doppler ultrasound, pseudoaneurysms appear as cystic structures filled with blood, displaying swirling arterial flow. In contrast, arteriovenous malformations (AVMs) show a dense network of vessels with low-resistance and high-velocity arterial flow. When both conditions occur together, the ultrasound will reveal characteristics of both: a vascular tangle with intense flow indicative of an AVM, alongside the swirling blood flow seen in a pseudoaneurysm [2].

In our case the abnormality was centred in the endometrial cavity, but the patient had normal beta hCG levels.  More so, there were associated tortuous myometrial feeder vessels with large vascular anechoic areas in the endometrial cavity showing swirling internal flow, thus making the possibility of RPOC and GTD less likely. Additionally, there was aneurysmal dilatation of the nidus with active contrast extravasation. Until recently, the only treatment options for AVM were hysterectomy or (bilateral) ligation of the internal iliac arteries [3,4,8]. However, in recent years, there has been a growing trend toward treating these cases with transcatheter embolization of the uterine arteries [8,13]. This approach allows the menstrual cycle to remain unaffected, and it preserves the possibility of pregnancy and normal vaginal delivery [8]. Thus, appropriate history, imaging findings along with negative serum beta hCG helps in confirming the diagnosis. 

This case highlights the importance of considering uterine AVM as a differential diagnosis in patients with intractable postpartum bleeding and differentiating it from other causes of postpartum hemorrhage. In the case of dilated vascular areas within the lesion, possibility of the nidus aneurysm should be considered. The use of combined imaging techniques, including Doppler ultrasound, CT angiography, and DSA, allowed for accurate diagnosis and minimally invasive treatment. Early identification and treatment of uterine AVM are essential to prevent severe hemorrhage and reduce the risk of future complications. Transcatheter embolization proved to be an effective treatment in this case, preserving fertility and normal uterine function.

Contributors

All authors contributed to the planning, literature review, and creation of this case report. Each author has reviewed and approved the final version of the manuscript.

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