From imaging to impact: A case of renal arteriovenous malformation

Abstract

Renal arteriovenous malformations (rAVMs) are rare vascular anomalies, presenting with gross hematuria and requiring prompt diagnosis and management. We reported a case of a middle-aged male presenting with persistent and unexplained gross hematuria. Initial cystoscopy revealed a significant burden in the urinary bladder without any identifiable bleeding source. Contrast-enhanced computed tomography followed by CT angiography demonstrated a vascular nidus with early venous filling at the lower pole of the left kidney, consistent with rAVMs. The patient had a successful selective transcatheter embolization involving polyvinyl alcohol particles, coils, and a lipiodol-based embolic agent. Postembolization angiography confirmed a substantial reduction in arteriovenous shunting, with the preservation of renal parenchyma. The patient reported transient postprocedure flank pain and hematuria; however, hemoglobin levels and renal function remained stable. This situation highlights the significance of evaluating vascular causes in cases of unexplained hematuria and supports the endovascular embolization as a viable, kidney-preserving treatment option.

Introduction

Renal arteriovenous malformations (rAVMs) are rare vascular abnormalities characterized by the abnormal communication between the renal arterial and venous systems without any intervening capillaries, accounting for <1% of all arteriovenous malformations [1]. rAVMs could be congenital or acquired. Congenital rAVMs represent only 20%-25% of rAVMs, and a prevalence of 0.04% [2]. Gross hematuria is the most common presentation of rAVMs; however, diagnosis is often delayed due to symptoms resembling other prevalent urological disorders. Computed tomography (CT) angiography is essential for diagnosis, whereas catheter angiography is the gold standard and facilitates simultaneous therapy. rAVMs are primarily managed by selective endovascular embolization, which offers a minimally invasive, kidney-sparing approach with a high success rate [3]. We present a case of rAVMs presenting with persistent gross hematuria to emphasize the importance of timely radiological imaging and the effectiveness of endovascular management.

Case presentation

A 45-year-old male presented with the complaint of persistent gross hematuria for 3 weeks, accompanied by passage of blood clots. Patient did not report any history of trauma, anticoagulant use, urolithiasis, any renal intervention, or bleeding disorder. The patient had no significant past medical and surgical history. The patient was hemodynamically stable, and on examination, he had mild discomfort in the left flank.

At an outside facility, cystoscopy revealed the urinary bladder filled with blood clots. Bladder washout was performed, and a double-J (DJ) ureteric stent was placed to ensure urinary drainage. The stent was removed 5 days later, and repeat cystoscopy showed no intravesical pathology. However, hematuria persisted.

Contrast-enhanced computed tomography (CT) of the abdomen and pelvis revealed a large hematoma within the left pelvicalyceal system extending into the upper ureter, with additional clot burden within the bladder. Notably, an arteriovenous malformation at the lower pole of the left kidney was suspected. Catheter angiography with potential embolization was recommended. A preprocedure CT angiogram was performed for detailed vascular mapping, which showed an abnormal vascular nidus and early venous filling at the lower pole of the left kidney (Fig. 1, Fig. 2).

Fig. 1.

(A-D) Preprocedural axial and coronal arterial-phase CT of the left kidney demonstrating a lower-pole vascular malformation with an abnormal vascular nidus and early venous filling.

Fig. 2.

(A and B) Preprocedural axial and coronal venous-phase CT of the left kidney demonstrating the same lower-pole vascular malformation with abnormal vascular nidus and early venous filling.

The patient underwent transcatheter embolization via the right femoral arterial access. Selective angiography of the left renal artery demonstrated multiple AV communications involving the mid and lower poles, supplied by small-caliber feeder vessels. Embolization was meticulously performed using a combination of polyvinyl alcohol (PVA) particles, coils, and a lipiodol-based embolic mixture. Postembolization angiography confirmed the complete occlusion of the AV shunting with preservation of the surrounding renal parenchyma (Fig. 3)

Fig. 3.

(A) Preintervention DSA confirming a high-flow arteriovenous malformation in the lower pole of the left kidney, (B) deployment of metallic coils for embolization, (C) postembolization digital subtraction angiography demonstrating successful coil embolization of the lower-pole left renal arteriovenous malformation, with complete occlusion of the abnormal arteriovenous shunt and no residual opacification.

Postprocedure, the patient experienced vomiting and persistent left flank pain, attributed to postembolization ischemic changes. Hematuria persisted temporarily and required bladder irrigation. The renal function parameters and hemoglobin levels remained stable. The patient was managed further conservatively with analgesia and supportive care.

Discussion

rAVMs are uncommon vascular anomalies resulting from the abnormal connections between the renal arterial and venous systems. The arteries and veins are not connected by the capillary networks in rAVMs; instead, they are interconnected by a distorted and dilated network of vessels, allowing arterial blood to flow directly into the veins [4]. rAVMs can be acquired or congenital. Acquired rAVMs constitute 70% and usually result from trauma, infection, or iatrogenic injuries [5]. Angiomatous, cirsoid, and aneurysmal are the 3 morphological types into which congenital renal arteriovenous malformations can be divided. Angiomatous malformations are smaller than 1 cm and contain a single big feeding vessel that supplies several draining veins, while cirsoid aneurysms are larger and have more than 4 feeding arteries. There is only 1 feeding and drainage artery in aneurysmal rAVMs [6]. Congenital rAVMs are considered specific spontaneous anomalies due to aberrant vascular development that occur in the first trimester of gestation. They constitute around 25% of all rAVMs and generally present in the third to fourth decades of life. Incidence of congenital rAVMs is slightly higher in females compared to males, with a slight predominance of right kidney involvement over the left [7]. This case presented a middle-aged man with rAVMs in the left kidney.

Hematuria, both micro and macro, is the major clinical presentation occurring in 75% of cases. Hematuria usually results from the rupture of dysplastic blood vessels. Blood loss could also result in the formation of clots in the pelvicalyceal system, leading to proximal obstruction [2]. Dames et al. [8] reported a case of rAVMs presented with gross hematuria [8]. Patients could also present with the signs of hypertension, cardiomegaly, or congestive heart failure resulting from an alteration in the dynamics of blood flow in the renal vasculature. Other symptoms include colicky pain, fullness, and continuous bruit in the flank [9]. The patient, in this case, also presented with gross and persistent hematuria.

Renal ultrasound or CT is the initial investigation for patients presenting with hematuria for the diagnosis of renal stones or malignancies. Furthermore, cystoscopy is also used to locate the source of bleeding. In many cases, routine evaluations, such as cystoscopy and imaging for stones or malignancies, frequently do not identify the source of bleeding, causing diagnostic delays [3]. As emphasized in our case, persistent hematuria without identifiable urological pathology should prompt the consideration of a vascular cause. A strong index of suspicion is imperative, especially when clot retention and flank discomfort are present without additional explanatory findings.

Doppler ultrasonography may show turbulent high-velocity flow and lower resistive indices, which suggest arteriovenous shunting. However, contrast-enhanced CT and CT angiography yield more definitive evaluation, including the visualization of a vascular nidus and early venous opacification during the arterial phase [10]. When rAVMs are suspected, it is essential to conduct targeted angiography, which may include renal arteriography, abdominal CT angiography (CTA), or magnetic resonance angiography (MRA). Renal arteriography is considered the gold standard for diagnosing rAVMs. It provides direct evaluation of the location, quantity, blood supply, and hemodynamic alterations of rAVMs, including very small lesions, and facilitates the administration of treatment concurrently with the diagnosis [11]. The imaging differential diagnosis for a rAVM is renal artery pseudoaneurysm and hypervascular renal malignancies, including renal cell carcinoma. On CT angiography, pseudoaneurysms generally present as a localized contrast-filled sac connected to an arterial branch, while rAVMs frequently exhibit a vascular nidus with several feeding arteries and early opacification of draining veins in the arterial phase [11]. Hypervascular renal tumors usually have a significant intratumoral vasculature and early enhancement; they are generally associated with a considerable enhancing soft-tissue mass [10]. The lack of a discrete pseudoaneurysmal sac or enhancing renal mass, together with the presence of a vascular nidus and early venous filling, supported the diagnosis of rAVM in the present case. Similarly, Wang and Zhao described a patient with persistent hematuria in whom CT angiography and subsequent angiography established the diagnosis of rAVM after routine investigations were inconclusive [3].

Endovascular embolization has become the preferred initial treatment for symptomatic rAVMs owing to its minimally invasive characteristics and the advantage of nephron-preserving function. The advancements in interventional radiology have markedly improved treatment outcomes. There are several embolic agents available, including polyvinyl alcohol (PVA) particles, detachable coils, n-butyl cyanoacrylate (NBCA) glue, ethylene vinyl alcohol copolymer, and lipiodol-based mixtures. The selection of the agent depends on the lesion's morphology, flow characteristics, and the operator's skill level [12]. In the present case, a combination of PVA particles, metallic coils, and a lipiodol-based liquid embolic agent was used because of the complex vascular structure and numerous feeding vessels supplying the lesion. PVA particles facilitated distal penetration into the nidus and occlusion of small-caliber feeders, while coils achieved controlled proximal occlusion of larger feeding arteries and decreased flow through the malformation. The addition of a lipiodol-based embolic mixture facilitated the embolization of residual high-flow arteriovenous communications that may not have been adequately managed with particles or coils alone.

Recent advancements in endovascular therapy have highlighted the significance of tailored embolization techniques for rAVMs. Hayashi et al. [13] demonstrated that embolization strategies tailored to the angiographic architecture of the lesion, combined with adjunctive catheter techniques, can achieve a high rate of technical success while preserving renal function [13]. Similarly, other studies have emphasized the significance of mixed embolic techniques utilizing coils, particles, and liquid embolic agents, which allow complete nidus occlusion and reduced recurrence rates in complex lesions. These advancements facilitate the use of individualized embolization strategies based on lesion morphology and flow characteristics [14].

Surgical management of rAVMs is partial or complete nephrectomy. It is invasive and only used in complex vascular anomalies or unstable patients, and is usually associated with high morbidity [15].

The complications associated with embolization are usually minimal and include postembolization syndrome, characterized by flank pain, fever, and nausea, as well as transient hematuria. In rare cases, nontarget embolization or segmental renal infarction may occur [16]. Employing meticulous techniques and selective catheterization helps to reduce parenchymal loss and maintain renal function. Some patients may experience recurrence or residual shunting, which is frequently managed through repeat embolization [5].

Overall, this case accentuates that early detection and immediate endovascular treatment are essential for preventing recurrent hematuria and preserving renal function. With the continuous progress in embolic materials and catheter techniques, selective embolization remains the primary method for the management of rAVMs.

This case is intrusive as it highlights the need to maintain suspicion for vascular anomalies when routine investigations fail to identify the etiology of hematuria, and demonstrates the role of modern endovascular techniques in achieving hemostasis while preserving renal parenchyma and function.

Conclusion

rAVMs, though rare, should be considered for patients presenting with persistent or unexplained gross hematuria after excluding the common etiologies. The early utilization of high-resolution imaging techniques, especially CT angiography and catheter-based angiography, is crucial for accurate diagnosis and treatment planning. Selective transcatheter embolization is the preferred treatment option, providing an effective, minimally invasive, and kidney-sparing method with positive outcomes. This case emphasizes the importance of maintaining a high level of suspicion regarding vascular origins of hematuria and underscores the critical role of interventional radiology in attaining hemostasis while preserving renal function.

Authors’ contributions

N.N and F.B. conceived and designed the case report. N.N, and U.Z were responsible for data collection and acquisition of data. K.S and K.J performed the literature review and wrote the manuscript. N.N and D.M reviewed and critically revised the manuscript. All authors have approved the final manuscript.

Patient consent

A written informed consent was obtained from the patient for the publication of this case report.