Endovascular Management of a Giant Renal Artery Aneurysm With Arteriovenous Malformation: A Case Report

Renal arteriovenous malformations (rAVMs) are rare vascular abnormalities where there is a direct connection between the renal artery and vein, which circumvents the normal capillary network. The endovascular approach is preferred due to its minimally invasive nature, shorter hospital stay, and lower risk of complications in comparison to open surgery. Open surgery is therefore indicated in emergent situations such as arteriovenous malformation (AVM) rupture, hemodynamic instability, failure of endovascular therapy, or complex vascular anatomy that makes the endovascular approach unfeasible. However, endovascular management can be complicated by anatomic variants, such as renal artery duplication, and concomitant pathology, like fibromuscular dysplasia (FMD). This case demonstrates how a multimodal embolization approach, including coil deployment and flow-directed liquid embolic under balloon occlusion, can achieve technical success and favorable clinical outcomes with minimal risk. A 53-year-old woman with a history of hypertension presented with chronic abdominal pain. Physical examination revealed a right-sided abdominal bruit. A renal ultrasound revealed a 3.8 cm saccular aneurysm with internal low-resistance arterial flow near the renal hilum, which was initially interpreted as a renal artery aneurysm. In order to better delineate anatomy, an abdominal computed tomography angiogram was obtained, which showed a direct connection between a single segmental branch and a large, saccular venous aneurysm, compatible with a Yakes type I rAVM. It also showed several additional abnormalities, including a duplicated right renal artery with a "beads on a string" morphology suggestive of concomitant FMD and a small arterial aneurysm. Because of the size of her venous aneurysm and concern for hemorrhage, she was referred for surgical evaluation. Surgical excision/ligation was deemed too invasive, so the patient was then referred to interventional radiology for endovascular treatment with coil embolization of the venous sac and balloon-assisted Onyx embolization of the nidus. The technique involved staged coil embolization of the venous sac followed by Onyx injection into the nidus under balloon occlusion to achieve flow control and precise embolic delivery. This case highlights recent technical advancements, such as dual lumen balloon microcatheters to control inflow and the liquid embolic Onyx, which facilitated successful endovascular management of a rAVM with associated venous aneurysm. While coils remain the most commonly used embolic material for rAVMs, they primarily occlude the feeding vessels without directly addressing the nidus, which can result in incomplete treatment and potential recurrence. That is why, by pairing them with Onyx, we can treat the feeding vessels and effectively penetrate and fill the nidus, offering a more comprehensive and durable occlusion.