Embolization of a Superior Mesenteric Arteriovenous Fistula Identied During Consultation for a Transjugular Intrahepatic Portosystemic Shunt Procedure: A Case Report

Superior mesenteric arteriovenous stula is a rare vascular anomaly often presenting with sequelae of portal hypertension, heart failure, or mesenteric ischemia. This report describes a 75-year-old woman with a history of extensive small bowel resection who presented with variceal bleeding. She was referred to vascular and interventional radiology for a transjugular intrahepatic portosystemic shunt procedure; however, her history was inconsistent with cirrhosis. This prompted further review of her imaging, which identied a superior mesenteric arteriovenous stula as the probable etiology of her varices. This was subsequently embolized with a vascular plug and follow-up upper endoscopy at 1-month demonstrated complete resolution of her varices. This patient was able to avoid a procedure with potentially catastrophic consequences, highlighting the necessity of comprehensive consultations by interventional physicians.

Variceal bleeding is suspected to be the leading cause of mortality associated with SMAVF [9]. If a SMAVF is not initially identi ed, such patients presenting with acute gastrointestinal bleeding might be referred to vascular and interventional radiology (VIR) for a transjugular intrahepatic portosystemic shunt (TIPS) procedure. However, a thorough consultation can preclude the potentially catastrophic consequences of creating a portosystemic shunt in the presence of an arteriovenous stula [5]. The present case report describes a patient presenting with gastrointestinal hemorrhage initially referred to VIR for a TIPS procedure, in whom a SMAVF was discovered and subsequently embolized.

Case Report
A 75-year-old woman presented to an outside hospital with hematochezia and hematemesis. She had a surgical history of two small bowel resections four and six years prior to presentation. Following these resections, she was left with 35 centimeters of small bowel and developed short-gut syndrome reliant on total parenteral nutrition (TPN). She had also developed ascites within the preceding four years, presumed to be secondary to parenteral nutrition-associated liver disease.
The patient was resuscitated with seven units of packed red blood cells and four units of fresh frozen plasma. Upper endoscopy at this time visualized grade 3 esophageal and grade 2 gastric varices. Balloon tamponade was performed with a Linton tube and the patient was transferred to a tertiary care hospital on octreotide and a proton pump inhibitor. VIR was consulted to evaluate the patient for a TIPS procedure; however, several ndings were inconsistent with a working diagnosis of portal hypertension due to cirrhosis.
The patient did not have typical cirrhotic risk factors (no hepatitis, alcohol use disorder, or obesity) and brosis was not seen on a liver biopsy 4 years prior, so long-term use of TPN was the primary factor that would predispose her to cirrhosis. These considerations, along with a lack of cirrhotic features on an abdominal computed tomography angiography (CTA) scan, indicated that cirrhotic liver disease was unlikely. Closer inspection of the abdominal CTA scan revealed abnormal hyperenhancement and dilation of both the superior mesenteric vein (SMV) and portal vein (PV) in the arterial phase. Further review con rmed the presence of a SMAVF distal to the intestinal branches of the superior mesenteric artery (SMA) (Fig. 1).
We proceeded with embolization of the SMAVF to reduce portal pressure. A 6-F 25 cm sheath was placed in the right common femoral artery.  (Fig. 2b). The patient was transferred to the intensive care unit and subsequently discharged in stable condition on postprocedural day 8. Although her ascites persisted, she had no further bleeding during the remainder of her hospitalization.
An upper endoscopy at 1 month post-procedurally demonstrated complete resolution of both esophageal and gastric varices. Liver elastography performed shortly after this visit revealed minimal scarring with a kPa of 9.1 (METAVIR stage F2). At her 2-and 3-month postprocedural follow-up visits, the patient's ascites had resolved, and she denied any recurrence of bleeding. This patient will continue to be followed in the VIR clinic inde nitely at 6-month intervals for surveillance of the SMAVF and liver disease management.

Discussion
The management of SMAVF is either surgical or endovascular. The surgical option provides de nitive stula closure, but is also associated with higher perioperative risk [6]. Endovascular repair is currently the prevailing option, particularly in patients with high surgical risk, prior abdominal surgeries, or emergent presentation [10]. It can be performed through a transarterial, transvenous, or combined approach, and typically involves covered stents or coil embolization for stula closure [6,8]. Vascular plugs also appear to be an effective option, with less risk for migration into the portal venous system [3,7]. Other potential complications of endovascular SMAVF closure are portal vein thrombosis and mesenteric ischemia [8].
Importantly, this report highlights the necessity of comprehensive consultations by interventional physicians, including a thorough history, physical exam, and review of the pertinent labs and imaging. If the patient had received a TIPS procedure as requested, she would not only be at signi cant risk for heart failure, but also recurrent variceal bleeding [5]. Fortunately, suspicion for an etiology of portal hypertension other than cirrhosis allowed this patient to avoid an unnecessary procedure and instead receive the appropriate treatment. Following embolization, she had both clinical improvement and endoscopic evidence of variceal resolution, suggesting that the etiology of her symptoms was secondary to the SMAVF instead of cirrhosis. The mild hepatic scarring demonstrated on elastography was instead suspected to be due to chronic TPN; however, chronic portal hypertension was unlikely due to the rapid resolution of her varices.
In summary, the present case describes a successful SMAVF closure via vascular plug embolization, in a patient presenting with gastrointestinal hemorrhage initially referred to VIR for a TIPS procedure.

Declarations
Ethical Approval and Consent to Participate: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Informed consent was obtained from all individual participants included in the study.
Consent for Publication: Written informed consent was obtained from the patient for publication of this case report and any accompanying images Availability of Data and Material: Not applicable.
Competing Interests: The authors declare that they have no competing interests.
Funding: This study was not supported by any funding.
Author's Contributions: AS performed the literature review. AS, ZB, and KK were all major contributors in writing the manuscript. KL and GV were directly involved in the periprocedural care of this patient and assisted with editing the manuscript. All authors read and approved the nal manuscript. Pre-and post-embolization angiography of superior mesenteric artery (a) Digital subtraction angiography (DSA) prior to embolization demonstrates superior mesenteric arteriovenous stula (long arrow) draining into dilated superior mesenteric vein (short arrow) and portal vein (arrowhead) (b) DSA following embolization with AMPLATZER Vascular Plug II (AGA Medical, Golden Valley, Minnesota) shows complete occlusion of stula with preservation of major superior mesenteric artery intestinal branches (short arrows)