Aneurysm and arteriovenous fistula of the liver and pancreatic vasculature

Pathophysiology and epidemiology

Splanchnic artery aneurysms are aneurysms involving the celiac, superior mesenteric, and inferior mesenteric arteries and their branches (see Chapter 2 ). These aneurysms are frequently referred to as visceral artery aneurysms; however, this term includes renal artery aneurysms as well. A true aneurysm is a dilation of an artery greater than 1.5 times its expected diameter that involves all three layers of the vessel wall. The most common etiology of aneurysm is atherosclerosis, but rare causes include fibromuscular dysplasia, Marfan syndrome, Ehlers-Danlos syndrome, polyarteritis nodosa, systemic lupus erythematosus, scleroderma, and mycotic aneurysms because of septic emboli from infective endocarditis. ^, In the early twentieth century, mycotic aneurysms were much more common and were associated with infective endocarditis, but these are uncommon now in industrialized nations after the development of effective antibiotics.

In contrast, a pseudoaneurysm (or “false aneurysm”) is caused by disruption of the intimal and medial layers of the vessel wall and is contained only by the adventitial layer or perivascular tissue. Iatrogenic injury from endovascular or surgical procedures are common causes of pseudoaneurysm, and rare causes include trauma and vasculitis (see Chapters 113 and 114 ). Pancreatitis is another common cause of splanchnic pseudoaneurysms (see Chapter 55, Chapter 56, Chapter 57, Chapter 58 ); in one series, it was the etiology in 86% of cases.

Based on autopsy and angiographic studies, the incidence of splanchnic artery aneurysms is between 0.1% and 2%. In a recent large series, 77% of aneurysms were true aneurysms, 15% were pseudoaneurysms, and 8% were indeterminate. The majority are located in the splenic artery (SA; 60%) followed by the hepatic artery (HA; 20%), with a small percentage located in the superior mesenteric artery (5%), the celiac artery (4%), and smaller celiac branches (4%). Approximately one-third of patients with a splanchnic artery aneurysm have a concomitant aneurysm elsewhere. Thus patients who are found to have a splanchnic artery aneurysm should be screened for other abdominal, thoracic, intracranial, and peripheral aneurysms. The main risk of splanchnic artery aneurysms is their potential to rupture and cause life-threatening hemorrhage that is challenging to control.

Computed tomography (CT) angiography is the diagnostic test study of choice (see Chapter 21 ). Three-dimensional (3D) vascular reconstructions of CT images are often helpful if intervention is being considered (see Chapters 13 , 14 , and 17 ). This imaging modality can characterize the lesion and provide useful information for operative planning, such as collateral blood supply, and in the case of HA aneurysm (HAA), information on the patency of PV flow. Magnetic resonance (MR) angiography is another option if iodinated contrast is contraindicated because of allergy or other reasons.

Hepatic artery aneurysms and pseudoaneurysms

Unlike SAAs, HAAs have a 2 to 1 male predominance. The median age at presentation is 60 years, although HAA can be seen at any age, including in children. HAAs are most frequently solitary (80%) and extrahepatic ( Fig. 115.1 ). The most common sites for HAA are the common hepatic (63%), right hepatic (28%), and left hepatic (5%) arteries. ^, Although accounting for only one-fifth of visceral aneurysms, HAAs are thought to have the highest risk of rupture. It is difficult to determine the true rupture rate, but reports in the literature range from 18% to 44%. ^,

Pseudoaneurysms account for approximately 50% of all aneurysms affecting the HA. They are usually associated with pancreatitis, trauma, or iatrogenic injuries from percutaneous, endovascular, or surgical procedures (see Chapter 55, Chapter 56, Chapter 57, Chapter 58 , 113 , 114 , and 116 ). They have been reported after numerous types of surgeries, including laparoscopic cholecystectomies, pancreaticoduodenectomies, liver resections, and liver transplants (LTs).

Presentation

The majority of splanchnic artery aneurysms are asymptomatic and are diagnosed incidentally on cross-sectional imaging. However, a substantial proportion are symptomatic, and 15% to 30% present with rupture, which has an associated mortality ranging from 7% to 30%. ^, In a large retrospective study of 233 patients with visceral artery aneurysms, 27% presented with symptoms such as abdominal pain, vomiting, chest pain, or gastrointestinal (GI) bleeding. Fifteen percent presented with a rupture, and all were symptomatic at the time of rupture. Anemia was a common sign at presentation, occurring in 54% of symptomatic patients and in all patients with a rupture. The risk of presenting with a rupture was substantially higher for pseudoaneurysms compared with true aneurysms (76% vs. 3%, respectively). Among patients who presented with a rupture, 78% had a pseudoaneurysm. There was no difference in size between ruptured and nonruptured aneurysms (mean diameter 1.5 cm vs. 1.6 cm, respectively), although the diameter of the aneurysm is often difficult to determine after it has ruptured. This suggests that size is not a reliable marker for rupture.

Rupture can occur into the peritoneum, retroperitoneum, or adjacent structures. Patients may present with severe hypotension with hemoperitoneum or GI bleeding. Rupture of an SAA can be accompanied by sudden onset of sharp abdominal pain in the epigastrium or left upper quadrant and left shoulder pain (Kehr sign). Occasionally, these patients will present with abdominal pain followed by hemodynamic instability 6 to 96 hours later. This “double-rupture” phenomenon is caused by initial bleeding with tamponade in the lesser sac, followed by subsequent delayed intraperitoneal hemorrhage. ^, Alternately, an SAA can erode into the stomach, colon, or pancreatic duct, resulting in GI bleeding, or into the PV, resulting in a splenic APF. Extrahepatic HAAs usually present with free rupture into the peritoneum. Intrahepatic aneurysms can rupture into the biliary system, resulting in hemobilia (see Chapter 116 ). Patients with hemobilia may present with Quincke’s triad of jaundice, right upper quadrant pain, and upper GI hemorrhage, although less than 35% of hemobilia cases present with all three of these signs and symptoms.

Indications for interventions

Emergent intervention is required for all ruptured aneurysms. Management of nonruptured aneurysms is less clear because splanchnic artery aneurysms are relatively rare, and there are no randomized control trials supporting particular management strategies. Nevertheless, in 2020, the Society of Vascular Surgeons published clinical practice guidelines based on expert opinion and a systematic review of 80 observational studies. Treatment for nonruptured pseudoaneurysms, regardless of size or location, is recommended because of the high risk of rupture. Nonruptured true SAAs of any size in women of childbearing age should be treated because of the high risk of rupture and associated high mortality. In addition, true SAAs that are symptomatic or more than 3 cm should be treated. True SAAs that are stable, asymptomatic, and less than 3 cm can be observed with annual CT angiograms or ultrasound (US).

True HAAs should be treated if they are symptomatic, more than 2 cm, or enlarged by more than 0.5 cm per year. In addition, a true HAA should be repaired, regardless of size, if it is associated with a vasculopathy, vasculitis, or positive blood cultures. If a true HAA is less than 2 cm and asymptomatic, it can be observed with annual CT angiograms (see Chapters 14 and 17 ). All aneurysms of the superior mesenteric, gastroduodenal, and pancreaticoduodenal arteries should be treated, regardless of size, because of the high risk of rupture. The European Society for Vascular Surgery has published similar recommendations.