Etiology
Pseudoaneurysms are an uncommon complication of chronic pancreatitis. Sixty-eight percent of visceral pseudoaneurysms are secondary to pancreatitis and pseudocyst formation and 10 to 17% of all patients with chronic pancreatitis develop pseudoaneurysms [
3,
4]. Visceral pseudoaneurysm formation is believed to be the result of leakage of proteolytic enzymes in the setting of pancreatitis with destruction of the vessel wall. They may also result from erosion of nearby pseudocysts into adjacent vessels [
3,
4]. Blunt or penetrating abdominal trauma and iatrogenic trauma, for example, after hepatobiliary or vascular surgery or after pancreatic head biopsy, may also cause pseudoaneurysms [
4,
5]. The proportion of pseudoaneurysms versus true aneurysms differs by arterial location [
6]. In case of gastroduodenal and superior mesenteric arteries Fankhauser
et al. reported more VAPAs than VAAs (89% versus 11% and 67% versus 33% respectively) [
7].
In both presented cases, it is likely that pseudoaneurysm formation was related to the chronic pancreatitis. In the first case the pseudoaneurysm was filled partially via a large defect in the top of the superior mesenteric artery and partially via the CHA through the pancreaticoduodenal arcade, the gastroduodenal artery, and gastric artery. It was complicated with fistulization to the portal vein. In the second case, there was a dissection of the GDA with formation of a pseudoaneurysm. In addition to the pancreatitis, the high-grade ostial stenosis of the coeliac trunk probably played an underlying role in the etiology of this pseudoaneurysm.
Presentation
Both patients presented with abdominal pain and anemia. The second patient also experienced rectal bleeding and melena. Visceral artery pseudoaneurysms are usually asymptomatic and identified as incidental, unexpected findings on imaging of the abdomen, particularly on CT or CT angiography [
8]. But unlike other visceral artery (pseudo-) aneurysms (VA(P)As), 70 to 90% of SMA aneurysms and almost all SMA pseudoaneurysms are symptomatic [
9].
Abdominal pain is the most common symptom of unruptured VA(P)As [
10‐
12]. In case of rupture, a gastrointestinal hemorrhage is the most common clinical presentation [
10‐
12]. Depending on the location it can cause hematemesis, melena, hematochezia, hemobilia, retroperitoneal hemorrhage, and hemorrhagic shock [
3,
13]. The pseudoaneurysm can also rupture in the duct of Wirsung, causing a so-called hemosuccus pancreaticus [
3,
4]. Pathogenesis of the bleeding is most probably related to intermittent erosion and breakdown of the aneurysm wall through the duodenal wall, common bile duct, pseudocyst or duct of Wirsung, secondary to pressure necrosis caused by the expanding pseudoaneurysm [
13]. A pulsatile mass or bruit is the second most common symptom of a VA(P)A of the superior and inferior mesenteric artery in contrast to other visceral arteries [
6,
11]. Other clinical symptoms of VAPAs are intraperitoneal or retroperitoneal bleeding, jaundice, compressive symptoms (nausea, vomiting) or gastric outlet obstruction [
5,
6,
10‐
12].
Treatment
According to the guidelines, treatment of a true visceral aneurysm is indicated when its diameter is >2 cm or three times greater than the respective normal artery [
5,
17‐
19]. Treatment is also indicated in case of rapid expansion of >0.5 cm/year, symptoms, woman who are pregnant or of childbearing age, and patients undergoing an orthotopic liver transplantation [
20‐
22]. On the contrary, a pseudoaneurysm must be treated immediately because the rate of rupture is much higher in pseudoaneurysms than in true aneurysms (76.3% versus 3.1%) [
5]. Depending upon the diameter and the location, pseudoaneurysm rupture is associated with a mortality rate ranging from 25 to 70% [
20].
Treatment options include surgical (arterial bypass, exclusion of the aneurysmal sac, vessel ligature), endovascular (embolization, stent placement) or percutaneous (thrombin injection) interventions. For vessels that supply an end organ without multiple sources of blood flow, patency of the feeding vessel should be preserved (either through stent placement or surgical revascularization). However, collaterals between the visceral arteries almost always exist, therefore most VAPAs can be treated by ligation or embolization.
If the different factors permit it, the less invasive endovascular interventions should be exhausted before proceeding with surgery. In case of failure, vascular surgery will still be a feasible alternative. Since endovascular treatment is less invasive and can be performed under local anesthesia, it offers a good therapeutic strategy for patients who are inoperable due to severe comorbidities.
The transcatheter selective embolization of pseudoaneurysms has become the most commonly used approach. Different materials can be used like coils, gelatin foam, polyvinyl alcohol (PVA) particles, trisacryl gelatin microspheres (TAGM), amplatzer vascular plugs (AVP), cyanoacrylate glue, ethylene vinyl alcohol copolymer (EVOH-Onyx®) or calcium alginate gel (ALGEL) [
23]. One can choose between proximal embolization or, whenever possible, the “sandwich” technique to occlude the artery proximally and distally to the pseudoaneurysm to prevent anterograde and retrograde filling [
3]. This technique was used in our second case.
If patency of the feeding vessel needs to be maintained, covered stents can be a good alternative treatment without losing the benefits of an endovascular intervention. However certain factors preclude their use. The length of the vessel on both sides of the pseudoaneurysm must be sufficiently long in order to ensure an adequate seal [
7,
24]. A length of at least 10 mm proximal and distal of the stent is recommended [
24]. Severe tortuosity or sharp angulation can make stent placement unfeasible. Hemp
et al. recommends treating tortuous arteries with a self-expanding covered stent while straight arteries can be treated with balloon-expandable stents [
24]. Using bare stents and coiling through the mesh of the stent with a microcatheter and microcoils is another alternative to preserve patency. The risk of stent thrombosis or restenosis resulting in potential end-organ ischemia must be taken into consideration. Given the complexity, location on the SMA, and size of the pseudoaneurysm, we chose to place a balloon-expandable covered stent in our first case.
No consensus has been reached regarding the duration of antiplatelet therapy after stenting. In our first case, we decided on clopidrogrel for 6 weeks and acetylsalicylic acid lifelong.
Fankhauser
et al. reported endovascular treatment of 185 aneurysms (64% VAPAs) with a success rate of 98%. Reintervention was required in 3% within 30 days. The 30-day aneurysm-related mortality was 3.4% and the periprocedural mortality rate was 6.2% [
7]. Sethi
et al. reported a success rate of 77% after coil embolization in 14 patients with a visceral pseudoaneurysm. Persistent perfusion in three patients (20%) was effectively managed by a secondary coil embolization [
25]. Both Won
et al. and Balderi
et al. reported a 100% success rate in 13 patients with a VAPA. Aneurysm-related mortality (
n = 0 and
n = 1) and morbidity (
n = 2 and
n = 1) was low in both studies [
26,
27].
Reported complications of endovascular therapy include access-related complications such as femoral artery pseudoaneurysms, thrombosis or embolism; access-site hematoma, pain, cellulitis or infection, and technical failure to catheterize the artery. In patients with poor renal function, the possibility of contrast agent-induced nephropathy must be considered. Other potential complications are distal thromboembolism, nontarget embolism, visceral ischemia, coil or stent migration, stent occlusion, post-embolization syndrome or intraprocedural pseudoaneurysm dissection or rupture. Possible late-term complications are reperfusion or recurrent bleeding of a pseudoaneurysm [
3,
4,
7,
10,
28].
Thrombin injection guided either by US or CT is another minimally invasive technique. It was first described in 2000 by Kang for the use of post-catheterization femoral pseudoaneurysms, but can also be used for visceral pseudoaneurysms [
29]. A pseudoaneurysm with a small neck and relatively slower flow is best suited for this procedure due to a lower propensity for distal embolization as well as lower probability of recanalization in the early post-injection period [
16,
30,
31]. Thrombin injection can also be performed endoluminally by placing a microcatheter into the aneurysm sac. A disadvantage of this technique is that thrombin is not radiopaque and distal embolization may not be recognized during the procedure [
24,
31]. Other possible complications are allergic reactions and infections [
31].
Open surgery is recommended in case of a hemodynamically unstable patient, failed endovascular repair or unsuited anatomy. Sachdev
et al. and Dohan
et al. however, suggested that hemodynamically unstable patients can be treated successfully with endovascular interventions [
32,
33]. Surgical treatment includes arterial bypass, exclusion of the aneurysmal sac or vessel ligature. In some cases, end-organ resection (that is, splenectomy, bowel resection) is needed [
34].
Finally, visceral pseudoaneurysms can also be treated laparoscopically. This technique has been described in true aneurysms of the splenic artery by laparoscopic artery ligation or aneurysmectomy [
35,
36].
Thus, treatment options are very varied. They can be used as monotherapy or in combination. Cumbie
et al. treated a superior mesenteric artery pseudoaneurysm using common hepatic artery to SMA bypass, exclusion of the pseudoaneurysm with ligation of the SMA proximal to the bypass, plug occlusion of the proximal SMA, and coil embolization of the pseudoaneurysm [
6]. In our first case, the SMA pseudoaneurysm was treated with stent placement and selective embolization of the afferent branches.