Pancreatic Pseudoaneurysm

Etiology

Pancreatic pseudoaneurysm develops in the background of pancreatitis or pancreaticobiliary surgery. Rarely it has been reported after pancreatic transplantation. Today another relatively common cause of pancreatic pseudoaneurysm is trauma and motor vehicle accidents. Some patients may develop the pseudoaneurysm after undergoing biliopancreatic surgery for malignancy or pancreas transplantation. The pseudoaneurysm tends to occur following an anastomotic leak, followed by an intraabdominal abscess. Pancreatic pseudoaneurysms tend to occur in the presence of enzyme-rich pancreatic fluid, which causes autodigestion and weakening of the walls of the nearby vessels.[4][5]

Epidemiology

In patients with chronic pancreatitis who undergo angiography, the incidence may be as high as 10%. There is a reported incidence of 5% to 10% occurrence of bleeding due to arterial causes in pancreatitis. When there is an associated pseudocyst formation in pancreatitis the frequency of bleeding due to arterial lesions rises to 15% to 20%.

Pathophysiology

The key vessel involved in pancreatic pseudoaneurysms is the splenic artery since it runs along the course of the pancreas before reaching the spleen. A pseudoaneurysm differs from a true aneurysm because the wall does not contain arterial tissue but consists of fibrous tissue which contains a hematoma that can enlarge or rupture. This damage occurs as a consequence of autodigestion and weakening of the arterial wall by pancreatic juices or a leak from a pancreatic anastomosis. Eventually, if the autodigestion continues, this leads to the formation of a total or partial vascular cystic structure. Because the splenic artery runs its course along with the pancreas towards the spleen, it is affected in pancreatitis. This anatomical position explains why the splenic artery is the commonest site of developing pseudoaneurysm in any visceral artery. The pseudoaneurysms can enlarge and rupture into an associated pseudocyst filling the biliopancreatic ducts. In such a case, bleeding occurs through the ampulla of Vater into the gastrointestinal tract. The pseudoaneurysms can also rupture into the peritoneal cavity or retroperitoneum. When there is bleeding through the ampulla of Vater from the pancreatic duct, it is known as Hemosuccus pancreaticus or pancreatitis.[6][7][8]

History and Physical

Most patients are asymptomatic until the pseudoaneurysm ruptures. Often, patients have nonspecific symptoms before a bleed. A high index of suspicion is necessary especially in patients with backgrounds of pancreatitis, alcoholism, or pancreaticobiliary surgery. When a patient experiences recurrent hematemesis or hematochezia, a pancreatic pseudoaneurysm should be ruled out. When a patient complains of a sudden increase in abdominal pain associated with falling hematocrit or becoming hemodynamically unstable postoperatively following pancreaticobiliary surgery, bleeding pseudoaneurysm should be ruled out.

At times the earliest warning postoperatively is minimal intermittent bleeding from an abdominal drain placed intraoperatively, before a catastrophic bleed. This initial bleed is known as sentinel bleed. A patient who is documented to have a pseudocyst, when there is a rapid enlargement of the cyst with the appearance of a pulsatile mass, strongly suggests a bleeding pseudoaneurysm. Apart from all the signs mentioned above the patient will present with obvious physical evidence of significant blood loss such as pallor, tachycardia, and hypotension.

A bruit is very rare but may be heard when there is a large pseudoaneurysm.

Evaluation

Angiography has been demonstrated to be the most informative investigation for diagnosis as well as treatment. CT angiography has a high rate of sensitivity and specificity but does not facilitate intervention concurrently. Angiography defines the character and location of the lesion as well as provides an opportunity to gain temporary control over the bleeding by transcatheter embolization or possible stenting.[9]

There is a classification of pancreatic pseudoaneurysms based on the following features:

• The type of blood vessel from which the pseudoaneurysm originates
• Absence or presence of communication with the GI tract
• Absence of presence of highly concentrated pancreatic fluid at the bleeding site.

It is important to note that CT angiography and CT angiography are only suitable for stable patients.

Treatment / Management

The current standard of therapy is to control the bleeding by endovascular transarterial catheter embolization or by the placement of a covered stent. Patients in whom arterial embolization is unsuccessful, or there is rebleeding after embolization surgery is the only option. The surgical procedure can be either direct ligation of the bleeding vessel or resection of the pancreas along with the pseudoaneurysm.[10][11][5](B2)

The percutaneous intervention does have a success rate of 70% to 90%. Embolization is often the choice of treatment in very ill unstable patients and in patients in whom the bleeding is diffuse. Embolization may also be an option when bleeding occurs following unsuccessful surgery or a complication of the surgery. Despite the wide use of percutaneous techniques to stop bleeding, the long-term history of the pseudoaneurysm is not well understood. There are limited data on whether these patients develop recurrent complications. Thrombin can also be injected percutaneously but this requires a pseudoaneurysm with a narrow neck.

A bleeding pseudoaneurysm communicating to a pseudocyst situated at the tail of the pancreas can be an indication for surgical intervention. Surgery carries a higher risk when compared to angiographic vascular intervention.

Sometimes surgery is undertaken to debride an abscess combined with hemostatic control. In patients who have had bleeding from pseudocysts, endoscopic drainage is not recommended. If surgery is undertaken, every effort should be made to stabilize the patient first. Once the abdomen is opened, packing of all four quadrants is necessary, and then removing the packs from the least suspicious area to the most suspicious area of bleeding. Often the bleeding is arrested initially by tamponade, digital compression, or cross-clamping of the supra celiac aorta. Gaining access to the site of bleeding may require a duodenotomy, gastronomy, or gastrectomy. Often ligation of the bleeding vessel is not recommended as the tissues are friable. One should ligate away from the area without jeopardizing blood perfusion to the adjacent organs.

Differential Diagnosis

Following are some important differentials that need to be considered while making the diagnosis of pancreatic pseudoaneurysm:

• Pancreatic abscess
• Cystic adenocarcinoma 
• Mesenteric cyst
• Hydatid cyst
• Aortic aneurysm

Prognosis

Patients who only have basic supportive measures have a mortality rate in excess of 90%. Even after surgery for pancreatic pseudoaneurysms, the mortality rates vary from 20-30%. The mortality for pancreatic pseudoaneurysm depends on the location of the pathology and not the type of treatment.

The highest mortality rates occur when the pseudoaneurysm is located in the head of the pancreas whereas surgery for the same pathology on the tail of the pancreas carries a low mortality

Embolization therapy has increased the success rates but there still is a high recurrence rate and overall mortality of about 16%.

Complications

A pancreatic pseudoaneurysm can rupture and the most common location for the rupture is into the cyst, which often presents with sudden onset of abdominal pain or bleeding. Other rare complications of pancreatic pseudoaneurysms include extrahepatic biliary tract obstruction and AV fistula formation. The more common complications are:

• Hemorrhage
• Shock
• Multiorgan failure
• Death