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Pancreatic Pseudoaneurysm

Author: Faisal Aziz; Chief Editor: John Geibel, MD, DSc, MA more...from eMedicine

Background

Permanent communication caused by an erosion of the pancreatic or peripancreatic artery into a pseudocyst gives rise to a pancreatic pseudoaneurysm, which is a rare but life-threatening complication.
Pancreatitis with secondary pseudocyst formation is the most common cause of pancreatic pseudoaneurysms, although they are known to occur in the absence of a pseudocyst. Pancreatitis with secondary pseudocyst formation is a recently recognized complication after resection of biliopancreatic cancer and after transplantation.
Pancreatic or peripancreatic bleeding is one of the most life-threatening complications of pancreatitis. Hemorrhage can occur in the pseudocyst per se, via the ampulla of Vater, or by fistulation into nearby hollow organs. The standard of care in dealing with pseudoaneurysms has been surgical intervention; however, with the recent advances in the field of interventional radiology, the paradigm has largely shifted toward endovascular treatment of pancreatic pseudoaneurysms.^[1]

Problem

A pseudoaneurysm differs from a true aneurysm in that its wall does not contain the components of an artery but consists of fibrous tissue, which usually continues to enlarge, creating a pulsating hematoma.
Pancreatic pseudoaneurysm is a malformation in the vessels of the pancreas and/or peripancreatic bed. These rather uncommon pseudoaneurysms are frequently accompanied by life-threatening complications, mainly rupture and bleeding. Better outcome requires accurate, timely, and appropriate diagnosis and medical and/or surgical intervention.

Epidemiology

Frequency

Pseudoaneurysm formation in patients with chronic pancreatitis who undergo angiography may have an incidence as great as 10%.
Some of the factors associated with pancreatic pseudoaneurysms include the following:

Severity and duration of pancreatitis
Presence of pseudocyst and associated splenic vein thrombosis and endoscopically visualized varices

Etiology

Moderate-to-severe pancreatitis with or without pseudocyst/abscess is the major etiologic factor for pseudoaneurysm formation.
Visceral pseudoaneurysms may form as a sequela to blunt and penetrating abdominal trauma.^[2]
Pseudoaneurysm formation may occur after biliopancreatic resection for cancer.

Patients who have an anastomotic leak and develop intra-abdominal abscess may subsequently be prone to delayed arterial hemorrhage.
Focal sepsis erodes through vessels and causes pseudoaneurysm formation and delayed rupture and bleeding.

Pancreatic transplantation is an occasionally reported third cause of pancreatic pseudoaneurysm formation.
Overall, the splenic artery is the most frequent site of visceral artery pseudoaneurysms, followed by the hepatic artery.^[3]

Pathophysiology

Pseudoaneurysms form when enzyme-rich peripancreatic fluid, often within a pseudocyst, leads to autodigestion and weakening of the walls of adjacent arteries.
These arteries then undergo aneurysmal dilatation, with the aneurysmal bulge most often contained within the pseudocyst. At this point, the dilated region is correctly termed an aneurysm rather than a pseudoaneurysm because the blood is still contained within the complete, although thinned, arterial wall.
Rupture of the aneurysm into the pseudocyst converts the pseudocyst into a pseudoaneurysm (defined as extravascular hematoma communicating with the intravascular space).
In some instances, a pseudocyst can erode into a nearby artery, causing the conversion of pseudocyst into a pseudoaneurysm.
Despite these distinctions, all of these forms are generally classified as pseudoaneurysm because the end result is the formation of a total or partial vascular cystic structure.

The literature confirms that differentiating a pseudoaneurysm from a bleeding pseudocyst is difficult.^[4]
This form of pseudoaneurysm should be distinguished from primary peripancreatic vessel aneurysm, which tends to occur more often in women. The rare rupture of primary aneurysm tends to occur in pregnancy and manifests as massive intraperitoneal bleeding with hemodynamic instability.

Presentation

Most patients with visceral artery pseudoaneurysms are asymptomatic. Symptomatic pseudoaneurysms can be nonspecific and require a high index of suspicion to establish the correct diagnosis. Symptoms include fatigue; nausea; vomiting; weight loss; chest, back, flank, and abdominal pain; a palpable, pulsatile mass; hematemesis; and bleeding from an intra-abdominal drain, placed at the time of surgery.^[5]
Because pancreatitis is the most common underlying cause of pancreatic pseudoaneurysm, most patients are males with alcoholism (80-90%) who have histories of episodic chronic pancreatitis and secondary pseudocyst formation.
The diagnosis of visceral artery pseudoaneurysm should be considered in any patient with a pseudocyst and a significant abdominal bruit.
The pseudoaneurysm tends to enlarge when subjected to sufficient intracystic pressure and ultimately ruptures into the gastrointestinal tract, biliopancreatic ducts, pseudocyst, peritoneal cavity, or retroperitoneum.
Although highly variable, clinical symptoms are very suggestive and include the following:

Anemia of unexplained cause
Recurrent or intermittent hematemesis or hematochezia in patients who have pancreatitis, particularly when due to chronic alcohol abuse or trauma
Rapid enlargement of a pseudocyst or a pulsatile abdominal mass, especially in the presence of abdominal bruit and hyperamylasemia
The syndrome known as hemosuccus pancreaticus, characterized by bleeding from the ampulla of Vater, colicky pain, and jaundice

Patients with pancreatitis may have the following symptoms:

Persistent or abrupt increase in abdominal pain
Decreasing hematocrit values and/or hemodynamic instability and/or gastrointestinal bleeding with no obvious intraluminal cause

The clinical picture may vary widely.
The most common form of bleeding is probably rupture into a pseudocyst with eventual bleeding through the pancreatic duct and, subsequently, the ampulla of Vater if the pseudocyst is connected with the pancreatic duct.

This "wirsungorrhagia" (ie, hemosuccus pancreaticus) manifests as intermittent pain caused by sudden filling with blood and resultant distention of the pancreatic duct and may sometimes be accompanied by elevated levels of pancreatic enzymes.
Once the intraductal pressure reaches a certain level, the bleeding stops and a clot forms. The clot subsequently lyses at a later stage, leading the cycle to repeat itself.

On the other hand, if the pseudocyst does not communicate with the duct of Wirsung, then blood accumulates in the pseudocyst, leading to sudden enlargement and causing abdominal pain and a drop in the hematocrit value.

Relevant Anatomy

The splenic artery, which is most commonly involved in pancreatic pseudoaneurysm, is one of the 3 branches of the celiac artery; the other two are the common hepatic artery and the left gastric artery. Because the splenic artery runs along the pancreatic bed before reaching the spleen, it is the artery most commonly affected by the erosive effect of pancreatitis.
After giving off the proper hepatic artery, the common hepatic artery becomes the gastroduodenal artery, which gives rise to the superior pancreaticoduodenal artery, which anastomoses with the inferior branch coming off the superior mesenteric artery to supply the head of the pancreas and the duodenum.
In addition to encasing the distal end of the common bile duct, the pancreas, a retroperitoneal organ, is near the C-loop of the duodenum laterally and the lesser sac anteriorly. This explains why the pseudoaneurysm can erode and bleed into the bowel, biliary tree, retroperitoneum, or peritoneal cavity.

Contraindications

Endoscopic drainage is contraindicated. Drainage is an inadequate treatment of a pseudocyst that has bled.

BÀI SOẠN VỀ SIÊU ÂM CHẨN ĐOÁN

Thứ Năm, 3 tháng 10, 2013

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