Permanent communication caused by erosion of the pancreatic or peripancreatic artery into a pseudocyst gives rise to a rare but life-threatening complication known as a pancreatic pseudoaneurysm. Pancreatitis with secondary pseudocyst formation is the most common cause of pancreatic pseudoaneurysms, although they have been known to occur in the absence of a pseudocyst.
A pseudoaneurysm differs from a true aneurysm in that its wall does not contain the components of an artery but instead consists of fibrous tissue, which usually continues to enlarge, creating a pulsating hematoma.
Overall, the splenic artery is the most frequent site of visceral artery pseudoaneurysms, followed by the hepatic artery.  Pseudoaneurysm formation may have an incidence as high as 10% in patients with chronic pancreatitis who undergo angiography.
Pancreatic pseudoaneurysms, though rather uncommon, are frequently accompanied by life-threatening complications, mainly rupture and bleeding. Hemorrhage can occur in the pseudocyst itself, via the ampulla of Vater, or by fistulation into nearby hollow organs.
Better outcome requires accurate, timely, and appropriate diagnosis and medical and/or surgical intervention. The standard of care in dealing with pseudoaneurysms has been surgical intervention. However, owing to advances in the field of interventional radiology, the paradigm has largely shifted toward endovascular treatment of pancreatic pseudoaneurysms. 
The literature confirms that differentiating a pseudoaneurysm from a bleeding pseudocyst is difficult. 
Pancreatic pseudoaneurysm should be distinguished from primary peripancreatic vessel aneurysm, which tends to occur more often in women. The rare rupture of a primary aneurysm tends to occur in pregnancy and manifests as massive intraperitoneal bleeding with hemodynamic instability.
The splenic artery, which is most commonly involved in pancreatic pseudoaneurysm, is one of the three branches of the celiac artery, the other two being 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. (See the image below.)
After giving off the proper hepatic artery, the common hepatic artery becomes the gastroduodenal artery, which gives rise to the superior pancreaticoduodenal artery. The pancreaticoduodenal artery 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 a pseudoaneurysm can erode and bleed into the bowel, biliary tree, retroperitoneum, or peritoneal cavity.
Rupture and Hemorrhage
The most life-threatening complications of pseudoaneurysms are rupture and subsequent hemorrhage. A pancreatic pseudoaneurysm tends to enlarge when subjected to sufficient intracystic pressure, ultimately rupturing into the gastrointestinal tract, biliopancreatic ducts, pseudocyst, peritoneal cavity, or retroperitoneum.
Hemorrhage carries a mortality of 13-40% and is almost always fatal if left unattended. Bleeding is usually brisk, but it varies from short, repeated, and self-limiting episodes to massive hemorrhage requiring emergent laparotomy.
The frequency of arterial lesion hemorrhage during pancreatitis ranges from 5% to 10%. However, when pseudocysts are present, the hemorrhage rate rises to 15-20% of cases.
The most common site of rupture is intracystic; the incidence of spontaneous hemorrhage arising from a pancreatic pseudocyst reportedly ranges from 1.4% to 8.4%. This bleeding can be localized in the cyst, causing sudden enlargement and abdominal pain, or bleeding can occur through the cyst into the pancreatic duct if a communication between these structures exists. (In this case, the patient will have gastrointestinal bleeding.)
Other sites of rupture include the biliopancreatic duct, peritoneal cavity, and retroperitoneum; sometimes, direct erosion into the duodenum and other parts of the gastrointestinal tract will occur.
Other, infrequent complications of pancreatic pseudoaneurysms include arteriovenous fistula formation and extrahepatic biliary tract obstruction.
Moderate-to-severe pancreatitis with or without pseudocyst/abscess is the major etiologic factor for pseudoaneurysm formation. However, a visceral pseudoaneurysm may develop as a sequela to blunt and penetrating abdominal trauma. 
Pseudoaneurysm formation may also 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 another, occasionally reported cause of pancreatic pseudoaneurysm formation. 
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, albeit 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 the pseudocyst into a pseudoaneurysm.
Despite these distinctions, all of these forms are generally classified as pseudoaneurysms, because the end result is the formation of a total or partial vascular cystic structure.
History and Physical Examination
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 the following  :
Pain in the chest, back, flank, and abdomen
Bleeding from an intra-abdominal drain, placed at the time of surgery
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
Because pancreatitis is the most common underlying cause of pancreatic pseudoaneurysm, most patients are males with alcoholism (80-90%) who have a history 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 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.
Pang et al proposed a management-based classification system for peripancreatic pseudoaneurysms that is based on the following three elements  :
Type of artery from which the pseudoaneurysm arises
Presence or absence of communication with the gastrointestinal tract
Presence or absence of a high concentration of pancreatic juice at the bleeding site
In this system, originating artery type is specified as follows:
Type I - Pseudoaneurysm arises from a minor artery but must be at least 5 mm away from its junction of origin from a type II or III artery
Type II - Aneurysm arises from a major artery that may be sacrificed without physiologic consequences (eg, splenic and gastroduodenal arteries)
Type III - Aneurysm arises from a major artery that cannot be sacrificed without significant consequences for the patient (e.g., the superior mesenteric artery or the hepatic artery proper)
Gastrointestinal tract communication is specified as follows:
Type A - No communication with the gastrointestinal tract
Type B - Communication with the gastrointestinal tract
Exposure to pancreatic juice is specified as follows:
Type 1 - No exposure to pancreatic juice
Type 2 - Exposure to pancreatic juice
Angiography is the criterion standard to determine diagnosis and treatment (see the image below). Digital subtraction provides high-resolution imaging of small arteries and allows percutaneous vascular intervention in the same setting. 
If the patient is hemodynamically stable, performing a preoperative angiogram helps to confirm the diagnosis. Angiography defines the character—unique or otherwise—of the lesion and allows therapeutic planning. Angiography greatly facilitates identification of the location and serves as a topographic guide for the pseudoaneurysm, which aids in operative proximal and distal control of the bleeding vessel.
Preoperative angiography may constitute an opportunity to gain temporary control over the bleeding vessel by performing transcatheter embolization, thus providing a time window for the surgeon to operate on a high-risk patient under optimum clinical conditions. 
Computed tomography (CT) angiography (CTA) has a sensitivity of up to 94.7% and a specificity of 90%. (See the image below.) 
Magnetic resonance angiography (MRA) is highly sensitive and specific. Limitations of MRA include its long study time, limited availability, high cost, and restrictions for patients with certain implantable devices and hardware.
Although occasional reports have alluded to the spontaneous thrombosis of some pancreatic pseudoaneurysms, the current consensus holds that all of these malformations should be treated to prevent the complication of bleeding. This is based on the fact that the natural history of visceral artery pseudoaneurysms is largely unknown. Treatment options include the following:
Endovascular coil embolization
Covered stent placement 
Percutaneous ultrasonographically guided thrombin injection
Open surgical repair
A study  of eight patients reviewed the nonsurgical management of pancreatic pseudocysts associated with arterial pseudoaneurysm. Two patients were treated with percutaneous thrombin injection, and six underwent angioembolization. All of these patients underwent subsequent endoscopic transpapillary drainage with complete resolution of pseudocysts in 6 weeks.
An 11-year retrospective study  identified 16 patients in whom a pseudocyst had eroded into a major blood vessel, with subsequent development of hemorrhage or false aneurysm. Ten patients underwent operative therapy, whereas six stable patients underwent angioembolization. The surgical morbidity was 62%, and the angioembolization morbidity was 50%. The study concluded by recommending angioembolization as initial therapy for hemodynamically stable patients.
Transarterial catheter angioembolization with or without endoscopic stent placement
Endovascular coil embolization has been used extensively in the treatment of visceral artery pseudoaneurysms. [1, 3, 14] Angioembolization is considered much less invasive than surgery. The procedure can be completed quickly and is comfortable for the patient. It also allows the performance of surgery under optimal conditions. (See the image below.)
The interventional approach has a reported success rate of 67-100% over the past few years. [3, 10] Most authorities agree that embolization is appropriate when bleeding is diffuse or emanating from the pancreatic head, following unsuccessful surgery, or during postoperative bleeding.
Failure results from an inability to selectively catheterize the bleeding vessel or from the misplacement or poor placement of embolization material. In addition to rebleeding, complications of this procedure include rupture of the pseudoaneurysm during embolization, arterial perforation by the catheter, intestinal necrosis, and aortic thrombosis.
Despite few reports of resolution of pseudocysts with embolization alone, little long-term follow-up care is available for patients treated angiographically, particularly for patients who have underlying pathology that predisposes them to recurrent complications.
Percutaneous ultrasonographically guided thrombin injection has been used to successfully treat visceral artery pseudoaneurysms. [15, 16, 17] Suitable anatomic features, such as a narrow neck, are necessary to allow for a successful intervention without intravascular "leakage" of thrombin with distal embolization. Some advocate balloon inflation across the neck of the pseudoaneurysm to minimize this complication. 
Percutaneous injection of thrombin into the head of the pancreas for treating pancreatic pseudoaneurysm has been described, but the significance, safety, and efficacy of this procedure remain to be seen. 
Absolute indications for emergency exploratory laparotomy include hemodynamic instability and failure of endovascular techniques to control active hemorrhage.
Basic surgical techniques for controlling hemorrhage from a pancreatic pseudoaneurysm include arterial ligation on both sides of the bleeding sites, pancreatic resection, and multiple intracystic/extracystic ligatures.
Some pseudocyst drainage procedures have been frequently performed concomitantly with the primary hemostatic surgery. Endoscopic drainage is contraindicated. Drainage is an inadequate treatment of a pseudocyst that has bled.
Manage the hemodynamically unstable patient in an emergency fashion. Approach the patient in much the same manner as you would a trauma patient. The patient's hemodynamic status and comorbid medical issues dictate the necessity for invasive hemodynamic monitoring.
The first priority is securing the airway, followed by obtaining good peripheral access. As with trauma patients, at least two wide-bore intravenous lines are preferable. Initial fluids of choice are isotonic crystalloids.
Send a type and cross of the blood to the blood bank while the need for O-negative and type-specific blood transfusion is being assessed. Patients should undergo emergent celiotomy to control the bleeding pseudoaneurysm as soon as possible.
If the diagnosis of a ruptured pseudoaneurysm has been seriously entertained and the patient is hemodynamically stable, some studies may be performed before the patient enters the operating theater.
Performing a preoperative angiogram has several benefits (see the image below). For one, identifying the bleeding vessel during surgery is difficult because of the friability, necrosis, and severe inflammation caused by pancreatitis. Also, because preoperative angiography identifies the bleeding vessel, it may dictate the optimal therapy. (Performing arterial ligation or pancreaticoduodenectomy on bleeding vessels involving the pancreatic head has been demonstrated to carry a high mortality.)
Furthermore, angiography may constitute an opportunity to gain temporary preoperative control over the bleeding vessel by performing transcatheter embolization, thus providing a time window for the surgeon to operate on a high-risk patient under optimum clinical conditions.
A generous midline incision is made from subxiphoid to pubis. Upon entering the peritoneal cavity, all four quadrants should be packed with lap packs. Lap packs are gradually removed from the least suspicious area for bleeding to the most suspicious area for bleeding.
Once adequate exposure is achieved, direct attention toward the most common source of bleeding; mainly, the peripancreatic vasculature.
Multiple effective measures to gain rapid control of the actively bleeding pseudoaneurysm have been described. These include manual tamponade, gauze packing, digital compression of the bleeding pseudoaneurysm or pseudocyst, and even supraceliac infradiaphragmatic cross-clamping of the aorta for brisk bleeding.
Institute these measures, especially in the actively bleeding, hemodynamically unstable patient, while aggressive volume resuscitation is being undertaken by the anesthesia team.
Gaining access to bleeding site
After establishing these initial measures, a more delicate and precise dissection can be performed in order to obtain definitive control of the bleeding vessels. Exposure of the bleeding site can sometimes be challenging, because the surrounding inflammation from pancreatitis obscures the visual field.
Several adjunctive techniques have been listed to gain operative access to the bleeding pseudoaneurysm; these include gastrotomy, duodenotomy, and major gastrectomy.
Bleeding control techniques
Once the bleeding vessel is identified, the surgeon may employ one of several surgical methods to control the bleeding. The basic surgical principle is to obtain proximal and distal control of the blood vessel before trying to ligate or resect it.
Intracystic ligation without proximal/distal control or resection is not recommended, because the friable tissues of the posterior pseudocyst wall do not hold sutures and the feeding vessel that lies deep within the substance of the pancreas is still patent.
For treatment of the pseudocyst, several surgical options are available, ranging from resection to external or internal drainage methods.
Carefully monitor the patient after surgery. The occurrence of postresectional hemorrhage is well documented in the literature, with a reported incidence of 5-19% and a mortality of 6-58%. This may be the result of ongoing pancreatitis and continuous damaging of the arteries, iatrogenic trauma to the vessels, and/or inadequate control of the bleeding vessels.
Whereas some surgeons have advocated surgical ligation of the bleeding vessel in the nonseptic patient and pancreatic resection in those with abscess or established fistula, interventional radiologists have strongly recommended angioembolization for postoperative hemorrhage.
Patients treated with supportive measures have a mortality in excess of 90%. The mortality following surgical treatment of arterial hemorrhage of pancreatic origin ranges from 28% to 56%. The mortality depends primarily on the anatomic location of the pseudoaneurysm, not on the surgical method used. 
Surgical intervention for treatment of pseudoaneurysm in the head of the pancreas has a 43% mortality, whereas surgery for a pseudoaneurysm in the body or tail of the pancreas has a mortality of 16%. (Pseudoaneurysms in the head of the pancreas necessitate a Whipple procedure, which likely contributes to the higher mortality.) The mortality for patients who suffer postoperative hemorrhage is 50-60%.
Embolotherapy has a high initial success rate (90-100%), though some reports indicate a recurrence rate of 37% and an overall mortality of 16%. Embolotherapy is the preferred initial therapy for bleeding originating from the head of the pancreas.
A major controversy is whether transarterial catheter angioembolization should be the definitive approach or if it should always be followed by surgical intervention, especially if bleeding is located in the tail or body of the pancreas and/or is associated with a pseudocyst. Some authors have found no rebleeding after seemingly successful angioembolization of the pseudoaneurysm. Other authors have found statistically significant rebleeding rates, which necessitated surgical resection after embolization.
Another major controversy is whether to perform arterial ligation or pancreatic resection on a bleeding pseudoaneurysm. Some authors have strongly advocated resection, because it is technically easier to perform than ligation in an inflammatory milieu.  Other authors have reported better outcome after performing proximal and distal arterial ligation and intracystic suture ligation.
A third controversy involves the management of postoperative bleeding, despite recent adoption of the operative option by more healthcare providers.