**4. Vascular complications (haemorrhage, pseudoaneurysm and thrombosis)**

Haemorrhage, pseudoaneurysm and thrombosis are the main vascular complications with an incidence ranging from 1% to 23% in patients with acute pancreatitis. Arterial complications are less frequent than venous complications (1.3-10% vs. 22%) [44].

The etiopathology of bleeding in patients with severe pancreatitis can be summarized in four main causes. The first one is due to the local spreading of lipolytic and proteolytic enzymes during a severe pancreatitis or necrosis that leads to the disruption of the tissue and the release of pancreatic fluids thus resulting in the arterial wall damage [45]. The second cause is related to a iatrogenic damage: improper surgical management of acute pancreatitis with an early operation for non-infected necrosis has been reported in Literature as a possible cause of wall arterial weakening thus leading to bleeding due to the activated enzymes [46]. Another iatrogenic source of damage is associated to the radiological positioning of drains that could give a direct trauma to the vessels and a continuous local inflammation that can diminish arterial wall integrity [47]. A third pathogenic mechanism is splenic vein thrombosis due to the necrotizing process, pseudocyst and severe inflammation that could lead to portal hypertension and, as a late sequelae, to esophageal varices formation [45]. The last remarkable pathogenic mechanism is the formation of a pseudoaneurysm that derived from the rupture of a vessels into a long-standing pseudocyst [48]. Symptoms are gastrointestinal bleeding, abdominal pain and splenomegaly and they depend on the localization of pseudoaneurysm. The most common vessels are splenic (35-50%), gastroduodenal (20%), and pancreaticoduodenal (20%) artery. Other vessels involved are tributaries of the gastric, colic and hepatic bloodstream [40, 49].

Ultrasound (US) and Computed Tomography (CT) are the gold standard to diagnose a vascular complication. Specially, CT imaging showed a higher sensibility in the diagnosis of pseudo-aneurysm, and US has an important role in identifying thrombosis or in patients with iodine allergy or renal insufficiency [50]. Enhancedcontrast CT locates necrotic areas, abscess cavity, pseudocysts, and bleeding site.

Angiography is the gold standard technique for the location and the control of the bleeding [45]. Interventional radiology is the first line treatment in both elective and emergency management of vascular complications. Angiography followed by trans-arterial embolization (TAE) is the gold standard management [51]. Different techniques can be used: the one preferred is the sandwich technique with coil located proximally and distally to the pseudoaneurysm to minimize the risk of potential rebleeding [52]. Haemostasis can be implemented with glue, N-butyl cyanoacrylate (NBCA), thrombin, ethiodised oil or gelfoam. Patients with unsuccessful TAE or in which is technically impossible, an emergency haemostatic surgery should be performed. Ligation of bleeding arteries is the technique of choice although related to a high rate of rebleeding. In extreme cases, open packing or salvage emergency pancreatectomy may represent the only chances for survival [45].

Vascular complications are rare but potentially fatal with a difficult management that is why they should be treated in a tertiary centre.
