**4. Chronic pancreatitis (CP)**

**3. Acute pancreatitis (AP)**

144 Challenges in Pancreatic Pathology

optimal evaluation.

thrombosis may be seen.

lis.

AP is a potentially severe disease with unpredictable outcome which can develop multiple complications with fast dynamics. The early differential diagnosis between a mild, edematous form and a severe, necrotic‐hemorrhagic one is very important in order to be able to adapt the treatment and to be able to try to prevent the occurrence of complications. Currently, contrast‐ enhanced CT (CE‐CT) is considered to be the reference method for the assessment and for staging AP [9]. But CE‐CT is an irradiating, relatively expensive technique, and animal studies have suggested a potential risk of aggravation of AP following CE‐CT due to pancreatic micro‐ circulation impairment by the contrast agent [10–12], even if in human studies this effect has not been proven [13, 14]. Another impediment for CE‐CT is the need for repetitive examina‐ tions according to the patient's evolution. This is why a safer, cheaper diagnostic tool would

Abdominal US is in most cases the first imaging method used to evaluate patients with AP since it is widely available, safe, rapid, and inexpensive. It is also nonirradiant, and thus, it can be repeated as often as needed to follow‐up the patient's evolution. On the other hand, US has limitations due to the poor acoustic window in AP secondary to large amount of bowel gas and also due to the patient's abdominal pain which makes him unable to cooperate for an

Standard abdominal US allows only assessment of the imaging aspect of the pancreas in AP, without being able to assess vascularity. But it also reveals suggestive signs for a severe AP such as hyperechoic bursa omentalis (**Figure 3**) and presence of intra‐peritoneal collections (peripancreatic, pericolic or in the Douglas space), while using Doppler US, a splenic vein

**Figure 3.** Acute pancreatitis, standard US: hypoechoic, inhomogeneous enlarged pancreas, hyperechoic bursa omenta‐

be useful for the diagnosis, staging, and follow‐up of patients with AP.

During the evolution of CP, inflammatory masses can appear, a characteristic feature of pseudotumoral CP. Differential diagnosis between this entity and pancreatic cancer is often difficult not only due to the similar imaging aspect but also due to similar clinical symptoms [18]. The US aspect of pseudotumoral CP is most often of a hypoechoic, imprecisely delineated mass in the head of the pancreas. CEUS is useful to differentiate among the two entities since pancreatic adenocarcinomas are hypoenhancing following contrast (due to massive desmo‐ plastic reaction as well as poor vascularity), while the inflammatory pseudotumor in CP will be enhancing in the arterial phase [19–21].

D'Onofrio et al. evaluated the performance of CEUS to diagnose pseudotumoral CP in a study that included 173 pancreatic masses. CEUS had 88.6% Se, 97.8% Sp, 91.2% PPV, and 96% accuracy for the diagnosis of pseudotumoral CP, while in 94% of cases the inflammatory mass showed moderate enhancement following contrast, similar to the adjacent pancreatic paren‐ chyma [20].

A more recent study showed that the blood flow ratio between the superior mesenteric artery and the pancreatic parenchyma evaluated by CEUS correlates with the grade of chronic pancreatitis and concluded that this safe and convenient method may be useful for the early diagnose of CP [22].

A special entity is *autoimmune pancreatitis*. It is characterized by a high level of gamma‐ globulins or IgG, presence of auto‐antibodies, mild or absent clinical symptoms. Imaging techniques reveal an enlarged, "sausage‐like" pancreas, with diffuse, irregular thinning of the Wirsung duct (WD), with possible stenosis of the retro‐pancreatic main biliary duct and rarely cysts or calcifications in the pancreatic parenchyma [20]. Autoimmune pancreatitis is some‐ times associated with other autoimmune diseases such as diabetes mellitus, inflammatory bowel disease, primary biliary cirrhosis, primary sclerosing cholangitis, or lupus.

On standard US, in autoimmune pancreatitis the imaging changes are most often diffuse. The pancreas is enlarged, hypoechoic and with a compressed Wirsung duct. Following contrast bolus, the pancreas is moderate or hyperenhancing in the early arterial phase, but also with inhomogeneous enhancement due to lymphocytic infiltration and fibrosis [20].
