**3. Acute pancreatitis (AP)**

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

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 optimal evaluation.

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 thrombosis may be seen.

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

CEUS allows visualization of pancreatic vascularity and thus is able to reveal necrotic areas which will not enhance following the contrast bolus (**Figure 4**). But the same limitations as for standard US apply for CEUS, which is useless if the acoustic window for the pancreas is poor.

**Figure 4.** Severe acute pancreatitis, CEUS, arterial phase: almost the entire pancreas is unenhancing, revealing exten‐ sive necrosis.

Rickes et al. evaluated the accuracy of CEUS for the diagnosis of AP severity, considering CE‐ CT as the reference method, and they found out that CEUS had 82% sensitivity (Se), 89% specificity (Sp), 95% positive predictive value (PPV), and 67% negative predictive value (NPV) for diagnosing severe AP, with a much lesser cost than CE‐CT [15]. Similar results were obtained by other authors, CEUS Se and Sp ranging from 86 and 97%, respectively [16], to 90.3 and 98.8%, respectively (97.4% accuracy) [17].

Thus, all these studies confirmed the value of CEUS for detecting pancreatic necrosis and for predicting the severity of AP. It showed similar results as compared with CE‐CT with fewer side effects since CEUS is nonirradiant and since the US contrast agents have no influence on microvascularity and can also be used in patients with renal failure.
