**4. Paraduodenal pancreatitis**

Paraduodenal pancreatitis (PDP) is a form of chronic pancreatitis which involves the duodenal wall near the papilla minor and the nearby pancreatic parenchyma or the space

### *Imaging of Pancreatitis DOI: http://dx.doi.org/10.5772/intechopen.106764*

interposed between them, named pancreatic groove [22]. The disease is strictly related to ethanol abuse, affecting mainly 40–50 years old males [23]. Clinical manifestations resemble those of chronic pancreatitis, with recurrent pain in the upper abdomen exacerbated by eating, nausea and weight loss. Rarer is obstructive jaundice, which is more typical of pancreatic cancer, but tumor markers are negative [24]. Different pathological entities are grouped in PDP diagnosis. Groove pancreatitis is the most common; it is characterized by the formation of scar tissue between the duodenal wall and the neighbor pancreatic parenchyma, caused by an anatomical or functional obstruction of minor papilla outflow [25, 26]. Even the presence of ectopic pancreatic tissue can cause paraduodenal pancreatitis, leading to paraduodenal wall cysts formation. These usually involve the descending part of the duodenum and are mostly located in the submucosa [24].

In paraduodenal pancreatitis, CT usually shows a hypoattenuating solid mass in the pancreatic groove with duodenal wall thickening often visible, sometimes associated with cystic lesions. The presence of duodenal wall thickening and cystic changes may help to differentiate PDP from pancreatic cancer, where these findings are rare. Duodenal stenosis with gastric outlet obstruction is an uncommon finding but it is more frequent than in pancreatic cancer [27, 28].

MRCP is the gold standard for the study of paraduodenal pancreatic lesions. In solid forms, MRI shows a hypointense lesion near the duodenal wall at T1-weighted imaging, with a variable signal in T2-weighting (**Figure 10**) [29].

The enhancement of these lesions both at CT and MRI is related to their high fibrous content, with a slow progressive enhancement, not visible in the arterial phase, where the lesion appears hypovascular, but with a later homogenous enhancement, thus allowing to distinguish PDP from PDAC, which usually tends to remain hypovascular even in the later acquisition phases (**Figure 10**) [24].

MRI is also fundamental for studying cystic forms of PDP, first of all highlighting their fluid content, and then studying their relationship with the duodenal wall,

### **Figure 10.**

*M, 45 yo. Alcohol abuse. Recurrent epigastric pain. Paraduodenal pancreatitis. A small cystic lesion in the groove area is appreciated (a), embedded in a hypointense soft tissue mass (b), hypovascular (c, d), with delayed enhancement (e). At MRCP the cystic lesion is well appreciated (arrow, f).*

with the ductal system and with the healthy pancreatic parenchyma or with fibrotic changes (**Figure 10**). MRCP sequences are essential for evaluating the relationship between the duodenum and intrapancreatic choledochus; in particular, while in pancreatic cancer the choledochus is more frequently irregularly stenotic and infiltrated by the neoplasm, with marked upstream dilation of the biliary tree, in PDP it is more frequently smoothly narrowed and displaced, and therefore the MRCP shows an increase in the physiological space between the choledochus and the lumen of the duodenum (**Figure 10**) [30]. In the same way, the gastroduodenal artery can be displaced in PDP instead of being infiltrated in pancreatic cancer (**Figure 10**).

Although imaging is important for the study of PDP, both for solid and cystic forms, it is not always possible to make a differential diagnosis, in particular with PDAC, cholangiocarcinoma or cancer of the duodenal wall which has a worse prognosis and require different treatments [29, 31]. Laboratory tests and tumor markers can help to sort out the diagnosis, but it is often necessary to combine EUS investigations with tissue sampling to rule out the presence of cancer.
