Primary mucinous cystic neoplasm (MCN) is found almost exclusively (>90 %) in women (mean age 40–50 years), located typically in the body and tail of the pancreas [1, 13]. Unlike the SCN, the MCN has potential malignancy [13]. A MCN predominantly manifests as a unilocular or mildly septated cystic lesion [2, 14] (Figs. 5.3, 5.4, 5.5, and 5.6). Although the cyst is typically mucin filled, the cystic contents have fluid density on CT, high signal intensity on T2W images, and low signal intensity on T1W images [12]. The internal architecture of the cyst may include papillary projections into the cyst on usually one or more septae [13]. The cyst wall, the septations, and the mural nodules enhance after contrast administration and become more clearly visible [12]. Peripheral calcifications of the cyst are uncommon (<20 %) [13]. In general, mural nodules and septa are better depicted with MRI, whereas calcification is better depicted with CT. Contrary to intraductal papillary mucinous neoplasms (see below), MCNs do not communicate with the pancreatic ductal system. Occasionally, concomitant obstructive pancreatitis may be seen in the distal gland [12, 13]. Peripheral “eggshell” calcification, an irregular wall, thickened septa, papillary projections, an eccentric solid mass, and local invasion of adjacent structures suggest strongly a malignant lesion [13, 14].

Intraductal papillary mucinous neoplasm (IPMN) is a spectrum of related neoplasms characterized by mucinous transformation of the pancreatic ductal epithelium producing an excessive amount of mucin and resulting in dilation of the pancreatic ductal system. IPMN may involve the main pancreatic duct (main-duct type), a side branch off the main duct (branchduct type), or a combination of both (mixed-duct type) (Figs. 5.7, 5.8, and 5.9). The imaging features of IPMN depend on the location of the tumor(s). The main-duct type appears as diffuse or segmental duct dilation [12, 15, 16]. Internal nodular components are best depicted on contrast-enhanced images, but they are usually not seen, because the tumor is small and flat [12, 15]. The branch-duct type appears as a unilocular cystic lesion or as clustered pleomorphic cysts and often involves the uncinate process [15, 16] (Figs. 5.7 and 5.8). The communication between the cystic lesion and the main pancreatic duct is a key feature in the diagnosis [2, 7] (Fig. 5.7c). IPMN may be multifocal and has malignant potential (more likely the main-duct type) [16]. Involvement of the main duct (especially when it is markedly dilated), presence of solid components, diffuse or multifocal involvement, large size of the lesion, associated biliary obstruction, and extension beyond the gland are signs of malignancy [12, 17].

Solid pseudopapillary tumors, cystic neuroendocrine neoplasms of the pancreas, acinar cell neoplasms, and primary pancreatic adenocarcinomas may on occasion appear as cystic masses. Solid pseudopapillary neoplasm is a rare pancreatic neoplasm that occurs predominantly in young women (<40 years old) and has low malignant potential [2, 18]. CT usually depicts a well-circumscribed lesion with a heterogeneous appearance (mixed solid and cystic components) owing to hemorrhagic degeneration [18, 19]. Calcifications may be present [18]. On MRI images, solid pseudopapillary neoplasms have heterogeneous signal intensity reflecting the complex nature of the mass (Fig. 5.10); moreover, areas of increased signal intensity on T1-weighted images can help identify blood products [18, 19] (Fig. 5.10b). Although pancreatic neuroendocrine neoplasms are typically solid and hypervascular masses, marked cystic changes may be seen [2, 20]. Imaging reveals typically a thick-walled cystic lesion, and the presence of hypervascular tissue that enhances avidly in the arterial phase suggests the diagnosis [2, 12]. Primary pancreatic adenocarcinomas and acinar cell neoplasms may rarely develop areas of cystic degeneration and necrosis (usually when they are large in size) and resemble other cystic pancreatic neoplasms [1, 6].