AJR:196,June 2011
Atif Khan, Faisal Khosa Ronald L. Eisenberg
Cystic lesions of the pancreas are a diverse group of lesions, ranging from benign processes to invasive malignant tumors, and often can be morphologically differentiated on CT and MRI on the basis of characteristic features. This is important because a precise diagnosis determines the treatment and surgical approach. Pancreatic cysts can be morphologically classified into four categories:
1. Unilocular cysts (cysts without septation or a solid component)—pancreatic pseudocyst, intraductal papillary mucinous neoplasm (IPMN) and mucinous cystadenoma. Pseudocyst and IPMN are the two most common entities in this category, but there are other possibilities, such as oligocystic serous cystadenoma, lymphoepithelial cyst, and cystic islet cell neoplasm.
2. Microcystic lesions (collection of microcysts)—serous cystadenoma.
3. Macrocystic lesions (multilocular cysts with fewer compartments, each > 2 cm)—mucinous cystadenoma, IPMN, and lymphoepithelial cyst.
4. Cysts with solid components, i.e., mucinous cystic neoplasm (mucinous cystadenoma and mucinous cystadenocarcinoma)—IPMN, solid and papillary epithelial neoplasm, and solid neoplasms that may show cystic degeneration (adenocarcinoma and islet cell tumors).
The demographics and distinguishing features of most common pancreatic cystic tumors are listed in Table 1. In general cystic lesions are hypodense on unenhanced CT unless there are hemorrhagic, proteinaceous, or mucinous components when the density is determined by the relative amounts of the various components. On contrast-enhanced CT, the enhancement characteristics also vary depending on the type of lesion. In an uncomplicated case, the cystic components are hypodense and do not enhance. If hemorrhage is present, the lesion may be hyperdense, isodense, or hypodense depending on the type of blood products. Similarly, uncomplicated cystic lesions on MRI show low signal intensity relative to normal pancreatic parenchyma on unenhanced Tl-weighted sequences and high signal intensity on T2-weighted images, although this also can vary if there are hemorrhagic, proteinaceous, or mucinous components within these lesions. On contrast-enhanced MRI, the enhancement characteristics also vary depending on the type of lesion.
The most common cystic lesions of the pancreas seen on imaging are pseudocysts, serous cystadenoma, mucin-containing lesions (IPMN, mucinous cystadenoma, or cystadenocarcinoma), and solid papillary epithelial neoplasm. Other rare pancreatic cystic lesions include true epithelial cysts, cystic islet cell tumors, and adenocarcinoma with cystic degeneration.