Mucinous cystedenoma ultrasound. The sonographic scan shows a hypoechoic lesion in the head of the pancreas. The lesions has a macrocystic pattern, as indicated by the large anechoic central areas
From the radiological point of view, a thickened wall, the presence of papillary projections arising from the wall or septae, evidence of peripheral calcifications, and invasion of the surrounding vascular structures are considered the best signs of malignancy (Fig. 3.2). The diagnosis will be clearer if extracapsular extension of the lesion is detected on CT contrast-enhanced images. When thick walls, thick septae, and calcifications are simultaneously present, the probability of malignancy is 95%. When fewer than three signs are present, the probability of malignancy decreases, and it is zero when there are no calcifications and the septae and the wall are thin. Since calcifications cannot be detected by magnetic resonance imaging (MRI), the primary imaging modality for these patients is CT.
Mucinous cystedenoma. Axial contrast-enhanced computed tomography scan shows a oligocystic-macrocystic lesion in the body-tail of the pancreas. The cystic lesion contains a mural nodule on the nondependent wall of the lesion (arrow)
The predominant fluid content of MCNs renders them brighter on T2- weighted MRI, which well depicts the presence, features, and distribution of the internal septae. Magnetic resonance cholangiopancreatography (MRCP) is optimal for the non-invasive assessment of the pancreatic duct system (Wirsung and Santorini ducts) (Fig. 3.3). When the mass is clearly isolated from the ductal system, thereby excluding the possibility of an intraductal tumor, further examination with MRCP is not required (Fig. 3.3).
Mucinous cystedenoma. Axial T2-weighted magnetic resonance image shows a cystic macrocystic lesion in the body-tail of the pancreas, with hypointense mural nodules on the nondependent wall of the lesion (arrow)
The overwhelming majority of MCNs occur in the body-tail of the pancreas, where the tumor presents as a round mass with a smooth surface and a fibrous pseudocapsule of variable thickness and frequently containing calcifications. The size of these neoplasms in their greatest dimension ranges from 2 to 35 cm, with an average of 6–10 cm. The cut section shows either a unilocular or a multilocular tumor with cystic spaces ranging in diameter from a few millimeters to several centimeters and containing either thick mucin or a mixture of mucin and hemorrhagic-necrotic material. The internal surface of unilocular tumors is usually smooth and glistening, whereas multilocular tumors often show papillary projections and mural nodules. There is no significant size difference among the different MCN categories, whereas the malignancy of the tumor correlates significantly with the presence of papillary projections and/or mural nodules and multilocularity. As noted above, the tumor does not communicate with the duct of Wirsung or the secondary ducts.
Microscopically, MCNs show two distinct components: an inner epithelial layer and an outer densely cellular “ovarian-like” stromal layer (Fig. 3.4). The mucin-producing epithelium exhibits a spectrum of differentiation, ranging from histologically benign appearing columnar epithelium to severely atypical epithelium.