CT & Sonography of Pancreatic Serous Cystadenoma

Cystic lesions of the pancreas are common, and 80-90% of these lesions are pseudocysts or retention cysts. Cystic neoplasms of the pancreas are less common, accounting for about 10-15% of all cystic pancreatic lesions. True cysts of the pancreas are rare.

The two most common cystic neoplasms of the pancreas are serous cystadenoma (which is benign )and mucinous cystic neoplasms.Serous cystadenoma is more common than mucinous cystic neoplasm, with a ratio of about 2:1. Intraductal papillary mucinous tumor (IPMT) is a more recently discovered cystic neoplasm that may be a variant of the mucinous cystic neoplasm (biologic behavior of mucinous cystic neoplasm and IPMT ranges from benign to malignant).

Radiography:

No radiographic abnormalities are associated with serous cystadenoma except those related to a mass that is large enough to displace or obstruct the bowel or those related to a prominent central calcification.
The main mimics of this tumor are pseudocysts and mucinous cystic tumors.

C.T. : Classically, these lesions have a mean diameter of 5-8 cm (range, 4-20 cm) and a lobulated external contour. They are composed of a grapelike cluster or honeycomb pattern of 6 or more uniformly sized cysts that are 2 cm or smaller. They tend to occur in the head or neck of the gland, although biliary obstruction is present in only about 15% of the cases.

In about 30% of the cases, a central, stellate, late-enhancing scar is present with calcification. Small septa and internal debris may be seen in individual cysts. Because the capsule of these tumors is poorly developed, there is often poor distinction of the tumor from the surrounding pancreatic parenchyma. No communication occurs with the pancreatic duct, except in rare cases.

Serous cystadenoma on a contrast-enhanced CT scan. Note the Swiss cheese–like enhancement and gentle external lobulation.

Serous cystadenoma on a nonenhanced CT scan. Note the central calcification, attenuation similar to that of water, and external lobulation.

Ultrasonography:

The cluster-of-grapes pattern and external lobulation may be seen. However, when the cysts are small, the mass can be echogenic (because of the large number of acoustic interfaces), and they can appear solid (see the image below). This finding can suggest the presence of an adenocarcinoma. The presence of increased through transmission, even if the mass is fairly echogenic, should suggest the diagnosis.

Sonogram of serous cystadenoma. The large mass in the head of the pancreas is externally lobulated, with some cystic-appearing regions, some solid-appearing regions, and increased through transmission. Image courtesy of Arnold C Friedman, MD, FACR.