Microcystic (Serous) Neoplasm

Microcystic neoplasms invariably are benign, with only a few malignant ones reported. In distinction with their mucinous counterpart, microcystic adenomas are not considered premalignant, with rare exceptions. Most of these tumors, also called serous cystadenomas, are well encapsulated and nodular and contain numerous small cysts and septa. The cysts are filled with serous fluid and contain little mucin.
Some authors believe the term microcystic serous adenoma is too limiting and that a macrocystic variant of the same neoplasm exists; the term serous cystadenoma is thus used for both morphologic variants.Nevertheless, the term macrocystic serous tumor is useful; these tumors are often misdiagnosed as either mucinous cystic neoplasms or pseudocysts. In fact, some tumors are misclassified even with intraoperative frozen section. Serum tumor markers with macrocystic serous tumors tend to be normal, although CA 125 and CA 19-9 are elevated in the cyst fluid in some of these tumors. The macrocystic variant of serous adenoma consists of a small uni- or bilocular cyst containing a thin wall without any mural nodules; these are indistinguishable from mucinous cystic tumors.
A rare variant is a histologically solid serous cystadenoma with cytologic, histochemical, and immunohistochemical features indistinguishable from a typical serous cystadenoma. Whether such a pancreatic tumor is a separate
pathologic entity is debatable. Symptomatic patients tend to have a large
tumor, with symptoms presumably due to compression of adjacent structures. Smaller tumors often are detected incidentally. An occasional microcystic adenoma having a sponge-like consistency will almost entirely replace the pancreas.
Imaging A majority of microcystic (serous) neoplasms contain many small cysts, a minority consist of larger cysts (macrolacunar) and a minority are mixed; imaging can suggest the diagnosis in a majority of the small and mixed cystic variety, but the larger cystic tumors are indistinguishable from other pancreatic cysts by either CT or MR Some of these tumors containing small cysts have a “honeycomb” appearance on imaging. At times the cysts are sufficiently small to suggest a solid tumor. A central scar with radiating septa is evident in some, and occasionally sunburst-like calcifications are detected
in the central scar. In some, thin septations enhance on immediate postcontrast images. Any solid component also enhances.
Even when large, these benign tumors tend not to obstruct the pancreatic duct. Also, only a small minority of serous cystadenomas communicate with the pancreatic duct. An occasional microcystic adenoma is sufficiently large
to compress and occlude the splenic vein, resulting in hepatopetal collaterals via gastric fundal varices.
Radiology images of three patients with pancreatic microcystic adenomas. A: Postcontrast CT identifies a mostly water density cystic tumor contained multiple septa and a thick rim in the pancreatic tail (arrow). B: This cystic neoplasm also contains septa and a thick rim (arrow).Other images revealed an obstructed splenic vein and numerous gastric fundal collateral veins. C: Microcystic adenoma in the pancreatic head and body (arrow).
Radiology images of microcystic adenoma. A: Coronal T1-weighted MR image reveals a pancreatic cyst (arrows). B: It does not enhance after contrast (arrow).
Radiology images of microcystic adenoma. Transverse US (A) and CT (B) identify a tumor in the pancreatic head (arrowhead)
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