Mesenchymal hamartomas of the liver: comparison of clinicopathologic features between cystic and solid forms

Mesenchymal hamartoma (MH) of the liver is an uncommon benign lesion related to ductal plate malformation. It is usually cystic and mainly composed of myxoid mesenchymal tissue with tortuous or cystic bile ducts. In order to characterize the clinicopathological features of MH, the Korean Gastrointestinal Pathology Study Group collected a total of 17 MH cases diagnosed in 7 hospitals from 1992 to 2002 and compared the clinicopathologic findings of cystic MH with those of solid variant. Among the 17 cases, 7 (41%) were solid. The solid form showed a higher serum level of alpha-fetoprotein (AFP), the smaller bile ducts, and more frequent proliferation of vessels. Serum AFP level was related to the amount of hepatocytes. Two of seven solid cases harbored a larger amount of evenly distributed hepatocytes and proliferation of small duct with focal hepatocyte-bile duct transition. These histologic findings are similar to those of mixed hamartoma. Therefore, the mixed hamartoma and the MH of both solid and cystic types could be the variants of one disease spectrum. And hepatocytes within MH might be rather a genuine tumor component than entrapped into the tumor. In conclusion, MH can show various clinicopathological features and recognition of these features will facilitate accurate diagnosis of MH.