Myofibroblasts in focal nodular hyperplasia of the liver.

Myofibroblasts have been identified by electron microscopy in a case of Focal Nodular Hyperplasia (FNH) of the liver associated with oral contraceptives. The contractile fibroblasts were observed in the immediate vicinity of, or in close contact with, the proliferating bile ductules and in the recesses between parenchymal cells. Transitional forms between fat-storing cells (Ito cells), fibroblasts and myofribroblasts were observed. Transition of fat-storing cells to myofibroblasts, possibly under the influence of oestrogens, may be responsible for the fibrosis and retraction in FNH.