Mesenchymal hamartoma (MH) of the liver is thought to develop from the ductal plates
of the prenatal liver. This immunohistochemical study was performed to gain insight
into the pathophysiology of its development.
Specimens from four MHs with adjacent liver, in one case from a biopsy and from the
resected lesion after 6 years follow-up, were investigated with immunostaining on
cryostatsectionswith antibodies against cytokeratins, vimentin, desmin and alpha-actin,
as well as von Willebrand factor (factor VIII), fibroblast growth factor (FGF) receptors,
FGF-1 (acidic FGF), FGF-2 (basic FGF), and the proliferation-associated Ki67 antigen.
Fibrous tissue of MH stained positive not only for vimentin, but also for desmin and
alpha-actin, whereas cytokeratins and factor VIII showed specific staining in biliary
cysts and endothelial cells, respectively. All mesenchymal cells expressed proteins
of the FGF receptor family. Although FGF-1 was only scarcely detectable, there was
an accumulation of FGF-2 in borderline areas of liver to MH. Multiple Ki67-positive
mesenchymal cells could be identified in these regions in all three MHs. However,
we could not detect any proliferative activity in the MHs after follow-up.
The proliferative process in MH is still active during early childhood. FGF-2 may
have a role in promoting this process. The positivity for desmin and alpha-actin of
the lesions suggests that fat-storing (Ito) cells of the immature liver may be involved
in the development of MH.