Background: We report here an unusual variant of hepatic mesenchymal hamartoma exhibiting a marked myoid differentiation and clinically imitating hilar malignancy.Case Report: A 17-year-old patient was admitted to the hospital with the suspicion of Klatskin’s tumor. Three months before he had presented with jaundice and light stools. Imaging techniques demonstrated a solid lesion (3 cm) situated in liver segment IV. Biochemical tests detected an increased level of bilirubin, alkaline phosphatase, AspAt, ALAT, and slightly increased CA19–9. Diagnosed with perihilar malignancy, the patient underwent left-sided hemihepatectomy with hepaticojejunostomy. The liver resection specimen showed an unencapsulated solid hilar tumor (5×3×3.5 cm), consisting of eosinophilic spindle-like cells with blunt-ended nuclei. Within the lesion we found numerous biliary ductules. Focally, numerous plasma cells and eosinophils were found, but no cystic spaces. There was no cellular atypia. Apart from the lesion the liver revealed intensified fibrosis of portal areas. Immunohistochemical studies demonstrated positivity of most spindle-like cells for SMActin, whereas only a few cells were CD34- and desmin-positive. Ki67 was positive in less than 5% cells.Conclusions: Given the indistinct border and heterogeneous morphology, with spindle-like myoid cells constituting most of the tissue, interspersed with biliary ductules, we suggest that this tumor is an unusual variant of mesenchymal hamartoma. As the mesenchymal component in this lesion was mainly represented by cells of muscular origin, we suggest classifying this lesion as an previously undescribed form of mesenchymal hamartoma, and propose the term, myoid hamartoma of the liver.

Keywords: Adolescent, Hamartoma - pathology, Liver Neoplasms - pathology, Adolescent, Hamartoma - pathology, Liver Neoplasms - pathology