Background: Intramuscular myxoma is a rare benign mesenchymal lesion. Only very rare cases of cutaneous localization of this tumor have been described, in particular related to the somatic soft tissues of the face. This unusual localization may clinically mimic nodular or cystic facial lesions having different origins.
Objective: The aim of our work was to well characterize the phenotype of the spindle cells characteristic of intramuscular mixoma.
Methods: Tissue samples were processed for morphological and ultrastructural studies. Moreover, immunohistochemical stainings were performed to characterize the expression of different nonmuscular and muscular cytoskeletal proteins.
Results: The tumor was composed of sparse spindle cells embedded in a prominent mucoid matrix. Besides the predominance of a fibroblast-like appearance, some neoplastic cells displayed immunohistochemical and ultrastructural features resembling either myofibroblasts or primitive mesenchymal cells, with a modulation of cell actin expression.
Conclusion: The presence of multiple phenotypes of nonmuscular, mesenchymal pathway of differentiation can be considered a peculiar feature of intramuscular myxoma.