Solitary infantile myofibromatosis of the mandible. Report of three cases.

Infantile myofibromatosis (IMF) is a benign localized (solitary) or generalized (multicentric) proliferation of fibroblastic tissue occurring exclusively in infants and children. Three cases of solitary IMF involving the posterior region of the mandible of young children are reported. These lesions manifested clinically as asymptomatic bony expansion and roentgenographically as circumscribed lytic areas. Microscopically these tumors showed a distinct zoning phenomenon of curving bundles or intertwining fascicles of plump, spindle-shaped cells at the periphery and solid sheets of less differentiated round cells in the center. Positive immunostaining for vimentin and actin, with the lack of desmin and S-100 protein reactivity, confirmed their myofibroblastic nature of these cells and supported the diagnosis of IMF. All three lesions were treated by curettage and the follow-up showed no incidence of recurrence or any other complications. As we demonstrate in these case reports, IMF should be included in the differential diagnosis of spindle cell neoplastic processes in children.