Unusual intracardiac tumor in a child. Inflammatory pseudotumor or "granulomatous" variant of myxoma?

An intracardiac tumor arising in the right atrium of a young child is reported. Morphologically, the lesion was reminiscent of "plasma cell granulomas," but unprecedented in this location. Based on clinical manifestations, laboratory findings, histologic and ultrastructural characteristics of the mass, the speculation is put forth that this lesion may represent a cardiac myxoma with atypical structural features. An extension of this proposal is a pathogenetic sequence that would try to reconcile the complex clinical course of some myxomas with the described structural observations. Alternative choices for classification of the lesion are also given consideration.