Foamy myocardial transformation of infancy: 'lipid' or 'histiocytoid' myocardiopathy.

Two cases of a distinctive infantile myocardiopathy were studied by light and electron microscopy. They represent the 15th and 16th reported examples of this condition, and include the first associated with morphologically classical endocardial fibroelastosis. The condition is characterized by the presence of clusters of foamy or granular cells scattered throughout the myocardium. Ultrastructural studies indicate (1) that lipid storage is not a feature of the condition, and (2) that the abnormal fibers are characterized by a reduced number of fibrils and an increased number of mitochondria. It is proposed that the lesion should be called "foamy myocardial transformation of infancy," and it is speculated that the condition is an acquired metabolic disorder, perhaps occurring in patients abnormally predisposed to such an acquisition.