Cardiac fibromatosis: an ultrastructural study.

The fine structure of a surgically resected cardiac fibroma is described. The tumor consisted primarily of fibroblasts set in a matrix composed of acid mucopolysaccharide and collagen. Many of the fibroblasts contained abundant myofilaments and dense bodies, suggesting differentiation or transformation of these cells to myofibroblasts. No striated muscle was identified. This study confirms the fact that the cardiac fibroma is derived from connective tissue elements and should not be considered either a hamartoma or a mesoblastic tumor. Structurally, as well as biologically, the cardiac fibroma closely resembles soft tissue fibromatoses and should be considered an example of cardiac fibromatosis.