Ultrastructural Aspects of Vacuolar Degeneration of Cardiomyocytes in Human Endomyocardial Biopsies

Vacuolar degeneration of cardiomyocytes is a histological finding commonly encountered during routine light microscopic examination of human endomyocardial biopsy specimens. The vacuoles appear as intracellular clear areas lacking myofibers. By itself, this finding has little diagnostic value, but may have important clinical implications when the vacuolar contents are of etiological significance (e.g., accumulation of abnormal metabolites), and the clinical importance is increased when the disease is treatable. Thanks to its great resolving power, electron microscopy can often reveal the contents of the vacuoles and lead to a correct diagnosis. It can be used to differentially diagnose lysosomal storage diseases such as Fabry, Danon, and Pompe disease, doxorubicin cardiomyopathy, mitochondrial cardiomyopathy, autophagic degeneration, and accumulation of subcellular organelles (mitochondria, lipofuscin, glycogen granules, endoplasmic reticulum, etc.) as a nonspecific finding in failing cardiomyocytes. Nonetheless, undiagnosed cases certainly remain. It is strongly recommended that small pieces of tissue samples be fixed for electron microscopy at every endomyocardial biopsy procedure, and electron microscopic examination should be performed when a marked vacuolar degeneration is found.