Ultrastructure of Myopericytoma: A Continuum of Transitional Phenotypes of Myopericytes

• Published in: Ultrastructural pathology 2012-05, Vol.36 (3), p.189-194
• Main Authors: Díaz-Flores, L., Gutiérrez, R., García, M.P., Valladares, F., Madrid, J. F.
• Format: Article
• Language: English
• Subjects: Actin Cytoskeleton - ultrastructure; Adult; Biomarkers, Tumor - metabolism; Cytoplasmic Structures - ultrastructure; Female; Hemangiopericytoma - metabolism; Hemangiopericytoma - ultrastructure; Humans; Immunoenzyme Techniques; Male; Middle Aged; Myocytes, Smooth Muscle - metabolism; Myocytes, Smooth Muscle - ultrastructure; Myofibroblasts; myopericytes; Neoplasms, Vascular Tissue - metabolism; Neoplasms, Vascular Tissue - ultrastructure; pericytes; Pericytes - metabolism; Pericytes - ultrastructure; Pinocytosis; smooth muscle cells
• ISSN: 0191-3123; 1521-0758
• DOI: 10.3109/01913123.2012.655855

The authors report the ultrastructural characteristics of myopericytoma, a recently described variant of perivascular (pericytic) tumors, mainly with regard to their myopericytic cells and vessels. Myopericytes range between pericytes and vascular smooth muscle cells (SMCs) in a morphologic continuum. The principal findings of the intermediate phenotypes are (1) elongated or annular morphology with processes of varying length and thickness (usually long and thin); (2) a continuous, irregularly thickened and zonally duplicated basement membrane; (3) heterocellular "peg and socket" junctions with neighboring endothelial cells, and scarce specialized junctions between myopericytes; (4) numerous micropinocytotic vesicles, whether continuous or forming focal rows; (5) abundant thin microfilaments, grouped in bundles with dense bodies and adhesion plaques; (6) poorly developed synthetic system (RER and Golgi); (7) pseudointracellular bodies formed by invagination of basement and plasma membranes, with numerous endocytic vesicles; and (8) zones of cytoplasmic rarefaction near micropinocytotic vesicles and intracellular organelles. The ultrastructure of myopericytes therefore makes it possible to distinguish them from pericytes, SMCs, and fibroblast/myofibroblasts, which is useful for myopericytoma diagnosis. The main pattern of the vessels, with perivascular concentric and multilayered growth of myopericytes (a thick wall in contrast to a small lumen) and lack of elastic material, also supports an intermediate form between pericytic and muscular microvasculature. The presence of myopericytes more similar to SMCs and of hemangiopericytoma-like vessels concurs with transitional forms with angioleyomyoma and true hemangiopericytoma, histogenetically representing a morphologic continuum for the perivascular tumors.