title: Ultrastructure of myopericytoma: a continuum of transitional phenotypes of myopericytes.
abstract: 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.
authors.affiliation: Department of Anatomy, Pathology, Histology and Radiology, Faculty of Medicine, University of La Laguna, Tenerife, Spain. kayto54@gmail.com
authors.forename: L
authors.initials: L
authors.lastname: Díaz-Flores
authors.forename: R
authors.initials: R
authors.lastname: Gutiérrez
authors.forename: M P
authors.initials: MP
authors.lastname: García
authors.forename: L
authors.initials: L
authors.lastname: Díaz-Flores
authors.forename: F
authors.initials: F
authors.lastname: Valladares
authors.forename: J F
authors.initials: JF
authors.lastname: Madrid
mesh_terms: D008841:Actin Cytoskeleton / Q000648:ultrastructure; D000328:Adult; D014408:Biomarkers, Tumor / Q000378:metabolism; D022083:Cytoplasmic Structures / Q000648:ultrastructure; D005260:Female; D006393:Hemangiopericytoma / Q000378:metabolism / Q000648:ultrastructure*; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D032389:Myocytes, Smooth Muscle / Q000378:metabolism / Q000648:ultrastructure; D009383:Neoplasms, Vascular Tissue / Q000378:metabolism / Q000648:ultrastructure*; D020286:Pericytes / Q000378:metabolism / Q000648:ultrastructure*; D010873:Pinocytosis
chemical_list: D014408:Biomarkers, Tumor