They are one of the types of extracellular vesicles, with sizes between 100nm and \$1 \mu m\$. They are formed by the outward budding of the producing cell plasma membrane[@pedrioli2021Extracellular Vesicles as Promising Carriers in Drug Delivery: Considerations from a Cell Biologist’s Perspective]. Mitofillin and actinin-4 are enriched in these EV's.
Microvescicles are heterogeneous in size[@elsharkasy2020Extracellular vesicles as drug delivery systems: Why and how?].