Pannus is an abnormal layer of fibrovascular tissue or granulation tissue. Common sites for pannus formation include over the cornea, over a joint surface (as seen in rheumatoid arthritis), or on a prosthetic heart valve. Pannus may grow in a tumor-like fashion, as in joints where it may erode articular cartilage and bone.
The term pannus is often used incorrectly to refer to a panniculus (a hanging flap of tissue).
The term “pannus” is derived from the Latin for “cloth”. Inflammation and exuberant proliferation of the synovium leads to formation of pannus and destruction of cartilage, bone, tendons, ligaments, and blood vessels. Basically, the hypertrophied synovium is called pannus. Pannus tissue is composed of aggressive macrophage- and fibroblast-like mesenchymal cells, macrophage-like cells and other inflammatory cells that release collagenolytic enzymes.