Ultrastructural changes in a case of mucoid degeneration of the brachial artery.

Summary An electron microscopic (EM) description of mucoid degeneration of the brachial artery in a 67 year old man is presented. In this case, the affected artery showed mucoid degeneration of the intima and media circumferentially, dissecting and destroying the muscle fibres. Ultrastructurally, mucoid degenerating muscle cells showed numerous large mucin-containing vesicles in the cytoplasm. Cells were widely separated by large accumulation of mucoid material, which appeared to penetrate the extracellular collagen fibre bundles. Most of the nuclei of the smooth muscle cells displayed typical necrotic changes undergoing dissolution or having already broken up into discrete fragments. This case of intimo-medial degeneration (IMMD) suggests that the condition could arise spontaneously anywhere in the inner coats of the arterial system away from the vessels that are close to synovial joints. This is a rare presentation of IMMD of arteries, which has been described mainly in the aorta and its major branches.