Atherosclerosis Histology

Gross Features

-    Key processes are intimal thickening and lipid accumulation

-    An atheroma consists of a raised, focal lesion of the intima with a soft, yellow core of lipid (cholesterol and cholesterol esters) covered by a firm, white, fibrous cap

-    Atheromatous plaques appear white to white-yellow and impinge on the arterial lumen

-    Vary in size from 0.3-1.5 cm in diameter, but may coalesce to form larger masses

-    Are eccentric, patchy and variable along the vessel length; are focal and sparsely distributed initially, but become more numerous and extensive as the disease progresses

-    Mainly affects abdominal aorta, coronary arteries, popliteal arteries, internal carotid arteries and the vessels of the circle of Willis (in descending order)

Microscopic Histology Features

-    Contain 3 principal components:

-    Cells (SMCs, macrophages, other leukocytes)

-    ECM (collagen, elastic fibers, proteoglycans)

-    Intracellular and extracellular lipid

-    Superficial fibrous cap is composed of SMCs and relatively dense ECM

-    Beneath and to the side of the cap (the “shoulder”) is a cellular area consisting of SMCs, macrophages and T-lymphocytes

-    Deep to the fibrous cap is a necrotic core containing a disorganized mass of lipid (cholesterol and cholesterol esters), cholesterol clefts, cell debris, foam cells, fibrin, variably organized thrombus and other plasma proteins

-    The periphery of the lesion demonstrates neovascularisation

•    Plaques continue to change and enlarge through cell death and degeneration, synthesis and remodelling of ECM, and organization of thrombus

•    Atheromas also undergo calcification; patients with calcificied coronaries are at increased risk for coronary events

•    Advanced atheromatous plaques can undergo the following changes:

-    Focal rupture, erosion or ulceration: can induce thrombus formation or release of debris producing microemboli (cholesterol emboli)

-    Hemorrhage into a plaque: may enlarge a plaque or induce its rupture

-    Superimposed thrombosis: may partially or completely occlude the arterial lumen; may be incorporated into the plaque and enlarge it

-    Aneurysmal dilatation: results from atherosclerosis-induced atrophy of the media with loss of elastic tissue causing weakness and a potential for rupture