Spontaneous Aortic Lesions in Rabbits I. Morphologic Characteristics

A number of morphologically distinct, spontaneously occurring lesions are present in the rabbit aorta. Intimal atheromata occur in newborn rabbits, decrease in incidence as the rabbit becomes weaned, and are a rarity in the adult. Intimal mesenchymal thickening is first seen in weanling rabbits and is almost universally present in the adult. Medial sclerotic changes involving exclusively the inner one-half of the media and termed “type A” lesions are present in weanling and adult, but not in newborn rabbits. Type A lesions have a variable gross appearance, but a fairly uniform microscopic appearance, which shows principally fragmentation and calcification of elastic lamina and accumulation of acid mucopolysaccharides. “Type B” lesions, medial sclerosis involving exclusively the outer half of the media, usually occur throughout the entire aorta, and only in adult rabbits.