Histopathological Characteristics of Calcified Lesions of the Aortic Orifice (Ostium Aortae) in Dogs.

We investigated the naturally occurring calcification of the aortic orifice (ostium aortae), which is the opening from the left ventricle into the ascending aorta, in dogs. Twenty-one beagle dogs were examined at the age of 6 weeks (N=6), 8 months (N=12), and 7-8 years (N=3). Typical calcification exhibiting a characteristic purplish color with hematoxylin and eosin staining was observed in 3 out of 12 dogs at the age of 8 months. The changes were found in the aortic wall above the seputal semilunar cusp. In addition to the typical calcification, small eosinophilic particles with a positive reaction for von Kossa technique was frequently observed in all dogs except for 2 animals in the 6-week-old group. The deposition of the eosinophilic particles increased with aging, and some particles had basophilic cores in 8-month-old and older dogs. These particles were preferentially localized at the aortic medial elastic fibers above the seputal semilunar cusp. Energy dispersive X-ray analysis revealed that the particles were composed of calcium phosphate. These results suggest that the small eosinophilic particles demonstrate the minimal calcification. The lesion deteriorates with aging and seems to be a based lesion for typical calcification.