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The pathogenesis of diffuse intimal thickening (DIT) is not well understood. In animals, it is positively correlated with size, and with the exception of the pig, is thought to involve the proximal more than the distal portions of vessels. DIT is often not visible grossly, so that it's study requires extensive microscopic sampling of tissue. Review of previous studies in animals suggests that microscopic sampling may not have been sufficient to determine exactly where DIT occurs throughout the entire length of a vessel. The present study is a longitudinal step-serial section examination of the entire descending thoracic aorta from 12 adult non-human primates of varying size and species and with varying degrees of DIT as determined previously by more limited cross-section techniques. The findings indicate that DIT is not more pronounced in the proximal versus the distal segments of the vessel, and is not correlated with branch orifices. Review of the literature suggests that DIT may not be a single process, but may vary in pathogenesis from vessel to vessel and from species to species.

This is a step section study of 3 fibrous plaques from the abdominal aorta of an ostrich. The distribution of gelatinous like lesions in these plaques suggested that the gelatinous lesions were formed by the influx of plasma at the plaque shoulders. Two gelatinous lesions extended like tunnels into the center of one of the plaques. The presence of focal necrosis and large cholesterol crystals in one of these gelatinous tunnels deep within the plaque suggested that gelatinous lesions might represent one mechanism by which fibrous plaques are converted to atheromatous plaques.