Ultrastructure of Canine Carotid Body and Aortic Body Tumors Comparison with Tissues of Thyroid and Parathyroid Origin

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Abstract
The microscopic structure of canine carotid and aortic body neoplasms was compared with that of other lesions of the neck and thorax. Carotid and aortic body adenomas consisted of clusters of large, polyhedral cells whose cytoplasm was filled with dense, membrane-bound granules and which lacked the normal relationship to sustentacular, nerve, and vascular cells. Unlike an ectopic thyroid adenoma, they had no thyroid follicles, PAS-stained cytoplasmic granules, acidic mucopolysaccharide foci, or dense tubules within the cisternae of the endoplasmic reticulum. Cells of the aortic body carcinoma were less differentiated than those of the adenoma. They contained fewer dense granules but had greater numbers of microfibrils and Golgi vesicles. Degeneration and necrosis of neoplastic tissue exaggerated differences from the adenomas. Cells from the metastatic tumor (pleural carcinomatosis) did not differ significantly from those of the primary tumor. Cells from thyroid and parathyroid lesions were significantly different ultrastructurally from those of carotid and aortic body tumors. Cells of the ectopic thyroid adenoma and thyroid carcinoma resembled normal follicular cells but were larger and contained characteristic PAS-stained granules and arrays of intracisternal microtubules. The parathyroid adenoma cells had few organelles; the dominant cytoplasmic structures were aggregates of membranes and residual bodies filled with lipofuscin.