Histochemical characteristics of parafollicular cells and medullary thyroid carcinoma

Normal canine parafollicular cells share a common set of histochemical characteristics, which include masked metachromasia and argyrophilia, with human as well as rat medullary thyroid carcinomas. Masked metachromasia, a property of polypeptide hormone-producing cells, was demonstrated by staining with toluidine blue or coriophosphine O after acid hydrolysis. Argyrophilia was demonstrated both by the Grimelius silver nitrate technic and by the Azzopardi modification of the Bodian method. With these technics, parafollicular cells in the dog and medullary carcinoma of human and rat origin showed nearly identical staining reactions. Fixation in glutaraldehyde was superior to formaldehyde in demonstrating masked metachromasia of normal dog parafollicular cells, while formaldehyde fixation was superior for the demonstration of argyrophilia of granules. In general, the Grimelius method was superior to the Azzopardi modification of the Bodian technic for the demonstration of argyophilia. The results of this study provided further support for the parafollicular cell origin of human and rat medullary thyroid carcinomas and also provided a useful set of histochemical criteria for the diagnosis of this neoplasm.