The carotid bodies in a case of ventricular septal defect.

A woman of 62 years with Turner's syndrome died in congestive cardiac failure secondary to a large ventricular septal defect with biventricular hypertrophy. During her last few months the lifelong left-to-right shunt underwent reversal exposing her carotid bodies to hypoxaemia. The carotid bodies were not enlarged, thus demonstrating that hyperplasia of glomic tissue is not brought about by increased myocardial mass per se. They were, however, abnormally cellular with more dark cells ( a variant of chief cells), many of which were abnormally large and showed ultrastructural features of metabolic activity. These changes may represent the earliest histological response of the carotid body to hypoxaemia and later, the dark cells may mature into the more familiar and common light variant. It seems likely that this dark cell activity precedes, probably by a long period, the sustentacular cell hyperplasia and proliferation of nerve axons which we have reported elsewhere as the chronic reaction of the carotid bodies to hypoxaemia.