Dark cell proliferation in carotid body hyperplasia

The histopathology of the enlarged carotid bodies, in both qualitative and quantitative terms, is described in two cases. One was in a woman of 80 years with systemic hypertension and the other in a man of 72 years with pan‐acinar emphysema complicated by chronic hypoxaemia. In both instances there was generalized hyperplasia of sustentacular cells, perhaps with involvement of Schwann cells and fibrocytes, with superimposed focal proliferation of dark or ‘pyknotic’ variants of chief cells. The functional significance of both forms of tissue response in the carotid bodies is speculated upon.