An invariably benign, encapsulated, firm round mass at the bifurcation of the common carotid artery, with nests of large polyhedral cells in alveolar or organoid arrangement. It is usually asymptomatic but large masses may encroach upon the parapharyngeal space and produce dysphagia, pain, and cranial nerve palsies. (Dorland, 27th ed; DeVita Jr et al., Cancer: Principles & Practice of Oncology, 3d ed, pp570-71).