The mean age of diagnosis is 40- 50 years of age but carotid paragangliomas may occur at any age. The term paraganglia was first used by Kohn in the early twentieth century and is the most appropriate nomenclature from an embryologic stand point. These nests of cells appear to originate from neural crest cells that have migrated in close association with the autonomic nervous system ganglion cells. The carotid body was first described by von Haller in 1743 and is a round, reddish-brown to tan structure found in the adventitia of the common carotid artery. The normal carotid body measures 3-5 mm in diameter but is often larger in people living at higher altitudes.
Afferent innervation is provided through the glossopharyngeal nerve.
The histologic appearance of the carotid body is identical to other paraganglia and includes two types of cells. Their cytoplasm contains dense core granules that store and release catecholamines. It is hyperplasia of the dark chief cells that leads to enlargement of the paraganglia during chronic hypoxia. Their function is not entirely clear. These cells are arranged into clusters with a core of chief cells surrounded by sustentacular cells embedded in a fibrous stroma.