Some authors have suggested that the migration of these embryonic paraganglionic cells
accounts for the occurrence of paragangliomas in areas with no known paraganglionic tissue like the nasal cavity [13,29,42,44].
A phaeochromocytoma is a rare neuro-endocrine tumour of the paraganglionic chromaffin cells affecting 2-8 persons per million per year.[1-6] Although usually benign, around 10% are found to be malignant.[1,2,7] They can arise in the adrenal medulla and also, in around 10% of cases, in the extra-adrenal paraganglionic cells
.[1,3-5] These extra-adrenal tumours are known as paragangliomas.
Two types of paraganglioma have been reported: the former form is multiple miliary tumors, which occur with chronic lung diseases and may be found in 3.0% of the normal population at autopsy and these tumors are probably arising due to ischemic conditions stimulating the preexisting paraganglionic cells
by small pulmonary emboli (3).
Carotid body tumors are composed by two cells types: the type I cells are the chief or paraganglionic cells
; the type II cells are the sustentacular cells.
The latter type arises within the middle ear from paraganglionic cells
on the promontory.