Paraganglia

Paraganglia (from Greek para = adjacent, and ganglion = tumor, nerve node) are organoid accumulations of endocrine active (neuroendocrine) cells without further nervous functions. Ontogenetically, they develop from sympathetic coblasts, cells that migrate from the neural crest and are thus of ectodermal origin. Paraganglia are thus functionally located between the autonomic nervous system and the endocrine system.

There are two different forms of paraganglia

• Chromaffine, sympathetic paraganglia (originate from the sympathetic nervous system and produce adrenalin, noradrenalin and dopamine; they belong to the chromaffine cells)
• Non-chromaffin, parasympathetic paraganglia (originate from the plant of the N. vagus and the N. glossopharyngeus)

Sympathetic paraganglia: Sympathetic paraganglia contain chromaffine parenchyma cells that produce catecholamines. These include the Corpora paraaortica (sugar candy organ) at the point of origin of the inferior mesenteric artery. This paraganglion can grow up to 3.0 cm in size. The adrenal medulla is also classified as a paraganglion due to its ontogenetic origin.

Parasympathetic paraganglia: Parasympathetic paraganglia contain non-chromaffine parenchyma cells. These include:

• Carotic paraganglion (at the division site of the A. carotis communis)
• Paraganglion aorticum (at the aortic arch)

Furthermore the following paraganglia still exist:

• Paraganglion jugulare (Fossa jugularis of the Os temporale)
• Paraganglion laryngicum superius (fold of the larynx)
• Paraganglion laryngicum inferius (fold of the larynx)
• Paraganglion tympanicum (in the middle ear)

While the regression of the chromaffine paraganglia already starts in the 2nd year of life, the pyaraganglion suprarenal (adrenal medulla) remains throughout life. From the paraganglia neuroendocrine tumors, paragangliomas, can originate, rare, primarily benign, unique neuroendocrine tumors. Paragangliomas can occur at any anatomical site with chromaffin-containing autonomous tissue from the base of the skull to the pelvis. Adrenal paragangliomas are called pheochromocytomas (PCCs).

In addition to the endocrine active parenchyma cells, paraganglia show a well vascularized interstitium and are surrounded by a connective tissue capsule on the outside.

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2. DeLellis RA et al (2004) World Health Organization Classification of Tumours: Pathology and Genetics of Tumours of Endocrine Organ. Lyon, France: IARC Press; S 147-166.
3. Fishbein L (2016) Pheochromocytoma and Paraganglioma: Genetics, Diagnosis, and Treatment. Hematol Oncol Clin North Am 30:135-150.
4. Karagiannis A et al (2007) Pheochromocytoma: an update on genetics and management. Endocrine-Related Cancer 14: 935-956.