External carotid plexus

The external carotid plexus refers to a meshwork of postganglionic neurons within the connective tissue encapsulating the external carotid artery. These postganglionic fibers are derived from three distinct external carotid nerves emanating from the upper pole of the superior cervical ganglion. These include:

• Inferior communicating branch (which also contributes to the intercarotid plexus),

• Anterior communicating branch (which directly contributes to the external carotid plexus),

• The interior communicating branch to the superior laryngeal nerve (which descends to formulate plexuses around the superior thyroid and lingual arteries, prior to anastomosing with the anterior communicating branch).

The external carotid plexus spreads further along the branches of the external carotid artery forming secondary plexuses around the facial, lingual, superior thyroid, occipital, ascending pharyngeal and superficial temporal arteries. This branching network distributes sympathetic neurons to majority of the mid and lower face region–its vasculature and sweat glands–carotid body, thyroid and parotid glands. Not surprisingly, ligation or damage to any of these branches of external carotid artery could result in neural abnormalities of facial muscles and sweat glands.

Some of the post-ganglionic sympathetic neurons may dissociate from external carotid and its secondary plexuses, to join distinct peripheral nerves as they enter into target tissues.