U-shaped nerve loop (syn. ansa hypoglossi) lying in the carotid triangle, embedded in anterior wall of the carotid sheath. Supplies all infrahyoid (strap) muscles except thyrohyoid.

Formation and Roots

Formed by union of two roots from ventral rami of C1, C2, C3.

Superior Root (Descendens Hypoglossi)

• C1 fibres hitch-hiking with hypoglossal nerve (CN XII)
• Leaves hypoglossal nerve just after it curves around the occipital artery
• Descends on outer surface of ICA, then on common carotid artery
• Gives branch to superior belly of omohyoid en route

Inferior Root (Descendens Cervicalis)

• Derived from C2 and C3 ventral rami
• Descends along posterior aspect of IJV, winds around it anteriorly
• Descends anteroinferiorly → joins superior root in front of common carotid artery at ~cricoid cartilage level

Loop Formation

Superior root + inferior root unite in front of common carotid artery

Position and Relations

Distribution (Branches)

Ansa cervicalis (C1, C2, C3) supplies all infrahyoid muscles except thyrohyoid (supplied by nerve to thyrohyoid, C1, branching from hypoglossal nerve before superior root descends)

Applied Anatomy

• Laryngeal reinnervation — in RLN palsy causing vocal cord paralysis/hoarseness, ansa cervicalis used as donor nerve for reinnervation; ansa branches anastomosed to RLN → restores muscle tone to paralysed vocal cord
• Surgical landmark — ansa lies on anterior wall of carotid sheath → landmark for identifying carotid sheath structures (CCA, IJV, vagus nerve) during neck dissection
• Thyrohyoid exception — thyrohyoid supplied by direct branch from hypoglossal (C1), not ansa cervicalis → ansa injury alone does NOT paralyse thyrohyoid

The ansa cervicalis (syn. ansa hypoglossi) is a U-shaped nerve loop lying in the carotid triangle of the neck, embedded in the anterior wall of the carotid sheath. It supplies all the infrahyoid (strap) muscles of the neck except the thyrohyoid.

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Formation and Roots

The ansa cervicalis is formed by the union of two roots derived from the ventral rami of C1, C2, and C3 spinal nerves.

Superior Root (Descendens Hypoglossi)

• Formed by C1 spinal nerve fibres that hitch-hike with the hypoglossal nerve (CN XII) for a short distance
• Leaves the hypoglossal nerve just after the nerve curves around the occipital artery
• Descends on the outer surface of the internal carotid artery, then on the common carotid artery
• Gives a branch to the superior belly of the omohyoid on its way down

Inferior Root (Descendens Cervicalis)

• Derived from C2 and C3 ventral rami
• Descends along the posterior aspect of the internal jugular vein, then winds around it anteriorly
• Descends anteroinferiorly to join the superior root in front of the common carotid artery at approximately the level of the cricoid cartilage

Formation of the Loop

The superior root and inferior root unite to form the ansa cervicalis (the “loop”) in front of the common carotid artery.

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Position and Relations

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Distribution (Branches)

The ansa cervicalis supplies the infrahyoid (strap) muscles, with the exception noted below:

Summary: Ansa cervicalis (C1, C2, C3) supplies all infrahyoid muscles except thyrohyoid (supplied by nerve to thyrohyoid, C1, which branches off the hypoglossal nerve before the superior root descends).

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Applied Anatomy

Ansa Cervicalis in Laryngeal Reinnervation

In cases of recurrent laryngeal nerve palsy (causing paralysis of intrinsic laryngeal muscles and hoarseness), the ansa cervicalis can be used as a donor nerve for reinnervation of the larynx. The ansa or its branches are anastomosed to the recurrent laryngeal nerve to restore some muscle tone to the paralysed vocal cord (ansa-to-recurrent laryngeal nerve anastomosis).

Surgical Importance — Ansa Cervicalis as a Landmark

During neck dissection, the ansa cervicalis lies on the anterior wall of the carotid sheath and serves as a surgical landmark for identifying the carotid sheath structures (common carotid artery, internal jugular vein, vagus nerve).

Thyrohyoid Exception — Clinical Significance

Because the thyrohyoid is not supplied by the ansa cervicalis but by a direct branch from the hypoglossal nerve (C1 fibres), damage to the ansa cervicalis alone does not paralyse the thyrohyoid muscle.

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