Thyroid structure, lymphatic drainage and recurrent laryngeal nerve anatomy
THE CONTEXT
Thyroid surgery requires knowledge of glandular organisation, lymphatic pathways and the differing courses of the recurrent laryngeal nerves.
Glandular structure and arterial supply
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The normal thyroid weighs 20–25 g.
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Its functioning unit is the lobule, supplied by a single arteriole and containing 24–40 follicles lined with cuboidal epithelium.
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The follicles contain colloid in which thyroglobulin is stored.
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The arterial supply is rich, with extensive anastomoses between the main thyroid arteries and branches of the tracheal and oesophageal arteries.
Lymphatic drainage
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An extensive lymphatic network lies within and around the thyroid; some channels drain directly to the deep cervical nodes.
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The subcapsular plexus principally drains to central compartment nodes at level VI: juxtathyroid ‘Delphian’ nodes, paratracheal nodes and nodes along the superior and inferior thyroid veins.
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Drainage then proceeds to the deep cervical nodes at levels II–V and mediastinal nodes at level VII.
Recurrent laryngeal nerve
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The recurrent laryngeal nerve is a branch of the vagus. It recurs around the aortic arch on the left and the subclavian artery on the right.
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The left nerve has a longer distance to reach the tracheo-oesophageal groove and runs in a medial plane; the right nerve has a shorter distance and follows a more oblique course.
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Approximately 2% of right-sided nerves are non-recurrent and enter the larynx from above.
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The nerve runs posterior to the thyroid and enters the larynx at the cricothyroid joint.