Midline Neck Swellings and Surgical Anatomy of the Thyroid Gland

Midline Neck Swellings and Surgical Anatomy of the Thyroid Gland

Enlist midline neck swellings. Describe surgical anatomy of thyroid gland with reference to embryology,blood supply relationship and nerves related to thyroid gland.

Answer.

Enlisting Of Midline Swellings Of Neck

The midline swellings of neck are:

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• Ludwig’s angina
• Enlarged sub-mental lymph node
• Sub-lingual dermoid cyst
• Thyroglossal cyst
• Sub-hyoid bursitis
• Goiter of thyroid, isthmus and pyramidal lobe
• Enlarged lymph node and lipoma in substernal space of burns
• Retrosternal goiter
• Thymic swelling
• Bony swelling arising from the manubrium sterni.

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Surgical anatomy of thyroid Gland

Reference To Embryology

• It develops from median down growth (midline diverticulum) of a column of cells from the pharyngeal flor between fist and second pharyngeal pouches.
• By 6 weeks of time the central column, which becomes thyroglossal duct, gets reabsorbed.
• The duct bifurcates to form thyroid lobes.
• Pyramidal lobe is formed by a portion of the duct.

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Reference To Blood Supply

Artery Supply

• The superior thyroid artery is a branch of external carotid artery, enters the upper pole of the gland, divides into anterior and posterior branches and anastomoses with ascending branch of inferior thyroid artery.
  Upper pole is narrow, hence ligation is easy.
• Inferior thyroid artery is a branch of thyrocervical trunk and enters the posterior aspect of the gland.
  It supplies the gland by dividing into 4 to 5 branches which enter the gland at various levels (not truly lower pole).
• Thyroidea ima artery is a branch of either brachiocephalic trunk or direct branch of arch of aorta and enters the lower part of the isthmus in about 2 to 3% of the cases.

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Venous Drainage

• Superior thyroid vein drains the upper pole and enters the internal jugular vein. The vein follows the artery.
• Middle thyroid vein is single, short and wide and drains into internal jugular vein.
• Inferior thyroid veins form a plexus which drain into in nominate vein. They do not accompany the artery.
• Kocher’s vein is rarely found (vein in between middle and inferior thyroid vein).

Reference To Nerve Supply

• External laryngeal nerve: Vagus gives rise to superior laryngeal nerve, which separates from vagus at skull base and divides into two branches.
  The large, internal laryngeal nerve is sensory to the larynx.
  The small external laryngeal nerve runs close to the superior thyroid vessels and supplies cricothyroid muscle (tensor of the vocal cord) and is sensory to upper half of the larynx.
  This nerve is away from the vessels near the upper pole.
  Hence, in thyroidectomy, the upper pedicle should be ligated as close to the thyroid as possible.

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• Recurrent laryngeal nerve: It is a branch of vagus, hooks around ligamentum arteriosum on the left and subclavian artery on the right, runs in tracheo, esophageal groove near the posteromedial surface. Close to the gland, the nerve lies in between (anterior or posterior) the branches of inferior thyroid artery.
  Hence, inferior thyroid artery should be ligated away from the gland, to avoid damage to recurrent laryngeal nerve.
  On right side it is 1 cm within the tracheoesophageal groove.
  The nerve traverses through the gland in about 5–8% of cases.
  The nerve may be very closely adherent to the posteromedial aspect of the gland.
  Nerve not seen may be far away in the tracheoesophageal groove.
• Non-recurrent laryngeal nerve is found in about l in 1,000 cases.
  Nerve has a horizontal course. In 25% of the cases it is within the ligament of Berry.