MRCS Part B (OSCE) - Online Resources

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• The thyroid gland consists of two lobes joined by the isthmus.
• It runs from the level of C5 to T1 vertebrae. The isthmus lies anterior to the 2^nd and 3^rd tracheal rings.
• The thyroid gland is surrounded by a capsule.
• The capsule is surrounded by the pretracheal fascia.

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• The thyroid gland produces thyroxine (T4) and triiodothyronine (T3) via the colloid cells. These hormones are important in regulating metabolism and growth.
• The parafollicular cells of the thyroid gland produces calcitonin which is important in calcium metabolism.

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The blood supply to the thyroid gland is derived from the:

• Superior thyroid arteries (branch of the external carotid).
• Inferior thyroid arteries (branch of the thryrocervical trunk of the subclavian artery).
• Thyroid Ima artery (<10%). It usually arises from brachiocephalic trunk but it may originate from common carotid, subclavian arteries or even from the aorta.

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The lymphatic drainage is via the paratracheal lymph nodes and deep cervical lymph nodes.

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• Pain
• Bleeding (haematoma)
• Infection
• Seroma
• Scar
• Nerve injuries: 1) superior laryngeal nerve injury resulting in damage to the cricothyroid muscle and therefore loss of high pitched voice; 2) recurrent laryngeal nerve injury resulting in difficulty in phonation and airway obstruction if bilateral.
• Hypocalcaemia
• Need for long term thyroid replacement therapy (in the case for total thyroid surgery)

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The vagus nerve provides the nerve supply to larynx through its following branches:

 

1. Superior laryngeal nerve which divides into:

• The external laryngeal nerve supplying the cricothyroid muscle that is a tensor muscle of the larynx and a cord adductor.
• The internal laryngeal nerve which is sensory to the laryngeal mucosa above the vocal cords.

B. Recurrent laryngeal nerve which supplies the remaining intrinsic laryngeal muscles and is sensory to the mucosa below the cords. "

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• Full neck examination
• FNA of the lump
• USS
• Thyroid function tests and thyroid auto-antibodies
• Flexible nasoendoscopy to assess for recurrent laryngeal nerve function (vocal cord movement)

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Papillary carcinoma

Features: 65-70% of thyroid malignancy, more common in women, 3^rd - 4^th decade, lymphatic metastases

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" a. Follicular carcinoma Features: 30% of thyroid malignancy, more common in women, 5th decade, haematogenous metastases b. Medullary thyroid cancer (MTC) Features: originates from the parafollicular C cells of thyroid, men and women equally affected, could present as a part of the multiple endocrine neoplasia 2 (MEN 2a and MEN 2b) c. Anaplastic carcinoma Features: rare, 7th decade, usually presents as a rapidly enlarging neck mass "

"a. Serum thyroglobulin b. T4 c. TSH (Thyroid-stimulating hormone) d. Calcitonin e. Antithyroglobulin antibodies titre (TgAb) f. Carcinoembryonic antigen (CEA) Note: Thyroglobulin is only made by normal thyroid cells and differentiated thyroid cancer cells. (papillary and follicular carcinomas) The C-cells secrete carcinoembryonic antigen (CEA), a glycoprotein which is a recognised tumour marker for medullary thyroid cancer (MTC). "