Head and Neck Surgery
About Thyroid Disorders
The thyroid gland produces the hormone thyroxine which is important for the regulation of many of the functions of the body. Thyroid disorders include disorders of function and a range of conditions that cause enlargement of the thyroid gland which may be diffuse or nodular.
Disorders of function can be either excessive (hyperthyroidism – too much thyroid hormone) or depressed (hypothyroidism – too little thyroid hormone). Assessment of thyroid function is made based on clinical assessment and measurement of thyroid hormones from a blood test. Both hyper and hypothyroidism require medical treatment and monitoring to keep thyroid function in the normal range.
A scan of thyroid gland and the surrounding area of the neck is useful and often required to provide additional diagnostic information about enlargement of the thyroid gland. An ultrasound scan of the thyroid gland is the most common type of scan as it both accurate and safe. CT and MRI scans are usually only required in the assessment of suspected thyroid cancers. Specialised functional scans of the thyroid (e.g nuclear medicine scans) may be required for assessment of hyperfunctioning nodules or for the assessment and treatment of patients after surgery to remove thyroid cancer.
Causes of nodular enlargement of the thyroid gland include thyroid nodules, cysts, benign tumours and cancers. The investigative workup for thyroid nodules is based on clinical findings, imaging (usually ultrasound scan) and fine needle aspiration cytology (FNAC). If there is no suggestion of tumour, these are termed benign thyroid nodules or cysts; if there is more than one nodule or cyst, it is called multinodular goitre (MNG).
Causes of dIffuse thyroid enlargement include Hashimoto’s thyroiditis and Graves disease and thyroid goitre. While these conditions are very different, both are autoimmune diseases where the body develops antibodies against its own thyroid tissue; both can have serious effects on the metabolism and function of multiple systems in the body through their effects on the level of circulating thyroid hormone; both are associated with complications that extend beyond the thyroid gland. In Hashimoto’s thyroiditis, chronic inflammation and damage to thyroid cells often leads to eventual hypothyroidism; there is also an increased risk of developing lymphoma of the thyroid gland. In Graves disease, autoantibodies against tissues around the eyeball may cause protrusion of the eyeball (exophthalmos) and restriction of the movement of the eye resulting in double vision. Thyroid goitre due to iodine deficiency can result in severe enlargement of the thyroid gland but usually found in areas of iodine deficiency e.g mountainous areas with limited access to seafood.
The management of thyroid disorders is depends on the diagnosis and on the degree of suspicion of cancer. For benign thyroid nodules, surgery is only required if the nodules are symptomatic; this is mainly due to size i.e visibility, interference with swallowing and rarely compression of the trachea causing difficulty breathing. Nodules with a very low risk of cancer need monitoring and surveillance. For nodules with suspicious features, surgery is required to get a histological diagnosis. The nodule is usually removed together with the side of the thyroid gland in which it lies. This is known as a hemithyroidectomy.
- The extent of resection of the thyroid gland depends on the condition being treated. Complete removal of the thyroid gland (total thyroidectomy) may be recommended in certain cases including thyroid cancer, large multinodular goitre (MNG) affecting both sides, Graves’ disease where non-surgical treatment is not suitable or has failed. In some patients with hyperthyroidism or MNG, subtotal thyroidectomy may be recommended, where a small portion of thyroid tissue is preserved to try to maintain adequate thyroid hormone production.
- In the treatment of thyroid cancer where there is suspected or proven spread of tumour beyond the thyroid gland, the operation will need to include removal of the neighbouring tissues that are involved by tumour. A neck dissection, i.e removal of lymph node regions, is usually also required for suspected or proven spread of cancer to the lymph nodes.