About the thyroid gland
The thyroid gland is one of the largest endocrine glands and consists of two connected lobes. The thyroid gland is found in the neck below the larynx. The thyroid gland controls how the body uses energy, makes proteins, and controls how sensitive the body is to the other hormones. The gland participates in these processes by producing thyroid hormones, the principal ones being triiodothyronine (T3) and thyroxine (referred to as tetraiodothyronine or T4). These hormones regulate the growth and rate of function of many other systems in the body. T3 and T4 are synthesized from iodine and tyrosine. The thyroid also produces calcitonin, which plays a role in calcium level regulation.
Thyroid disorders include hyperthyroidism (abnormally increased activity), hypothyroidism (abnormally decreased activity), thyroiditis – inflammation of the thyroid, thyroid nodules – which need testing to determine whether they are benign or thyroid cancer. All these disorders may give rise to a goitre, which is an enlarged thyroid gland.
Thyroid cancer can cause several symptoms including:
- A lump or swelling in your neck is the most common symptom.
- Pain in your neck and sometimes in your ears.
- Difficulty swallowing.
- Difficulty breathing or have constant wheezing.
- Your voice may be hoarse.
- A frequent cough that is not related to a cold.
If you have a lump in your neck that could be thyroid cancer, your doctor may do a biopsy of your thyroid gland to check for cancer cells. A biopsy is a routine procedure in which a small piece of the thyroid tissue is removed, usually with a needle, and then checked by a cytologist.
Sometimes the results of a biopsy are not clear. In this case, you may need surgery to remove all or part of your thyroid gland for formal diagnosis by histopatholgy. Thyroid nodules are a common management problem and lesions larger than 1 cm require assessment by ultrasound-guided fine needle biopsy.
Thyroid nodule fine needle cytology results are graded according to the Bethesda system.
- Nondiagnostic or Unsatisfactory, risk of malignancy = 1-4%
- Benign, risk of malignancy = 0-3%
- Atypia of Undetermined Significance or Follicular Lesion, risk of malignancy ~5-15%
- Follicular Neoplasm or Suspicious for a Follicular Neoplasm, risk of malignancy = 15-30%
- Suspicious for Malignancy, risk of malignancy = 60-75%
- Malignant, risk of malignancy = 97-99%
Solitary thyroid nodules are common. The majority are benign. Investigation should include careful history and examination and thyroid function tests. Toxic nodules are rarely malignant and require radionuclide scan for assessment. Thyroid nodules greater than 10 to 15 mm require evaluation by fine needle biopsy. Formal diagnostic excision is required for patients with atypical fine needle cytology. This is because it is not possible to distinguish a follicular carcinoma from a follicular adenoma on cytology alone. This category must simply be interpreted as indicating a follicular tumour and up to 20% will be malignant.
Hemithyroidectomy via skin crease incision, with submission of the specimen to formal pathological examination, remains the standard of care, with completion total thyroidectomy for patients with cancers other than low risk papillary cancer and ‘minimally invasive’ follicular cancer without vascular invasion. The key issue for patients with a solitary thyroid nodule remains the assessment as to which nodules require surgical excision and which can be followed conservatively.