Thyroid
Anatomy
Structure
The thyroid is found in the neck in front of the larynx, around C5,6,7 and T1. It weighs about 25g. The term thyroid means shield, though it looks more like a butterfly. There are two lobes, joined in the middle by the isthmus. !!Functions Produces three hormones:
- thyroxine (T3)
- triiodothyronine (T4)
- calcitonin
Blood supply
Blood supply is, unsurprisingly, from the thyroid arteries, and drains to the thyroid veins. Check out this picture of the larynx blood supply for more info.
Clinical Conditions
Hyperthyroidism
Leads to excessive levels of T3 and T4. This leads to symptoms such as:
- Hair loss
- Anxiety
- Goitre
- Weight loss
- Tremor
- Tachycardia
- Diarrhoea
- Menorrhagia
Long term, it can lead to osteoperosis.
Graves disease
The commonest type, usually associated with a big goitre. It happens when an IgG antibody is produced, which mimics the action of TSH, thus causing growth in gland tissue and overproduction. Look out for exophthalmos (bulgy eyes).
Toxic nodular goitre
Rare, where one of more of the lumps in a goitre becomes hypersecretory.
Hypothyroidism
Also known as myxoedema, results from lack of circulating T3 and T4. Presents with:
- Loss of outer third of eyebrows (IMPORTANT)
- Weight gain
- Constipation
- Bradycardia
- May have goitre
- General slowing down physically and mentally
If it happens in the newborn, it can lead to permanent cretinism, unless therapy is undergone immediately.
Hasimoto's thyroiditis
Commonest cause of hypothyroidism. Basically the thyroid is attacked by the body. At first the gland will hypertrophy (grow), but soon it will atrophy and fibrose. Treatment is by thyroxine tablets.
Iatrogenic
Certain drugs, such as Lithium, can cause hypothyroidism, and surgical removal of the tissue has a similar effect.
Tumour
Patients presenting with a solid mass in the thyroid is a common problem. Usually it will prove to be a particularly large node in a multinodular goitre, but it can also be neoplastic.
Benign
Tumours of the thyroid are generally benign, with the only real danger being potential malignancy, or of tracheal compression/patient discomfort.
Malignant
Carcinoma of the thyroid is a fairly rare tumour, and has a good prognosis, since it presents early – patients tend to notice a lump on their neck – and is usually well differentiated. It is known to be very associated with radiation exposure.
Main types are:
- Papillary, under 45s, slow growing, excellent prognosis
- Follicular, 20-55s, can be targeted by radioactive iodine, good prognosis.
- Anaplastic, Elderly, aggressive, poor prognosis.