What tests may be performed prior to Thyroid Surgery?
1. Chest Xray / CT Scan
This will tell your physician whether the goitre has caused any narrowing of the windpipe or if there is an extension into the chest (retrosternal goitre). Interestingly the degree of windpipe (tracheal) displacement does not always correspond to the extent of narrowing or airway obstruction. If there is a suggestion of a retrosternal goitre a CT scan of the neck and chest or an MRI of these areas may be performed.
A normal chest x-ray on the left and on the right a chest x-ray showing deviation and compression of the trachea by a retrosternal goitre( plunging thyroid) - click to enlarge
A CT scan of huge goitre - click to enlarge
2. Ultrasound
This test does not use X-Rays and can demonstrate the structure of the thyroid. It can distinguish cysts from solid nodules but cannot distinguish cancers from innocent nodules (benign nodules). However certain features such as "comet tails" are suggestive of a benign nodule
3. Nuclear Medicine Scan
This test must not be used in pregnancy. It is useful in a thyrotoxic patient where it shows the extent of the overactivity in the thyroid. Nodules that take up radioactivity are rarely cancerous though this is not impossible.
A hot thyrotoxic nodule. (This the black rounded area on the left side of the scan picture it is in the patients right lobe of thyroid) - click to enlarge
4. Lung Function Tests
These may be necessary in retrosternal goitre to separate local pressure effects, caused by the goitre, from hidden asthma. The common method used is a flow volume loop. The correct diagnosis is essential because simple thyroid surgery, if the thyroid is at fault, will cure breathing problems. In extrathoracic obstruction the flow volume loop is changed and the inspiratory airflow is reduced whereas in asthma the expiratory air flow is reduced.
The extent of tracheal displacement does not relate well to the degree of airway obstruction. If there is a 75% reduction in the cross-sectional area of the trachea however, then noisy breathing (stridor) may occur.
5. Blood Tests
The activity of the thyroid can be checked by performing tests of iodothyronine levels (T4 and T3) and the pituitary influence on the thyroid (TSH). In overactivity, the T3 and T4 are high and the TSH is lower than normal. Rarely the T4 is normal while the T3 is raised with a low TSH (T3 thyrotoxicosis). The calcium level checks the status of the parathyroid glands. If the calcium is abnormal a blood parathyroid test (PTH) is performed. The immune status of the thyroid may be checked (thyroid antibodies). This may help to predict the need for thyroid replacement following subtotal thyroidectomy.
6. Biopsy
Unless there are special circumstances, all single nodules in the thyroid should be subjected to a fine needle aspiration (FNA). This test is similar to a blood test and involves needling the thyroid. It is not 100% accurate. It has two roles: it can be therapeutic, in the case of a simple cyst which may be aspirated to dryness and avoid the need for surgery, or diagnostic in differentiating cancers from innocent nodules.
Fine needle aspiration results should be viewed with a cynical eye. The test is of no value in separating cancers from innocent nodules in follicular lesions. If the FNA is used as a means of separating a benign from a malignant lesion, and no surgery is undertaken, it is essential that the test is repeated within 6 months and, if negative for cancer, again in a year. Fine needle aspiration should be combined with ultrasound to allow accurate sampling of different areas of the thyroid mass. This is particularly important in large cystic masses as it allows any suspicious areas of the cyst wall to be biopsied.
In the case of lymphoma of the thyroid, it is usually necessary to do core biopsy which is similar to an FNA but uses a larger diameter needle. This latter procedure is usually carried out under local anaesthetic.
Please see the introduction section of thyroid surgery where the results of FNA of the thyroid are discussed in detail.
7. Voice Box Assessment (Laryngoscopy)
It is valuable for the surgeon to get an independent assessment of the throat pre-operatively. This test is mandatory when there is a suggestion of voice change, a positive fine needle biopsy for cancer, or there has been previous thyroid surgery. The use of voice box assessment is discussed in detail by our ENT specialist Mr Will Grant, in the section entitled Thyroid and the Voice.
