Thyroid CT Scans and Scintiscans

A CT scan of the neck gives valuable additional information to an ultrasound of the thyroid. It is typically requested to assess the degree of compression (squashing) of the trachea (wind pipe). It also gives information on the extent of any retrosternal extension (how far behind) the sternum (breastbone) the thyroid extends and is used in the planning of surgery for very large thyroid glands.

A CT scan of the neck involves lying on your back and having an injection of contrast agent into a vein in your arm. You pass quickly through the CT machine and the whole procedure is over in a matter of a few minutes. Even people with claustrophobia usually easily tolerate a CT scan. This is because a CT scan does not involve a tunnel like an MRI scan, rather a CT scan is more shaped like a loop.   

Thyroid scintiscans (thyroid scintigraphy / thyroid nuclear medicine scans) use radioactive iodine or technetium, to create images of the thyroid gland and help determine the function (activity) of the thyroid gland. Ultrasound, CT and MRI are more useful than a thyroid scintiscan when looking at the anatomy of the thyroid gland.

Thyroid Scintiscans are most useful in the following situations:

1. Assessing causes of hyperthyroidism.
2. Assessing sites of persistent thyroid tissue or cancer following surgery. (see section on radioactive iodine in the thyroid section of this website.)

In Graves’ disease we see intense diffuse uptake of radioactive tracer throughout the thyroid gland.  

In toxic multinodular goitre we see intense multifocal uptake of the radioactive tracer in the thyroid gland.  

In an autonomous hot thyroid nodule we see intense localised uptake of the tracer in the hot nodule.  

Thyroid scintiscans can be useful in patients with persistent or recurrent papillary thyroid carcinoma or follicular thyroid carcinoma to determine the site of persistent or recurrent cancer. Unfortunately, not all papillary or follicular thyroid cancers show up on thyroid scintiscans.