If you have a thyroid nodule, your doctor may use thyroid scans to assist in the evaluation of the nodule. A thyroid scan provides graphic representations that depict how the radioactive probe is distributed in the thyroid gland.
The thyroid scan is useful in showing where the nodules have less (”cold”) or greater (”hot”) absorption of radioactive iodine in comparison with normal paranodular tissue. The data helps in classifying nodules as “cold” (hypofunctional), “warm” (functioning normally), or “hot” (hyperfunctional). The thyroid scan produces an image that illustrates the basic shape of your thyroid gland, and the pattern of relative concentration of the radioactive imaging agent that has been introduced.
A “cold” nodule usually occurs in the isthmus (the central stalk) or at the fringes of the thyroid. The contours of the gland thus remain normal with little distortion. It may indicate that the patient has a thyroid cancer, and a thyroid lobectomy (a procedure where the surgeon removes a single lobe of your thyroid) is often recommended by doctors.
However, it must be noted that thyroid nodules such as cysts, benign follicular lesions, colloid nodules and hyperplastic nodules are all cold when scanned, so the doctor approaches the diagnosis carefully. “Hot” nodules (which happen because RAI uptake in surrounding tissue is unimpeded) can also indicate a malignancy.
Thyroid scan is, in fact, not a cost effective method for all patients who show symptoms of thyroid nodule. In the following situations, however, a thyroid scan may be useful:
- To determine how a nodule in a Graves’ disease patient is functioning, since a cold nodule usually becomes a candidate for biopsy and partial thyroidectomy (rather than iodine ablation or drug therapy for hyperthyroidism);
- To establish the status of a nodule’s functioning, where it has been shown to be a follicular neoplasm through the fine needle aspiration method;
- To differentiate the functional status of each separate nodule in instances of multinodular goiter; and,
- To help describe the presence of nodules, especially when there are indications of multinodularity or substernal extension.
Iodine-123 (I-123), Iodine-131 (I-131) and Technetium pertechnetate (Tc-99) are the most commonly used radioactive probes for thyroid scanning. I-123 is usually the preferred isotope, but some specialists would like to use Tc-99. Both I-123 and Tc-99 are effective imaging agents, though there may be occasions when they yield contrary results. Tc-99 may show a nodule to be functioning normally, while I-123 may show it as cold. For this reason, it is not an uncommon practice to conduct a thyroid scan with I-123 if a nodule appears hot with Tc-99.
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