Thyroid nodules

Thyroid nodules have a high incidence in the general population.By autopsy series, there is up to a 50% incidence of single or multiple nodules. In unselected populations, there is up to a 4% incidence by palpation.

In general, work-up of a nodule may include the following general categories:

history and physical exam,
thyroid imaging,
thyroid function tests, and
Features in the history which increase the likelihood that a given nodule represents carcinoma include:
young age,
male sex,
family history of medullary carcinoma, and
history of radiation exposure to the neck.
Physical findings suggesting carcinoma include:
nodule > 2cm,
tracheal deviation, and
enlarged cervical lymph nodes.

Thyroid imaging
A variety of imaging modalities can be used to image thyroid nodules including thyroid scintigraphy, ultrasound, CT, and MRI. Practically speaking, scintigraphy and ultrasound have been most widely used to help differentiate benign versus malignant disease.
The three agents commonly used in thyroid scintigraphy include Tc-99m, I-123, and I-131. I-123 is often used because it is physiologic (both transported and organified) and it gives a reasonably low total body dose. However, I-123 exams usually require that the patient returns 24 hours following the administration of the tracer making this a two day procedure. Radiation dose with Tc-99m is also reasonably low and there is the advantage that images can be obtained the same day. However, there is the occasional problem of discordant nodules when using Tc-99m (tumors may be hot on Tc-99m, cold on I-123). The possibility of discordant nodules arises because Tc-99m is only transported and not organified, and some tumors can transport Tc-99m. I-131 is not used for normal thyroid imaging because of the high radiation burden and poor imaging characteristics. Types of nodules and the most common I-123 imaging findings are given below:

Type of Nodule I-123 features
Functioning Adenoma Increased
Non-functioning Adenoma Decreased
Multinodular goiter Increased and Decreased
Colloid Nodule Decreased
Cyst Decreased
Malignant Tumor Decreased
Local Thyroiditis Increased or Decreased

Scintigraphic findings in thyroid nodules are non-specific. Focal areas of decreased uptake are often called cold nodules. These cold regions are of concern because they can potentially represent malignant disease; however, the likelihood of carcinoma for any given cold nodule is generally considered to be less than 20% with more recent literature showing an incidence of only 4% (1). On the other hand, finding multiple cold areas interspersed between regions of increased activity can indicate a multinodular gland where there is a low incidence of associated malignancy.
A focal area of increased uptake is called a hot nodule. These hot nodules virtually never represent malignant disease but instead usually represent either autonomous or hypertrophic adenomas. Thyroid function tests and suppression scans can play a role in working up these hot lesions.

As with scintigraphy, ultrasound findings in the work-up of nodules are often non-specific. Occasionally, a simple cyst can be found and in this situation no further work-up is usually required. However, simple cysts are rare and any nodule found usually requires more investigation. Some clinicians use ultrasound to guide biopsies or to follow the size of nodules

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