Article by Brian Saunders, MD and Paul Gauger, MD
Division of Endocrine Surgery, Department of Surgery
University of Michigan Medical Center
 

Thyroid nodules are very common, and most are not cancerous. Clinically detectable nodules (defined as palpable or visible nodules greater than 1 cm) are present in about 5% of the population and, fewer than 5% of these are thyroid cancer. Cancer of the thyroid accounts for about 1% of all cancers in the US. Approximately 92% of thyroid cancers have a good or excellent prognosis for cure. Included in this 92% are thyroid cancers such as papillary (80%), follicular (10%), and hurthle cell (2%). The remaining 8% of thyroid malignancies include anaplastic (or undifferentiated), medullary, lymphoma, and metastatic tumors from other cancers.
It is during routine physical exams, or during examination for another head/neck problem, that most thyroid nodules are discovered.
The thyroid is a butterfly shaped gland that sits in front of the trachea, midway between the thyroid cartilage (“Adam’s apple”) and the top of the sternum (Figure 1).

The gland weighs about 20 grams in the average adult. It synthesizes and secretes thyroid hormone. Thyroid hormone acts on many different cell types within the body. Its generalized effect is to control the metabolic rate of the body.
Population studies have demonstrated that thyroid nodules are two-fold more common among women than men. However, nodules in men are relatively more likely to be malignant. The risk of a malignant nodule is greater too if the patient is older than 60 years of age or less than 15 years old. Similarly, about half of the thyroid nodules in children less than 15 years of age are malignant. 
Once discovered, the first step in the evaluation of a thyroid nodule will be a complete history and physical examination. Multiple characteristics of a thyroid nodule can raise or lower the clinical suspicion of a thyroid cancer. For example, slow growth over months or years is more consistent with a benign growth, or a favorable thyroid cancer. Rapid onset of pain is often associated with bleeding into a benign cyst or goiter. Rapid growth over days to weeks is most consistent with a cyst, though rarely can be found in anaplastic cancer or intrathyroidal lymphoma. Hoarseness associated with a nodule can suggest malignancy. Symptoms of hyperthyroidism associated with a nodule suggest an autonomous functioning nodule or a diffuse toxic goiter (both benign processes).
There are a number of personal or family risk factors that may increase the likelihood that a thyroid nodule contains a malignancy. Exposure of the head or neck to radiation treatments (e.g., for acne or recurrent tonsillitis), especially during infancy of childhood, raises one’s chances of developing a thyroid cancer. Different types of thyroid cancers can run within a family. For example, there can be a familial association with medullary thyroid cancer or occasionally papillary cancer.
The aim of any evaluation of a thyroid nodule is to determine if it is benign or malignant, and, if malignant, begin the appropriate treatment (Figure 2). Any thyroid nodule large enough to cause airway or digestive tract obstruction may require emergent thyroid surgery without further evaluation. Thyroid function can be assessed with a blood test to measure the level of thyroid stimulating hormone (TSH). Decreased TSH suggests a hyperactive thyroid gland or nodule. This is typically benign, but may require treatment. A normal or elevated TSH would suggest a non-functioning or normally functioning nodule. The next step would then be thyroid imaging and/or a biopsy to obtain a tissue diagnosis. In addition, any nodule that has progressively gotten larger or a nodule that is firm or hard and different than the surrounding thyroid should be biopsied.
The first imaging study is most often an ultrasound of the thyroid. An ultrasound cannot distinguish benign from malignant nodules. However, an ultrasound is very useful for determining the size and number of nodules. Very often, a single palpable nodule is simply the dominant nodule in a thyroid that has multiple nodules. Should the physician decide to follow a nodule over time, a thyroid ultrasound provides an easy way to track the size of a nodule. For example, a nodule that is less than 1cm in a patient without any risk factors (i.e., family history of thyroid cancers or personal history of head/neck irradiation) may be observed by serial ultrasound examinations. An ultrasound can also be useful for providing directed biopsies of small lesions.
Currently the most useful diagnostic tool in the management of thyroid nodules is a biopsy known as a fine needle aspirate (FNA). The widespread use of FNA as a pre-operative test has reduced the number of people requiring thyroid surgery by nearly 50%. An FNA is performed as an office procedure. The patient will lie flat on her back, with a roll underneath the shoulders to extend the neck. The skin over the thyroid will be cleaned, and a needle will be passed into the thyroid 3-4 times to obtain aspirations from different parts of the nodule.
There are four different diagnostic categories that can result from an FNA. First, the sample can represent benign lesions. This occurs 65-75% of the time. This requires no further treatment (unless the lesion continues to grow causing obstruction to breathing or eating, or causing unacceptable cosmetic disfigurement in the neck). Second, the specimen can be a follicular lesion. This occurs 20% of the time, and should be treated with a surgical removal of part or all of the thyroid gland to determine whether it is a benign or malignant type. Third, the biopsy can show a clearly malignant lesion. This represents 5% of all thyroid aspirates. This again should be treated with surgical removal of the thyroid gland. Finally, the sample can be nondiagnostic. This occurs 10-20% of the time, and requires a repeat FNA. However, after three nondiagnostic biopsies, a surgical removal of the affected thyroid lobe is usually recommended.
Nodules in the thyroid gland are very common. Some of these may be cancerous, but many are benign. It is very important to determine if a nodule is malignant so that the appropriate treatment can be initiated. The evaluation of a thyroid nodule requires a multi-disciplinary team approach, involving primary care physicians, medical endocrinologists, endocrine surgeons, radiologists, and pathologists.