Most patients undergo thyroidectomy due to the finding of a suspicious thyroid nodule, detected either at routine physical exam or upon neck imaging obtained for a separate indication. The finding of a thyroid nodule should prompt evaluation of thyroid function and an assessment for possible malignancy.

Evaluation of a thyroid nodule begins with measurement of serum thyroid stimulating hormone (TSH). If the concentration of TSH is low, this suggests negative feedback suppression by a hyperfunctioning adenoma. Thyroid scintigraphy can be obtained to confirm the functional status of the nodule. Hyperfunctioning nodules are metabolically active and will demonstrate greater uptake than the background thyroid gland. These so-called “hot nodules” are rarely malignant and do not require biopsy. Non-functioning nodules will demonstrate lower metabolic activity than the surrounding thyroid tissue; these cold nodules should be biopsied to rule out cancer. If at the outset the concentration of TSH is normal or high, there is no need for scintigraphy; since the concern for a malignancy is greater with a non-functioning nodule, and a fine needle aspiration biopsy will be recommended regardless.

Fine needle aspiration (FNA) is a minor procedure that can be completed in the office with local anesthesia. A high-resolution neck ultrasound is utilized to help target the lesion and is also useful to assess for other nodules and or enlarged lymph nodes in the region (Fig. 18.1). Results of an FNA can be broadly classified as non-diagnostic, benign, indeterminate, or malignant. Non-diagnostic results indicate that the lesion was not effectively sampled, and repeat biopsy is required. If results of the FNA are suspicious for, or clearly indicative of malignancy, then surgery is recommended. An intermediate designation may indicate a variety of findings, but is frequently used when the lesion is a follicular neoplasm. FNA cannot distinguish between a benign follicular adenoma and a follicular thyroid cancer since an examination of tissue architecture is required, whereas only cytology is obtained by FNA. In these cases, proceedding with a unilateral thyroid lobectomy is generally recommended.

The four histologic classes of thyroid cancer include the papillary, follicular, medullary, and anaplastic types. Papillary thyroid cancer is by far the most common subtype and carries an excellent prognosis. In general, lesions less than 1 cm in size can be managed by a unilateral thyroid lobectomy, and a total thyroidectomy is used for larger tumors. Papillary thyroid cancers may spread to the regional lymph nodes, however a neck lymphadenectomy is only indicated if pathologic appearing nodes are encountered.

Follicular thyroid cancer is the second most common type of thyroid cancer. Unlike papillary cancer, follicular thyroid cancer spreads via hematogenous routes, most commonly to the bone or lung. Although specific criteria vary by center, a total thyroidectomy is typically recommended for follicular thyroid cancers since they tend to be more locally invasive.

Radioactive iodine therapy is used following total thyroidectomy for either papillary or follicular cancers in order to destroy any remaining thyroid tissue as well as adjuvant therapy for micro-metastatic disease. Complete ablation of all thyroid tissue allows the use of serum thyroglobulin as a tumor marker in surveillance for recurrence.

Medullary thyroid cancer develops from the parafollicular cells of the thyroid that produce calcitonin and are involved in calcium homeostasis. Although medullary thyroid cancer can be sporadic, all patients should be evaluated for multiple endocrine neoplasia syndrome Type II, which is commonly associated with this malignancy. Total thyroidectomy is the recommended treatment since bilateral or multifocal disease is common. Calcitonin levels serve as a tumor marker and can be used for surveillance of recurrence.

In sharp contrast to the other thyroid tumors, anaplastic thyroid cancer is a very aggressive malignancy whose survival is generally measured in months. Many individuals with anaplastic tumors will have either a prior history of—or a synchronous finding of—a papillary or follicular thyroid cancer, suggesting that these aggressive tumors may arise from a well-differentiated lesion. Patients with anaplastic cancer typically present with a rapidly enlarging neck mass. Regional or distant metastases are present at the time of initial diagnosis in the vast majority of cases, making surgical resection not beneficial. Systemic chemotherapy and/or radiation therapy may be utilized, although their ability to impact survival is limited.