Abstract and Introduction
Abstract
Background: Thyroid nodules are common, yet treatment modalities range from observation to surgical resection. Because thyroid nodules are frequently found incidentally during routine physical examination or imaging performed for another reason, physicians from a diverse range of specialties encounter thyroid nodules. Clinical decision making depends on proper evaluation of the thyroid nodule.
Methods: The current literature was reviewed and synthesized.
Results: Current evidence allows the formulation of recommendations and a general algorithm for evaluating the incidental thyroid nodule.
Conclusions: Only a small percentage of thyroid nodules require surgical management. Diagnosis and treatment selection require a risk stratification by history, physical examination, and ancillary tests. Nodules causing airway compression or those at high risk for carcinoma should prompt evaluation for surgical treatment. In nodules larger than 1 cm, fine-needle aspiration biopsy is central to the evaluation as it is accurate, low risk, and cost effective. Subcentimeter nodules, often found incidentally on imaging obtained for another purpose, can usually be evaluated by ultrasonography. Other laboratory and imaging evaluations have specific and more limited roles. An algorithm for the evaluation of the thyroid nodule is presented.
Introduction
Fundamental to evaluation of the thyroid nodule is differentiating medical from surgical disease. Although not mutually exclusive, five categories of thyroid nodules classify this broad spectrum of pathology hyperplastic, colloid, cystic (containing fluid), inflammatory, and neoplastic, with the last being the most feared. The indications for surgical management of the thyroid are suspicion of malignancy, compressive symptoms, hyperthyroidism, airway control in anaplastic cancer, and cosmesis. Clinically significant airway compression, even for a benign goiter, indicates consideration of surgical treatment because with time, the thyroid will grow, and in so doing will make surgery more difficult and risky. In contrast, primary therapy for clearly benign noncompressive thyroid lesions, such as a toxic multinodular goiter, remains medical, as the surgical risks to the parathyroids and recurrent laryngeal nerves are much greater than the risks of medical therapy. The steps leading to a decision for operative intervention are the most involved when evaluating a nodule with potential for malignancy. The challenge is largely because thyroid nodules are common, yet thyroid carcinoma is not. In the United States, approximately 275,000 new thyroid nodules are detected each year, but only 1 in 20 palpable nodules is malignant, and the annual incidence of clinically detected thyroid carcinoma is only 2 to 4 per 100,000 population. This knowledge alone may be of some comfort to the patient whose asymptomatic nodule was unexpectedly identified by imaging, an operation, or routine physical examination. Nevertheless, three quarters of thyroid carcinomas are asymptomatic.
About 5% of adults in the United States have a palpable thyroid nodule. Nodules are more common as age increases and as iodine intake decreases, and they occur more frequently in women. Including nonpalpable nodules detected by ultrasonography, increases nodule prevalence from 30% in patients younger than 50 years of age to 50% in patients greater than 60 years of age. Due to anatomic factors, approximately 90% of all thyroid nodules are not palpable. Furthermore, half of patients with clinically apparent solitary nodules are found to have nonpalpable multinodular goiters on ultrasonography or surgical thyroidectomy. An earlier perception that solitary nodules are more likely malignant than a nodule within a goiter is now replaced with a general acceptance that the risk of cancer is similar in patients with solitary or multiple nodules. Other types of nodules previously considered to be of low risk for cancer (long-standing nodules, nodules present in the hyperthyroid patient, and cystic lesions) have also been demonstrated to have at least an average risk of cancer. Evaluating the thyroid nodule is an involved process that begins with taking a history, performing the physical examination, and then choosing appropriate additional tests.