Thyroid nodules are common, and a large proportion has mixed cystic and solid components. In some studies, a nodule is called a cyst only if it is predominantly cystic on ultrasonography, but in others the term is applied to nodules that are predominantly solid but have small areas of cystic degeneration. Thus, depending upon the criteria used, up to 50 percent of solitary thyroid nodules are cystic. Most recur after fine needle aspiration. The appropriate evaluation and management of patients with cystic thyroid nodules is an area of controversy.
This topic review will focus on the unique challenges presented by patients with cystic thyroid lesions. The general approach to thyroid nodules is reviewed separately. (See "Diagnostic approach to and treatment of thyroid nodules".)
Like most thyroid nodules, cystic thyroid nodules often come to attention when noted by the patient or as an incidental finding during a routine physical examination or radiologic procedure such as carotid ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI) of the neck (so-called "thyroid incidentalomas") .
However, some patients develop symptoms, and cystic thyroid lesions (not subacute thyroiditis) are the most common cause of thyroid pain. As an example, sudden hemorrhage or hemorrhagic infarction of a solid thyroid nodule can result in a predominantly cystic and painful neck mass. Even relatively small hemorrhagic cysts of only 1 to 2 mL may be associated with considerable neck discomfort and dysphagia. More extensive hemorrhage may cause hoarseness and vocal cord paralysis and may compromise the airway, especially if the nodule is located within or below the thoracic inlet . (See "Clinical manifestations and evaluation of obstructive or substernal goiter".) In addition, chronic intermittent degeneration of a thyroid tumor can result in intermittent neck discomfort.
True simple thyroid cysts lined by benign epithelial cells are rare. As an example, in one ultrasound study of 1985 patients with 3483 nodules larger than 10 mm, there were only seven completely cystic nodules . Most cystic nodules are partly solid structures that have undergone cystic degeneration (mixed or complex nodules). Complex nodules are common. In a review of 1128 patients with 1458 thyroid nodules who underwent ultrasound-guided fine needle aspiration (FNA), 53.5 percent were partially cystic, with 13.7 percent described as >75 percent cystic .