Fine-needle aspiration biopsy of thyroid nodules

When further investigation is required

Thyroid ultrasound and FNA biopsy based on the clinical picture are the mainstay of investigation in suspected thyroid nodules (Table 1). Increased likelihood of thyroid malignancy from clinical history and physical examination findings should prompt an ultrasound to determine FNA biopsy eligibility based on nodule size and sonographic features. Findings from the clinical history that increase the likelihood of malignancy include rapid growth of a neck mass, head and neck irradiation, total body irradiation for bone marrow transplantation, familial thyroid carcinoma, or thyroid cancer syndromes (eg, multiple endocrine neoplasia type 2, familial adenomatous polyposis, Cowden disease).¹ Relevant physical examination findings suggestive of malignancy include dysphonia, dysphagia, dyspnea, regional lymphadenopathy, and fixation of the nodule to surrounding tissue.¹ Measurement of serum thyroid-stimulating hormone (TSH) should be included in the initial workup of a nodule greater than 1 cm in any dimension, as recent American Thyroid Association guidelines report a positive association between serum TSH levels and increased risk of nodule malignancy and more advanced staging of thyroid cancer.¹ Moreover, previous studies estimate a 16% chance of malignancy with TSH levels below 0.06 mIU/L; a 25% chance with levels between 0.4 and 1.39 mIU/L; and a 52% chance when levels are greater than 5.00 mIU/L.³

With respect to ultrasound, specific findings on imaging can help consolidate a decision in determining which nodules mandate FNA biopsy. Microcalcifications, hypoechogenicity, irregular margins, taller-than-wide shape, invasion of normal structures, and lymphadenopathy are all independent features highly suggestive of malignancies.¹ When considering suspicious features, one should also consider Hashimoto thyroiditis in the working diagnosis, as it might masquerade as a malignant lesion. Signs of recent upper respiratory tract infections, cervical pain, elevated inflammatory markers, fever, swelling, and symptoms of hypothyroidism all allude to this benign inflammatory condition.⁴ Conversely, imaging reports of a predominantly cystic nodule, cholesterol deposits forming punctate, echogenic foci with ring-down or comet-tail artifacts, solid debris with septations causing a spongiform appearance, and slow growth are associated with benign thyroid nodules.¹ A highly cystic composition might be particularly reassuring, as reports have cited that 88% of thyroid cancers are uniformly solid or have minimal cystic changes of less than 5%, with marked cystic changes of more than 50% occurring in only 2.5% of cancers, all of which had numerous other suspicious sonographic findings.⁵ Table 1 presents a summary of these recommendations including categorization of nodules based on the degree of suspicious features and likelihood of malignancy. If cytology results of an FNA biopsy are nondiagnostic, the biopsy should be repeated with ultrasound guidance and on-site cytologic evaluation.