A thyroid nodule is a discrete lesion within the thyroid gland that is palpable and/or ultrasonographically distinct from surrounding thyroid parenchyma. Approximately 5% of patients have palpable thyroid nodules, but ultrasound detects nodules in up to 60% of patients. Regardless of how they are discovered (palpation or imaging) the risk of harboring malignancy is about 5% so appropriate evaluation is imperative.
History and PE
A patient may present with obstructive symptoms (e.g. difficulty swallowing or breathing, voice changes) or symptoms of hyperthyroidism. The only risk factors for cancer are radiation exposure and a positive or family history. A physical examination is helpful in order to determine the size and location of the thyroid nodule, consistency, and to observe the presence or absence of cervical lymphadenopathy.
How do we evaluate a new thyroid nodule?
If the nodule is >1 cm then a TSH measurement should be obtained. If TSH is suppressed this warrants further work-up of hyperthyroidism such as thyroid function testing and/or a thyroid uptake scan.
Ultrasound is the most useful form of imaging and should be obtained in all patients. It confirms the presence and size of a thyroid nodule while identifying additional thyroid nodules (50% of patients will have additional nodules, 15% >1 cm) and suspicious lymphadenopathy.
Thyroid Scintigraphy is reserved for the evaluation of patients with hyperthyroidism – it allows you to distinguish between Graves (diffuse uptake) and Toxic Nodules (focal uptake).
CT and MRI are rarely indicated though each may be useful under differing circumstances. CT and MRI are typically used in patients with significant substernal extension, extensive nodal disease, or suspected medullary thyroid cancer. Avoid the use of IV contrast as this delays radioactive iodine treatment if needed.
How do we decide which nodules need to be evaluated further and which need to be resected?
Evaluation: Fine Needle Aspiration (FNA)
Fine-needle aspiration is the most accurate and cost effective method for evaluating a thyroid nodule. FNA should be performed on all nodules >1 cm (up to 4) and any nodule with suspicious features. FNA is best performed under ultrasound (US) guidance.