Thyroid Nodule Evaluation
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Direct answer
A thyroid nodule is a discrete swelling within the gland, and the clinical task is to exclude malignancy, which is present in only a small minority. Evaluation starts with a TSH and high-resolution ultrasound; a nodule with a suppressed TSH is assessed by radionuclide scan, because a hyperfunctioning "hot" nodule is rarely malignant. Fine-needle aspiration cytology, reported on the Bethesda system, is the diagnostic mainstay for sonographically suspicious nodules.
What you must remember
- Suspicious clinical features — hard fixed nodule, rapid growth, hoarseness from recurrent laryngeal nerve palsy, cervical lymphadenopathy, extremes of age, male sex and previous neck irradiation.
- Suspicious ultrasound features — microcalcifications, marked hypoechogenicity, irregular margins, taller-than-wide shape, extrathyroidal extension and abnormal nodes; risk is stratified using TI-RADS-type systems.
- FNAC is the investigation of choice for a solid nodule with normal or raised TSH; Bethesda categories run from non-diagnostic to suspicious for malignancy and guide repeat aspiration, surveillance or surgery.
- A hot (autonomous) nodule with suppressed TSH is confirmed on radioiodine or technetium scan and is very rarely cancer; options include observation, antithyroid drugs, radioiodine or surgery.
- Papillary carcinoma is the commonest thyroid malignancy — lymphatic spread, Orphan-Annie eye nuclei, nuclear grooves and psammoma bodies — with an excellent prognosis.
- Follicular carcinoma spreads haematogenously and needs histology for vascular and capsular invasion; medullary carcinoma arises from C cells, secretes calcitonin, links to MEN 2 and RET mutations; anaplastic carcinoma afflicts the elderly with dismal outcomes.
- Before any thyroid surgery, check vocal cord movement; after total thyroidectomy, monitor calcium.
Common confusion
Hot and cold nodules are perpetually confused. A cold nodule simply takes up less isotope and, while most are benign, virtually all thyroid cancers appear cold — so cold raises suspicion. A hot nodule with a suppressed TSH autonomously produces hormone and is almost never malignant, which is why scintigraphy is used only when TSH is low. Also, a nodule within a multinodular goitre carries broadly similar malignancy risk to a solitary nodule, so "dominant nodule in a goitre" still needs evaluation.
Exam-focused takeaway
Expect a sequence question — TSH and ultrasound first, FNAC for suspicious solid nodules, scintigraphy when TSH is suppressed. Histology buzzwords (Orphan-Annie nuclei, psammoma bodies, amyloid stroma with calcitonin staining) appear in slide-based questions. Hoarseness with a hard fixed nodule is the red-flag vignette pointing straight to carcinoma and surgery.
Frequently asked questions
What is the first-line evaluation of a thyroid nodule?
Serum TSH plus high-resolution ultrasound. The TSH result and ultrasound pattern then decide whether FNAC, scintigraphy or surveillance follows.
When is a radionuclide scan used?
When TSH is suppressed, to confirm a hyperfunctioning hot nodule, which is very rarely malignant. Cold nodules cannot be distinguished from benign lesions on scan alone.
What does the Bethesda system do?
It standardises FNAC reporting into diagnostic categories, each with a malignancy risk and recommended action — from repeat sampling for non-diagnostic lesions to surgery for suspicious or malignant cytology.
Which tumour marker is followed in medullary carcinoma?
Calcitonin, often with carcinoembryonic antigen. Medullary carcinoma is associated with MEN 2 syndromes and RET proto-oncogene mutations, demanding family screening.
Why is hoarseness significant with a nodule?
It suggests recurrent laryngeal nerve involvement by an infiltrating carcinoma. Cord movement should be checked before thyroidectomy in every patient.