Common finding; majority benign. Risk-stratify by ultrasound and FNA, then treat by histology.
Also known as: thyroid nodule, thyroid cancer, papillary thyroid cancer, follicular thyroid cancer, medullary thyroid cancer, anaplastic thyroid cancer, Bethesda system
Overview
A thyroid nodule is a discrete lesion within the thyroid gland radiologically distinct from surrounding parenchyma. Thyroid cancer encompasses papillary (~85%), follicular (~10%), medullary (~3%), and anaplastic (~1%) carcinomas, plus lymphoma.
Epidemiology
Palpable nodules in ~5% of women and 1% of men; ultrasound detects nodules in ~50% of adults >60. Only ~5-10% of nodules are malignant. Thyroid cancer incidence rising (largely papillary, partly detection bias). Female-to-male ratio 3:1 except medullary (equal) and anaplastic (slight female predominance).
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Female sex, age extremes (<20 or >70 raise concern for any given nodule)
Hashimoto thyroiditis (thyroid lymphoma)
Pathophysiology
Nodules arise from clonal proliferation of follicular cells (benign or malignant), focal hyperplasia, or cyst formation. Papillary cancer typically harbors BRAF V600E or RET/PTC rearrangements; follicular cancer harbors RAS or PAX8/PPARγ; medullary cancer (C-cell derived) harbors RET mutations and produces calcitonin; anaplastic cancer arises from dedifferentiation with TP53 mutations.
Clinical presentation
Symptoms
Most asymptomatic; found incidentally on exam or imaging
Medullary thyroid carcinoma — C-cell origin; elevated calcitonin and CEA; sporadic or familial (MEN2A, MEN2B, FMTC); screen for pheochromocytoma BEFORE surgery
Anaplastic thyroid carcinoma — Elderly patient with rapidly enlarging neck mass, fixed to surrounding structures, compressive symptoms; dismal prognosis
Thyroid lymphoma — Rapidly growing mass in long-standing Hashimoto thyroiditis; treat with chemoradiation, not surgery
Hyperfunctioning (toxic) nodule — Suppressed TSH; hot on RAIU scan; very rarely malignant — skip FNA
Diagnostic workup
Diagnostic criteria
FNA is the gold standard. Surgical histology required for follicular neoplasms (Bethesda IV) — capsular or vascular invasion defines malignancy.
Labs
TSH first — if suppressed, perform RAIU scan (hot nodules rarely malignant, skip FNA)
If TSH normal/elevated, proceed to ultrasound
Calcitonin and CEA if medullary cancer suspected or family history of MEN2
Thyroglobulin (post-thyroidectomy tumor marker for differentiated cancer)
Plasma metanephrines BEFORE any thyroid surgery in MEN2 to exclude pheochromocytoma
Imaging
Ultrasound with TI-RADS or ATA risk stratification — assesses size, composition (cystic vs solid), echogenicity, margins, shape (taller-than-wide), calcifications (microcalcifications worrisome)
FNA criteria (ATA 2015): high suspicion ≥1 cm, intermediate ≥1 cm, low suspicion ≥1.5 cm, very low suspicion ≥2 cm (or observe), benign no FNA
Bethesda System for FNA reports: I non-diagnostic, II benign, III AUS/FLUS, IV follicular neoplasm, V suspicious for malignancy, VI malignant
CT/MRI for substernal extension or compressive symptoms (avoid iodinated contrast if possible — delays RAI therapy)
Whole-body iodine scan and thyroglobulin for surveillance after thyroidectomy
Diagnostic algorithm
Bethesda Category
Description
Risk of Malignancy
Management
I
Non-diagnostic / unsatisfactory
5-10%
Repeat FNA
II
Benign
0-3%
Clinical follow-up, US in 12-24 months
III
AUS / FLUS
10-30%
Repeat FNA, molecular testing, or lobectomy
IV
Follicular neoplasm / suspicious for follicular neoplasm
25-40%
Lobectomy (histology needed)
V
Suspicious for malignancy
50-75%
Lobectomy or near-total thyroidectomy
VI
Malignant
97-99%
Total thyroidectomy ± neck dissection ± RAI
Bethesda System for Reporting Thyroid Cytopathology — malignancy risk and management.
Lifelong levothyroxine dependence after total thyroidectomy
Recurrence — monitored with thyroglobulin + neck ultrasound (differentiated cancers) or calcitonin (medullary)
PANCE pearls
Suppressed TSH → RAIU scan first (skip FNA if hot).
Microcalcifications, taller-than-wide shape, hypoechogenicity, irregular margins, and extrathyroidal extension are the most worrisome US features for papillary cancer.
Follicular neoplasm on FNA (Bethesda IV) cannot differentiate adenoma from carcinoma — requires lobectomy for definitive histology.
Always screen for pheochromocytoma BEFORE thyroidectomy in patients with medullary cancer or MEN2.
Post-thyroidectomy thyroglobulin should be undetectable in patients without residual disease (assuming negative anti-thyroglobulin antibody).
A rapidly enlarging thyroid mass in long-standing Hashimoto → think thyroid lymphoma.
References
ATA 2015 — American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer (Haugen et al., Thyroid 2016)
ATA Medullary 2015 — Revised American Thyroid Association Guidelines for the Management of Medullary Thyroid Carcinoma (Wells et al., Thyroid 2015)
ATA Anaplastic 2021 — 2021 American Thyroid Association Guidelines for Management of Patients with Anaplastic Thyroid Cancer (Bible et al., Thyroid 2021)
Bethesda System 2023 — The 2023 Bethesda System for Reporting Thyroid Cytopathology (Ali et al., Thyroid 2023)
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