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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Question 1EndocrineEasy
A 62-year-old woman is referred after a painless thyroid nodule was noted on a routine neck examination. Ultrasound shows a 1.2 cm solid, isoechoic nodule that is wider than tall, with smooth margins and two coarse macrocalcifications; the radiologist reports it as American College of Radiology Thyroid Imaging Reporting and Data System (ACR TI-RADS) 4, moderately suspicious. There is no cervical lymphadenopathy. TSH is 1.8 microunits/mL (reference range 0.4 to 4.0). Which of the following is the most appropriate next step in management?
AUltrasound-guided fine-needle aspiration
BLevothyroxine suppression therapy
CFollow-up thyroid ultrasound in 12 months
DRadionuclide thyroid scan with iodine-123
EReferral for diagnostic thyroid lobectomy
Reveal answer & full explanation
Correct answer: C — Follow-up thyroid ultrasound in 12 months
AUltrasound-guided fine-needle aspiration
BLevothyroxine suppression therapy
CFollow-up thyroid ultrasound in 12 months✓
DRadionuclide thyroid scan with iodine-123
EReferral for diagnostic thyroid lobectomy
Why Follow-up thyroid ultrasound in 12 months is correct
ACR TI-RADS scores five sonographic categories and sums the points; this nodule earns 4 points (solid 2, isoechoic 1, wider than tall 0, smooth margins 0, macrocalcifications 1), which is TR4, moderately suspicious
ACR pairs each actionable level, TR3 through TR5, with a size threshold, and TR4 carries two different cutoffs: fine-needle aspiration at 1.5 cm or larger, imaging follow-up at 1.0 cm or larger. At 1.2 cm this nodule is above the surveillance threshold but below the biopsy threshold, so the correct action is watching it
ACR recommends repeat ultrasound for a TR4 nodule at 1, 2, 3, and 5 years; significant growth (20% in two dimensions with at least 2 mm, or 50% by volume) does not by itself mandate biopsy - it means the new size is re-applied to the TR level, so aspiration follows once the nodule reaches the 1.5 cm TR4 cutoff, or sooner if new suspicious features re-score it as TR5, where the cutoff drops to 1.0 cm
Nothing here overrides the size rule: there are no suspicious cervical nodes to sample and no extrathyroidal extension, so risk stratification rests on the sonographic pattern paired with size
A normal TSH places the patient on the ultrasound branch of the algorithm rather than the functional branch, so uptake imaging has no role in grading this nodule
ATA 2015 reaches the same conclusion by a different route: a solid isoechoic nodule without microcalcifications, irregular margins, or taller-than-wide shape is a low-suspicion pattern, for which FNA is reserved for nodules 1.5 cm or larger
Why the others are wrong
Ultrasound-guided fine-needle aspiration - the right modality applied at the wrong size: the TR4 aspiration cutoff is 1.5 cm and this nodule is 1.2 cm, so cytology now would sample a lesion the guideline says to watch, and a Bethesda III result would launch her into repeat aspiration, molecular testing, or surgery she never needed (the trap is biopsying on the word suspicious without pairing the category to its size cutoff - only a TR5 nodule is aspirated down to 1.0 cm)
Radionuclide thyroid scan with iodine-123 - an uptake scan belongs on the low-TSH branch of the algorithm, where it identifies an autonomously functioning hot nodule that carries negligible malignancy risk and needs no aspiration; with TSH normal at 1.8 microunits/mL there is no biochemical hyperthyroidism for a scan to localize, and uptake cannot grade malignancy risk in a euthyroid patient
Referral for diagnostic thyroid lobectomy - diagnostic surgery follows cytology, not an imaging report: diagnostic lobectomy is the pathway for a Bethesda III to IV nodule when molecular testing is unfavorable or unavailable, and this patient has no cytology at all because the nodule has not yet reached the size at which it is biopsied; surgery without cytology is reserved for structural indications such as compressive symptoms or substernal goiter, not for a 1.2 cm incidental nodule (the trap is escalating two steps at once on the word suspicious)
Levothyroxine suppression therapy - TSH suppression with levothyroxine was once used to shrink benign-appearing nodules, but it does not reliably reduce nodule size or grade cancer risk, and in a 62-year-old woman a suppressed TSH risks atrial fibrillation and bone loss; ATA recommends against it, and a TR4 nodule below its aspiration cutoff only needs ultrasound surveillance (the trap is treating a nodule the guideline says to watch)
Additional high-yield points
ACR TI-RADS thresholds worth memorizing as category/FNA/follow-up: TR1 and TR2 need neither; TR3 FNA at 2.5 cm or larger, follow-up at 1.5 cm or larger; TR4 FNA at 1.5 cm or larger, follow-up at 1.0 cm or larger; TR5 FNA at 1.0 cm or larger, follow-up at 0.5 cm or larger
Point assignment: composition (cystic or spongiform 0, mixed cystic and solid 1, solid 2), echogenicity (anechoic 0, hyperechoic or isoechoic 1, hypoechoic 2, very hypoechoic 3), shape (taller-than-wide 3), margin (lobulated or irregular 2, extrathyroidal extension 3), echogenic foci (macrocalcifications 1, peripheral rim 2, punctate echogenic foci 3); 0 points TR1, 2 TR2, 3 TR3, 4 to 6 TR4, 7 or more TR5
Echogenic-foci points are assigned per feature type, not per calcification, so a nodule with several macrocalcifications still earns 1 point for that category
Size thresholds are overridden by suspicious cervical lymph nodes or extrathyroidal extension: aspirate the abnormal node, and biopsy a nodule showing extrathyroidal extension even when it sits below its size cutoff; extrathyroidal extension also takes the maximum 3 points in the ACR margin category, so it raises the TR level as well. Neither finding sends a patient to the operating room ahead of cytology
A high-risk history (childhood head or neck irradiation, familial papillary or medullary thyroid cancer, MEN2) raises pretest probability and argues for sampling a nodule sitting just under its cutoff, although it does not formally change the ACR size thresholds
Levothyroxine suppression is not nodule management: it does not reliably shrink nodules, and driving TSH down in an iodine-sufficient population buys atrial fibrillation and bone loss, which is why ATA recommends against it
Cytology is graded by the Bethesda system: I non-diagnostic (repeat FNA), II benign (surveillance), III atypia of undetermined significance (repeat FNA, molecular testing such as Afirma or ThyroSeq, or diagnostic lobectomy), IV follicular neoplasm (molecular testing or diagnostic lobectomy - repeat FNA does not help), V to VI suspicious or malignant (therapeutic surgery - lobectomy for low-risk unifocal intrathyroidal disease 4 cm or less, otherwise total thyroidectomy)
Question 2EndocrineMedium
A 30-year-old female has a 3cm thyroid mass, hoarseness, ipsilateral cervical lymphadenopathy, a family history of multiple endocrine neoplasia type 2A (MEN2A), and a calcitonin of 4,800 pg/mL. Genetic testing confirms a RET proto-oncogene mutation. Which of the following is the most likely diagnosis?
AHürthle cell thyroid carcinoma
BFollicular thyroid carcinoma
CAnaplastic thyroid carcinoma
DMedullary thyroid carcinoma
EPapillary thyroid carcinoma
Reveal answer & full explanation
Correct answer: D — Medullary thyroid carcinoma
AHürthle cell thyroid carcinoma
BFollicular thyroid carcinoma
CAnaplastic thyroid carcinoma
DMedullary thyroid carcinoma✓
EPapillary thyroid carcinoma
Why Medullary thyroid carcinoma is correct
RET proto-oncogene mutation confirms a hereditary syndrome; markedly elevated calcitonin (4,800 pg/mL) is the tumor marker for medullary thyroid carcinoma (MTC)
RET proto-oncogene mutations drive MTC in both sporadic and hereditary forms
Why the others are wrong
Hürthle cell thyroid carcinoma — an oncocytic carcinoma derived from follicular epithelium; it does not arise from parafollicular C cells, does not raise calcitonin, and carries no germline RET point mutation or MEN2A association
Follicular thyroid carcinoma — derived from follicular cells, not parafollicular C-cells; does not produce calcitonin; not linked to RET/MEN2A
Papillary thyroid carcinoma — most common thyroid cancer; can have RET/PTC rearrangements but not RET point mutations; does not secrete calcitonin
Anaplastic thyroid carcinoma — hoarseness with a neck mass and nodal spread suggests an aggressive invasive cancer, but anaplastic carcinoma is a dedifferentiated tumor of follicular epithelium that typically presents as a rapidly enlarging mass in older adults; it does not secrete calcitonin and has no germline RET or MEN2A association
Additional high-yield points
Critical pre-operative step: rule out pheochromocytoma BEFORE thyroid surgery — undiagnosed pheo during surgery can cause hypertensive crisis
Order plasma or urine metanephrines first; if pheo present: adrenalectomy first, THEN thyroidectomy
Surgical treatment: total thyroidectomy plus central neck dissection for MTC
Prophylactic thyroidectomy offered to RET mutation carriers based on codon-specific risk stratification
Calcitonin serves as the tumor marker for MTC diagnosis and recurrence monitoring
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Female sex (nodules and thyroid cancer are more common in women), but a given nodule is more likely malignant in a man; age <20 or >70 raises 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 (solid hypoechoic plus irregular margins, microcalcifications, taller-than-wide shape, or extrathyroidal extension) ≥1 cm; intermediate (solid hypoechoic, smooth margins) ≥1 cm; low suspicion (solid iso/hyperechoic, or partially cystic with an eccentric solid area) ≥1.5 cm; very low suspicion (spongiform) ≥2 cm (or observe); purely cystic no FNA
ACR TI-RADS size cutoffs (FNA / follow-up US): TR1-TR2 neither; TR3 FNA ≥2.5 cm, follow ≥1.5 cm; TR4 FNA ≥1.5 cm, follow ≥1.0 cm; TR5 FNA ≥1.0 cm, follow ≥0.5 cm
Bethesda System for FNA reports (2023): I nondiagnostic, II benign, III atypia of undetermined significance (AUS), 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)
Surveillance after thyroidectomy: serum thyroglobulin with anti-Tg antibodies and neck ultrasound (first at 6-12 months, then interval by risk and response to therapy); diagnostic whole-body iodine scan only for selected higher-risk patients, not routinely for low-risk excellent responders
Diagnostic algorithm
Bethesda Category
Description
Risk of Malignancy
Management
I
Nondiagnostic
13% (5-20%)
Repeat FNA with ultrasound guidance
II
Benign
4% (2-7%)
Clinical and ultrasound follow-up (US in 12-24 months)
III
Atypia of undetermined significance (AUS)
22% (13-30%)
Repeat FNA, molecular testing, diagnostic lobectomy, or surveillance
IV
Follicular neoplasm
30% (23-34%)
Molecular testing or diagnostic lobectomy (histology needed)
V
Suspicious for malignancy
74% (67-83%)
Lobectomy or near-total thyroidectomy (molecular testing may guide extent of surgery)
VI
Malignant
97% (97-100%)
Lobectomy for low-risk ≤2 cm; lobectomy or total thyroidectomy for low-risk 2-4 cm; total thyroidectomy ± neck dissection for >4 cm, gross extrathyroidal extension, or nodal/distant metastasis
Bethesda System for Reporting Thyroid Cytopathology (2023) — average risk of malignancy (range) and management.
Treatment
Papillary / follicular (differentiated)
Lobectomy for low-risk unifocal tumors ≤2 cm without gross extrathyroidal extension, nodal, or distant metastasis (cT1N0M0); lobectomy or total thyroidectomy for low-risk 2-4 cm tumors (ATA 2025)
Total thyroidectomy for tumors >4 cm, gross extrathyroidal extension, clinically involved lymph nodes (cN1), distant metastasis, or bilateral disease; also reasonable with prior head/neck radiation
Therapeutic central or lateral neck dissection for clinically involved lymph nodes; prophylactic central neck dissection is not routine for small, noninvasive, clinically node-negative (cT1-T2 cN0) papillary cancer
Radioactive iodine (I-131) after total thyroidectomy: routine for high-risk disease or distant metastases, considered selectively for intermediate risk, not routine for low risk. I-131 is concentrated in follicular cells by the sodium-iodide symporter and destroys them by local beta emission
Levothyroxine with a response-based TSH goal (ATA 2025): within the normal reference range for excellent or indeterminate response; below the reference range only for biochemical or structural incomplete response. Long-term TSH suppression is not suggested for low- or intermediate-risk patients without evidence of disease
Medullary
Total thyroidectomy with central neck dissection — RAI ineffective (no iodine uptake by C cells)
Screen for and treat pheochromocytoma BEFORE surgery (alpha then beta blockade)
Genetic testing for RET mutations — prophylactic thyroidectomy for MEN2B by age 1, MEN2A by age 5
Tyrosine kinase inhibitors (vandetanib, cabozantinib, selpercatinib) for advanced/RET-mutant disease; the US indication of pralsetinib for MTC was withdrawn in 2023
Surgical: recurrent laryngeal nerve injury (hoarseness, airway), hypoparathyroidism (transient or permanent), bleeding/hematoma (an expanding neck hematoma, usually within 24 h, with stridor or airway compromise needs immediate bedside opening of the skin and deep strap-muscle sutures to decompress, then return to the OR for hemostasis; do not delay for imaging or transfer)
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)
ATA DTC 2025 — 2025 American Thyroid Association Management Guidelines for Adult Patients with Differentiated Thyroid Cancer (Ringel MD, Sosa JA, et al., Thyroid 2025;35(8):841-985)
ACR TI-RADS 2017 — ACR Thyroid Imaging, Reporting and Data System (TI-RADS): White Paper of the ACR TI-RADS Committee (Tessler FN et al., J Am Coll Radiol 2017;14(5):587-595)
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