Endocrine

Thyroid nodule: ATA evaluation algorithm

Clinical Overview and When to Suspect Thyroid Nodule

— Patient or clinician palpates a neck mass

— Incidental finding on carotid US, CT chest, neck MRI, or FDG-PET (focal FDG uptake → ~35% malignancy risk)

— New compressive symptoms: dysphagia, globus, positional dyspnea, hoarseness

— Symptoms of hyper- or hypothyroidism with nodular gland

— Childhood head/neck irradiation or total body radiation

— Family history of medullary thyroid cancer, MEN2, FAP, Cowden, Carney complex

— Rapid growth, fixed nodule, vocal cord paralysis, ipsilateral cervical adenopathy

— Age <20 or >70 with new nodule

Definition: Discrete lesion within the thyroid gland radiologically distinct from surrounding parenchyma. Palpable nodules occur in ~5% of adults; ultrasound detects nodules in 20–70% — prevalence rises with age, female sex, iodine deficiency, and prior head/neck radiation.

Clinical significance: The central question is malignancy risk (~7–15% of nodules are cancer) and whether the nodule is autonomously functioning (toxic). The ATA 2015 guideline provides the dominant US framework for evaluation.

When to suspect / evaluate:

High-risk historical features pushing toward biopsy:

Step 3 management: First test in any newly discovered thyroid nodule is serum TSH plus dedicated thyroid/neck ultrasound — not FNA, not CT, not thyroid scan up front. The TSH directs the next branch point; the US sonographic pattern determines FNA threshold.

Board pearl: A low TSH (suggesting autonomy) is the one scenario where you obtain a radioiodine uptake scan before FNA — a hyperfunctioning ("hot") nodule is almost never malignant, so FNA is unnecessary and you pivot to treating hyperthyroidism. A normal or high TSH means you proceed directly to risk-stratify by ultrasound.

Ambulatory framing: Most evaluation occurs in primary care or endocrinology clinic; inpatient discovery (incidental on trauma CT) should be deferred to outpatient workup unless airway compromise exists.

Presentation Patterns and Key History

— Found on imaging done for unrelated reason (carotid Doppler, cervical spine MRI, PET for oncology staging)

— Patient denies neck symptoms; gland nontender

— Step 3 pathway: confirm with dedicated thyroid US, check TSH

— Often noted while shaving, applying makeup, or by a partner

— Ask about growth rate over weeks–months (rapid growth raises concern for anaplastic carcinoma, lymphoma, or hemorrhage into cyst)

— Dysphagia to solids, choking sensation, positional dyspnea (worse supine), nocturnal cough

— Hoarseness → suspect recurrent laryngeal nerve invasion (malignancy until proven otherwise)

— Heat intolerance, palpitations, weight loss, tremor, insomnia, atrial fibrillation (especially in elderly with TMNG — "apathetic hyperthyroidism")

— Radiation exposure: childhood mantle/scalp XRT, Chernobyl/Fukushima exposure

— Family history: MTC, MEN2A/2B, papillary thyroid cancer in ≥2 first-degree relatives, FAP/Gardner, Cowden (PTEN), Carney complex

— Iodine status: dietary, amiodarone, recent IV contrast, kelp/seaweed supplements

— Medications: lithium (goiter), TKIs, immune checkpoint inhibitors (thyroiditis)

— Pregnancy status (affects RAI use and surgical timing)

Asymptomatic incidental nodule (most common):

Patient-noticed neck lump:

Compressive symptoms (suggest size >3–4 cm or substernal extension):

Hyperthyroid features → think toxic adenoma or toxic multinodular goiter:

Hypothyroid features → Hashimoto thyroiditis with dominant nodule or rarely large infiltrative malignancy

Key history checklist (memorize for boards):

Board pearl: A patient presenting with flushing, secretory diarrhea, and a thyroid nodule screams medullary thyroid carcinoma — check calcitonin and CEA, and screen for pheochromocytoma (plasma metanephrines) before any neck surgery to avoid intraoperative hypertensive crisis from undiagnosed MEN2.

Step 3 management: Document growth trajectory by comparing with any prior imaging — stability over ≥2 years markedly lowers malignancy concern and may justify continued surveillance instead of FNA.

Physical Exam Findings (and Functional Assessment)

— Patient seated, neck slightly extended; observe with swallow of water (thyroid moves with deglutition; lymph nodes and thyroglossal cysts behave differently — thyroglossal cyst moves with tongue protrusion)

— Look for surgical scars, dilated neck veins, Pemberton sign (facial plethora on arm elevation → substernal goiter with thoracic inlet obstruction)

— Estimate size, number, consistency (firm/hard vs rubbery), mobility, tenderness

— Sliding under sternum on swallow suggests retrosternal extension

— Hard, fixed, irregular nodule

— Ipsilateral cervical lymphadenopathy (especially levels III, IV, VI)

— Vocal cord paralysis / hoarseness on history with confirmation by laryngoscopy

— Rapid growth in days–weeks (anaplastic carcinoma in elderly)

— Hyperthyroid signs: tachycardia, fine tremor, lid lag, warm moist skin, hyperreflexia, proximal myopathy, atrial fibrillation

— Hypothyroid signs: bradycardia, delayed reflex relaxation, dry skin, periorbital edema

— Graves-specific signs (orbitopathy, pretibial myxedema, thyroid bruit) — usually diffuse goiter, but can coexist with nodule (Marine-Lenhart syndrome)

— Cystic lateral neck node in an adult is metastatic papillary thyroid cancer until proven otherwise — do not call it a branchial cleft cyst without ruling out PTC by FNA with thyroglobulin washout.

Inspection:

Palpation (posterior approach standard):

High-risk exam features (raise malignancy suspicion):

Functional/systemic assessment:

Key distinction: A tender, painful thyroid points to subacute (de Quervain) thyroiditis or hemorrhage into a cyst — not malignancy. Subacute thyroiditis follows viral URI, has elevated ESR/CRP, and a low RAIU, distinguishing it from Graves.

Lymph node exam pearl:

Board pearl: Examine the entire neck, supraclavicular fossae, and assess voice quality. Document any preoperative voice change before any planned thyroidectomy — medicolegally critical given recurrent laryngeal nerve risk.

Step 3 management: Physical exam alone is insensitive (~50%) for nodules; never defer ultrasound based on a "normal" neck exam if imaging found one.

Diagnostic Workup — Initial Labs and Imaging

— Serum TSH

— Dedicated thyroid and cervical lymph node ultrasound (with sonographic pattern characterization)

— TSH low (suppressed): obtain radioiodine (I-123) uptake and scan

– Focal uptake = autonomous "hot" nodule → very low malignancy risk → no FNA; treat hyperthyroidism (RAI ablation, antithyroid drugs, or surgery)

– Cold nodule on scan with low TSH → proceed with FNA per sonographic criteria

— TSH normal or high: do not order a thyroid scan; proceed straight to ultrasound-based risk stratification for FNA decision

— High suspicion (>70–90% malignancy risk): solid hypoechoic nodule with ≥1 of: irregular margins, microcalcifications, taller-than-wide shape, rim calcification with extrusive soft tissue, extrathyroidal extension, or suspicious lymph nodes

— Intermediate suspicion (10–20%): hypoechoic solid nodule with smooth margins, no other high-risk features

— Low suspicion (5–10%): isoechoic or hyperechoic solid nodule, or partially cystic with eccentric solid area

— Very low suspicion (<3%): spongiform or partially cystic without suspicious features

— Benign (<1%): purely cystic

— High suspicion: FNA at ≥1 cm

— Intermediate: ≥1 cm

— Low: ≥1.5 cm

— Very low: ≥2 cm or surveillance

— Pure cyst: no FNA (drain only if symptomatic)

First two tests in every newly identified nodule (memorize):

Interpreting TSH — the branch point:

Ultrasound features — ATA sonographic risk categories:

FNA size thresholds (ATA 2015):

Step 3 management: Do not order CT with iodinated contrast as initial workup — iodine load delays any future RAI scan/therapy by 1–3 months. Reserve CT/MRI for substernal goiter or suspected invasion.

Board pearl: Calcitonin is not routinely recommended by ATA but is reasonable when medullary thyroid cancer is suspected (family history, diarrhea, MEN2 features) — markedly elevated calcitonin (>100 pg/mL) strongly suggests MTC.

Diagnostic Workup — FNA Cytology and Molecular Testing

— Bethesda I — Nondiagnostic/unsatisfactory (~5–10% risk): repeat US-guided FNA in 4–12 weeks; consider core biopsy or surgery if persistently nondiagnostic in suspicious nodule

— Bethesda II — Benign (<3%): clinical/US surveillance — repeat US in 12–24 months

— Bethesda III — AUS/FLUS (~10–30%): repeat FNA or molecular testing; some go to diagnostic lobectomy

— Bethesda IV — Follicular neoplasm / suspicious for FN (~25–40%): molecular testing or diagnostic hemithyroidectomy (cytology cannot distinguish follicular adenoma from carcinoma — needs capsular/vascular invasion seen on histology)

— Bethesda V — Suspicious for malignancy (~50–75%): surgery (lobectomy or total thyroidectomy)

— Bethesda VI — Malignant (~97–99%): surgery — extent based on size, extension, nodes

— Best applied to indeterminate cytology (Bethesda III/IV) to refine risk and avoid unnecessary diagnostic surgery

— A "benign" molecular result drops malignancy risk to ~3–5% → surveillance

— Mutation hits (BRAF V600E, RET/PTC, TERT promoter, RAS) raise risk → surgery

Fine-needle aspiration biopsy (FNA): Gold-standard tissue diagnosis; ultrasound-guided is preferred. Reported using the Bethesda System for Reporting Thyroid Cytopathology (six categories) — memorize malignancy risks and next step:

Molecular testing (Afirma GSC, ThyroSeq, ThyGeNEXT/ThyraMIR):

Key distinction: Papillary thyroid cancer is diagnosed on cytology (nuclear features: grooves, pseudoinclusions, Orphan Annie nuclei). Follicular cancer cannot be diagnosed by FNA — requires surgical histology to demonstrate capsular/vascular invasion. This is why Bethesda IV often goes to lobectomy.

Thyroglobulin washout of suspicious lateral neck node FNA: elevated Tg in needle washout confirms metastatic differentiated thyroid cancer even when cytology is equivocal.

Board pearl: Cystic nodules with solid mural component → aspirate the solid component under US guidance; pure cyst fluid is often nondiagnostic.

Step 3 management: Don't repeat FNA on a clearly benign nodule that is stable on US — over-biopsy adds cost and anxiety without benefit.

Risk Stratification and Management Logic

— Is the nodule functional (autonomous)? → TSH ± scan

— Is the nodule malignant or suspicious? → US pattern + FNA Bethesda

— Is the nodule compressive or cosmetic? → size/symptoms

— Apply pattern category → apply size threshold → decide FNA vs surveillance

— Multiple nodules: risk-stratify each nodule by its own US pattern (do not assume the largest is the cancer)

— High-suspicion US, no FNA yet (size <1 cm): repeat US in 6–12 months

— Low/intermediate suspicion: repeat US in 12–24 months

— Very-low suspicion / spongiform: repeat US ≥24 months or consider no further imaging

— Benign FNA: repeat US in 12–24 months; if stable, extend interval; if growth (≥20% in 2 dimensions and ≥2 mm, or ≥50% volume), repeat FNA

— Endocrinology: indeterminate cytology, functional nodules, complex multinodular goiter, pediatric/pregnant patients

— Surgery: Bethesda V/VI, Bethesda IV with high-risk molecular profile, compressive symptoms, substernal extension, suspected anaplastic or medullary cancer

— History of head/neck irradiation

— Family history of thyroid cancer

— Positive PET-avid nodule

— Elevated calcitonin

— Suspicious cervical lymph nodes (FNA the node, not just the thyroid nodule)

Three core determinations after initial workup:

ATA sonographic-pattern + size algorithm (essential):

Surveillance schedule for nodules not meeting FNA criteria or with benign FNA:

When to refer to endocrinology vs surgery:

Special situations triggering lower thresholds:

Step 3 management: A nodule <1 cm typically does not undergo FNA regardless of US appearance unless there are red flags (suspicious nodes, ETE, history of XRT, MTC family history). This avoids overdiagnosis of clinically indolent micropapillary cancers.

Board pearl: In the CCS-style vignette, after "thyroid nodule found": order TSH and thyroid ultrasound simultaneously on day 1. Avoid scattershot ordering of T3, T4, antibodies, CT, or scan up front — the simulator rewards the algorithm.

Pharmacotherapy — Drug Management of Thyroid Nodules

— Levothyroxine suppression therapy is NOT recommended by ATA for benign nodules in iodine-sufficient areas — modest size reduction does not justify long-term subclinical hyperthyroidism (bone loss, AF risk)

— Methimazole is preferred antithyroid drug (5–40 mg/day; titrate to TSH/free T4)

– Avoid in first trimester of pregnancy (use PTU in T1; transition to methimazole T2/T3)

— Beta-blocker (propranolol or atenolol) for symptomatic control of adrenergic symptoms while awaiting definitive therapy

— Definitive therapy is typically radioactive iodine (I-131) ablation or surgery; ATDs alone rarely produce durable remission in autonomous nodules (unlike Graves)

— Standard levothyroxine replacement, dose ~1.6 µg/kg/day in healthy adults; lower (12.5–25 µg) start in elderly or cardiac disease; titrate to TSH

— Levothyroxine TSH suppression tailored to recurrence risk:

– High-risk: TSH <0.1 mU/L

– Intermediate: 0.1–0.5

– Low-risk with excellent response: 0.5–2.0 (avoid prolonged suppression)

— Monitor thyroglobulin and anti-Tg antibodies as tumor markers

— Levothyroxine replacement only (no TSH suppression — MTC is C-cell derived, TSH-independent)

— Advanced/progressive disease: vandetanib or cabozantinib (RET-targeted TKIs); selpercatinib/pralsetinib for RET-mutant disease

Benign nontoxic nodule: No medical therapy is routinely indicated.

Toxic (hyperfunctioning) adenoma or toxic multinodular goiter:

Hypothyroidism from Hashimoto with nodule:

Differentiated thyroid cancer post-thyroidectomy (long-term):

Medullary thyroid carcinoma:

Anaplastic thyroid cancer: BRAF V600E mutant → dabrafenib + trametinib; aggressive multimodality care

Board pearl: Iodinated contrast or amiodarone can precipitate thyrotoxicosis (Jod-Basedow) in autonomous nodules — screen TSH before elective contrast in patients with multinodular goiter.

Step 3 management: Before starting methimazole, document baseline CBC and LFTs; warn patient about agranulocytosis (fever, sore throat → stop drug, check CBC) and hepatotoxicity.

Procedures — Surgery, RAI, and Ablation

— Indications: Bethesda IV with suspicious molecular profile, Bethesda V, unilateral DTC ≤4 cm without ETE or nodal disease, indeterminate nodule needing histologic diagnosis

— Advantages: preserves contralateral lobe function (~70% don't need LT4), avoids parathyroid risk on opposite side, single recurrent laryngeal nerve at risk

— Indications: DTC >4 cm, bilateral disease, gross ETE, clinically apparent nodal metastases, history of head/neck radiation, known familial thyroid cancer syndrome, MTC (always total + central neck dissection), anaplastic when resectable

— Risks (counsel and document): recurrent laryngeal nerve injury (~1–2% permanent, hoarseness/aspiration), hypoparathyroidism (~1–3% permanent hypocalcemia), hematoma (airway emergency in first 24 h), superior laryngeal nerve injury (voice pitch changes)

— Remnant ablation / adjuvant therapy after total thyroidectomy in intermediate/high-risk DTC

— Therapy for toxic adenoma/TMNG

— Pre-treatment: low-iodine diet 1–2 weeks; rhTSH (Thyrogen) stimulation or LT4 withdrawal to raise TSH >30

— Contraindications: pregnancy, breastfeeding (delay 6–12 weeks after weaning); avoid pregnancy for 6 months post-RAI; men avoid conception for ~4 months

Thyroid lobectomy (hemithyroidectomy):

Total (or near-total) thyroidectomy:

Radioactive iodine (I-131):

Ethanol ablation: Recurrent benign thyroid cysts (after 2+ reaccumulations); also for small-volume neck nodal recurrences of PTC

Thermal ablation (RFA, microwave, laser): Increasingly used for benign symptomatic solid nodules; not first-line for malignancy in US practice

CCS pearl: Pre-op for thyroidectomy — confirm vocal cord function by laryngoscopy if any voice changes; check calcium, PTH, vitamin D; ensure euthyroid state (especially in Graves/toxic goiter) to avoid thyroid storm — preoperative methimazole + beta-blocker ± iodine (SSKI/Lugol) 10 days pre-op for Graves.

Board pearl: Post-thyroidectomy expanding neck hematoma → open the wound at the bedside to relieve airway compression before transport to OR.

Special Populations — Elderly and Renal/Hepatic Impairment

— Higher prevalence of multinodular goiter and incidental nodules; absolute malignancy risk per nodule is lower, but cancers (when present) tend to be more aggressive (higher rate of poorly differentiated and anaplastic carcinoma; PTC after age 55 upstages in AJCC 8)

— Apathetic hyperthyroidism: presents as weight loss, atrial fibrillation, depression, CHF rather than classic adrenergic symptoms — check TSH in every elderly patient with new AF

— Surgical risk increased: cardiopulmonary comorbidity, longer recovery, higher hypocalcemia risk

— Consider active surveillance for low-risk papillary microcarcinoma (≤1 cm, no ETE, no nodes) in older adults — favorable risk–benefit

— Iodine clearance reduced → caution with iodinated contrast (delays RAI by months) and SSKI/Lugol

— Higher prevalence of subclinical hypothyroidism; check TSH but treat conservatively

— RAI dosimetry: I-131 is renally cleared; reduced GFR may increase whole-body retention — endocrinology/nuclear medicine adjusts activity

— Calcitonin can be falsely elevated in advanced CKD — interpret cautiously when screening for MTC

— Methimazole preferred over PTU in most settings; PTU has black-box hepatotoxicity warning. Avoid PTU in pre-existing liver disease except first-trimester pregnancy or thyroid storm

— Monitor LFTs at baseline and during first 6 months of therapy

Elderly patients:

LT4 dosing in elderly: Start 12.5–25 µg/day, especially with CAD; titrate slowly every 6–8 weeks. Over-replacement risks AF and osteoporotic fracture.

Chronic kidney disease:

Hepatic impairment:

Frailty consideration: For frail elders with limited life expectancy and a low-risk nodule, observation is often more appropriate than biopsy — discuss goals of care.

Step 3 management: In an 80-year-old with new-onset AF and a multinodular goiter, check TSH before assuming "lone AF" — autonomously functioning nodules are a reversible cause and change rate-control vs ablation strategy.

Board pearl: Rapidly enlarging neck mass in an elderly patient with hoarseness → think anaplastic thyroid carcinoma (or thyroid lymphoma in Hashimoto background) — urgent core biopsy, secure airway, oncology referral.

Special Populations — Pregnancy and Pediatrics

— Thyroid nodules discovered in pregnancy are evaluated with TSH and US; radionuclide scans and RAI are contraindicated

— If TSH is suppressed in T1, consider physiologic suppression from hCG (β-hCG cross-reactivity); recheck after T1

— FNA is safe in any trimester; defer in T3 if surgery would be delayed anyway

— Bethesda VI / V (DTC) found in pregnancy:

– If stable on serial US and no aggressive features → surgery can be deferred until postpartum

– If significant growth (≥50% volume or ≥20% in 2 dimensions) before 24–26 weeks, or nodal disease → surgery in second trimester (safest window)

— Avoid TSH suppression therapy goals tighter than ~0.1–1.0 in pregnant DTC patients to protect fetus

— T1: PTU (lower teratogenic risk than methimazole — methimazole linked to aplasia cutis, choanal/esophageal atresia)

— T2/T3: switch to methimazole (PTU hepatotoxicity risk)

— Higher malignancy rate (~22–26%) than adults — every pediatric nodule is biopsied if ≥1 cm or with suspicious features regardless of size

— Lower threshold for total thyroidectomy in pediatric DTC due to higher nodal/pulmonary metastasis rates

— Screen for MEN2: prophylactic thyroidectomy for RET mutation carriers — timing depends on mutation codon (MEN2B: in first year of life; MEN2A: by age 5)

Pregnancy:

Antithyroid drugs in pregnancy:

Postpartum thyroiditis: Painless, often with palpable gland — not a "nodule" per se but on differential of new neck symptoms within 12 months postpartum; biphasic (thyrotoxic then hypothyroid).

Pediatric thyroid nodules:

Board pearl: All children with a thyroid nodule deserve an US-guided FNA; size cutoffs used in adults do not apply.

Step 3 management: A pregnant patient with newly diagnosed PTC and stable disease on US through pregnancy → counsel that postpartum surgery does not worsen prognosis for well-differentiated cancer — avoids fetal risk of T1/T3 surgery and anesthesia.

Complications and Adverse Outcomes

— Local invasion: trachea, esophagus, recurrent laryngeal nerve → hoarseness, hemoptysis, dysphagia

— Cervical nodal metastases (PTC commonly), distant mets to lung/bone (FTC hematogenous), aggressive course in MTC and anaplastic

— Tracheal deviation/compression, superior vena cava syndrome (Pemberton sign), dysphagia, hoarseness, sleep-disordered breathing

— Subclinical or overt hyperthyroidism from autonomous nodule → atrial fibrillation, osteoporosis, bone fractures, heart failure

— Thyroid storm triggered by surgery, infection, iodine load in inadequately treated toxic nodule

— Recurrent laryngeal nerve injury: transient ~5%, permanent 1–2% — hoarseness, weak voice, aspiration; bilateral injury → airway emergency requiring tracheostomy

— Hypoparathyroidism: transient hypocalcemia common (perioral numbness, Chvostek, Trousseau, tetany, QT prolongation); permanent 1–3%

— Bleeding/hematoma → airway compromise within first 24 h

— Superior laryngeal nerve injury → loss of high pitch

— Seroma, infection, hypertrophic scar

— Sialadenitis, xerostomia, dysgeusia (hydration, sour candy, lemon drops)

— Nasolacrimal duct stenosis

— Secondary malignancies (small absolute risk, increases with cumulative dose)

— Gonadal effects: temporary; recommend contraception 6 months

— Iatrogenic subclinical hyperthyroidism → AF, accelerated bone loss

Untreated / undiagnosed malignancy:

Compressive complications of large/substernal goiter:

Functional complications:

Surgical complications (counsel and document for informed consent):

RAI complications:

Levothyroxine over-replacement:

CCS pearl: Post-op patient with circumoral tingling, anxiety, carpopedal spasm within 24 h of total thyroidectomy → check ionized calcium and PTH immediately; start IV calcium gluconate for symptomatic or severe hypocalcemia, plus oral calcium carbonate and calcitriol. Avoid waiting for next-day labs.

Board pearl: Always check TSH-suppressed bone density every 1–2 years in patients on long-term TSH-suppressive LT4, particularly postmenopausal women.

When to Escalate Care — ICU, Consult, Inpatient Triage

— Stridor, positional dyspnea, hemoptysis, rapidly enlarging mass → suspect anaplastic carcinoma, hemorrhage into cyst, or compressive goiter — secure airway (awake fiberoptic if difficult), urgent ENT consult

— Post-thyroidectomy expanding neck hematoma → open wound at bedside, then OR

— Hyperpyrexia, AMS, tachyarrhythmia, CHF; Burch-Wartofsky score ≥45

— ICU: propranolol + PTU (preferred over methimazole in storm for peripheral T4→T3 block) + iodine (≥1 h after PTU) + hydrocortisone + cooling + treat trigger

— Tetany, seizures, QT prolongation → IV calcium gluconate (10 mL of 10% over 10 min, then drip), telemetry, magnesium repletion

— Inpatient workup: urgent core biopsy, BRAF testing, multidisciplinary tumor board, airway assessment, possible tracheostomy planning

— Endocrinology: indeterminate cytology, autonomous nodules, complex MNG, pediatric/pregnant nodules, MTC family history

— Endocrine surgery / ENT: Bethesda V/VI, compressive goiter, substernal extension, recurrence

— Genetics: suspected MEN2, FAP, Cowden, Carney complex

— Nuclear medicine: RAI scan/therapy planning

— Radiation oncology / medical oncology: anaplastic, advanced MTC, radioiodine-refractory DTC (lenvatinib, sorafenib)

— Most thyroid nodule workups are outpatient

— Admit for: airway compromise, thyroid storm, severe hypocalcemia, surgical complications, aggressive cancers needing rapid multimodal therapy

Airway emergencies (admit, urgent ENT/surgery):

Thyroid storm (toxic nodule precipitant — surgery, infection, contrast load):

Severe symptomatic hypocalcemia post-op:

Suspected anaplastic thyroid cancer:

Specialist consult triggers:

Inpatient vs outpatient triage:

Step 3 management: A patient with toxic MNG and contrast-induced thyrotoxicosis ("Jod-Basedow") presenting with AF with RVR — inpatient management with beta-blocker, methimazole, and consideration of cholestyramine to reduce enterohepatic recirculation; definitive RAI delayed until iodine load clears.

CCS pearl: Order continuous telemetry and serial Ca/PTH for the first 24 h after total thyroidectomy.

Key Differentials — Other Thyroid Lesions

— Colloid nodule / hyperplastic nodule: most common; spongiform on US; very low-suspicion ATA pattern; surveillance only

— Follicular adenoma: indeterminate cytology (Bethesda III/IV); cannot exclude carcinoma without surgical histology

— Hashimoto thyroiditis with pseudonodule: lymphocytic infiltrate creating discrete-appearing area; heterogeneous gland on US, positive anti-TPO; lymphoma risk slightly elevated

— Subacute (de Quervain) thyroiditis: painful tender gland post-viral, elevated ESR, low RAIU, transient thyrotoxicosis then recovery; not truly a nodule but mimics

— Simple/hemorrhagic cyst: purely cystic on US; aspirate only if symptomatic

— Papillary thyroid carcinoma (PTC): 80% of thyroid cancers; lymphatic spread; excellent prognosis; BRAF V600E driver

— Follicular thyroid carcinoma (FTC): hematogenous spread to lung/bone; needs histology (capsular/vascular invasion); RAS mutations common

— Hürthle (oncocytic) cell carcinoma: variant; less RAI-avid, more aggressive than typical FTC

— Medullary thyroid carcinoma (MTC): C-cell origin, calcitonin/CEA markers; sporadic 75%, familial 25% (MEN2A/2B, FMTC); screen RET, plasma metanephrines pre-op

— Anaplastic thyroid carcinoma: elderly, rapidly enlarging fixed mass, dismal prognosis, BRAF V600E in ~25% → targeted therapy

— Primary thyroid lymphoma: Hashimoto background, rapid growth, B-cell origin → chemo/XRT (not surgery)

— Metastasis to thyroid: renal cell carcinoma classic; also breast, melanoma, lung

Benign thyroid nodule differentials (same category):

Malignant thyroid lesions:

Key distinction: PTC is diagnosed by cytology (nuclear features); FTC requires surgical histology — this dictates whether Bethesda IV gets a diagnostic lobectomy.

Board pearl: A patient with longstanding Hashimoto thyroiditis presenting with a rapidly enlarging neck mass → think thyroid lymphoma, not just a new adenoma — core biopsy, not just FNA.

Key Differentials — Non-Thyroid Neck Masses

— Thyroglossal duct cyst: midline, moves with tongue protrusion (not just swallowing), young patients; treat with Sistrunk procedure

— Dermoid/epidermoid cyst: subcutaneous, midline, doughy

— Laryngocele: air-filled, enlarges with Valsalva

— Reactive lymphadenopathy: infection-associated, tender, mobile, resolves

— Branchial cleft cyst: lateral, anterior to SCM, young patients — but in adults, cystic lateral neck mass = metastatic PTC until proven otherwise

— Carotid body tumor (paraganglioma): pulsatile, splays carotid bifurcation ("lyre sign" on imaging); plasma metanephrines

— Lymphoma: rubbery, multiple, B-symptoms

— Metastatic squamous cell carcinoma: smoker, alcohol, ipsilateral oral/pharyngeal primary; HPV-related oropharyngeal cancer

— Tuberculous lymphadenitis (scrofula): chronic, matted, draining sinus

— Parathyroid adenoma rarely palpable; consider with hypercalcemia and elevated PTH; sestamibi scan to localize

— Parathyroid carcinoma — very rare, hard fixed mass with severe hypercalcemia

— Carotid aneurysm: pulsatile, expansile

— Salivary gland tumor (submandibular, parotid tail): different location but can confuse exam

— Lipoma, sebaceous cyst: superficial, mobile

— Distinguish substernal goiter from anterior mediastinal mass (thymoma, teratoma, lymphoma, retrosternal thyroid)

Anterior/midline neck masses (mimic thyroid):

Lateral neck masses:

Parathyroid lesions:

Vascular and other:

Mediastinal / substernal extension:

Key distinction: A midline mass that elevates with tongue protrusion is a thyroglossal duct cyst; one that elevates only with swallowing is thyroid origin. Test this on every neck mass exam.

Board pearl: A pulsatile, expansile mass that you can compress between two fingers and feel a thrill or hear a bruit → vascular (carotid aneurysm, carotid body tumor) — do not FNA; image first with duplex or CTA.

Step 3 management: When in doubt about the origin of a neck mass, dedicated neck ultrasound is the cheapest, fastest first study — even before considering CT.

Long-Term Plan, Discharge, and Secondary Prevention

— No medication; lifestyle education; reassurance

— Repeat US: 12–24 months initially; if stable across 2 exams, extend to every 2–3 years; consider discontinuation after sustained stability

— Re-FNA if significant growth (≥20% in 2 dimensions and ≥2 mm, or ≥50% volume), new suspicious sonographic features, or new clinical concern

— Many patients remain euthyroid; if TSH rises >2 mU/L and they're symptomatic or risk warrants, start low-dose LT4

— Surveillance: neck US every 6–12 months for first 2 years, then annually; trend Tg (rises slowly if remnant lobe; not as reliable as after total thyroidectomy)

— LT4 dosed for TSH target based on risk stratification and response to therapy

— Thyroglobulin (Tg) + anti-Tg antibodies every 6–12 months

— Neck US at 6–12 months, then annually

— Stimulated Tg (rhTSH) or whole-body iodine scan in selected patients

— Serial calcitonin and CEA trends — doubling time predicts prognosis

— Neck US; CT chest/abdomen/MRI liver if calcitonin >150 pg/mL

— Avoid unnecessary iodine loads (kelp supplements, excessive contrast)

— Sun protection unrelated, but smoking cessation improves Graves orbitopathy if comorbid

— In MEN2 kindreds: genetic counseling, cascade RET testing in first-degree relatives, screen for pheochromocytoma and primary hyperparathyroidism

— Levothyroxine (start ~1.6 µg/kg or per pathology)

— Calcium carbonate (1–3 g/day elemental) + calcitriol (0.25–0.5 µg BID) if PTH low or symptomatic; taper as PTH recovers

— Pain control; avoid sedating opioids in elderly

Benign nodule after FNA — long-term plan:

After lobectomy for DTC (low-risk):

After total thyroidectomy for DTC:

MTC surveillance:

Secondary prevention and counseling:

Discharge medication checklist after thyroidectomy:

Board pearl: Persistent post-op hypocalcemia >6 months = permanent hypoparathyroidism — requires lifelong calcium + calcitriol, monitor 24-h urinary calcium to avoid nephrocalcinosis.

Step 3 management: Counsel female DTC patients of reproductive age to avoid pregnancy for 6 months after RAI and confirm euthyroid state preconception.

Follow-Up, Monitoring, and Counseling

— Initial repeat US 12–24 months after benign FNA

— If stable in size and appearance × 2 exams, extend to 2–3 years

— Annual clinical exam in primary care; ask about new symptoms (compression, voice change)

— Repeat US in 6–12 months; consider re-FNA or molecular testing

— Excellent response: undetectable Tg, negative US — annual TSH/Tg, can liberalize TSH target

— Indeterminate: stable low-level Tg or nonspecific US — every 6–12 months

— Biochemical incomplete: rising Tg without structural disease — image (US, CT, PET) and consider therapy

— Structural incomplete: visible disease — surgery, RAI, TKI, or XRT

— TSH every 6–8 weeks during LT4 titration; every 6–12 months once stable

— Tg + anti-Tg Ab every 6–12 months post-thyroidectomy

— Calcitonin/CEA for MTC

— Bone density in long-term TSH-suppressed patients, particularly postmenopausal women

— ECG / heart rate awareness in elderly on LT4

— Most thyroid nodules are benign and indolent

— FNA is the safest, most accurate test — discuss accuracy, repeat-rate, and rare nondiagnostic results

— For DTC: emphasize excellent prognosis of typical PTC (>98% 10-year survival in low-risk)

— For RAI recipients: pregnancy timing, hydration, sialagogue use, isolation precautions per state regulations

— Voice therapy if post-op dysphonia; SLP referral

— Swallowing evaluation if aspiration

Follow-up cadence — benign nodule:

Follow-up — indeterminate cytology not surgically resected:

Follow-up — DTC post-treatment risk stratification (Dynamic Response to Therapy):

Monitoring parameters:

Counseling pillars:

Rehab considerations:

CCS pearl: On the simulator, after thyroidectomy for DTC, advance the clock, recheck TSH at 6 weeks to titrate LT4 and neck US at 6–12 months — the simulator rewards interval follow-up, not redundant daily checks.

Board pearl: A rising Tg with negative neck US should prompt diagnostic whole-body iodine scan or FDG-PET (the latter especially when Tg-doubling time is short or RAI-refractory disease is suspected).

Ethical, Legal, and Patient Safety Considerations

— Must explicitly disclose risks of recurrent laryngeal nerve injury (voice change, aspiration, possible tracheostomy with bilateral injury) and permanent hypoparathyroidism

— Document pre-op voice assessment; in selected patients (prior neck surgery, posterior extension, fixed nodule) obtain pre-op laryngoscopy to document baseline cord function — a missed pre-existing paralysis can be a major medicolegal issue if discovered post-op

— Alternative therapies and observation must be discussed (e.g., active surveillance for papillary microcarcinoma)

— Many incidentally detected sub-centimeter nodules carry trivial clinical risk; discuss harms of further testing (anxiety, biopsy complications, surgical morbidity, lifelong LT4)

— Use shared decision-making and document patient preferences

— Counsel on isolation: limit close contact with children and pregnant women, sleep alone, separate utensils, hydrate, void frequently — per NRC and state guidelines

— Pregnancy contraindicated; delay conception 6 months (women) / ~4 months (men)

— Breastfeeding must be stopped permanently for that lactation cycle before RAI

— RET testing in MEN2 families: discuss implications for the patient and at-risk relatives; offer pre-test counseling; respect autonomy of unaffected minors with sensitivity to timing (prophylactic thyroidectomy timing is medically driven)

— Patient discharged after thyroidectomy without clear LT4 dose, follow-up TSH date, or calcium plan → high readmission risk

— Use structured discharge summary with medication reconciliation, follow-up appointments, parameters to watch (perioral tingling, neck swelling, fever)

— Wrong-side thyroid surgery (rare but reported) → disclose openly, root-cause analysis, mandatory event reporting per institutional/state requirements

Informed consent for thyroidectomy (high-yield Step 3 scenario):

Incidentalomas — overdiagnosis and shared decision-making:

Radiation safety after RAI:

Genetic testing ethics:

Transition of care risks (Step 3 favorite):

Mandatory reporting and disclosure of error:

Step 3 management: When a hoarse patient is referred for thyroidectomy, document the voice complaint and obtain laryngoscopy first — failing to do so before surgery exposes you to a medical-legal claim that "the surgery caused the hoarseness."

Board pearl: Always perform a time-out in the OR confirming correct patient, side, and procedure — Joint Commission Universal Protocol.

High-Yield Associations and Rapid-Fire Facts

— MEN2A: MTC + pheochromocytoma + primary hyperparathyroidism (RET)

— MEN2B: MTC + pheochromocytoma + mucosal neuromas + marfanoid habitus (RET M918T)

— Familial MTC: MTC only

— FAP/Gardner: cribriform-morular variant of PTC

— Cowden syndrome (PTEN): follicular thyroid cancer, breast, endometrial cancers

— Carney complex: PTC/FTC with cardiac myxomas, lentigines

— DICER1 syndrome: pediatric MNG, pleuropulmonary blastoma

— BRAF V600E → classical PTC, anaplastic — targetable (dabrafenib + trametinib in ATC)

— RAS → follicular pattern (FTC, FVPTC)

— RET/PTC rearrangements → radiation-induced PTC, pediatric PTC

— RET germline point mutations → MEN2, FMTC

— TERT promoter → aggressive behavior, worse prognosis

— PAX8-PPARγ → FTC

— Microcalcifications = psammoma bodies → suspicious for PTC

— Taller-than-wide on transverse imaging = suspicious

— Spongiform (>50% small cystic spaces) = benign pattern

— Cervical lymph node: cystic change, hyperechoic foci, peripheral vascularity = metastatic

— Thyroglobulin (Tg): DTC marker post-thyroidectomy; useless with intact gland; anti-Tg antibodies interfere

— Calcitonin & CEA: MTC markers; calcitonin doubling time prognostic

— Palpable nodule malignancy risk ~5–15%

— PET-avid focal nodule malignancy risk ~35%

— PTC 10-year survival low-risk >98%

— Methimazole agranulocytosis ~0.3%

— Lithium: goiter, hypothyroidism

— Amiodarone: type 1 (iodine-induced thyrotoxicosis in nodular gland), type 2 (destructive thyroiditis)

— Immune checkpoint inhibitors: thyroiditis (often biphasic)

— TKIs (sunitinib): hypothyroidism

Genetic and syndromic associations:

Mutational drivers (high-yield):

Imaging pearls:

Tumor markers:

Numbers worth memorizing:

Drug-induced thyroid disease:

Board pearl: When you see diarrhea + flushing + thyroid mass → MTC; check plasma metanephrines before any neck surgery to exclude concurrent pheochromocytoma in MEN2.

Key distinction: Hot nodule = autonomous, almost never cancer; Cold nodule = ~10–15% malignancy risk.

Board Question Stem Patterns

— Stem: "55-year-old woman has a 1.5-cm thyroid nodule found on carotid Doppler."

— Best next step: serum TSH + dedicated thyroid US (not FNA, not CT)

— Stem: "Nodule + TSH 0.05; weight loss, palpitations."

— Best next step: I-123 uptake and scan — if hot, treat hyperthyroidism (no FNA)

— Stem: "Hypoechoic nodule, taller-than-wide, microcalcifications, 1.2 cm, TSH 1.8."

— Best next step: US-guided FNA

— Stem: "FNA shows follicular neoplasm."

— Best next step: molecular testing or diagnostic lobectomy — cannot distinguish adenoma from carcinoma by cytology alone

— Stem: "Father had MTC at age 35; patient has 8-mm thyroid nodule."

— Best next step: RET germline testing + calcitonin + plasma metanephrines; consider prophylactic total thyroidectomy if RET-positive

— Stem: "20-week gestation; 2-cm nodule, TSH normal."

— Best next step: US-guided FNA (safe in pregnancy); avoid radionuclide scans

— Stem: "Perioral tingling 12 h post-op."

— Best next step: ionized calcium and PTH; treat with IV calcium gluconate if symptomatic; start oral calcium + calcitriol

— Best next step: core needle biopsy to evaluate for primary thyroid lymphoma

— Best next step: TSH; if suppressed → uptake scan → treat toxic MNG (RAI or surgery)

— Best next step: neck US + FNA with thyroglobulin washout — concern for metastatic PTC, not branchial cleft cyst

Pattern 1 — Incidental nodule on imaging:

Pattern 2 — Suppressed TSH:

Pattern 3 — Normal TSH with high-suspicion sonography:

Pattern 4 — Bethesda IV cytology:

Pattern 5 — Family history of MTC:

Pattern 6 — Pregnant patient with new nodule:

Pattern 7 — Post-thyroidectomy hypocalcemia:

Pattern 8 — Rapidly enlarging neck mass in Hashimoto patient:

Pattern 9 — Elderly with new AF and multinodular goiter:

Pattern 10 — Cystic lateral neck mass in 45-year-old:

Step 3 management: When the stem gives you a nodule and asks "best next step," default to TSH + neck US. Any answer that orders FNA, CT, or thyroid scan before these two is wrong.

Board pearl: Watch the TSH value — it almost always reveals which branch of the ATA algorithm the question is testing.

One-Line Recap

— TSH + US first, always — do not order CT, FNA, or thyroid scan up front

— Low TSH → I-123 scan; hot nodule = treat hyperthyroidism, skip FNA; cold nodule with low TSH → biopsy per US pattern

— ATA size thresholds for FNA: high suspicion ≥1 cm, intermediate ≥1 cm, low ≥1.5 cm, very-low ≥2 cm or observe, pure cyst no FNA

— Bethesda cheat sheet: I repeat FNA; II surveillance; III repeat/molecular; IV molecular or lobectomy; V/VI surgery

— Follicular cancer cannot be diagnosed on FNA — needs histologic capsular/vascular invasion

— Pregnancy: FNA OK, radionuclide scans/RAI contraindicated; PTU in T1, methimazole in T2/T3

— MTC red flags: flushing + diarrhea + family history → calcitonin/CEA, RET testing, screen pheo before surgery

— Post-thyroidectomy watch for hematoma (airway), hypocalcemia (PTH), and RLN injury (voice)

— TSH suppression target after DTC depends on recurrence risk and dynamic response — avoid over-suppression in low-risk to protect bone and heart

One-liner: Every newly identified thyroid nodule starts with TSH + dedicated thyroid ultrasound; a suppressed TSH triggers a radioiodine scan (hot = no FNA), while a normal/high TSH directs FNA based on ATA sonographic pattern and size thresholds, with Bethesda cytology and selective molecular testing determining surgery versus surveillance.

Rapid recap bullets:

Board pearl: When the question asks for the first step in a thyroid nodule vignette, the answer is virtually always TSH and thyroid ultrasound — the rest of the algorithm flows from there.

CCS pearl: Advance the clock — recheck TSH 6 weeks after LT4 changes; neck US at 6–12 months after thyroidectomy; lifelong calcium monitoring if permanent hypoparathyroidism.