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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Initial thyroid nodule test: TSH. If TSH is low, radionuclide scan to identify a hot nodule
- Hot nodules are rarely malignant and usually do not need FNA
- Normal/high TSH: ultrasound risk stratification and FNA based on size + suspicious features
- Most common thyroid cancer: papillary carcinoma, associated with radiation exposure and lymphatic spread
- Medullary thyroid cancer arises from C cells, produces calcitonin, and is associated with MEN2/RET
Overview
Thyroid nodules are common and usually benign, but evaluation aims to identify clinically significant cancer while avoiding over-biopsy. The initial step is TSH measurement. A suppressed TSH suggests an autonomously functioning nodule, which should be evaluated with radionuclide scan because hyperfunctioning nodules are rarely malignant. If TSH is normal or elevated, high-resolution thyroid ultrasound determines sonographic risk and whether fine-needle aspiration is needed. Thyroid cancers include papillary, follicular, medullary, and anaplastic carcinoma.
Epidemiology
Thyroid nodules are palpable in about 5% of adults but much more common on ultrasound. Malignancy risk is higher with childhood head/neck radiation, family history of thyroid cancer, rapid growth, hoarseness, firm fixed nodule, cervical lymphadenopathy, male sex, age <20 or >60, and suspicious ultrasound findings. Papillary thyroid carcinoma is the most common thyroid malignancy and generally has an excellent prognosis. Anaplastic thyroid carcinoma is rare but aggressive and often presents with a rapidly enlarging neck mass.
Clinical Features
Symptoms
Often asymptomatic; nodule found incidentally or by palpation
Neck pressure, dysphagia, dyspnea, or choking from large goiter
Hoarseness suggesting recurrent laryngeal nerve involvement
Rapidly enlarging painful mass suggesting hemorrhage, thyroiditis, lymphoma, or anaplastic cancer
Symptoms of hyperthyroidism if autonomously functioning nodule
Signs
Palpable thyroid nodule or multinodular goiter
Firm, fixed, irregular nodule
Cervical lymphadenopathy
Vocal cord paralysis or hoarse voice
MEN2 clues: mucosal neuromas, marfanoid habitus, pheochromocytoma, hyperparathyroidism
Investigations
First-line
TSHFirst test in thyroid nodule evaluation. Low TSH prompts radionuclide scan; normal/high TSH prompts ultrasound-based risk assessment
Thyroid ultrasoundAssess size, composition, echogenicity, margins, calcifications, shape, and cervical lymph nodes
Fine-needle aspiration cytologyIndicated based on ultrasound pattern and size threshold; Bethesda system guides malignancy risk and next steps
Second-line
Radionuclide thyroid scanIf TSH is suppressed. Hot nodule = autonomous function and low malignancy risk; cold nodule may need FNA based on ultrasound
Calcitonin and RET testingIf medullary thyroid cancer suspected or known MEN2/family history
Serum calcium and PTHIf MEN2A or hyperparathyroidism features are present
Specialist
Molecular testingCan refine risk in indeterminate FNA cytology but does not replace clinical and ultrasound assessment
LaryngoscopyIf hoarseness, prior neck surgery, invasive cancer concern, or before thyroid surgery in selected patients
Management
American Thyroid Association Guidelines for Thyroid Nodules and Differentiated Thyroid Cancer1
Risk stratify the nodule
- Measure TSH first
- If TSH is low, perform radionuclide scan; manage hot nodules as hyperthyroidism rather than cancer workup in most cases
- If TSH is normal/high, perform ultrasound and decide FNA by sonographic risk and size
2
FNA and cytology-driven management
- Benign cytology: surveillance ultrasound rather than immediate surgery unless compressive or growing
- Malignant or suspicious cytology: surgical referral
- Indeterminate cytology: repeat FNA, molecular testing, lobectomy, or surveillance depending on risk
3
Differentiated thyroid cancer
- Papillary: thyroidectomy or lobectomy depending on size/risk; consider radioactive iodine for higher-risk disease
- Follicular: hematogenous spread; diagnosis requires capsular or vascular invasion, often after lobectomy specimen
- Long-term follow-up with thyroglobulin and neck ultrasound after thyroidectomy for differentiated cancers
4
Medullary and anaplastic cancer
- Medullary: total thyroidectomy with lymph node assessment; evaluate for RET mutation and pheochromocytoma before surgery
- Anaplastic: urgent multidisciplinary care, airway assessment, palliative/systemic therapy; prognosis is poor
Complications
- Airway compromise: Large goiter, hemorrhage, or anaplastic cancer can compress the trachea
- Recurrent laryngeal nerve involvement: Hoarseness indicates invasive disease until proven otherwise
- Metastatic disease: Papillary spreads to lymph nodes; follicular spreads hematogenously to bone/lung
- Post-thyroidectomy hypocalcemia: From hypoparathyroidism after surgery
- Overdiagnosis: Small incidental papillary microcarcinomas may never become clinically significant
USMLE Step 2 CK Exam Tips
- 1Thyroid nodule next best step: TSH first
- 2Low TSH + nodule = radionuclide scan; hot nodule is rarely cancer and usually does not need FNA
- 3Normal/high TSH + suspicious ultrasound = FNA based on size threshold
- 4Papillary thyroid carcinoma: Orphan Annie eye nuclei, psammoma bodies, radiation exposure, lymphatic spread
- 5Follicular carcinoma spreads hematogenously and requires capsular/vascular invasion for diagnosis
- 6Medullary thyroid carcinoma: calcitonin, amyloid stroma, MEN2/RET; rule out pheochromocytoma before surgery
- 7Anaplastic carcinoma: elderly patient with rapidly enlarging hard neck mass and compressive symptoms
- 8Hoarseness or fixed nodule is a red flag for malignancy
practicetest your knowledge on thyroid nodules & thyroid cancerApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — endocrine and beyond.
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