A 54-year-old woman is evaluated in the ambulatory clinic for a palpable mass in her anter… — USMLE Step 3

A 54-year-old woman is evaluated in the ambulatory clinic for a palpable mass in her anterior neck, which she noticed two weeks ago while applying lotion. She denies dysphagia, hoarseness, palpitations, weight changes, or heat intolerance. Her medical history is unremarkable, and she takes no medications. Vital signs are within normal limits. Physical examination reveals a firm, non-tender, mobile $2.0 \text{ cm}$ nodule in the left thyroid lobe. No cervical lymphadenopathy is present. Laboratory studies show a serum thyroid-stimulating hormone (TSH) level of $2.4 \text{ mIU/L}$ (normal: $0.4 - 4.0 \text{ mIU/L}$ ). A dedicated thyroid ultrasound demonstrates a $2.1 \text{ cm}$ solid, markedly hypoechoic nodule in the left lower pole. The nodule has irregular, microlobulated margins and contains internal punctate echogenic foci. Based on these imaging results, which of the following is the most appropriate next step in management?

Ultrasound-guided fine-needle aspiration biopsyAnswer
B
Radionuclide thyroid scintigraphy
C
Repeat thyroid ultrasound in 12 months
D
Computed tomography scan of the neck with intravenous contrast
E
Measurement of serum thyroglobulin level

Answer

Ultrasound-guided fine-needle aspiration biopsy

The correct action is to perform an ultrasound-guided fine-needle aspiration biopsy. The initial workup of a thyroid nodule involves checking a TSH level and obtaining a dedicated thyroid ultrasound. Because the TSH is normal, the nodule is non-functioning. The ultrasound reveals multiple high-risk sonographic features: solid composition, marked hypoechogenicity, irregular margins, and punctate echogenic foci (representing microcalcifications). Any nodule

\geq 1 \text{ cm}

with these highly suspicious imaging characteristics requires direct tissue sampling via fine-needle aspiration to evaluate for malignancy, particularly papillary thyroid carcinoma.

Step-by-Step Solution

Evaluate the patient's clinical presentation and initial laboratory results.

The patient has a palpable thyroid nodule with a normal TSH level.

A normal or elevated TSH level indicates that the nodule is non-functioning, eliminating the need for a radionuclide scan.

Interpret the specific findings of the thyroid ultrasound.

The nodule is solid, hypoechoic, greater than

1 \text{ cm}

in size, has irregular margins, and contains microcalcifications (punctate echogenic foci).

These specific sonographic features are highly suspicious for a malignant process, particularly papillary thyroid carcinoma.

Determine the next appropriate management step based on the interpreted imaging.

Tissue diagnosis via fine-needle aspiration (FNA) is required.

Current guidelines mandate FNA for nodules

\geq 1 \text{ cm}

that exhibit high-risk sonographic characteristics to definitively rule in or rule out malignancy.

Key Concept

Thyroid Nodule Imaging Risk Stratification

Estimated Time:1m 15s

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