A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 45-year-old woman comes to the physician with a lump on her throat that has steadily increased in size over the past 5 months. She does not have difficulties swallowing, dyspnea, or changes in voice. Examination shows a 3-cm, hard swelling on the left side of her neck that moves with swallowing. There is no cervical or axillary lymphadenopathy. The remainder of the examination shows no abnormalities. Thyroid functions tests are within the reference range. Ultrasound of the neck shows an irregular, hypoechogenic mass in the left lobe of the thyroid. A fine-needle aspiration biopsy is inconclusive. The surgeon and patient agree that the most appropriate next step is a diagnostic lobectomy and isthmectomy. Surgery shows a 3.5-cm gray tan thyroid tumor with invasion of surrounding blood vessels, including the veins. The specimen is sent for histopathological examination. Which of the following is most likely to be seen on microscopic examination of the mass?
-
A
Undifferentiated giant cellsIncorrect. Undifferentiated giant cells describe anaplastic thyroid carcinoma — a rapidly growing, often fatal tumor of elderly patients, not this slowly growing mass.
-
B
Capsular invasionCorrect. Follicular carcinoma is diagnosed by capsular (and/or vascular) invasion on the resected specimen, since the cytology alone cannot distinguish it from a follicular adenoma.
-
C
Infiltration of atypical lymphoid tissueIncorrect. Atypical lymphoid infiltration would suggest primary thyroid lymphoma, typically in the setting of Hashimoto thyroiditis — not described here.
-
D
Orphan Annie nucleiIncorrect. Orphan Annie eye nuclei (along with psammoma bodies and nuclear grooves) are the histologic hallmarks of papillary thyroid carcinoma, which spreads via lymphatics, not blood vessels.
-
E
Amyloid deposition within the stromaIncorrect. Stromal amyloid deposits are the histologic hallmark of medullary thyroid carcinoma (a calcitonin-secreting C-cell tumor), not follicular carcinoma; medullary cancer is also associated with MEN2 syndromes.
↑ Tap an answer to reveal the reasoning
Answer: B. A middle-aged woman with a slowly enlarging, hard thyroid nodule, normal thyroid function tests, and an ultrasound showing an irregular, hypoechoic mass — with a gross specimen showing vascular invasion (including veins) on lobectomy — has follicular thyroid carcinoma. Follicular carcinoma cannot be distinguished from a benign follicular adenoma on fine-needle aspiration alone because both consist of follicular cells; the diagnosis hinges on histologic evidence of CAPSULAR INVASION and/or VASCULAR INVASION on the surgical specimen. That is why FNA was 'inconclusive' and lobectomy was needed.
Follicular carcinoma spreads hematogenously (to lung and bone) rather than via lymphatics, distinguishing it from papillary carcinoma (lymphatic spread; classic nodal involvement; psammoma bodies; 'Orphan Annie eye' nuclei). Anaplastic thyroid carcinoma is composed of undifferentiated giant/spindle cells and tends to present in elderly patients with rapidly enlarging, fixed masses with airway compromise. Thyroid lymphoma (atypical lymphoid infiltrate) typically arises in a background of Hashimoto thyroiditis.
Treatment is total thyroidectomy followed by radioiodine ablation for residual or metastatic disease (follicular cells take up iodine), then TSH suppression with levothyroxine. The presence of vascular invasion at surgery defines minimally invasive vs. widely invasive disease and informs prognosis.
**Why each option:**
**A.** Undifferentiated giant cells describe anaplastic thyroid carcinoma — a rapidly growing, often fatal tumor of elderly patients, not this slowly growing mass.
**B.** Correct. Follicular carcinoma is diagnosed by capsular (and/or vascular) invasion on the resected specimen, since the cytology alone cannot distinguish it from a follicular adenoma.
**C.** Atypical lymphoid infiltration would suggest primary thyroid lymphoma, typically in the setting of Hashimoto thyroiditis — not described here.
**D.** Orphan Annie eye nuclei (along with psammoma bodies and nuclear grooves) are the histologic hallmarks of papillary thyroid carcinoma, which spreads via lymphatics, not blood vessels.