If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 1 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.
This month’s stumper
A 36-year-old woman comes to the physician because of a "bulge in her neck." She recently immigrated to the United States from Ukraine and says that her family moved due to radiation exposure in her town. The mass has increased in size over the past six months. Physical examination shows asymmetrical enlargement of the thyroid gland. An ill-defined 5 cm firm nontender mass is present in the left lobe. The gland moves upon swallowing. Needle aspiration of the thyroid shows neoplastic cells with atypical features and nuclear grooves. Hemi-thyroidectomy and regional cervical lymph node dissection are performed, and the specimen is sent for pathologic analysis.
Which of the following histologic features would most likely also be present?
A. Elongated azurophilic needles within myeloblasts.
B. Epithelioid macrophages within granulomas.
C. Laminated, concentric, calcific spherules.
D. Spindle cell and giant cell differentiation.
E. Uniform cells forming small follicles containing colloid.
The correct answer is C.
Kaplan Medical explains why
This patient presents with papillary thyroid carcinoma, which is the most common and has the best prognosis of all thyroid cancers. Radiation exposure is a major risk factor, and the disease tends to spread along lymphatic channels.
Major pathologic features of this cancer include:
- Ground-glass, clear nuclei ("Orphan Annie").
- Nuclear grooves.
- Papillary fronds with fibrovascular cores.
- Psammoma bodies.
Psammoma bodies are laminated, concentric, calcific spherules, reflecting necrotic, degenerated papillary structures, seen most frequently in papillary carcinoma of the thyroid, serous papillary cystadenocarcinoma of the ovary, meningioma, and malignant mesothelioma.
Why the other answers are wrong
Choice A: Elongated azurophilic needles within myeloblasts describes Auer rods, which are cytoplasmic inclusions found in myelogenous leukemia (AML). Radiation exposure can cause mutagenesis of hematopoietic cells within the bone marrow and development of AML. However, AML rarely occurs in the thyroid gland.
Choice B: Epithelioid macrophages within granulomas reflects a granulomatous process, such as granulomatous thyroiditis or sarcoidosis. Subacute granulomatous thyroiditis (de Quervain thyroiditis) affects women more than men, most commonly presents between ages 40-50 with thyroid pain, a history of prior viral infection, and would cause diffuse inflammation and enlargement of the thyroid gland, rather than a distinct mass. Sarcoidosis can have noncaseating granulomas occur in any part of the body and is not associated with prior radiation exposure.
Choice D: Spindle cell and giant cell differentiation describes anaplastic thyroid carcinoma. These aggressive tumors with a poor prognosis, which can arise de novo or from papillary or follicular carcinomas. Patients are usually older with a mean age of 65 years. Histologically, the tumor can exhibit large, pleomorphic cells with multinucleated osteoclast-like cells or spindle cells with sarcomatous appearance.
Choice E: Uniform cells forming small follicles containing colloid describes follicular carcinoma. This tumor occurs more commonly occur in women, age between 40-60 years, and found more commonly in areas with iodine deficiency; not with radiation exposure.
Tips to remember
- Papillary thyroid cancer is characterized by papillary cell clusters, distinct nuclear clearing and grooves, and psammoma bodies.
- Psammoma bodies are laminated concentric calcific spherules.
- Psammoma bodies can also be found in serous papillary cystadenocarcinoma of the ovary, meningioma, and malignant mesothelioma.
For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.
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