Histology USMLE Step 1 Practice Question
A 52-year-old man with a 30-year history of occupational asbestos exposure presents to clinic with progressive dyspnea and pleuritic chest pain over the past 6 months. Vital signs are notable for tachypnea (RR 22/min) and mild hypoxemia (SpO2 89% on room air). Chest X-ray demonstrates bilateral lower lobe pleural thickening and pleural plaques. A transbronchial lung biopsy is performed. Light microscopy reveals numerous golden-brown, dumbbell-shaped structures with a distinctive refractile appearance contained within alveolar macrophages. These structures stain positive with Prussian blue stain. Which of the following best describes the composition and formation of these observed structures?
Answer choices
- ASilicate particles from occupational exposure that have undergone fibrosis and calcification within macrophage granulomas
- BHemosiderin aggregates derived from chronic pulmonary hemorrhage that accumulate in tissue macrophages
- CAsbestos fibers coated with a ferruginous layer of iron and protein (ferruginous bodies)Correct answer
- DTalc granules surrounded by a foreign body giant cell reaction with iron oxide deposition
- ECoal dust particles with surrounding anthracotic pigmentation and macrophage infiltration
- FCrystalline silicon dioxide particles modified by macrophage lysosomal enzyme activity
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.