A 54 year old farmer presents to his physician with chronic cough. Chest x-ray demonstrates a mass lesion with hilar lymphadenopathy. Biopsy of the mass demonstrates multiple, tiny yeast forms within macrophages. Which of the following is the most likely diagnosis?
**Core Concept**
The clinical presentation of a chronic cough, mass lesion, and hilar lymphadenopathy, combined with the histological finding of yeast forms within macrophages, is suggestive of a fungal infection affecting the lungs.
**Why the Correct Answer is Right**
The presence of multiple, tiny yeast forms within macrophages is characteristic of **Histoplasmosis**, a fungal infection caused by inhaling the spores of **Histoplasma capsulatum**. The yeast forms of the fungus are typically found within macrophages, which is a hallmark of histopathological diagnosis. The clinical presentation, including chronic cough and hilar lymphadenopathy, is also consistent with histoplasmosis, which is an opportunistic infection that affects immunocompromised individuals.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Coccidioidomycosis, caused by Coccidioides spp., typically presents with a different set of symptoms, including fever, night sweats, and weight loss, and is more commonly found in the southwestern United States.
**Option B:** This option is incorrect because Blastomycosis, caused by Blastomyces dermatitidis, typically presents with skin lesions and lung disease, but the histological findings are different from Histoplasmosis, with the presence of large, budding yeast forms.
**Option C:** This option is incorrect because Paracoccidioidomycosis, caused by Paracoccidioides brasiliensis, is a fungal infection that affects the lungs and skin, but it is more commonly found in Latin America and the histological findings are different from Histoplasmosis.
**Option D:** This option is incorrect because Aspergillosis, caused by Aspergillus spp., typically presents with allergic reactions, invasive disease, or chronic pulmonary aspergillosis, but the histological findings are different from Histoplasmosis, with the presence of septate hyphae.
**Clinical Pearl / High-Yield Fact**
Histoplasmosis is a common opportunistic infection in immunocompromised individuals, and the diagnosis is often made based on histopathological findings of yeast forms within macrophages. A high index of suspicion is required, especially in patients with chronic cough and hilar lymphadenopathy.
**Correct Answer:** C.