Rhinosporidiosis — DTM&H MCQ

Correct answer: A — Rhinosporidium seeberi

The correct answer is A, Rhinosporidium seeberi. This organism is a mesomycetozoean (previously classified as a fungus) that causes slowly progressive, friable polypoid masses of the nasal mucosa and conjunctiva. Histopathology shows thick-walled sporangia measuring 50 to 1000 micrometres, packed with hundreds of endospores 5 to 10 micrometres in diameter, a finding considered pathognomonic and diagnostic without the need for culture, since the organism cannot be grown on artificial media. The endemic Middle Eastern and South Asian distribution and the nasal mass in this stem fit the classic clinical picture of rhinosporidiosis, and management is surgical excision with wide local excision and electrocoagulation of the base to reduce recurrence. Why the other options are wrong: B. Mucor species: causes angioinvasive mucormycosis with broad, non-septate hyphae and tissue infarction/necrosis, typically in diabetic or immunocompromised patients, not sporangia with endospores. C. Aspergillus fumigatus: forms septate hyphae with acute-angle branching on histology; it causes invasive or allergic sinus disease, not endosporulating sporangia. E. Cryptococcus neoformans: appears as narrow-based budding yeasts with a mucicarmine-positive capsule on histology, not large endospore-filled sporangia, and typically causes meningitis or pulmonary disease. D. Histoplasma capsulatum: presents as small intracellular yeasts (2 to 4 micrometres) within macrophages, seen in disseminated or pulmonary histoplasmosis, not large sporangia with hundreds of endospores. Key point: Large sporangia containing hundreds of endospores on histology of a nasal or conjunctival polyp is pathognomonic for Rhinosporidium seeberi, distinguishing it from true fungal causes of nasal masses.

Reference: PathologyOutlines.com, Rhinosporidiosis (nasal), Nose and sinuses pathology topic, 2024, https://www.pathologyoutlines.com/topic/nasalrhinosporidiosis.html