A 25 years old female complains of recurrent rhinitis, nasal discharge and bilateral nasal blockage since one year. She has history of asthma and allergy. On examination multiple ethmoidal polyps are noted with mucosal thickening and impacted secretions in both the nasal cavities. Biopsy is taken and the material is cultured which shown the growth of many hyphae and pseudohyphae with dichotomous branching typically at 45deg. Which of the following is the most likely responsible organism?

**Core Concept**
The patient's symptoms and biopsy results suggest a fungal infection of the nasal cavity, specifically a type of fungal rhinosinusitis characterized by the presence of hyphae and pseudohyphae with dichotomous branching.

**Why the Correct Answer is Right**
The growth of hyphae and pseudohyphae with dichotomous branching at 45° is characteristic of *Aspergillus* species, which are common causes of fungal rhinosinusitis in individuals with allergies and asthma. The presence of dichotomous branching, in particular, is a hallmark of *Aspergillus* infections. This type of branching is typically seen in *Aspergillus* species, which are known to cause a range of diseases, from allergic reactions to invasive aspergillosis.

**Why Each Wrong Option is Incorrect**
* **Option A:** *Mucor* species typically cause mucormycosis, a type of fungal infection that is characterized by the growth of non-septate hyphae, not dichotomous branching.
* **Option B:** *Candida* species can cause a range of infections, but they are typically characterized by the presence of pseudohyphae and blastoconidia, not dichotomous branching.
* **Option D:** *Histoplasma* species are typically found in soil and cause histoplasmosis, a type of fungal infection that is characterized by the growth of small, budding yeast cells, not hyphae or pseudohyphae with dichotomous branching.

**Clinical Pearl / High-Yield Fact**
Dichotomous branching at 45° is a key feature of *Aspergillus* infections, and it is essential to recognize this characteristic to make a correct diagnosis. This type of branching is typically seen in *Aspergillus* species, and it can be used to differentiate them from other types of fungal infections.

**Correct Answer:** C. *Aspergillus*.

✓ Correct Answer: A. Aspergillus fumigatus