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 45 degree. Which of the following is the most likely responsible organism?

**Core Concept**
The patient's symptoms and biopsy results are consistent with a fungal infection of the nasal cavity, specifically involving the ethmoidal sinuses. The presence of hyphae and pseudohyphae with dichotomous branching at a 45-degree angle is characteristic of certain fungal species.

**Why the Correct Answer is Right**
The patient's symptoms of recurrent rhinitis, nasal discharge, and bilateral nasal blockage, along with a history of asthma and allergy, suggest an allergic fungal rhinosinusitis (AFRS). The biopsy findings of hyphae and pseudohyphae with dichotomous branching at a 45-degree angle are typical of Aspergillus species, which are commonly implicated in AFRS. The presence of impacted secretions and mucosal thickening in the nasal cavities further supports this diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** While Aspergillus species are a common cause of fungal sinusitis, other species such as Mucor and Rhizopus may also be involved in invasive fungal sinusitis, particularly in immunocompromised patients. However, the biopsy findings in this case are more characteristic of Aspergillus.
**Option B:** Alternaria species are a common cause of allergic fungal rhinosinusitis, but they typically do not exhibit dichotomous branching at a 45-degree angle, which is a characteristic feature of Aspergillus.
**Option C:** Candida species are more commonly associated with mucocutaneous and systemic infections rather than fungal sinusitis.
**Option D:** Histoplasma capsulatum is a dimorphic fungus that typically causes pulmonary infections rather than fungal sinusitis.

**Clinical Pearl / High-Yield Fact**
Dichotomous branching at a 45-degree angle is a key feature of Aspergillus species, which can help differentiate them from other fungal species. This characteristic branching pattern is often seen in histopathological preparations of fungal cultures.

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

✓ Correct Answer: A. Aspergillus fumigatus