**Core Concept**
Fungal sinusitis is a type of invasive fungal infection that affects the paranasal sinuses, often causing significant morbidity and mortality. The condition can be categorized into non-invasive and invasive forms, with the latter being more severe and life-threatening.

**Why the Correct Answer is Right**
Invasive fungal sinusitis is a serious condition that requires prompt treatment. Amphotericin B is a broad-spectrum antifungal agent that is often used to treat invasive fungal infections, including invasive fungal sinusitis. This medication works by binding to ergosterol in the fungal cell membrane, leading to cell lysis and death. Invasive fungal sinusitis is a medical emergency that requires aggressive treatment, including antifungal medications like Amphotericin B, alongside surgical intervention to debride infected tissue and restore sinus drainage.

**Why Each Wrong Option is Incorrect**
**Option A:** Surgery is not the sole treatment for fungal sinusitis. While surgical intervention may be necessary to manage complications or restore sinus function, antifungal medications are also essential for treating the underlying infection.

**Option B:** Aspergillus species are common pathogens in invasive fungal sinusitis, but they are not the most common organism. Other fungi, such as Mucorales, are also frequently implicated in this condition.

**Option C:** While Amphotericin B is used to treat invasive fungal sinusitis, it is not the only antifungal agent that can be used. Other medications, such as posaconazole or voriconazole, may also be effective in certain cases.

**Option D:** Fungal sinusitis is not exclusive to immunodeficient conditions. While individuals with compromised immune systems are at increased risk, this condition can also affect healthy individuals, particularly those with underlying anatomical abnormalities or allergies.

**Clinical Pearl / High-Yield Fact**
Fungal sinusitis can cause significant morbidity and mortality if left untreated. Prompt recognition and treatment, including antifungal medications and surgical intervention, are essential for managing this condition effectively.

**Correct Answer:** C. Amphotericin B i.v is used for invasive fungal sinusitis