**Core Concept**
Functional Endoscopic Sinus Surgery (FESS) is a minimally invasive surgical procedure used to treat sinusitis and other sinus-related disorders. It involves the use of an endoscope to visualize the sinuses and remove blockages, such as polyps or bone, to restore normal sinus drainage.

**Why the Correct Answer is Right**
FESS is indicated in cases of chronic sinusitis, nasal polyps, and other conditions where medical management has failed. The procedure is also used to treat complications of sinusitis, such as orbital and intracranial abscesses. During FESS, the surgeon uses specialized instruments to remove the blockages and restore the normal anatomy of the sinuses, allowing for proper drainage and function.

**Why Each Wrong Option is Incorrect**
**Option A:** FESS is not primarily used for treating allergic rhinitis, which can be managed with medical therapy such as antihistamines and corticosteroids.
**Option B:** While FESS can be used to treat nasal polyps, it is not the primary indication, as polyps can often be managed with medical therapy or other surgical procedures.
**Option C:** FESS is not typically used for treating acute sinusitis, as the condition often resolves with medical management.

**Clinical Pearl / High-Yield Fact**
FESS is often used as a last resort after medical management has failed, and the procedure has a high success rate in improving symptoms and quality of life for patients with chronic sinusitis.

**Correct Answer: C. FESS is not typically used for treating acute sinusitis, as the condition often resolves with medical management.**