**Core Concept**
Allergic Fungal Sinusitis (AFS) is a rare, chronic inflammatory condition primarily affecting the paranasal sinuses, characterized by an allergic response to fungal antigens. The condition is often associated with asthma and other allergic diseases. AFS is a distinct entity from other forms of fungal sinusitis.

**Why the Correct Answer is Right**
Orbital invasion is not a diagnostic criterion for AFS. Orbital involvement may be seen in more aggressive forms of fungal sinusitis such as invasive fungal sinusitis, but it is not a characteristic feature of AFS. AFS typically presents with non-invasive, expansile masses within the sinuses, without significant bone erosion or orbital extension. The correct diagnostic criteria for AFS include the presence of allergic eosinophilic mucin, high attenuation on CT scans due to the presence of fungal spores and eosinophilic debris, and a history of type I hypersensitivity.

**Why Each Wrong Option is Incorrect**
**Option A:** Areas of High Attenuation on CT scan are indeed a diagnostic criterion for AFS, as they represent the presence of fungal spores and eosinophilic debris within the mucin.
**Option C:** Allergic Eosinophilic mucin is a hallmark of AFS, characterized by the presence of eosinophils, Charcot-Leyden crystals, and fungal spores within the mucin.
**Option D:** Type I Hypersensitivity is also a diagnostic criterion for AFS, as patients often have a history of allergies and asthma.

**Clinical Pearl / High-Yield Fact**
A key differentiating feature between AFS and other forms of fungal sinusitis is the presence of allergic eosinophilic mucin and a history of type I hypersensitivity. This can be remembered using the mnemonic "A-FS": Allergic, Fungal, Sinusitis.

**✓ Correct Answer: B. Orbital invasion**