**Core Concept**
Ohngren's classification is a system used in otorhinolaryngology to categorize maxillary sinusitis based on the location of the maxillary sinus mucosal disease. This classification helps in determining the extent of the disease and guiding treatment decisions.

**Why the Correct Answer is Right**
The Ohngren's classification is based on the anatomical relationship between the maxillary sinus and the nasal cavity. The classification divides the maxillary sinus into two regions: the anterior (or prenasal) region and the posterior (or retroantral) region. This classification is crucial in planning surgical approaches and in understanding the spread of disease in the maxillary sinus.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Ohngren's classification is specific to maxillary sinusitis and does not apply to other conditions.
**Option B:** This option is incorrect because the classification is based on the anatomical relationship between the maxillary sinus and the nasal cavity, not the location of the disease in the nasal cavity.
**Option C:** This option is incorrect because the Ohngren's classification is not used to describe the extent of disease in other sinuses, such as the frontal or sphenoid sinuses.

**Clinical Pearl / High-Yield Fact**
Ohngren's classification is a useful tool for otorhinolaryngologists to understand the extent of maxillary sinus disease and to plan effective treatment strategies. It is essential to remember that the classification is based on the anatomical relationship between the maxillary sinus and the nasal cavity.

**Correct Answer: C.**