## **Core Concept**
Orbital cellulitis is a severe infection of the orbital tissues posterior to the orbital septum. It is often a complication of infections or conditions that spread to the orbit from adjacent structures.

## **Why the Correct Answer is Right**
The correct answer, **d) All of these**, encompasses the various potential sources of orbital cellulitis.
- **Parasinusitis (a)**, particularly ethmoid sinusitis, is a well-known cause because of the thin bony separation between the ethmoid sinuses and the orbit, allowing for easy spread of infection.
- **Faciomaxillary trauma (b)** can introduce bacteria directly into the orbital tissues or create a pathway for infection from the sinuses or skin.
- **Endoscopic sinus surgery (c)**, though performed to treat sinus issues, can lead to orbital cellulitis if there is accidental entry into the orbit or if post-operative infection occurs.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it only lists one cause, whereas the question asks for a comprehensive complication.
- **Option B:** This option is incorrect because it only mentions two causes and excludes another valid cause.
- **Option C:** This option is incorrect because it only mentions one cause.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that orbital cellulitis can lead to serious complications, such as permanent vision loss, if not promptly treated. Early recognition and imaging (e.g., CT scan) are crucial for diagnosis and management.

## **Correct Answer: D. All of these**