## **Core Concept**
Acute sinusitis in children often involves specific sinuses due to their anatomical and developmental characteristics. The condition is commonly seen in the context of viral upper respiratory tract infections. Understanding the sinuses' anatomy and their development in children is crucial.

## **Why the Correct Answer is Right**
The correct answer, , indicates that the maxillary sinus is the most commonly involved sinus in children with acute sinusitis. This is because the maxillary sinuses are among the first to develop and are relatively large compared to other sinuses in children. Their pneumatization starts early, and they are more prone to infection due to their size and the anatomy of the ostiomeatal complex.

## **Why Each Wrong Option is Incorrect**
* **Option A:** The ethmoid sinuses are indeed involved in sinusitis, especially in children, due to their complex structure and early development. However, they are not the most frequently involved sinus when compared to the maxillary sinus.
* **Option B:** The sphenoid sinus is less commonly involved in acute sinusitis in children, primarily because it develops later in childhood and is not as frequently affected by common viral infections.
* **Option D:** The frontal sinus is the least likely to be involved in acute sinusitis in young children because it typically develops later, often becoming pneumatized around the age of 6 years, and its involvement is more common in older children and adults.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the maxillary and ethmoid sinuses are the most commonly affected by acute sinusitis in children. The clinical presentation may include nasal congestion, facial pain, and cough. Given the nonspecific nature of symptoms, diagnosis relies on a combination of clinical findings and imaging studies.

## **Correct Answer:** . Maxillary sinus.