## **Core Concept**
The patient's symptoms suggest a case of **recurrent acute sinusitis** or **chronic sinusitis**, which is characterized by inflammation of the paranasal sinuses lasting more than 12 weeks. The presence of mucopurulent discharge from the middle meatus and inflamed sinus openings points towards an infection involving the **ostium secondary** (secondary ostium) area, which is a common site for chronic sinusitis.

## **Why the Correct Answer is Right**
The investigation of choice for diagnosing chronic sinusitis or complications arising from it, especially when looking for anatomical issues or complications, is **CT (Computed Tomography) scan of the sinuses**. CT scans provide detailed images of the sinuses and can help identify anatomical abnormalities, extent of disease, and complications such as **osteitis**, **abscesses**, or **fungal balls**. This detailed imaging is crucial for planning treatment, including surgery if necessary.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While an **X-ray** of the sinuses can provide some information, it lacks the detail needed to assess the extent of disease or anatomical abnormalities, making it less useful for guiding treatment decisions in chronic or recurrent sinusitis.
- **Option B:** **MRI (Magnetic Resonance Imaging)** is generally not the first choice for evaluating sinusitis because it is less sensitive than CT for detecting the bony changes and calcifications that can occur in chronic sinusitis.
- **Option D:** **Ultrasound** is not typically used for evaluating sinusitis due to its inability to penetrate bone and provide detailed images of the sinuses.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **CT scan of the sinuses** is the gold standard imaging technique for chronic sinusitis, especially when complications are suspected or when planning surgical intervention. The Lund-Mackay scoring system is often used to quantify the extent of disease on CT scans.

## **Correct Answer:** . CT Scan of sinuses.