**Question:** Definitive diagnosis of sinusitis is by-

A. Computed tomography (CT) scan
B. Nasal endoscopy
C. Culture and sensitivity
D. Blood tests

**Correct Answer:** A. Computed tomography (CT) scan

**Core Concept:** Sinusitis is an inflammation of the paranasal sinus mucosa, which can be caused by various factors such as infections, allergies, or autoimmune disorders. The definitive diagnosis of sinusitis requires a comprehensive evaluation that includes clinical examination, imaging studies, and sometimes microbiological investigations.

**Why the Correct Answer is Right:** Computed tomography (CT) scan is the most reliable and accurate method for diagnosing sinusitis, especially when compared to the other options. A CT scan provides detailed images of the paranasal sinuses, allowing for visualization of inflammation, mucosal thickening, opacification, and assessing the extent of disease involvement.

**Why Each Wrong Option is Incorrect:**

**Option B (Nasal endoscopy):** While nasal endoscopy helps in assessing the nasal mucosa, turbinates, and the nasal cavity, it does not provide comprehensive information about the paranasal sinuses. Therefore, it is insufficient for making a definitive diagnosis of sinusitis.

**Option C (Culture and sensitivity):** Culture and sensitivity tests are useful for identifying the causative pathogen in a sinusitis case. However, they are not a primary diagnostic tool for sinusitis itself. Definitive diagnosis relies on clinical findings, imaging, and microbiological evaluation.

**Option D (Blood tests):** Blood tests are helpful in ruling out other potential causes of sinusitis, such as systemic infections or autoimmune disorders. However, they are not sufficient for confirming or excluding sinusitis diagnosis. A combination of clinical examination, imaging studies, and sometimes microbiological investigations is essential for a definitive diagnosis.

**Core Concept (Clinical pearl):** A thorough clinical examination, including nasal endoscopy, is essential for suspecting sinusitis. However, definitive diagnosis requires imaging studies (e.g., CT scan) to visualize the extent of inflammation and assess sinus involvement. Additionally, microbiological investigations may be necessary in specific cases to identify the causative pathogen.

**Clinical Pearls:**

1. **Anatomical Understanding:** Understanding the anatomy of paranasal sinuses (Four pairs of sinuses: frontal, ethmoid, maxillary, and sphenoid) is crucial for recognizing signs and symptoms of sinusitis.
2. **Diagnostic Imaging:** Computed tomography (CT) scan is the gold standard for evaluating sinusitis due to its ability to visualize the sinus anatomy and identify abnormalities like mucosal thickening, opacification, and bone erosion.
3. **Microbiological Investigations:** For cases with sinusitis, identifying the causative pathogen is essential. Culture and sensitivity tests are valuable in determining the causative microorganisms or allergens responsible for sinusitis.

**Why Option A is Incorrect:** Nasal endoscopy is essential for ruling out nasal polyps, foreign bodies, and anatomical abnormalities like deviated nasal septum. However, it is not sufficient for diagnosing sinusitis.