**Question:** A patient presents with a solitary pulmonary nodule (SPN) on X-ray. The best investigation to come to a diagnosis would be -

A. Chest CT scan
B. Chest X-ray
C. Bronchoscopy
D. Pleural biopsy

**Correct Answer:** **A. Chest CT scan**

**Core Concept:**
A solitary pulmonary nodule (SPN) is a focal pulmonary abnormality that is visible on chest imaging studies like X-ray or CT scan. SPNs can be benign or malignant, and further investigations are required to differentiate between these two entities.

**Why the Correct Answer is Right:**
A chest CT scan is the most appropriate investigation for a patient with a solitary pulmonary nodule on chest X-ray because it provides greater detail and resolution than chest X-ray. A CT scan can visualize the size, shape, margin, and calcification patterns of the nodule, which are critical features for differential diagnosis.

**Why Each Wrong Option is Incorrect:**

**B. Chest X-ray:** While chest X-ray is a basic screening tool, it lacks the resolution to accurately assess the features of a pulmonary nodule. It is not as sensitive as CT scan for detecting small or calcified nodules, which are common in malignant nodules.

**C. Bronchoscopy:** Bronchoscopy is an invasive procedure used to visualize and biopsize the airways, not the pulmonary parenchyma. It is not suitable for diagnosis of pulmonary nodules.

**D. Pleural biopsy:** Pleural biopsy involves obtaining a sample from the pleural space for diagnosis. It is not suitable for diagnosing pulmonary nodules, which require assessment of the nodule itself.

**Clinical Pearl:**

A solitary pulmonary nodule should be investigated promptly, as early detection and diagnosis of malignant nodules are crucial for appropriate treatment and prognosis. A chest CT scan is the gold standard for diagnosing and characterizing pulmonary nodules, allowing for a more accurate diagnosis and prompt management of the patient.