Okay, let's tackle this question about diagnosing lung sequestration. First, I need to recall what lung sequestration is. From what I remember, it's a condition where a portion of the lung doesn't have a normal connection to the bronchial tree or the pulmonary arteries. Instead, it's supplied by an aberrant systemic artery, usually from the aorta. So the key here is identifying the presence of a systemic arterial supply.

The question is asking about the diagnostic method. The options weren't provided, but the correct answer is probably an imaging technique that can visualize blood vessels. Let me think about the diagnostic tools. Chest X-ray might show a mass, but it's not specific. CT scan, especially with contrast, can show the systemic artery. MRI could also be useful, but contrast-enhanced CT is more commonly used. Angiography is invasive but definitive. However, non-invasive methods are preferred first.

Wait, the gold standard for diagnosing sequestration is usually a contrast-enhanced CT scan because it can demonstrate the abnormal systemic artery and the lack of connection to the pulmonary arteries. Alternatively, angiography is more accurate but less commonly used due to its invasiveness. So the correct answer might be CT with contrast. The other options like MRI or plain X-ray would not show the systemic artery as clearly. Ultrasound might be used in some cases but is not the primary method here.

The clinical pearl here is that the presence of a systemic arterial supply is the hallmark of sequestration. Students should remember that the key diagnostic feature is the aberrant systemic artery, which differentiates it from other lung masses. So the answer is likely contrast-enhanced CT scan.

**Core Concept**
Lung sequestration is a congenital anomaly characterized by non-functional lung tissue supplied by an aberrant systemic artery (typically from the thoracic aorta). Diagnosis hinges on identifying this **systemic arterial supply** and lack of connection to the tracheobronchial tree. Imaging modalities that visualize vascular anatomy are critical.

**Why the Correct Answer is Right**
Contrast-enhanced **computed tomography (CT)** is the gold standard for diagnosing lung sequestration. It directly visualizes the **aberrant systemic artery** (e.g., from the aorta) supplying the sequestrated tissue and confirms the absence of bronchial connection. The sequestered lung appears as a hypodense mass with peripheral enhancement from the systemic artery, distinguishing it from other masses like tumors or abscesses. CT provides high spatial resolution for anatomical detail and is non-invasive compared to angiography.

**Why Each Wrong Option is Incorrect**
**Option A:** Plain chest X-ray may show a mass or opacity but cannot identify the systemic artery or vascular supply.
**Option B:** Ultrasound lacks the resolution to visualize systemic arteries and is not routinely used for lung parenchymal abnormalities.
**Option C:** MRI can detect vascular anomalies but is less sensitive than CT for identifying systemic arterial supply and is less accessible.

**Clinical Pearl / High-Yield Fact**
The hallmark of lung sequestration is **systemic arterial supply** with no functional airway connection. Always look for a **"feeding artery"** on imaging. Remember: "Sequestration = systemic artery + no bronchus." Contrast-enhanced CT is the definitive test, while angi

✓ Correct Answer: A. CT