A 58-year-old man with a 3-day history of acute onset dyspnea, pleuritic chest pain, and tachycardia (HR 110/min) is suspected of having pulmonary embolism. Clinical probability is intermediate based on Wells score. Chest X-ray is normal. What is the investigation of choice to confirm or exclude pulmonary embolism in this patient?

Question

Accepted Answer

C. Computed tomography pulmonary angiography (CTPA). ## Investigation of Choice for PE Confirmation

**Key Point:** CTPA (Computed Tomography Pulmonary Angiography) is the gold standard and first-line imaging modality for confirming or excluding pulmonary embolism in patients with intermediate to high clinical probability.

### Why CTPA is Preferred

| Feature | CTPA | V/Q Scan | Pulmonary Angiography |
|---------|------|---------|----------------------|
| Sensitivity | 94–98% | 60–90% (depends on probability) | 99% |
| Specificity | 95–98% | 90–95% | 99% |
| Speed | Rapid (minutes) | Slow (hours) | Invasive, time-consuming |
| Radiation dose | Moderate | Low | High |
| Availability | Widely available | Limited | Rarely used |
| Operator dependent | No | Yes | Yes |
| Can diagnose alternative pathology | Yes | No | No |

**High-Yield:** CTPA is the imaging test of choice because it:
1. Has excellent sensitivity and specificity for PE detection
2. Can identify alternative diagnoses (pneumonia, aortic dissection, pneumothorax)
3. Is rapid and non-invasive
4. Is widely available in most hospitals
5. Allows assessment of RV size and function

### Clinical Context

**Clinical Pearl:** In this patient with intermediate Wells probability and normal CXR, CTPA is indicated. If CTPA is contraindicated (e.g., renal insufficiency, iodine allergy), then V/Q scan or compression ultrasound of lower limbs would be alternatives.

### Role of Other Investigations

- **V/Q scan:** Used when CTPA is contraindicated or in patients with low-intermediate probability and normal CXR; less specific than CTPA
- **Pulmonary angiography:** Invasive gold standard; reserved only for cases where CTPA is inconclusive and clinical suspicion remains very high
- **Echocardiography:** Useful for assessing hemodynamic consequences (RV strain) but cannot confirm PE diagnosis

Answer

A. Ventilation-perfusion (V/Q) scan

Answer

B. Pulmonary angiography

Answer

D. Echocardiography

Explanation

Investigation of Choice for PE Confirmation

Why CTPA is Preferred

Clinical Context

Role of Other Investigations

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Feature	CTPA	V/Q Scan	Pulmonary Angiography
Sensitivity	94–98%	60–90% (depends on probability)	99%
Specificity	95–98%	90–95%	99%
Speed	Rapid (minutes)	Slow (hours)	Invasive, time-consuming
Radiation dose	Moderate	Low	High
Availability	Widely available	Limited	Rarely used
Operator dependent	No	Yes	Yes
Can diagnose alternative pathology	Yes	No	No