Radiographic Evaluation of a Pulmonary Embolism

1. Radiographic Evaluation of a Pulmonary Embolism Jim Hadstate September 27, 2007

2. Presentation • Dyspnea • Pleuritic chest pain • Low-grade fever • Tachycardia

3. Evaluation • ABG – Respiratory alkalosis, hypoxia • ECG – Sinus tachycardia & S1Q3T3 • D-Dimer – A negative result rules out PE • CXR • V/Q Scan • Spiral CT with contrast • Angiogram

4. CXR • Initial CXR usually normal. • May progress to show atelectasis, plueral effusion and elevated hemidiaphram. • Hampton’s hump and Westermark sign are classic findings but are not usually present.

5. CXR • Hampton’s Hump – consists of a pleura based shallow wedge-shaped consolidation in the lung periphery with the base against the pleural surface.

6. CXR • Westermark sign – Dilatation of pulmonary vessels proximal to embolism along with collapse of distal vessels, often with a sharp cut off.

7. V/Q Scan • Ventilation-perfusion scanning is a radiological procedure which is often used to confirm or exclude the diagnosis of pulmonary embolism. It may also be used to monitor treatment. • Ventilation (V) – Achieved by the inhalation of Technetium DTPA. DTPA is an elongated version of EDTA and is a heavy metal chelator. Ventilation is assessed under a gamma camera. • Perfusion (Q) – Achieved by injecting the patient with Technetium 99m, which is coupled with macro aggregated albumin (MAA). An embolus shows up as a cold area when the patient is placed under a gamma camera.

8. Abnormal V/Q Scan

9. Abnormal V/Q Scan Perfusion Ventilation

10. V/Q Scan Results Likelihood of pulmonary embolism according to scan category and clinical probability in PIOPED study

11. Spiral CT • Spiral CT first introduced in 1990s • In older CT scanners, the X-ray source would move in a circular fashion to acquire a single slice. Once the slice had been completed, the scanner table would move to position the patient for the next slice. • In helical CT the X-ray source and detectors are attached to a freely rotating gantry. During a scan, the table moves the patient smoothly through the scanner. The name derives from the helical or spiral path traced out by the X-ray beam.

12. Spiral CT • Major advantage of Spiral CT is speed: • Often the patient can hold their breath for the entire study, reducing motion artifacts. • Allows for more optimal use of intravenous contrast enhancement. • Spiral CT is quicker than the equivalent conventional CT permitting the use of higher resolution acquisitions in the same study time. • Contraindicated in cases of renal disease. • Sensitive for PE in the proximal pulmonary arteries, but less so in the distal segments.

13. CT Angiogram • Quickly becoming the test of choice for initial evaluation of a suspected PE. • CT unlikely to miss any lesion. • CT has better sensitivity, specificity and can be used directly to screen for PE. • CT can be used to follow up “non diagnostic V/Q scans.

14. CT Angiogram • Chest computed tomography scanning demonstrating extensive embolization of the pulmonary arteries.

15. Pulmonary angiogram • Gold Standard. • Positive angiogram provides 100% certainty that an obstruction exists in the pulmonary artery. • Negative angiogram provides > 90% certainty in the exclusion of PE.

16. Pulmonary angiogram • Left-sided pulmonary angiogram showing extensive filling defects within the left pulmonary artery and its branches.

17. Summary • Plain chest radiograph – Usually normal and non-specific signs. • Radionuclide ventilation-perfusion lung scan. • CT Angiography of the pulmonary arteries – Quickly becoming method of choice. • Pulmonary angiography – Gold standard but invasive.

19. References • Up to date Online. Diagnosis of Acute Pulmonary Embolism. Last revised March 7, 2007. • Pulmonary Embolism. http://www.e-radiography.net