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Radiographic evaluation of a Pulmonary Embolism

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  • 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 2 6 0 Normal or near normal Clinical probability of emboli 4 15 40 Low 15 28 66 Intermediate 56 86 95 High Low Intermediate High Scan Category
  • 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.
  • 18.  
  • 19. References
    • Up to date Online. Diagnosis of Acute Pulmonary Embolism. Last revised March 7, 2007.
    • Pulmonary Embolism. http://www.e-radiography.net

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