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Radiographic evaluation of a Pulmonary Embolism
 

Radiographic evaluation of a Pulmonary Embolism

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    Radiographic evaluation of a Pulmonary Embolism Radiographic evaluation of a Pulmonary Embolism Presentation Transcript

    • Radiographic Evaluation of a Pulmonary Embolism Jim Hadstate September 27, 2007
    • Presentation
      • Dyspnea
      • Pleuritic chest pain
      • Low-grade fever
      • Tachycardia
    • 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
    • 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.
    • CXR
      • Hampton’s Hump – consists of a pleura based shallow wedge-shaped consolidation in the lung periphery with the base against the pleural surface.
    • CXR
      • Westermark sign – Dilatation of pulmonary vessels proximal to embolism along with collapse of distal vessels, often with a sharp cut off.
    • 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.
    • Abnormal V/Q Scan
    • Abnormal V/Q Scan Perfusion Ventilation
    • 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
    • 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.
    • 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.
    • 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.
    • CT Angiogram
      • Chest computed tomography scanning demonstrating extensive embolization of the pulmonary arteries.
    • 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.
    • Pulmonary angiogram
      • Left-sided pulmonary angiogram showing extensive filling defects within the left pulmonary artery and its branches.
    • 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.
    •  
    • References
      • Up to date Online. Diagnosis of Acute Pulmonary Embolism. Last revised March 7, 2007.
      • Pulmonary Embolism. http://www.e-radiography.net