Radiographic Evaluation of a Pulmonary Embolism Dr Mohamed El Safwany, MD.

Intended learning outcome The student should learn at the end of this lecture principles of Radiological evaluation of Pulmonary Embolism.

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

PerfusionVentilation

V/Q Scan Results Clinical probability of emboli Scan Category HighIntermediateLow High Intermediate Low40154 Normal or near normal 062 Likelihood of pulmonary embolism according to scan category and clinical probability in PIOPED study

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.

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.

Text Book David Sutton’s Radiology Clark’s Radiographic positioning and techniques

Assignment Two students will be selected for assignment.

Question Describe value of CT in evaluation of pulmonary embolis?

Thank You Thank You

References Up to date Online. Diagnosis of Acute Pulmonary Embolism. Last revised March 7, Pulmonary Embolism.