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Pulmonary Embolism

Leyla Azmoun, MD
Piran Aliabadi, MD
B Leonard Holman, MD

December 12, 1995

Presentation

A 59-year-old woman presents to the emergency room with shortness of breath and chest pain on deep inspiration. She has been immobilized for the past two weeks due to fracture of her left foot and ankle. On physical exam, she is dyspneic and tachycardic with a respiratory rate of 22 and a heart rate of 100. Her lungs are clear on auscultation. There is moderate swelling of her left lower extremity. Her oxygen saturation is 93% on room air and her ECG is unremarkable.

Imaging Findings

AP and lateral plain radiographs of the chest
Perfusion scintigraphy
Ventilation scintigraphy
Repeat perfusion scan 5 days later

AP and lateral plain radiographs of the chest show no abnormality in the pulmonary parenchyma. The cardiomediastinal silhouette is unremarkable. There is a small right pleural effusion (arrow).

Planar lung views of the perfusion study using Tc-99m MAA shows absent perfusion to most of the right lung (arrows). There are also large segmental perfusion defects in the lingula, left basal segments, and anteroposterior segment of the left upper lobe (arrows).

Ventilation imaging with Xe-133 gas in the posterior projection shows normal ventilation of the lungs, and therefore, a significant ventilation-perfusion mismatch. These findings indicate a high probability (greater than 80%) for a pulmonary embolism.

The patient was treated with systemic thrombolysis and a repeat perfusion study in 5 days showed near-complete resolution of segmental perfusion defects.

Diagnosis

Pulmonary embolism

Discussion

Pulmonary embolism is a potentially fatal disorder that is often difficult to diagnose clinically. Fewer than one-fourth of patients show the classic signs and symptoms of tachypnea, pleuritic chest pain, dyspnea, cough and hemoptysis. The predisposing risk factors for pulmonary embolism include postoperative or immobilized state, cancer, congestive heart failure or a hypercoagulable condition. Given the nonspecific clinical presentation, pulmonary emboli require a radiographic diagnosis. Pulmonary arteriography is the only definitive means of establishing a diagnosis of pulmonary embolus. However, it is an invasive and expensive technique that should not be used as a screening test. A radionuclide ventilation-perfusion scan is a highly sensitive and accurate test for detection of pulmonary emboli. The V/Q scan shows pulmonary emboli as segmental regions of reduced or absent pulmonary perfusion associated with normal ventilation, known as a ventilation-perfusion mismatch. Patients are classified as having low (0-19%), intermediate (20-79%) or high (80-100%) probability of pulmonary embolus based on the size and number of perfusion defects in comparison with the ventilation pattern and radiographic findings. Pulmonary arteriography is generally reserved for patients with an intermediate probability of pulmonary embolism based on the V/Q scan or those in whom a definitive diagnosis is required prior to any contemplated interventional treatment.

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