Diagnosis of Pulmonary Embolism
The cornerstone of confirmation or exclusion in the diagnosis of pulmonary thromboembolism is imaging modalities specific for deep vein thrombosis and pulmonary embolism, which include:
I. Deep vein thrombosis
1. Venography
It is the method of choice to diagnose and visualize the extension of deep vein thrombosis. Now, it is rarely performed because of its invasive nature and the presence of accurate non-invasive modalities.
2. Duplex ultrasonography
It is currently the standard method for initial screening and diagnosis of deep vein thrombosis. By being reliable, non-invasive, of wide variability and easy interpretation, it gained its current position in the workup, and it is routinely ordered for all patients admitted to the ER with query deep vein thrombosis.
3. Magnetic resonance imaging
Rarely ordered for this purpose and with a limited value.
II. Imaging specific for pulmonary embolism:
1. CT pulmonary angiography
It is now considered to be the gold standard for diagnosis and risk stratification of pulmonary embolism, as it has a very high sensitivity and specificity. CT pulmonary angiography localizes the thrombus and its extension, and can be used for follow up and to exclude other mediastinal and parenchymal causes. It is also very helpful to confirm presence of lung infarction.
2. Ventilation – perfusion scanning (V/Q)
An important modality in the diagnosis of pulmonary embolism by showing segmental hypoperfusion. It could be used when CT pulmonary angiography is not available or contraindicated due to renal causes.
3. Magnetic resonance imaging
May be used if CT is not available or contra indicated due to renal causes. If gadolinium enhancement, i.e. contrast, is used, its specificity and sensitivity will be significantly higher.
4. Echocardiography
It is of a limited role due to its low sensitivity and specificity, though it is done in almost all cases in order to exclude other cardiac causes of chest pain or dyspnea. Its sensitivity and specificity are about 59% and 77%.
Sometimes it can visualize a central pulmonary artery thrombus and this is a highly positive value.
From all the above, it is clearly obvious that the diagnosis of pulmonary embolism in a step-wise manner resembles a sort of puzzle. Doctors use the approach described above in most hospitals worldwide. It is not wise to start with higher imaging techniques to exclude the presence of the disease due to cost-effectiveness causes and to limit side effects of contrast, minimize waiting lists in emergency rooms and avoid of unnecessary admissions.
