|Figure 1:Axial CT section of Pulmonary angiogram|
|Figure 2: Coronal CT section of Pulmonary angiogram|
|Figure 3: Coronal CT section of Pulmonary angiogram|
|Figure 4: Axial CT section of lower thorax-Lung window|
Pulmonary embolism (PE) refers to embolic occlusion of the pulmonary arterial system. The majority of cases result from thrombotic occlusion and therefore the condition is frequently termed pulmonary thrombo-embolism which is what this article mainly covers.
Clinical signs and symptoms are non-specific . Dyspnoea, chest pain, and haemoptysis have been described as a classic triad in pulmonary embolism.
- primary hypercoagulable states
- recent surgery
- prolonged bed rest / immobility
- oral contraceptive use
- presence of certain venous aneurysms
The right ventricular failure due to pressure overload is considered the primary cause of death in severe PE .
D-dimer (ELISA) is commonly used as a screening test in patients with a low and moderate probability clinical assessment, on these patients:
- normal D-dimer has almost 100% negative predictive value (virtually excludes PE): no further testing is required
- raised D-dimer is seen with PE but has many other causes and is, therefore, non-specific: it indicates the need for further testing if pulmonary embolism is suspected
On patients with a high probability clinical assessment, a D-dimer test is not helpful because a negative D-dimer result does not exclude pulmonary embolism in more than 15%. Patients are treated with anticoagulants while awaiting the outcome of diagnostic tests .
Depends to some extent on whether it is acute or chronic. Overall has a predilection for the lower lobes.
Described chest radiographic signs include:
- Fleishner sign: enlarged pulmonary artery (20%)
- Hampton hump: peripheral wedge of airspace opacity and implies lung infarction (20%)
- Westermark’s sign: regional oligaemia and highest positive predictive value (10%)
- Pleural effusion(35%)
- Knuckle sign
Specificity of chest x-ray signs :
- Westermark sign -specificity: ~92%
- Vascular redistribution -specificity: ~87%
- Hampton hump -specificity: ~82%
- Pleural effusion -specificity: ~70%
- Elevated diaphragm -specificity: ~85%
Acute pulmonary emboli
Acute pulmonary thrombo-emboli can occasionally be detected on non-contrast chest CT as intraluminal hyperdensities .
CT pulmonary angiography (CTPA) will show filling defects within the pulmonary vasculature with acute pulmonary emboli. When observed in the axial plane this has been described as the polo mint sign. The central filling defect from the thrombus is surrounded by a thin rim of contrast, appearing like the popular sweet, the polo mint.
Chronic pulmonary emboli
Features noted with chronic pulmonary emboli include:
- webs or bands, intimal irregularities
- abrupt narrowing or complete obstruction of the pulmonary arteries
- “pouching defects” which are defined as chronic thromboembolic organised in a concave shape that “points” toward the vessel lumen
It is difficult to obtain technically adequate images for pulmonary embolism patients using MRI. Magnetic resonance pulmonary angiography should be considered only at centers that routinely perform it well and only for patients for whom standard tests are contraindicated. Technically adequate magnetic resonance angiography has a sensitivity of 78% and a specificity of 99% .
VQ scan will show ventilation-perfusion mismatches. A high probability scan is defined as showing two or more unmatched segmental perfusion defects according to the PIOPED criteria.