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Pulmonary embolism

A 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.

Other embolic sources include

air embolism
fat embolism
tumour embolism : comprised of tumour thrombus
amniotic fluid embolism

Pathology

Risk factors

primary hypercoagulable states
- protein C deficiency
- antithrombin III
- lupus anticoagulant
recent surgery
pregnancy
prolonged bed rest / immobility
malignancy
oral contraceptive use

Clinical Assessment

Pre‐test probability scores are intended to replace empirical assessment of patients with suspected pulmonary embolism.

Wells score
Geneva score

Serological tests

D-Dimer (ELISA)

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 suspected⁴.

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 tests⁴.

Radiographic features

Depends to some extent on whether it is acute or chronic. Overall has a predilection for the lower lobes.

Plain film

Described chest radiographic signs include

Fleishner sign : enlarged pulmonary artery : 20%
Hampton hump : peripheral wedge of airspace opacity = implies lung infarction : 20%
Westermark sign : regional oligaemia - highest + ve predictive value (PPV) : 10%
pleural effusion : 35%

Sensitivity and specificity of Chest x-ray signs ¹

Westermark sign
- sensitivity : ~ 14 %
- specificity : ~ 92% %
- PPV : ~ 38 %
- NPV : ~ 76 %
vascular redistribution
- sensitivity : ~ 10 %
- specificity : ~ 87 % %
- PPV : ~ 21 %
- NPV : ~ 74 %
Hampton’s hump
- sensitivity : ~ 22 %
- specificity : ~ 82 %
- PPV : ~ 29 %
- NPV : ~ 76 %
pleural effusion
- sensitivity : ~ 36 %
- specificity : ~ 70 %
- PPV : ~ 28 %
- NPV : ~ 76 %
elevated diaphragm
- sensitivity : ~ 20 %
- specificity : ~ 85 %
- PPV : ~ 30 %
- NPV : ~ 76 %

CTPA

Will show filling defects within the pulmonary vasculature with acute pulmonary emboli.

Features noted with chronic pulmonary emboli include

webs or bands, intimal irregularities ³
abrupt narrowing or complete obstruction of the pulmonary arteries ³
“pouching defects” which are defined as chronic thromboemboli organised in a concave shape that “points” toward the vessel lumen ³

VQ scan

Will show ventilation-perfusion mismatches. A high probability scan is defined as showing two or more unmatched segmental perfusion defects acccording to the PIOPED criteria