Pulmonary embolism
Updates to Article Attributes
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.
Other embolic sources include:
- air embolism
- fat embolism
- tumour embolism: comprised of tumour thrombus
- hydatid pulmonary embolism
- talc pulmonary embolism
- iodinated oil pulmonary embolism
- metallic mercury pulmonary embolism
- amniotic fluid embolism
- cement embolism: comprised of PMMA
- catheter embolism
- septic pulmonary embolism
Clinical presentation
Clinical signs and symptoms are non-specific 14. Dyspnoea, chest pain, and haemoptysis have been described as a classic triad in pulmonary embolism. The ECG may show an S1Q3T3 pattern.
Pre‐test probability scores are intended to replace empirical assessment of patients with suspected pulmonary embolism:
Pathology
Risk factors
- primary hypercoagulable states
- recent surgery
- pregnancy
- prolonged bed rest / immobility
- malignancy
- oral contraceptive use
- presence of certain venous aneurysms
- e.g. popliteal venous aneurysm 15
The right ventricular failure due to pressure overload is considered the primary cause of death in severe PE 14.
Markers
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 4
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 4.
Radiographic features
Depends to some extent on whether it is acute or chronic. Overall has a predilection for the lower lobes.
Plain radiograph
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 11
Sensitivity and specificity of chest x-ray signs 1:
- Westermark sign
- sensitivity: ~14%
- specificity: ~92%
- positive predictive value: ~38%
- negative predictive value: ~76%
- vascular redistribution
- sensitivity: ~10%
- specificity: ~87%
- positive predictive value: ~21%
- negative predictive value: ~74%
- Hampton hump
- sensitivity: ~22%
- specificity: ~82%
- positive predictive value: ~29%
- negative predictive value: ~76%
- pleural effusion
- sensitivity: ~36%
- specificity: ~70%
- positive predictive value: ~28%
- negative predictive value: ~76%
- elevated diaphragm
- sensitivity: ~20%
- specificity: ~85%
- PPV: ~30%
- NPV: ~76%
CT
Acute pulmonary emboli
Acute pulmonary thrombo-emboli can occasionally be detected on non-contrast chest CT as intraluminal hyperdensities 12.
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 9.
Chronic 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 thromboembolic organised in a concave shape that “points” toward the vessel lumen 3
MRI
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% 13.
Nuclear medicine
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.
Treatment and prognosis
Providing cardiopulmonary support is the initial treatment. Anticoagulation is doneprovided in patients without risk of active bleeding. If the emboli are large or there is a large clot burden, thrombolysis is an option. In some cases, embolectomy and placement of vena caval filters are required.
Complications
- acute emboli
- pulseless electrical activity in the context of a large obstructing saddle embolus
- acute or chronic emboli
-
right ventricular dysfunction
- CT features suggestive of right ventricular dysfunction include 8
- abnormal position of the interventricular septum
- inferior vena caval contrast reflux
- RVD (right ventricular diameter):LVD (left ventricular diameter) ratio >1 on reconstructed four chamber views
- RVD:LVD ratio >1 on standard axial views is not considered to be a good predictor of right ventricular dysfunction 8
- CT features suggestive of right ventricular dysfunction include 8
-
right ventricular dysfunction
- subacute-to-chronic emboli
Differential diagnosis
- pulmonary artery sarcoma
- artefact may cause pseudo-filling defects and can be caused by:
-<a href="/articles/fleischner-sign-1">Fleishner sign</a>: enlarged pulmonary artery (20%)</li>- +<a href="/articles/fleischner-sign-enlarged-pulmonary-artery">Fleishner sign</a>: enlarged pulmonary artery (20%)</li>
-</ul><h5>MRI</h5><p>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% <sup>13</sup>.</p><h5>Nuclear medicine</h5><p>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 <a href="/articles/modified-pioped-criteria-for-diagnosis-of-pulmonary-embolus">PIOPED criteria</a>.</p><h4>Treatment and prognosis</h4><p>Providing cardiopulmonary support is the initial treatment. Anticoagulation is done in patients without risk of active bleeding. If the emboli are large, thrombolysis is an option. In some cases, embolectomy and placement of vena caval filters are required.</p><h5>Complications</h5><ul>- +</ul><h5>MRI</h5><p>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% <sup>13</sup>.</p><h5>Nuclear medicine</h5><p>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 <a href="/articles/modified-pioped-criteria-for-diagnosis-of-pulmonary-embolus">PIOPED criteria</a>.</p><h4>Treatment and prognosis</h4><p>Providing cardiopulmonary support is the initial treatment. Anticoagulation is provided in patients without risk of active bleeding. If the emboli are large or there is a large clot burden, thrombolysis is an option. In some cases, embolectomy and placement of vena caval filters are required.</p><h5>Complications</h5><ul>
-</ul><h4>Differential diagnosis</h4><ul><li><a href="/articles/pulmonary-artery-sarcoma">pulmonary artery sarcoma</a></li></ul>- +</ul><h4>Differential diagnosis</h4><ul>
- +<li><a href="/articles/pulmonary-artery-sarcoma">pulmonary artery sarcoma</a></li>
- +<li>artefact may cause pseudo-filling defects and can be caused by:<ul>
- +<li>breathing motion</li>
- +<li>patient movement</li>
- +<li>transient contrast bolus interruption <sup>16</sup> - due to <a title="Valsalva maneuver" href="/articles/valsalva-manoeuvre">valvsalva</a> or <a title="PFO" href="/articles/patent-foramen-ovale">PFO</a>, where causes unopacified blood to enter the right ventricle and pulmonary arteries. Scanning in end expiration can reuced or elimination this artefact.</li>
- +</ul>
- +</li>
- +</ul>
References changed:
- 16. Martin L. Gunn. Pearls and Pitfalls in Emergency Radiology. (2013) ISBN: 9781139619899 - <a href="http://books.google.com/books?vid=ISBN9781139619899">Google Books</a>
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