Diagnostic Imaging Pathways - Pulmonary Embolism (Haemodynamically Unstable)
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This pathway provides guidance on the imaging of haemodynamically unstable adult patients with suspected pulmonary embolism.
Date reviewed: January 2012
Date of next review: 2017/2018
Published: January 2012
Quick User Guide
Move the mouse cursor over the PINK text boxes inside the flow chart to bring up a pop up box with salient points.
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The relative radiation level (RRL) of each imaging investigation is displayed in the pop up box.
| SYMBOL | RRL | EFFECTIVE DOSE RANGE |
 | None | 0 |
 | Minimal | < 1 millisieverts |
 | Low | 1-5 mSv |
 | Medium | 5-10 mSv |
 | High | >10 mSv |
Images
Image GalleryNote: These images open in a new page | ||
|---|---|---|
| 1 |  |
Hampton's Hump Image 1 (Plain Radiograph): There is a peripheral wedge shaped opacity representing pulmonary infarction and atelectasis secondary to a pulmonary embolus (arrow). This radiographic sign is referred to as Hampton's Hump. |
| 2a |  |
Bilateral Pulmonary Embolism Image 2a and 2b (Computed Tomography): Axial and reconstructed images of bilateral pulmonary arterial emboli (arrows) |
| 2b |  |
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| 3 |  |
Bilateral Pulmonary Embolism Image 3 (Ventilation Perfusion Scan): The ventilation series demonstrates uniform distribution of tracer throughout both lung fields. The perfusion series demonstrates generalised reduced tracer uptake in the right lung with multiple segmental and subsegmental perfusion defects throughout both lung fields. These findings have a high probability for recent pulmonary embolism. |
Teaching Points
Teaching Points
- Suspected PE in the setting of haemodynamic instability represents a specific clinical problem as it is immediately life threatening and requires urgent investigation and treatment
- Multidetector CT pulmonary angiography is a highly sensitive and specific test which can directly demonstrate PE through filling defects within contrast filled pulmonary arteries. Although CT emits ionising radiation, the urgency of the situation justifies its use as a first line investigation if it is immediately available
- If CTPA is not available, beside echocardiography is the most useful test as it can provide indirect signs of acute pulmonary hypertension due to PE and can also assess for cardiac differential diagnoses of shock
ct
Computed Tomography Pulmonary Angiography (CTPA)
- Demonstrates pulmonary embolism by showing a filling defect within contrast filled pulmonary arteries
- The performance of CTPA varies in the literature depending on whether single slice or multidetector CT (MDCT) is used and also on the expertise of the institution
- The sensitivity and specificity of 4-row MDCT in the largest trial to date (PIOPEDII Trial) is reported at 83% and 96% respectively. The negative predictive value in high risk patients is 60%. Single slice CT has a sensitivity and specificity of approximately 85% 10,11,12
- MDCT has a number of advantages over older scanners including
- CTPA is associated with significantly higher radiation exposure compared to radionuclide (VQ) scans. The effective dose of CTPA is estimated at around 8-10 mSv, compared to around 1.3 mSv for a VQ scan. 13,14 However, due to the urgency of the clinical situation in patients with haemodynamic instability, CTPA is the preferred modality if immediately available due to its accuracy and rapidity
- CT is also able to provide information on alternative diagnoses that may mimic PE 7,8
- Limitations include
- Radiation exposure
- Risk of contrast allergy and renal impairment
- Subsegmental emboli may be difficult to visualise
- Subject to interpretive pitfalls such as respiratory motion artifact, streak artifact and problems related to patient body habitus. Lymph nodes may also result in false positives 9
echo
Bedside Echocardiography
- Bedside echocardiography is a useful test in the situation of suspected PE with haemodynamic instability
- Transthoracic echo may detect indirect signs of acute pulmonary hypertension and right ventricular overload or may detect a right heart thrombus in transit. Transoesophageal echo allows direct visualisation of thrombus in the pulmonary arteries 13
- Echocardiographic signs of PE include
- Increased right ventricular size
- Decreased right ventricular function
- Tricuspid regurgitation
- Reported sensitivity ranges from 60-70%. In the setting of haemodynamic instability, the absence of echocardiographic signs of right ventricular overload or dysfunction practically excludes PE as a cause of the instability 10,14
- Echo may also assist in the differential diagnosis of shock by detecting cardiac tamponade, acute valvular dysfunction, acute myocardial infarction and hypovolaemia
- Echo is currently not recommended in the diagnostic approach to haemodynamically stable, normotensive patients 13
References
References
References are graded from Level I to V according to the Oxford Centre for Evidence-Based Medicine, Levels of Evidence. Download the document
- McCollough CH, Zink FE. Performance evaluation of a multi-slice CT system. Med Phys. 1999;26:2223-30. (Level II evidence)
- Schoepf UJ, Holzknecht N, Helmberger TK, et al. Subsegmental pulmonary emboli: improved detection with thin-collimation multi-detector row spiral CT. Radiology. 2002;222:483-90. (Level IV evidence)
- Schoepf UJ, Costello P. CT angiography for diagnosis of pulmonary embolism: state of the art. Radiology. 2004;230:329-37. (Review article)
- Patel S, Kazerooni EA, Cascade PN. Pulmonary embolism: optimization of small pulmonary artery visualization at multi-detector row CT. Radiology. 2003;227:455-60. (Level II evidence). View the reference
- Remy-Jardin M, Tillie-Leblond I, Szapiro D, et al. CT angiography of pulmonary embolism in patients with underlying respiratory disease: impact of multislice CT on image quality and negative predictive value. Eur Radiol. 2002;12:1971-8. (Level IV evidence)
- Coche E, Verschuren F, Keyeux A, et al. Diagnosis of acute pulmonary embolism in outpatients: comparison of thin-collimation multi-collimation multi-detector spiral CT and planar ventilation-perfusion scintigraphy. Radiology 2003;229:757-65. (Level III evidence)
- Kim KI, Muller NL, Mayo JR. Clinically suspected pulmonary embolism: utility of spiral CT. Radiology. 1999;210:693-7. (Level III evidence)
- Garg K, Sieler H, Welsh CH, et al. Clinical validity of helical CT being interpreted as negative for pulmonary embolism: implications for patient treatment. AJR Am J Roentgenol. 1999;172:1627-31. (Level IV evidence)
- Aviram G, Levy G, Fishman JE. Pitfalls in the diagnosis of acute pulmonary embolism on spiral computer tomography. Curr Probl Diagn Radiol. 2004;33:74-84. (Level IV evidence)
- Roy P-M, Colombet I, Durieux P, Chatellier G, Sors H, Meyer G. Systematic review and meta-analysis of strategies for the diagnosis of suspected pulmonary embolism. BMJ. 2005;331:259-67. (Level I evidence). View the reference
- Patel S, Kazerooni EA. Helical CT for the evaluation of acute pulmonary embolism. AJR Am J Roentgenol. 2005;185:135-49. (Review article)
- Stein PD, Fowler SE, Goodman LR et al. Multidetector computed tomography for acute pulmonary embolism. N Engl J Med. 2006;354:2317-27. (Level II evidence). View the reference
- Torbicki A, Perrier A, Konstantinides S, Agnelli G, Galie N, Pruszczyk P, et al. Guidelines on the diagnosis and management of acute pulmonary embolism: the Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology (ESC). Eur Heart J. 2008;29(18):2276-315. (Practice guideline). View the reference
- Miniati M, Monti S, Pratali L, Di Ricco G et al. Value of transthoracic echocardiography in the diagnosis of pulmonary embolism: results of a prospective study in unselected patients. Am J Med. 2001;110(7):528-35. (Level II/III evidence). View the reference
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