Introduction
Background
Computed tomography angiography in a young man who experienced acute chest pain and shortness of breath after a transcontinental flight. This image demonstrates a clot in the anterior segmental artery in the left upper lung (LA2) and a clot in the anterior segmental artery in the right upper lung (RA2).
Computed tomography angiogram in a 69-year-old man with known pulmonary arterial hypertension and a history of chronic pulmonary embolism. This image shows an eccentric mural thrombus with punctate calcification along the anterior wall of the right lower interlobar artery.
Pulmonary embolism (PE) was clinically described in the early 1800s, and von Virchow first described the connection between venous thrombosis and PE.1,2 In 1922, Wharton and Pierson reported the first radiographic description of PE.3
Since that time, imaging has played an important role in the diagnosis of PE. For many years, ventilation-perfusion (V/Q) scintigraphy has been the main imaging modality for the evaluation of patients with suspected PE. However, with the advent of and the widespread availability of faster computed tomography (CT) scanners, CT scanning has emerged as another important diagnostic test for the evaluation of not only PE, but also deep venous thrombosis (DVT) in select patients.
For excellent patient education resources, visit eMedicine's Lung and Airway Center and Circulatory Problems Center. Also, see eMedicine's patient education articles Pulmonary Embolism and Blood Clot in the Legs.
Related eMedicine topics:
Deep Venous Thrombosis and Thrombophlebitis
Deep Venous Thrombosis, Lower Extremity
Perioperative DVT Prophylaxis
Thromboembolism
Pathophysiology
Three primary influences predispose a patient to thrombus formation; these form the so-called Virchow triad: (1) endothelial injury, (2) stasis or turbulence of blood flow, and (3) blood hypercoagulability.1,2,4
More than 90% of all PEs arise from thrombi within the large deep veins of the legs, typically the popliteal vein and the larger veins above it.1,2,4 The pathophysiologic consequences of thromboembolism in the lung largely depend on the cardiopulmonary status of the patient and on the size of the embolus, which, in turn, dictates the size of the occluded pulmonary artery.
PE has 2 important consequences: (1) an increase in pulmonary artery pressure due to blockage of flow and, possibly, vasospasm caused by neurogenic mechanisms and/or release of mediators (eg, thromboxane A2 and serotonin) and (2) ischemia of the downstream pulmonary parenchyma. Thus, occlusion of major vessels or of more than 60% of the arterial bed suddenly increases the pulmonary artery pressures, diminishes cardiac output, and causes right-sided heart failure (acute cor pulmonale) or even death. Usually, hypoxemia develops as a result of multiple mechanisms. If smaller vessels are occluded, the result is less catastrophic, or the event may be even clinically silent.
Conditions associated with an increased risk of thrombosis include the following:
- Primary (genetic) conditions
- Mutations in factor V
- Antithrombin III deficiency
- Protein C or protein S deficiency
- Fibrinolysis defects
- Secondary (acquired) conditions
- High risk for thrombosis
- Prolonged bed rest or immobilization (many hours of travel)
- Myocardial infarction
- Tissue damage (surgery, fracture, burns)
- Cancer
- Prosthetic cardiac valves
- Disseminated intravascular coagulation
- Lupus anticoagulant
- Atrial fibrillation
- Cardiomyopathy
- Nephrotic syndrome
- Hyperestrogenic states
- Oral contraceptive use
- Sickle cell anemia
- Smoking
Frequency
United States
DVT and PE are associated with approximately 300,000-600,000 hospitalizations each year, and as many as 50,000 individuals die each year as a result of PE.5
Mortality/Morbidity
Treatment with anticoagulation or catheter-directed pharmacologic agents is highly effective but not without complications. Therefore, the diagnosis of PE, requires a high degree of certainty. Conversely, untreated PE can be fatal. Treatment reduces the mortality rate from 30% to less than 10%.
Race
No racial predispositions to thromboembolism are known.
Sex
The incidence of venous thromboembolic events in the older population is greater among men than women. In patients younger than 55 years, the incidence of PE is higher in females. The overall age- and sex-adjusted annual incidence of venous thromboembolism is reported to be 117 cases per 100,000 people (DVT, 48 cases per 100,000; PE, 69 cases per 100,000).6
Age
PE is predominantly a disease in older individuals. The incidence of venous thromboembolic events in the elderly is more common among men than women. In patients younger than 55 years, the incidence of PE is higher in females. The overall age- and sex-adjusted annual incidence of venous thromboembolism is reported to be 117 cases per 100,000 people (DVT, 48 cases per 100,000; PE, 69 cases per 100,000).6
Anatomy
Knowledge of bronchovascular anatomy is the key to the accurate interpretation of CT scans obtained for the evaluation of PE. A systematic approach in identifying all vessels is important. The bronchovascular anatomy has been described on the basis of the segmental anatomy of lungs. The segmental arteries are seen near the accompanying branches of the bronchial tree and are situated either medially (in the upper lobes) or laterally (in the lower lobes, lingula, and right middle lobe).
Presentation
PE should be considered whenever unexplained dyspnea occurs. Dyspnea with or without associated anxiety, pleuritic chest pain, and hemoptysis are common but nonspecific symptoms of PE. Any of these symptoms may also develop with other conditions, such as pneumonia, exacerbated chronic obstructive lung disease, congestive heart failure, and lung cancer. PE may cause light-headedness and syncope, but these may also be the result of other conditions that cause hypoxemia or hypotension.
Clinical findings alone are not reliable in the diagnosis of PE. This fact is underscored by the high incidence of unsuspected PE in autopsy series. Physical examination of the patient with PE may reveal tachypnea, tachycardia, fever, and pleuritic rub, all of which are nonspecific findings. Hypoxemia is common in acute PE, but it is not universally present. Even the alveolar-arterial difference may be normal in rare cases of PE, particularly in younger patients without concomitant lung disease. Nonspecific electrocardiographic (ECG) abnormalities may develop in acute PE; these include T-wave changes, ST-segment abnormalities, and left- or right-axis deviation.
Preferred Examination
In patients with possible PE, chest radiographic findings may indicate if lung scanning (V/Q) or helical CT scanning should be the next method of evaluation. If the chest radiograph is normal, V/Q findings may be diagnostic; if the chest radiograph is abnormal, helical CT should be performed.4,5,7
A quantitative D-dimer assay is reported to have high negative predictive value and may be effective for excluding the need for pulmonary CT angiography (CTA) in selected cases.8 Conventional pulmonary angiography is invasive, time consuming, and more expensive than other tests. The role of conventional angiography is limited to patients in whom other results are nondiagnostic or the clinical suspicion is high.6,9,10 In patients with suspected DVT, the workup should start with leg ultrasonography.
Limitations of Techniques
V/Q findings may be nondiagnostic.
Iodinated contrast agents are needed for helical CT pulmonary angiography, and their use may not be possible in patients with impaired renal function or in patients with a severe allergy to the contrast material.
Small (subsegmental) emboli may be missed with CT angiography. Compared with CT scanning, conventional pulmonary angiography requires more expertise and support staff. Conventional angiography is also invasive, time consuming, more expensive, and less available. In addition, a chronic central mural thrombus that is easily seen with CT scanning may be missed at pulmonary angiography.11
Differential Diagnoses
Other Problems to Be Considered
Aortic dissection
Lung trauma
Mediastinitis, acute
Pneumomediastinum
More on Acute Pulmonary Embolism (Helical CT) |
 Overview: Acute Pulmonary Embolism (Helical CT) |
| Imaging: Acute Pulmonary Embolism (Helical CT) |
| Multimedia: Acute Pulmonary Embolism (Helical CT) |
| References |
| Next Page » |
References
Boyden EA. Segmental Anatomy of the Lungs: Study of the Patterns of the Segmental Bronchi and Related Pulmonary Vessels. New York, NY: McGraw-Hill; 1955:23-32.
Mitchell RN, Kumar V. Hemodynamic disorders, thrombosis, and shock. In: Kumar V, Cotran RS, Robbins SL, eds. Basic Pathology. 6th ed. Philadelphia, Pa: WB Saunders; 1997:60-80.
Wharton LR, Pierson JW. Minor forms of pulmonary embolism after abdominal operations. JAMA. 1922;79:1904-10.
Remy-Jardin M, Pistolesi M, Goodman LR, et al. Management of suspected acute pulmonary embolism in the era of CT angiography: a statement from the Fleischner Society. Radiology. Nov 2007;245(2):315-29. [Medline]. [Full Text].
Patel S, Kazerooni EA. Helical CT for the evaluation of acute pulmonary embolism. AJR Am J Roentgenol. Jul 2005;185(1):135-49. [Medline]. [Full Text].
Silverstein MD, Heit JA, Mohr DN, et al. Trends in the incidence of deep vein thrombosis and pulmonary embolism: a 25-year population-based study. Arch Intern Med. Mar 23 1998;158(6):585-93. [Medline]. [Full Text].
Stein PD, Woodard PK, Weg JG, et al. Diagnostic pathways in acute pulmonary embolism: recommendations of the PIOPED II Investigators. Radiology. Jan 2007;242(1):15-21. [Medline]. [Full Text].
Abcarian PW, Sweet JD, Watabe JT, Yoon HC. Role of a quantitative D-dimer assay in determining the need for CT angiography of acute pulmonary embolism. AJR Am J Roentgenol. Jun 2004;182(6):1377-81. [Medline]. [Full Text].
Doshi SK, Negus IS, Oduko JM. Fetal radiation dose from CT pulmonary angiography in late pregnancy: a phantom study. Br J Radiol. Apr 14 2008;[Medline].
Yankelevitz DF, Gamsu G, Shah A, et al. Optimization of combined CT pulmonary angiography with lower extremity CT venography. AJR Am J Roentgenol. Jan 2000;174(1):67-9. [Medline]. [Full Text].
Oser RF, Zuckerman DA, Gutierrez FR, Brink JA. Anatomic distribution of pulmonary emboli at pulmonary angiography: implications for cross-sectional imaging. Radiology. Apr 1996;199(1):31-5. [Medline]. [Full Text].
Yasui T, Tanabe N, Terada J, et al. Multidetector-row computed tomography management of acute pulmonary embolism. Circ J. Dec 2007;71(12):1948-54. [Medline]. [Full Text].
Patel S, Kazerooni EA, Cascade PN. Pulmonary embolism: optimization of small pulmonary artery visualization at multi-detector row CT. Radiology. May 2003;227(2):455-60. [Medline].
Remy-Jardin M, Remy J, Deschildre F, et al. Diagnosis of pulmonary embolism with spiral CT: comparison with pulmonary angiography and scintigraphy. Radiology. Sep 1996;200(3):699-706. [Medline]. [Full Text].
Loud PA, Katz DS, Klippenstein DL, Shah RD, Grossman ZD. Combined CT venography and pulmonary angiography in suspected thromboembolic disease: diagnostic accuracy for deep venous evaluation. AJR Am J Roentgenol. Jan 2000;174(1):61-5. [Medline]. [Full Text].
Garg K, Kemp JL, Wojcik D, et al. Thromboembolic disease: comparison of combined CT pulmonary angiography and venography with bilateral leg sonography in 70 patients. AJR Am J Roentgenol. Oct 2000;175(4):997-1001. [Medline]. [Full Text].
Remy-Jardin M, Remy J, Wattinne L, Giraud F. Central pulmonary thromboembolism: diagnosis with spiral volumetric CT with the single-breath-hold technique--comparison with pulmonary angiography. Radiology. Nov 1992;185(2):381-7. [Medline]. [Full Text].
Goodman LR, Curtin JJ, Mewissen MW, et al. Detection of pulmonary embolism in patients with unresolved clinical and scintigraphic diagnosis: helical CT versus angiography. AJR Am J Roentgenol. Jun 1995;164(6):1369-74. [Medline]. [Full Text].
Mayo JR, Remy-Jardin M, Müller NL, et al. Pulmonary embolism: prospective comparison of spiral CT with ventilation-perfusion scintigraphy. Radiology. Nov 1997;205(2):447-52. [Medline]. [Full Text].
Garg K, Welsh CH, Feyerabend AJ, et al. Pulmonary embolism: diagnosis with spiral CT and ventilation-perfusion scanning--correlation with pulmonary angiographic results or clinical outcome. Radiology. Jul 1998;208(1):201-8. [Medline]. [Full Text].
Drucker EA, Rivitz SM, Shepard JA, Boiselle PM, et al. Acute pulmonary embolism: assessment of helical CT for diagnosis. Radiology. Oct 1998;209(1):235-41. [Medline]. [Full Text].
Gupta A, Frazer CK, Ferguson JM, et al. Acute pulmonary embolism: diagnosis with MR angiography. Radiology. Feb 1999;210(2):353-9. [Medline]. [Full Text].
Meaney JF, Weg JG, Chenevert TL, et al. Diagnosis of pulmonary embolism with magnetic resonance angiography. N Engl J Med. May 15 1997;336(20):1422-7. [Medline]. [Full Text].
The PIOPED Investigators. Value of the ventilation/perfusion scan in acute pulmonary embolism. Results of the prospective investigation of pulmonary embolism diagnosis (PIOPED). JAMA. May 23-30 1990;263(20):2753-9. [Medline].
Diffin DC, Leyendecker JR, Johnson SP, Zucker RJ, Grebe PJ. Effect of anatomic distribution of pulmonary emboli on interobserver agreement in the interpretation of pulmonary angiography. AJR Am J Roentgenol. Oct 1998;171(4):1085-9. [Medline]. [Full Text].
Garg K, Sieler H, Welsh CH, Johnston RJ, Russ PD. Clinical validity of helical CT being interpreted as negative for pulmonary embolism: implications for patient treatment. AJR Am J Roentgenol. Jun 1999;172(6):1627-31. [Medline]. [Full Text].
Goodman LR, Lipchik RJ, Kuzo RS, et al. Subsequent pulmonary embolism: risk after a negative helical CT pulmonary angiogram--prospective comparison with scintigraphy. Radiology. May 2000;215(2):535-42. [Medline]. [Full Text].
Jackson CL, Franklin J. With a system of nomenclature the bronchial tree and lungs correlated. Chest. 1943;9:319-26. [Full Text].
Novelline RA, Baltarowich OH, Athanasoulis CA, et al. The clinical course of patients with suspected pulmonary embolism and a negative pulmonary arteriogram. Radiology. Mar 1978;126(3):561-7. [Medline].
Piasecki DP, Poynton AR, Mintz DN, et al. Thromboembolic disease after combined anterior/posterior reconstruction for adult spinal deformity: a prospective cohort study using magnetic resonance venography. Spine. Mar 15 2008;33(6):668-72. [Medline].
Schoepf UJ, Costello P. CT angiography for diagnosis of pulmonary embolism: state of the art. Radiology. Feb 2004;230(2):329-37. [Medline]. [Full Text].
Further Reading
Keywords
acute pulmonary embolism, helical CT, helical computed tomography, helical computer tomography, pulmonary thromboembolism, PE, deep vein thrombosis, deep venous thrombosis, DVT, thromboembolic disease, ventilation-perfusion scintigraphy, V/Q scintigraphy, V/Q scan, V-P scan, D-dimer assay, D-dimer
