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CT Angiography of Pulmonary Embolism: Diagnostic Criteria and Causes of Misdiagnosis¹

¹ From the Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Founders Building 202, 55 Fruit St, Boston, MA 02114. Recipient of a Certificate of Merit award for an education exhibit at the 2003 RSNA scientific assembly. Received January 13, 2004; revision requested March 10 and received April 16; accepted April 16. All authors have no financial relationships to disclose. Address correspondence to C.W. (e-mail: cwittram@partners.org).

View larger version (30K): [in a new window]   Figure 1.  Graph illustrates that the number of pulmonary angiographic studies performed per inpatient with suspected thromboembolic disease decreased significantly between 1992 and 2001 (P = .02). (Fig 1 modified and Figs 1-3 reprinted, with permission, from reference 12.)

View larger version (29K): [in a new window]   Figure 2.  Graph illustrates that the number of ventilation-perfusion scans performed per inpatient with suspected thromboembolic disease decreased significantly between 1992 and 2001 (P = .0003). (Fig 1 modified and Figs 1-3 reprinted, with permission, from reference 12.)

View larger version (20K): [in a new window]   Figure 3.  Graph illustrates that the number of CT studies performed for pulmonary embolism per inpatient increased significantly between 1992 and 2001 (P = .006). Figures 1-3 demonstrate the timing of changes that occur when a new technology replaces an old one; in this case, a downturn in the use of pulmonary angiography and ventilation-perfusion scintigraphy almost exactly coincides with a steep increase in CT pulmonary angiography usage. (Fig 1 modified and Figs 1-3 reprinted, with permission, from reference 12.)

View larger version (73K): [in a new window]   Figure 4.  Acute occlusive pulmonary embolism in a 32-year-old woman who presented with chest pain. CT scan shows a pulmonary embolus within the posterobasal segment of the right lower lobe artery (arrow). The artery is enlarged compared with adjacent patent vessels.

View larger version (62K): [in a new window]   Figure 5a.  Acute pulmonary embolism in a 45-year-old woman who presented with chest pain. (a) CT scan shows a pulmonary embolus that affects the segmental artery of the laterobasal segment of the right lower lobe. This partial filling defect surrounded by contrast material produces the polo mint sign (arrow). (b) CT scan shows acute emboli that affect subsegmental arteries of the laterobasal segment (arrows).

View larger version (65K): [in a new window]   Figure 5b.  Acute pulmonary embolism in a 45-year-old woman who presented with chest pain. (a) CT scan shows a pulmonary embolus that affects the segmental artery of the laterobasal segment of the right lower lobe. This partial filling defect surrounded by contrast material produces the polo mint sign (arrow). (b) CT scan shows acute emboli that affect subsegmental arteries of the laterobasal segment (arrows).

View larger version (118K): [in a new window]   Figure 6.  Acute pulmonary embolism in a 66-year-old man who presented with chest pain and dyspnea. CT scan shows an acute pulmonary embolus that causes a partial filling defect surrounded by contrast material (railway track sign) (arrow). Another acute pulmonary embolus affects the left main pulmonary artery (arrowhead).

View larger version (73K): [in a new window]   Figure 7.  Acute pulmonary embolism in a 58-year-old woman who presented with chest pain and dyspnea. CT scan demonstrates a pulmonary embolus that results in an eccentrically positioned partial filling defect, which is surrounded by contrast material and forms acute angles with the arterial wall (arrows).

View larger version (132K): [in a new window]   Figure 8.  Acute pulmonary embolism in a 58-year-old woman who presented with chest pain and dyspnea. CT scan shows an acute pulmonary embolus with ancillary findings of a peripheral wedge-shaped area of hyperattenuation in the lung (arrow), a finding that may represent an infarct, as well as a linear band (arrowhead).

View larger version (86K): [in a new window]   Figure 9.  Acute pulmonary embolism in a 42-year-old man who presented with chest pain and severe dyspnea. CT scan reveals that the short axis of the right ventricle (dashed line) is wider than that of the left ventricle (solid line), a situation that was caused by acute pulmonary embolism and created right ventricular strain.

View larger version (86K): [in a new window]   Figure 10a.  Acute central pulmonary embolism in an asymptomatic 87-year-old woman. (a) Unenhanced CT scan demonstrates subtle regions of hyperattenuation (arrow). (b) Confirmatory CT pulmonary angiogram demonstrates acute pulmonary embolism within the right main and left interlobar pulmonary arteries.

View larger version (78K): [in a new window]   Figure 10b.  Acute central pulmonary embolism in an asymptomatic 87-year-old woman. (a) Unenhanced CT scan demonstrates subtle regions of hyperattenuation (arrow). (b) Confirmatory CT pulmonary angiogram demonstrates acute pulmonary embolism within the right main and left interlobar pulmonary arteries.

View larger version (68K): [in a new window]   Figure 11.  Chronic pulmonary embolism in a 27-year-old man with dyspnea. CT scan shows complete occlusion of vessels in the left lung (arrowheads) that are smaller than adjacent patent vessels. Note the collateral blood supply from a branch of the right hemidiaphragmatic artery (arrow).

View larger version (71K): [in a new window]   Figure 12.  Chronic pulmonary embolism in a 62-year-old man with dyspnea. CT scan shows an eccentrically located thrombus that forms obtuse angles with the vessel wall (arrows). Note the dilated collateral bronchial artery (arrowhead).

View larger version (78K): [in a new window]   Figure 13.  Chronic pulmonary embolism in the same patient as in Figure 11. CT scan reveals a small, recanalized pulmonary artery with contrast material in the central lumen (arrow).

View larger version (88K): [in a new window]   Figure 14.  Chronic pulmonary embolism in a 56-year-old man with dyspnea. CT scan shows a flap (arrow) within a small right interlobar pulmonary artery. Collateral bronchial artery dilatation is also noted (arrowhead).

View larger version (78K): [in a new window]   Figure 15.  Chronic pulmonary embolism in the same patient as in Figure 12. CT scan shows a large chronic pulmonary embolus in the main and left main pulmonary arteries (arrowhead). Arrows indicate collateral bronchial arteries.

View larger version (87K): [in a new window]   Figure 16.  Chronic pulmonary embolism in a 60-year-old woman with dyspnea. CT scan demonstrates a mosaic perfusion pattern. The dark regions of underperfused lung are seen to contain vessels (arrows) that are smaller than the adjacent patent vessels in the normally perfused lung.

View larger version (73K): [in a new window]   Figure 17.  Chronic pulmonary embolism in a 62-year-old man with dyspnea. CT scan shows pulmonary arterial wall calcification (arrows), a secondary sign of chronic pulmonary embolism.

View larger version (60K): [in a new window]   Figure 18.  Pulmonary arterial hypertension secondary to chronic pulmonary embolism in the same patient as in Figure 12. On a CT scan, the pulmonary artery measures 41 mm in diameter (black line), a finding that indicates hypertension.

View larger version (77K): [in a new window]   Figure 19.  Chronic pulmonary embolism in the same patient as in Figure 12. CT scan demonstrates pericardial fluid (arrows) associated with pulmonary arterial hypertension secondary to chronic pulmonary embolism.

View larger version (149K): [in a new window]   Figure 20a.  Respiratory motion artifact in a 61-year-old man with dyspnea. (a) CT scan (lung window) shows composite images of vessels (seagull sign) (arrows). (b) CT scan (mediastinal window) demonstrates a low-attenuation abnormality caused by partial volume averaging of vessel and adjacent lung (arrow), a finding that can simulate pulmonary embolism.

View larger version (91K): [in a new window]   Figure 20b.  Respiratory motion artifact in a 61-year-old man with dyspnea. (a) CT scan (lung window) shows composite images of vessels (seagull sign) (arrows). (b) CT scan (mediastinal window) demonstrates a low-attenuation abnormality caused by partial volume averaging of vessel and adjacent lung (arrow), a finding that can simulate pulmonary embolism.

View larger version (124K): [in a new window]   Figure 21.  Image noise in scans of a 39-year-old woman with chest pain. CT scan clearly depicts image noise pixels within the contrast material-filled heart chambers, a confluence of which could be misinterpreted as pulmonary embolism (arrow). Unlike true emboli, however, these apparent abnormalities are not well-defined filling defects. Small pulmonary emboli could be obscured by a large amount of image noise.

View larger version (99K): [in a new window]   Figure 22a.  Beam-hardening artifact in a 63-year-old man with respiratory failure. (a) On a CT scan, a pulmonary artery catheter causes adjacent beam-hardening artifacts within the main and right pulmonary arteries that mimic pulmonary embolism (arrows). Small pulmonary emboli are noted in the left pulmonary artery. (b) CT scan produced with bone window settings clearly depicts the pulmonary artery catheter. Adjacent beam-hardening artifacts are also seen.

View larger version (107K): [in a new window]   Figure 22b.  Beam-hardening artifact in a 63-year-old man with respiratory failure. (a) On a CT scan, a pulmonary artery catheter causes adjacent beam-hardening artifacts within the main and right pulmonary arteries that mimic pulmonary embolism (arrows). Small pulmonary emboli are noted in the left pulmonary artery. (b) CT scan produced with bone window settings clearly depicts the pulmonary artery catheter. Adjacent beam-hardening artifacts are also seen.

View larger version (54K): [in a new window]   Figure 23.  Flow-related artifact in a 60-year-old woman with pleuritic chest pain. Coronal reformatted image of the right interlobar artery and the posterobasal segment of the pulmonary artery demonstrates dense contrast material superior and inferior to a region of poorly enhanced blood (arrow).

View larger version (91K): [in a new window]   Figure 24a.  Flow-related artifact in a 73-year-old woman with chest pain. (a) CT scan shows poor enhancement of the interlobar and middle lobe pulmonary arteries due to flow-related artifact. More distally, the pulmonary arteries were well enhanced. Note also the fluid-filled, dilated esophagus. (b) Repeat CT pulmonary angiogram demonstrates segmental pulmonary emboli within the medial and lateral segmental branches of the middle lobe artery (arrows).

View larger version (106K): [in a new window]   Figure 24b.  Flow-related artifact in a 73-year-old woman with chest pain. (a) CT scan shows poor enhancement of the interlobar and middle lobe pulmonary arteries due to flow-related artifact. More distally, the pulmonary arteries were well enhanced. Note also the fluid-filled, dilated esophagus. (b) Repeat CT pulmonary angiogram demonstrates segmental pulmonary emboli within the medial and lateral segmental branches of the middle lobe artery (arrows).

View larger version (83K): [in a new window]   Figure 25a.  Acute pulmonary embolism in a 59-year-old man. (a) CT scan (window width = 400 HU, window level = 40 HU) demonstrates thrombus within the right interlobar artery (arrow). (b) CT scan (window width = 552 HU, window level = 276 HU) shows acute pulmonary embolism within the medial segment of the middle lobe artery (arrow) that was missed on the image in a. The window width is equal to the mean attenuation of the main pulmonary artery plus two standard deviations, and the window level equals one-half of this value (29). (c) CT scan (window width = 700 HU, window level = 100 HU) demonstrates thrombus within the right interlobar artery and the medial segment of the middle lobe artery. Figure 25 illustrates the effect of different window settings on detection of pulmonary embolism.

View larger version (78K): [in a new window]   Figure 25b.  Acute pulmonary embolism in a 59-year-old man. (a) CT scan (window width = 400 HU, window level = 40 HU) demonstrates thrombus within the right interlobar artery (arrow). (b) CT scan (window width = 552 HU, window level = 276 HU) shows acute pulmonary embolism within the medial segment of the middle lobe artery (arrow) that was missed on the image in a. The window width is equal to the mean attenuation of the main pulmonary artery plus two standard deviations, and the window level equals one-half of this value (29). (c) CT scan (window width = 700 HU, window level = 100 HU) demonstrates thrombus within the right interlobar artery and the medial segment of the middle lobe artery. Figure 25 illustrates the effect of different window settings on detection of pulmonary embolism.

View larger version (85K): [in a new window]   Figure 25c.  Acute pulmonary embolism in a 59-year-old man. (a) CT scan (window width = 400 HU, window level = 40 HU) demonstrates thrombus within the right interlobar artery (arrow). (b) CT scan (window width = 552 HU, window level = 276 HU) shows acute pulmonary embolism within the medial segment of the middle lobe artery (arrow) that was missed on the image in a. The window width is equal to the mean attenuation of the main pulmonary artery plus two standard deviations, and the window level equals one-half of this value (29). (c) CT scan (window width = 700 HU, window level = 100 HU) demonstrates thrombus within the right interlobar artery and the medial segment of the middle lobe artery. Figure 25 illustrates the effect of different window settings on detection of pulmonary embolism.

View larger version (66K): [in a new window]   Figure 26.  Streak artifact in a 35-year-old woman with chest pain. CT scan shows streak artifact from dense contrast material within the superior vena cava (arrows). The artifact can be recognized by its nonanatomic, radiating nature.

View larger version (131K): [in a new window]   Figure 27a.  Lung algorithm artifact in a 70-year-old woman with dyspnea. (a) CT scan obtained with an edge-enhancing algorithm shows a lung algorithm artifact that mimics acute pulmonary embolism (arrows). This finding is seen when viewed with mediastinal or pulmonary embolism-specific windows and manifests as a bright ring around pulmonary arteries, particularly if associated with a flow artifact. (b) CT scan obtained with the standard algorithm does not demonstrate this artifact. No embolism was present.

View larger version (118K): [in a new window]   Figure 27b.  Lung algorithm artifact in a 70-year-old woman with dyspnea. (a) CT scan obtained with an edge-enhancing algorithm shows a lung algorithm artifact that mimics acute pulmonary embolism (arrows). This finding is seen when viewed with mediastinal or pulmonary embolism-specific windows and manifests as a bright ring around pulmonary arteries, particularly if associated with a flow artifact. (b) CT scan obtained with the standard algorithm does not demonstrate this artifact. No embolism was present.

View larger version (105K): [in a new window]   Figure 28a.  Partial volume artifact in a 52-year-old woman with dyspnea. (a) On a 3.75-mm-thick CT scan, partial volume averaging of vessel and lung creates an artifact that mimics pulmonary embolism within the anterior segment of the left upper lobe pulmonary artery (arrow). The apparent pulmonary embolism is ill defined. (b) Contiguous CT scan obtained inferior to a demonstrates normal lung adjacent to the left upper lobe pulmonary artery. (c) Contiguous CT scan obtained immediately superior to a demonstrates a contrast material-filled pulmonary artery, a finding that confirms that the low attenuation seen in a was due to partial volume artifact.

View larger version (98K): [in a new window]   Figure 28b.  Partial volume artifact in a 52-year-old woman with dyspnea. (a) On a 3.75-mm-thick CT scan, partial volume averaging of vessel and lung creates an artifact that mimics pulmonary embolism within the anterior segment of the left upper lobe pulmonary artery (arrow). The apparent pulmonary embolism is ill defined. (b) Contiguous CT scan obtained inferior to a demonstrates normal lung adjacent to the left upper lobe pulmonary artery. (c) Contiguous CT scan obtained immediately superior to a demonstrates a contrast material-filled pulmonary artery, a finding that confirms that the low attenuation seen in a was due to partial volume artifact.

View larger version (107K): [in a new window]   Figure 28c.  Partial volume artifact in a 52-year-old woman with dyspnea. (a) On a 3.75-mm-thick CT scan, partial volume averaging of vessel and lung creates an artifact that mimics pulmonary embolism within the anterior segment of the left upper lobe pulmonary artery (arrow). The apparent pulmonary embolism is ill defined. (b) Contiguous CT scan obtained inferior to a demonstrates normal lung adjacent to the left upper lobe pulmonary artery. (c) Contiguous CT scan obtained immediately superior to a demonstrates a contrast material-filled pulmonary artery, a finding that confirms that the low attenuation seen in a was due to partial volume artifact.

View larger version (115K): [in a new window]   Figure 29.  Stair step artifact in an 84-year-old man with dyspnea and chest pain. CT scan shows low-attenuation lines that traverse a vessel on coronal reformatted images (arrows). This artifact can be recognized by its nonanatomic nature and is easily distinguished from pulmonary embolism.

View larger version (74K): [in a new window]   Figure 30a.  CT scans demonstrate normal hilar lymph nodes in both upper lobes (arrows in a), adjacent to the right and left interlobar arteries (arrows in b), in the middle lobe and lingula (arrows in c), and in both lower lobes (arrows in d).

View larger version (65K): [in a new window]   Figure 30b.  CT scans demonstrate normal hilar lymph nodes in both upper lobes (arrows in a), adjacent to the right and left interlobar arteries (arrows in b), in the middle lobe and lingula (arrows in c), and in both lower lobes (arrows in d).

View larger version (82K): [in a new window]   Figure 30c.  CT scans demonstrate normal hilar lymph nodes in both upper lobes (arrows in a), adjacent to the right and left interlobar arteries (arrows in b), in the middle lobe and lingula (arrows in c), and in both lower lobes (arrows in d).

View larger version (75K): [in a new window]   Figure 30d.  CT scans demonstrate normal hilar lymph nodes in both upper lobes (arrows in a), adjacent to the right and left interlobar arteries (arrows in b), in the middle lobe and lingula (arrows in c), and in both lower lobes (arrows in d).

View larger version (73K): [in a new window]   Figure 31.  CT scan shows the vascular bifurcation between the left lower lobe and lingular arteries as a curved line surrounded by contrast material (arrow). Contiguous images demonstrated the true nature of this finding.

View larger version (93K): [in a new window]   Figure 32.  CT scan shows unenhanced pulmonary veins (arrows), which can mimic complete occlusive pulmonary embolism. However, this pitfall can be recognized by observing veins on contiguous images to the level of the right atrium.

View larger version (98K): [in a new window]   Figure 33.  Mucus plugs in an 83-year-old woman with dyspnea. CT scan shows mucus plugs (arrows), which can mimic acute pulmonary embolism. The posterobasal segment of the right lower lobe bronchus is dilated as well as mucus filled. Identification of the normal accompanying pulmonary arteries (arrowheads) allows the correct interpretation of this finding.

View larger version (108K): [in a new window]   Figure 34a.  Left-sided heart failure in a 56-year-old woman with dyspnea. (a) CT scan shows peribronchovascular interstitial thickening caused by perivascular edema (arrow), a finding that can mimic chronic pulmonary embolism. (b) CT scan (lung window) demonstrates the accompanying findings of diffuse peribronchovascular thickening, ground-glass attenuation, smooth interlobular septal thickening (arrows), and bilateral pleural effusions. These findings indicate the true nature of the patient’s condition.

View larger version (154K): [in a new window]   Figure 34b.  Left-sided heart failure in a 56-year-old woman with dyspnea. (a) CT scan shows peribronchovascular interstitial thickening caused by perivascular edema (arrow), a finding that can mimic chronic pulmonary embolism. (b) CT scan (lung window) demonstrates the accompanying findings of diffuse peribronchovascular thickening, ground-glass attenuation, smooth interlobular septal thickening (arrows), and bilateral pleural effusions. These findings indicate the true nature of the patient’s condition.

View larger version (151K): [in a new window]   Figure 35a.  Localized increase in vascular resistance in a 65-year-old man with dyspnea. (a) CT scan shows a flow artifact caused by a localized increase in vascular resistance (arrow), a finding that can mimic acute pulmonary embolism. Note also the medium-sized left pleural effusion and atelectasis. (b, c) CT scans obtained immediately superior (b) and inferior (c) to a demonstrate an apparent ill-defined filling defect (arrow) that is too high in attenuation to represent pulmonary embolism. (d) Subsequent angiogram demonstrates slight distortion of the posterobasal segment of the left lower lobe pulmonary artery (arrow) but no evidence of pulmonary embolism. (e) More oblique angiogram of the left pulmonary artery also demonstrates no evidence of pulmonary embolism (arrow).

View larger version (167K): [in a new window]   Figure 35b.  Localized increase in vascular resistance in a 65-year-old man with dyspnea. (a) CT scan shows a flow artifact caused by a localized increase in vascular resistance (arrow), a finding that can mimic acute pulmonary embolism. Note also the medium-sized left pleural effusion and atelectasis. (b, c) CT scans obtained immediately superior (b) and inferior (c) to a demonstrate an apparent ill-defined filling defect (arrow) that is too high in attenuation to represent pulmonary embolism. (d) Subsequent angiogram demonstrates slight distortion of the posterobasal segment of the left lower lobe pulmonary artery (arrow) but no evidence of pulmonary embolism. (e) More oblique angiogram of the left pulmonary artery also demonstrates no evidence of pulmonary embolism (arrow).

View larger version (164K): [in a new window]   Figure 35c.  Localized increase in vascular resistance in a 65-year-old man with dyspnea. (a) CT scan shows a flow artifact caused by a localized increase in vascular resistance (arrow), a finding that can mimic acute pulmonary embolism. Note also the medium-sized left pleural effusion and atelectasis. (b, c) CT scans obtained immediately superior (b) and inferior (c) to a demonstrate an apparent ill-defined filling defect (arrow) that is too high in attenuation to represent pulmonary embolism. (d) Subsequent angiogram demonstrates slight distortion of the posterobasal segment of the left lower lobe pulmonary artery (arrow) but no evidence of pulmonary embolism. (e) More oblique angiogram of the left pulmonary artery also demonstrates no evidence of pulmonary embolism (arrow).

View larger version (153K): [in a new window]   Figure 35d.  Localized increase in vascular resistance in a 65-year-old man with dyspnea. (a) CT scan shows a flow artifact caused by a localized increase in vascular resistance (arrow), a finding that can mimic acute pulmonary embolism. Note also the medium-sized left pleural effusion and atelectasis. (b, c) CT scans obtained immediately superior (b) and inferior (c) to a demonstrate an apparent ill-defined filling defect (arrow) that is too high in attenuation to represent pulmonary embolism. (d) Subsequent angiogram demonstrates slight distortion of the posterobasal segment of the left lower lobe pulmonary artery (arrow) but no evidence of pulmonary embolism. (e) More oblique angiogram of the left pulmonary artery also demonstrates no evidence of pulmonary embolism (arrow).

View larger version (144K): [in a new window]   Figure 35e.  Localized increase in vascular resistance in a 65-year-old man with dyspnea. (a) CT scan shows a flow artifact caused by a localized increase in vascular resistance (arrow), a finding that can mimic acute pulmonary embolism. Note also the medium-sized left pleural effusion and atelectasis. (b, c) CT scans obtained immediately superior (b) and inferior (c) to a demonstrate an apparent ill-defined filling defect (arrow) that is too high in attenuation to represent pulmonary embolism. (d) Subsequent angiogram demonstrates slight distortion of the posterobasal segment of the left lower lobe pulmonary artery (arrow) but no evidence of pulmonary embolism. (e) More oblique angiogram of the left pulmonary artery also demonstrates no evidence of pulmonary embolism (arrow).

View larger version (97K): [in a new window]   Figure 36.  Pulmonary artery stump in situ thrombosis in a 69-year-old man who had undergone right pneumonectomy for lung cancer. CT scan demonstrates pulmonary artery stump in situ thrombosis that affects the right pulmonary artery (arrow).

View larger version (93K): [in a new window]   Figure 37.  Pulmonary artery sarcoma in a 65-year-old woman with dyspnea. Contrast-enhanced CT scan shows a heterogeneously enhancing, lobulated mass within the main pulmonary artery (arrow). A metastatic deposit is noted within the right pulmonary artery (arrowhead).

View larger version (79K): [in a new window]   Figure 38.  Tumor embolus in a 78-year-old woman with dyspnea and endometrial stromal sarcoma that invaded the inferior vena cava. CT scan shows a large tumor embolus within the right lower lobe pulmonary artery (arrow).

View larger version (133K): [in a new window]   Figure 39.  Tumor emboli in a 60-year-old man with dyspnea and primary renal cell carcinoma. CT scan shows tumor emboli that manifest as vascular dilatation and beading of subsegmental arteries of the posterobasal segment of the right pulmonary artery (arrow).

View larger version (124K): [in a new window]   Figure 40.  Tumor emboli in a 60-year-old man with dyspnea and primary renal cell carcinoma. CT scan shows tumor emboli with a tree-in-bud appearance within secondary pulmonary lobule arterioles (arrow). Tumor emboli rarely have such an appearance at CT.