Pulmonary Thromboembolism

1. Pulmonary Thromboembolism Imaging approach & OB consideration By N.AyoubiYazdi

2. Imaging modalities • CXR • Doppler US of lower extrimities vein • Pulmonary CT angiogeraphy • Pulmonary scintigeraphy • Pumonary MR angiogeraphy • DSA angiogeraphy

3. CXR • normal chest radiograph does not exclude pulmonary embolism • The sensitivity and specificity :only 33% and 59%, respectively. • The main value of chest radiographs : detection of diagnoses that may clinically simulate PE, such as pneumothorax, pulmonary edema, or rib fractures. • In addition, a recent chest radiograph is required for the interpretation of ventilation/perfusion (V/P) scintigraphy

4. CXR • Initial CXR usually normal. • May progress to show atelectasis, plueral effusion and elevated hemidiaphram. • Hampton’s hump and Westermark sign are classic findings but are not usually present.

5. Hints on CXR to suggest PE • Hampton’s hump • Pulmonary oligemia (Westermark’s sign) • Elevated diaphragm(s)/volume loss • Atelectasis (Fleischner lines) • Pleural effusion • Cardiomegaly • Interstitial edema

6. Hamptons hump • sensitivity: ~22%  • specificity: ~82% • positive predicitve value: ~29% • negative predictive value: ~76%

7. Westermarks sign • Westermark sign – Dilatation of pulmonary vessels proximal to embolism along with collapse of distal vessels, often with a sharp cut off. • sensitivity: ~14%  • specificity: ~92%  • positive predictive value: ~38% • negative predictive value:~76%

8. Fleischner lines

9. CT Angiogram • Quickly becoming the test of choice for initial evaluation of a suspected PE. • CT unlikely to miss any lesion. • CT has better sensitivity, specificity and can be used directly to screen for PE. • CT can be used to follow up “non diagnostic V/Q scans.

10. CT Angiogram • Chest computed tomography scanning demonstrating extensive embolization of the pulmonary arteries.

13. CT Angiogram

14. V/Q Scan • Ventilation-perfusion scanning is a radiological procedure which is often used to confirm or exclude the diagnosis of pulmonary embolism. • If CXR is negative and CTA is contraindicated or nondiagnostic

15. Abnormal V/Q Scan Perfusion Ventilation

16. Pulmonary angiogram • Gold Standard. • Positive angiogram provides 100% certainty that an obstruction exists in the pulmonary artery. • Negative angiogram provides > 90% certainty in the exclusion of PE.

17. Pulmonary angiogram • Left-sided pulmonary angiogram showing extensive filling defects within the left pulmonary artery and its branches.

18. ACR Appropriateness Criteria

19. PTE in pregnancy

20. PTE in pregnancy • Pregnancy is associated with a fivefold increase in the prevalence of venous thromboembolism, and pulmonary embolism • The greatest risk is in postpartum period, which is increased as approximately 30-fold

21. PTE in pregnancy • The role of D-dimer assay in pregnant patients is limited by a rise above reference levels as the pregnancy progresses, producing false-positive results. • There are also some false-negative case reports in pregnanacy D-dimer assey.

22. So: role of imaging is more important In pregnancy

23. Approach

24. algorithm for imaging pregnant patients with suspectedPTE

25. First-Line Imaging Tests • Chest Radiography • Lower Extremity US

26. ChestRadiography • determine whether to perform lung scintigraphy (considered only if chest radiographic findings are normal, to minimize the nondiagnostic rate) or CT pulmonary angiography

27. Lower Extremity US • positive result eliminate the need for further Imaging • a first-line test among pregnant women with symptoms of DVT • be aware that negativeresults warrant further imaging in the setting of clinically suspected pulmonary embolism

28. DVT of the left common femoral vein

29. Second-Line Imaging Tests • CT Pulmonary Angiography • Lung Scintigraphy • Magnetic Resonance Imaging • Conventional Pulmonary Angiography

30. CT Pulmonary Angiography • disadvantages: • radiation exposure(maternal breasts and fetus) • risks of iodinated contrast material • nondiagnosticrate of CT pulmonary angiography may be slightly higher in pregnant patients due to increased circulatory volume and altered cardiac output, which may increase flow artifacts

31. Pulmonary embolism in a 25-year-oldwoman at 14 weeks gestation who presented with chest pain and hemoptysis.

32. CT Pulmonary Angiography • Methods of Reducing the Radiation Dose: • to the Maternal Breast and Fetus Thin-layer bismuth breast shield • Lead shielding • Reduction in tube current • Reduction in tube voltage • Increase in pitch • Increase in detector collimation thickness • Reduction of z-axis • Oral bariumpreparation • Elimination of lateral scout image • Fixed injection timing rather than test run • Elimination of any additional CT sequences

33. Lung Scintigraphy • diagnostic when the results are normal or indicate a high probability of pulmonary embolism, • for patients with normal chest radiographic findings and no history of asthma or chronic lung disease • The major advantage: lower radiation dose to the maternal breast; • major disadvantage:its inability to provide an alternative diagnosis

34. Posteroanterior (a) and lateral (b) chestradiographs and perfusion-only V/Q scan (4 mCi of technetium-99m macroaggregated albumin) (c) obtained in a 38-year-old woman at 24 weeks gestation who presented with shortness of breath and occasional hemoptysis show normal findings.

35. Radiation Risk

36. Radiation Risk • fetal risks from radiation doses of less than 50 mGy are negligible • doses of 100 mGy and more result in a combined increased risk of organ malformation and the development of childhood cancer of only about 1%

37. Radiation Risk • even a combination of imagings( chest radiography, lung scintigraphy, CT pulmonary angiography, and traditional pulmonary angiography )exposesthe fetus to around 1.5 mGyof radiation(below the accepted limit of 50 mGy) • Fetal dose by CTPA is about 0.03-0.66 mGy • lung scintigraphy is more (about 0.32-0.74 mGy) • scintigraphy, radiotracer is injected intravenously and lead to direct fetal exposure

38. Radiation Risk • no measurably increased prenatal death, malformation, or impaired mental development • but carcinogenesis • Leukemia is the most common malignancy to develop in childhood after in utero radiation.

39. Radiation Risk • estimated breast dose from CTPA is 150 times more than scintigraphy • Use of breast shields could reduce this dose up to 73%

40. Contrast Material

41. Contrast Material • risks of iodine contrast agents are similar to general population • no fetal risks from intravenous contrast (they are classified as category B by FDA) • infant thyroid function

42. Contrast Material • The more important risk is for gadolinium, which has had teratogenic effect in animal group C by FDA • So a need for further improvement in unenhanced MR imaging techniques, which currently allow accurate evaluation of only the central and first-order arterial branches • recent guidelines do not recommend termination of breastfeeding after contrast material administration

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