Pulmonary Thromboembolism Imaging approach OB consideration By N

Pulmonary Thromboembolism Imaging approach & OB consideration By N. Ayoubi Yazdi

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

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

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.

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

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

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%

Fleischner lines

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.

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

CT Angiogram

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

Abnormal V/Q Scan Perfusion Ventilation

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.

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

ACR Appropriateness Criteria Procedure Rating (1=least appropriate, 9=most appropriate) Comments RRL CXR 9 To exclude other causes of acute CP MIN CTA chest (noncoronary) 9 Current standard of care for detection of PE MED CTA chest with CT venography 7 If suspicion for DVT is high and/or if US is inconclusive MED US lower extremity with doppler 7 If CXR is negative and index of suspicion is high NONE Tc-99 m V/Q scan lung 6 If CXR is negative and CTA is contraindicated or nondiagnostic MED Pulmonary angiography with RH catheterization 5 If suspicion is high and CTA nonconclusive HIGH MRA pulmonary arteries 4 If patient is unable to have iodinated contrast, may be alternative to V/Q scan NONE TEE 2 Limited experience. Used for main pulmonary artery emboli NONE TTE 2 To assess RV function after diagnosis of PE NONE

PTE in pregnancy

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 increased as approximately 30 -fold period, which is

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 also some false-negative case reports in pregnanacy D-dimer assey.

So: role of imaging is more important In pregnancy

Approach

algorithm for imaging pregnant patients with suspected PTE

First-Line Imaging Tests Chest Radiography Lower Extremity US

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

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 negative results warrant further imaging in the setting of clinically suspected pulmonary embolism

DVT of the left common femoral vein

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

CT Pulmonary Angiography disadvantages: radiation exposure (maternal breasts and fetus) ü risks of iodinated contrast material ü nondiagnostic rate 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 ü

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

CT Pulmonary Angiography Methods 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 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 barium preparation Elimination of lateral scout image Fixed injection timing rather than test run Elimination of any additional CT sequences

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

Posteroanterior (a) and lateral (b) chestradiographs and perfusion-only V/Q scan (4 m. Ci of technetium-99 m 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.

Radiation Risk

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

Radiation Risk even a combination of imagings( chest radiography, lung scintigraphy, CT pulmonary angiography, and traditional pulmonary angiography )exposesthe fetus to around 1. 5 m. Gy of radiation(below the accepted limit of 50 m. Gy) Fetal dose by CTPA is about 0. 03 -0. 66 m. Gy lung scintigraphy is more (about 0. 32 -0. 74 m. Gy) scintigraphy, radiotracer is injected intravenously and lead to direct fetal exposure

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.

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

Contrast Material

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

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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