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 PerfusionVentilation

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 ProcedureRating (1=least appropriate, 9=most appropriate) CommentsRRL CXR9To exclude other causes of acute CP MIN CTA chest (noncoronary)9Current standard of care for detection of PE MED CTA chest with CT venography 7If suspicion for DVT is high and/or if US is inconclusive MED US lower extremity with doppler 7If CXR is negative and index of suspicion is high NONE Tc-99m V/Q scan lung6If CXR is negative and CTA is contraindicated or nondiagnostic MED Pulmonary angiography with RH catheterization 5If suspicion is high and CTA nonconclusive HIGH MRA pulmonary arteries4If patient is unable to have iodinated contrast, may be alternative to V/Q scan NONE TEE2Limited experience. Used for main pulmonary artery emboli NONE TTE2To assess RV function after diagnosis of PE NONE

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

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.

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) risks of iodinated contrast material 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

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

CT Pulmonary Angiography  Methods of Reducing the Radiation Dose: 1. to the Maternal Breast and Fetus Thin-layer bismuth breast shield 2. Lead shielding 3. Reduction in tube current 4. Reduction in tube voltage 5. Increase in pitch 6. Increase in detector collimation thickness 7. Reduction of z-axis 8. Oral barium preparation 9. Elimination of lateral scout image 10. Fixed injection timing rather than test run 11. 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 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.

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%

Radiation Risk  even a combination of imagings ( chest radiography, lung scintigraphy, CT pulmonary angiography, and traditional pulmonary angiography )exposesthe fetus to around 1.5 mGy of radiation(below the accepted limit of 50 mGy )  Fetal dose by CTPA is about mGy  lung scintigraphy is more (about mGy)  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

 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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