Pulmonary

ThromboembolismImaging 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 signWestermark sign – – Dilatation of Dilatation of pulmonary vessels pulmonary vessels proximal to embolism proximal to embolism along with collapse of along with collapse of distal vessels, often distal vessels, often with a sharp cut off.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 CriteriaProcedure 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-99m 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 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 withchest pain and hemoptysis.

CT Pulmonary Angiography Methods of Reducing the Radiation

Dose:1. to the Maternal Breast and Fetus Thin-layer

bismuth breast shield2. Lead shielding3. Reduction in tube current4. Reduction in tube voltage5. Increase in pitch6. Increase in detector collimation thickness7. Reduction of z-axis8. Oral barium preparation9. Elimination of lateral scout image10.Fixed injection timing rather than test run11.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

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 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

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

THANK YOU