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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