CT Angiography CT Angiography of of

PulmonaryPulmonary EmbolismEmbolism

ByDR. Naglaa Mahmoud

KCCC

IntroductionIntroduction

PE is the third most common acute CVS disease that results in thousands of deaths each year because it often goes undetected.

The majority of pulmonary emboli begin in the pelvic or lower extremity veins.

Importance of early diagnosis:

10% of symptomatic PE are fatal in the first hour.

Most of the deaths occur when the diagnosis is delayed or never made.

While if diagnosedif diagnosed, they are rarely fatal , they are rarely fatal and rarely recurand rarely recur.

Clinical picture: Dyspnea 73% Pleuritic Pain 66% Cough 43% Leg Swelling 33% Leg Pain 30% Hemoptysis 15% Palpitations 12% Wheezing 10% Angina-Like pain 5%

The signs and symptoms are non specific and serve only to raise the suspicion of PE.

Predisposing Factors:Predisposing Factors:

• Immobility: post surgery, major trauma, obesity.

• Blood coagulopathy: malignancy.

• Slow circulation: pregnancy, congestive heart failure.

DIFFERENTIAL DIAGNOSISDIFFERENTIAL DIAGNOSISCHFCHFAsthma / COPD exacerbationAsthma / COPD exacerbationPneumothoraxPneumothoraxPneumoniaPneumoniaPleural diseasePleural diseaseChest wall PainChest wall PainMyocardial infarctionMyocardial infarctionPericarditisPericarditisInfradiaphragmatic processInfradiaphragmatic processe.g. cholecystitis, splenic infarction, e.g. cholecystitis, splenic infarction, pancreatitis.pancreatitis.

Imaging of pulmonary Imaging of pulmonary embolismembolism

(1) Chest x-ray findings, non specific, may include:

• Normal

• Diaphragm elevation

A diaphragm may A diaphragm may be elevated, be elevated, reflecting volume reflecting volume loss in the affected loss in the affected lung.lung.

Atelectasis is quite common.

Pleural based opacity (Hampton’s hump).

Pleural effusions are common and most often unilateral occupying less than 15% of a hemithorax.

Westermark’s Sign is a sign that represents a focus of oligemia seen distal to a pulmonary embolus.

Prominent central pulmonary artery (with extensive PE).

(2) Ventilation-perfusion scintigraphy• It has to be correlated with chest x-ray.•There are 3 V/Q lung scan patterns:

1. A normal perfusion scan rule out PE:

2. High probability scan:

3. All other lung scan patterns:

• (~ 60% of all the scans) are non diagnostic, include:

“low probability”,

“intermediate probability”, and

“indeterminate probability”.

• Further testing is required in patients with this V/Q scan.

Advantages of V/Q Lung Scans include:Advantages of V/Q Lung Scans include:

1. A normal V/Q scan rules out PE.1. A normal V/Q scan rules out PE. 2. Low radiation dose.2. Low radiation dose. 3. Iodine-based contrast is not used.3. Iodine-based contrast is not used.Limitations of V/Q Lung Scans include: Limitations of V/Q Lung Scans include:

1. The majority of V/Q scans are non 1. The majority of V/Q scans are non

diagnostic.diagnostic.

2. Do not provide an alternate diagnosis in the 2. Do not provide an alternate diagnosis in the

patients without PE.patients without PE.

3. High cost.3. High cost.

(3) Pulmonary angiography

• Some still consider it as the standard technique for diagnosis of PE, but in reality it is infrequently performed as it is:

• Expensive.

• Technically more difficult.

• Risky.

• Moreover there are limitations for unequivocal diagnosis of isolated peripheral pulmonary emboli.

(4) Lower limb ultrasonography

Since the treatment for DVT and PE is the same,

the demonstration of clot in the leg using Duplex US in a patient who is clinically suspected to have PE, usually no further diagnostic work-up is pursued.

(5) Computed tomographic pulmonary (5) Computed tomographic pulmonary angiography (CTPA)angiography (CTPA)

The development of multi-The development of multi-detector CT scanners, made detector CT scanners, made CTPA an important diagnostic CTPA an important diagnostic technique in suspected PE, technique in suspected PE, especially in patients with especially in patients with abnormal chest x-ray in whom abnormal chest x-ray in whom scintigraphic results are more scintigraphic results are more likely to be non diagnostic.likely to be non diagnostic.

Technique of CTPATechnique of CTPA

Pre-scanning RFT and history of allergy to CM must be checked.

Light-speed 16-section CT scanning of the thorax in a caudo-cranial direction.

Introduction of an 18- or 20-gauge catheter into an antecubital vein.

The chest field of view is the widest rib-to rib distance acquired during breath hold after

inspiration.

Rate of CM injection is 4 ml / sec for a total CM injection is 4 ml / sec for a total dose of 135 ml.dose of 135 ml.

Scanning delay is determined by:

Dividing the acquisition time for lung imaging by 2 and subtracting the result from the total injection time (34 seconds).

Images are displayed with three different gray scales for interpretation:

Lung window (1500/600).

Mediastinal window (400/40).

Pulmonary embolism–specific (700/100) window.

Multiplanar Reformatted images through the longitudinal axis of a vessel are used to:

Overcome difficulties encountered with axial sections of obliquely or axially oriented arteries.

Reformatted images can help differentiation between:

True pulmonary embolism

and

Patient-related, technical, anatomic, and pathologic factors that can mimic pulmonary embolism.

Contrast-enhanced CT of LL veins can be performed using the same contrast bolus used for CTPA.

Images of the iliac, femoral, and popliteal veins are obtained 4 minutes after the onset of contrast injection.

CTV in a case with PE shows acute LCF DVT. Expansion of the vein is evident with marked wall thickening and enhancement, and the adjacent fat is edematous.

CTV shows DVT in right external iliac vein.

CT Diagnostic Criteria for

Acute Pulmonary Embolism:

1. Arterial occlusion with failure to enhance the entire lumen due to a large filling defect; the artery may be enlarged compared with adjacent patent vessels.

2. A partial filling defect surrounded by contrast material, producing the “polo mint” sign on images acquired perpendicular to the long axis of a vessel

3. The “railway track” sign on longitudinal images of the vessel.

4. A peripheral intraluminal filling defect that forms acute angles with the arterial wall.

Peripheral wedge-shaped areas of hyperattenuat-ion (infarcts), with linear bands, are ancillary findings with acute pulmonary embolism. However, these radiologic features are not specific.

A diagnosis of PE is established on the basis of individual transverse sections, although,

extensive or

isolated PE,

as well as normal pulmonary vasculature can be visualized by means of 3D reconstructions.

Extensive acute central PE with "saddle embolus" extending into both central pulmonary arteries.

Isolated peripheral pulmonary embolus in sixth-order pulmonary arterial branch shown as a peripheral filling defect.

Normal pulmonary vessels.

What about small What about small peripheral clots?peripheral clots?

Recent studies proved that,

small peripheral clots that might have gone unnoticed in the past are now frequently detected, often in patients with minor symptoms.

Consecutive transverse sections show isolated peripheral pulmonary embolus in a subsegmental pulmonary artery in the left lung.

Oblique sagittal multiplanar reformation also shows embolus.

Coronal volume-rendered display (posterior view) shows isolated peripheral filling defect.

Advantages of CTPA include:1. Direct visualization of emboli.

2. The current generation of 16 MDCT scanner allows for coverage of the entire chest with 1 mm or sub-millimeter resolution within a short single breath hold less than 10 seconds.

3. This high spatial resolution allows evaluation of pulmonary vessels down to sixth-order branches.

4. Provide the alternate diagnosis in patients without PE.

5. cost-effective procedure.

Limitations of CTPA include:Limitations of CTPA include:

1. Allergy to CM.

2. Patients with renal insufficiency.

3. Pregnancy.

4. Severe obesity.

CTPA Trouble Shooting

The most common reasons for non The most common reasons for non diagnostic CT images are:diagnostic CT images are:

Poor contrast enhancement of pulmonary Poor contrast enhancement of pulmonary vessels, overcome by: vessels, overcome by:

Faster scanning timesFaster scanning times, use of automated bolus-triggering or saline chasing techniques.

Motion artifacts: Shorter breath-hold times reduce the

occurrence of respiratory motion artifacts.

Artifacts due to transmitted cardiac pulsation are reduced by retrospective ECG gating of the CT.

Retrospective ECG-gated CTPA. (a) During systole, severe stair-step artifacts along the course of pulmonary vessels due to transmitted cardiac motion.

(b) During diastole, cardiac pulsation artifacts are reduced.

How to proceed ?How to proceed ?

Before proceeding to imaging, Before proceeding to imaging, the most important first-linethe most important first-line for for

diagnosis of PE is diagnosis of PE is D-dimerD-dimer testing, the testing, the results of which, if negative, rules out results of which, if negative, rules out PE.PE.

A patient with a normal D-dimer and a A patient with a normal D-dimer and a low pre-test probability does not low pre-test probability does not require further diagnostic imaging.require further diagnostic imaging.

PE symptoms +/- DVT SYMPTOMSLower Extremity Evaluation (Duplex u/s)

(-) (+)TreatCTPA

(+) (-)

TreatPoor quality

CTPA

Repeat CTPA/ (Angio?)

Good qualityCTPA

STOP

High clinical suspicion

(Angio?)

conclusionconclusion

• The development of MDCT technique has made CTPA the first-line imaging test in daily clinical routine for patients suspected of having PE as it is:

• Fast• Non invasive• Has a high sensitivity and

specificity• Can detect small emboli in

peripheral pulmonary arteries.

THANK YOUTHANK YOU