Pulmonary Thromboembolism Imaging

Pulmonary EmbolismEvaluationPulmonary EmbolismEvaluation

Adam Guttentag M.D.Adam Guttentag M.D.

The PE ParadoxThe PE Paradox

Very common disease—usually missedVery common disease—usually missed

Commonly considered clinical diagnosis—usually wrongCommonly considered clinical diagnosis—usually wrong

In other words…In other words…

In most patients with PE, we don’t think of thediagnosis and…In most patients with PE, we don’t think of thediagnosis and…

In most patients in whom the diagnosis ispursued, it is not present.In most patients in whom the diagnosis ispursued, it is not present.

Pulmonary EmbolismPulmonary Embolism

Large numbers of patients die of PELarge numbers of patients die of PE

3rd most common cause of death3rd most common cause of death

650,000 deaths per year650,000 deaths per year

70% of PE found at autopsy was not suspected pre-mortem.70% of PE found at autopsy was not suspected pre-mortem.

1/3 who survive initial event will die of PE in thefuture. Mortality much less in treated patients.1/3 who survive initial event will die of PE in thefuture. Mortality much less in treated patients.

Many hospitalized patients have unsuspected DVT.Many hospitalized patients have unsuspected DVT.

You must think of the diagnosis in order to make it.You must think of the diagnosis in order to make it.

Problems with clinical evaluation Problems with clinical evaluation

Symptoms and signs are very nonspecificSymptoms and signs are very nonspecific

Classic sx: chest pain, dyspnea, hemoptysisClassic sx: chest pain, dyspnea, hemoptysis

not always presentnot always present

Non-classic sx: syncope, wheezing, arrhythmiaNon-classic sx: syncope, wheezing, arrhythmia

Labs not helpfulLabs not helpful

Hypoxia not a reliable findingHypoxia not a reliable finding

Degree of hypoxia not proportional to extent of PEDegree of hypoxia not proportional to extent of PE

Elevated WBC commonElevated WBC common

Classic ECG findings in only 20%Classic ECG findings in only 20%

Dozens of differential dx’sDozens of differential dx’s

Radiologic EvaluationRadiologic Evaluation

Most work ups for DVT/PE are negativeMost work ups for DVT/PE are negative

At best, about 1/3 of PE workups will be positive.At best, about 1/3 of PE workups will be positive.

With easy availability of MDCT in ERs, manyhospitals have positive rate of <20%.With easy availability of MDCT in ERs, manyhospitals have positive rate of <20%.

Radiologic EvaluationRadiologic Evaluation

“Gestalt” evaluation of likelihood of PE is good, butnot adequate, even with experienced MDs.“Gestalt” evaluation of likelihood of PE is good, butnot adequate, even with experienced MDs.

Use pretest probability systems, especially ifinexperienced residents are making workup decisions.Use pretest probability systems, especially ifinexperienced residents are making workup decisions.

Geneva, Wells criteriaGeneva, Wells criteria

Have a standardized protocol for evaluating patientswith possible PE.Have a standardized protocol for evaluating patientswith possible PE.

Pulmonary ThromboembolismImaging QuestionsPulmonary ThromboembolismImaging Questions

Is it reasonable to image everyone in whom thediagnosis is raised?Is it reasonable to image everyone in whom thediagnosis is raised?

How do we improve our patient selection toavoid over-utilizing expensive imaging?How do we improve our patient selection toavoid over-utilizing expensive imaging?

What imaging modalities are available?What imaging modalities are available?

Varies by institutionVaries by institution

What is the best use of various imagingmodalities?What is the best use of various imagingmodalities?

DVT / PE ImagingDVT / PE Imaging

Chest X-rayChest X-ray

Nuclear V/Q scanNuclear V/Q scan

CT pulmonary arteriogram (CTPA)CT pulmonary arteriogram (CTPA)

Doppler Ultrasound of legsDoppler Ultrasound of legs

MR AngiographyMR Angiography

Conventional Pulmonary AngiogramConventional Pulmonary Angiogram

Chest X-rayChest X-ray

Essential first step in imagingsequence.Essential first step in imagingsequence.

Rule in other causes of symptoms:Rule in other causes of symptoms:

Pneumothorax, CHF, pneumonia, etcPneumothorax, CHF, pneumonia, etc

Can be used to guide sequence oftests for PE.Can be used to guide sequence oftests for PE.

Signs of PE:Signs of PE:

Regional oligemia (rare)Regional oligemia (rare)

Platelike atelectasis (common)Platelike atelectasis (common)

Elevated hemidiaphragmElevated hemidiaphragm

Localized consolidation (Hamptonhump)Localized consolidation (Hamptonhump)

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Doppler UltrasoundDoppler Ultrasound

Advantages:Advantages:

Highly accurate forevaluation of femoral andpopliteal veinsHighly accurate forevaluation of femoral andpopliteal veins

RapidRapid

InexpensiveInexpensive

Disadvantages:Disadvantages:

No evaluation of PENo evaluation of PE

Limited in very obesepatientsLimited in very obesepatients

Operator dependentOperator dependent

Nuclear V/Q scanNuclear V/Q scan

Advantages:Advantages:

RapidRapid

High prob and normalscans reliable in mostpatientsHigh prob and normalscans reliable in mostpatients

Requires little patientcooperation.Requires little patientcooperation.

No contrast.No contrast.

Disadvantages:Disadvantages:

Indirect imaging ofvessels.Indirect imaging ofvessels.

Not available 24/7everywhere.Not available 24/7everywhere.

Intermediate prob scannot much help.Intermediate prob scannot much help.

Low prob not much helpin patient with highsuspicion.Low prob not much helpin patient with highsuspicion.

CT AngiographyCT Angiography

Advantages:Advantages:

Multislice technologywidely availableMultislice technologywidely available

RapidRapid

AccurateAccurate

Direct imaging of vesselsDirect imaging of vessels

Can add venography withsame injection to evaluatethe legs and central veinsCan add venography withsame injection to evaluatethe legs and central veins

Disadvantages:Disadvantages:

Requires contrast injectionRequires contrast injection

Renal function, allergiesRenal function, allergies

Radiation dose highRadiation dose high

Requires breath hold of 8-18 seconds for bestaccuracyRequires breath hold of 8-18 seconds for bestaccuracy

Conventional AngiographyConventional Angiography

Advantages:Advantages:

“Gold standard”“Gold standard”

Direct imaging of vesselsDirect imaging of vessels

High sensitivityHigh sensitivity

High confidence innegative testHigh confidence innegative test

Disadvantages:Disadvantages:

InvasiveInvasive

Small but real risksSmall but real risks

5% morbidity, <1%mortality5% morbidity, <1%mortality

Poor interobserver agreementfor smaller vesselsPoor interobserver agreementfor smaller vessels

Requires specializedpersonnel, equipmentRequires specializedpersonnel, equipment

Limited availabilityLimited availability

MR AngiographyMR Angiography

Advantages:Advantages:

No radiationNo radiation

No iodinated contrastNo iodinated contrast

(requires contrast, though)(requires contrast, though)

Direct imaging of vesselsDirect imaging of vessels

RapidRapid

Disadvantages:Disadvantages:

Limited availabilityLimited availability

Requires contrastinjectionRequires contrastinjection

Critically ill patientsrequire special ventilator,monitoring equipmentCritically ill patientsrequire special ventilator,monitoring equipment

PE: Radiologic workupPE: Radiologic workup

Einstein algorithmEinstein algorithm

Patient with suspected

PE / DVT

Chest x-ray normal?

Bun/Creat abnormal?

Contrast Allergy?

Can’t hold breath?

DVT Sx?

inter

high

normal

further eval

for PE

low

PAgram

Venous

Doppler

yes

V/Q

scan

yes toany

Treat

Venous

Doppler

V/Q scanV/Q scan

PIOPED study established standardized criteriafor assigning likelihood of PEPIOPED study established standardized criteriafor assigning likelihood of PE

True likelihood depends on pretest assessmentof likelihood of PETrue likelihood depends on pretest assessmentof likelihood of PE

High prob V/Q + low risk pt = 50% chance of PEHigh prob V/Q + low risk pt = 50% chance of PE

Low prob V/Q + high risk pt = 16% chance of PELow prob V/Q + high risk pt = 16% chance of PE

At AEMC, V/Q performed as first test if CXRnormal and no COPDAt AEMC, V/Q performed as first test if CXRnormal and no COPD

Intermediate probability scan in only 11%.Intermediate probability scan in only 11%.

V/Q scanV/Q scan

Perfusion scan: microembolization ofpulmonary vascular bed with labeled aggregatesof albuminPerfusion scan: microembolization ofpulmonary vascular bed with labeled aggregatesof albumin

Ventilation scan: may be performed withTechnicium labeled DTPA aerosol or Xenon gasVentilation scan: may be performed withTechnicium labeled DTPA aerosol or Xenon gas

Fetal dose similar to CTPAgram in pregnantpatientsFetal dose similar to CTPAgram in pregnantpatients

Normal V/Q scanNormal V/Q scan

ventilation

perfusion

High probability V/Q scanHigh probability V/Q scan

CT PAgram - TechniqueCT PAgram - Technique

Best on modern multidetector CTBest on modern multidetector CT

4, 8 or 16 channels4, 8 or 16 channels

Scan at thinnest slice width possible for breath holdScan at thinnest slice width possible for breath hold

1mm best-good evaluation of most subsegmental vessels1mm best-good evaluation of most subsegmental vessels

2.5 - 3 mm satisfactory for segmental vessels2.5 - 3 mm satisfactory for segmental vessels

High injection rate of contrast for maximum vesselenhancementHigh injection rate of contrast for maximum vesselenhancement

3-4 cc/sec3-4 cc/sec

Breath hold 8 sec for 16 channel scanner, 18 sec for 4channelsBreath hold 8 sec for 16 channel scanner, 18 sec for 4channels

Window and levels settings customized to scanWindow and levels settings customized to scan

CT PAgramCT PAgram

How good is good enough?How good is good enough?

Respiratory motion, lung disease, poor enhancementmay limit evaluation of small vesselsRespiratory motion, lung disease, poor enhancementmay limit evaluation of small vessels

If only segmental vessels are well seen, and scanis normal, can the workup stop?If only segmental vessels are well seen, and scanis normal, can the workup stop?

What is the risk of missing subsegmentalembolism?What is the risk of missing subsegmentalembolism?

Isolated subsegmental PE in 6-30% of cases.Isolated subsegmental PE in 6-30% of cases.

CT PAgramCT PAgram

Follow up studies have shown that there is lowrisk of embolism in 6-12 months followingnegative CT evaluation.Follow up studies have shown that there is lowrisk of embolism in 6-12 months followingnegative CT evaluation.

Important to include a study of the legs.Important to include a study of the legs.

Any subsegmental emboli missed are probablyclinically insignificant in most patients.Any subsegmental emboli missed are probablyclinically insignificant in most patients.

Remember that conventional angiography maynot be reliable for small vessels.Remember that conventional angiography maynot be reliable for small vessels.

Positive CTPA—Acute PEPositive CTPA—Acute PE

Acute PEAcute PE

Signs of massive embolismSigns of massive embolism

Clinical: loud P2, JVD—signs of RV failure, PAHTNClinical: loud P2, JVD—signs of RV failure, PAHTN

Dilated Main PA and right ventricleDilated Main PA and right ventricle

Reflux of contrast into IVCReflux of contrast into IVC

Straightening of IV septum or bowing towardsLV lumenStraightening of IV septum or bowing towardsLV lumen

Massive PE with right heart failureMassive PE with right heart failure

MPR may help define PEMPR may help define PE

Thick slab MIP

Pulmonary infarctionPulmonary infarction

Not commonNot common

Bronchial arteries usually supply sufficient flowBronchial arteries usually supply sufficient flow

Generally found with coexisting LV dysfunction,pulmonary venous HTNGenerally found with coexisting LV dysfunction,pulmonary venous HTN

Peripheral consolidation broadly based on pleuraPeripheral consolidation broadly based on pleura

“melting snowball” over several days to weeks“melting snowball” over several days to weeks

Chronic PEChronic PE

Cause of chronic pulmonary hypertension, dyspneaCause of chronic pulmonary hypertension, dyspnea

May not have known hx of acute PEMay not have known hx of acute PE

Most acute PE resolves without residuaMost acute PE resolves without residua

CT findings:CT findings:

Crescentic thrombus along wall of vessels, not in centerCrescentic thrombus along wall of vessels, not in center

Rapid tapering of vessels, small sizeRapid tapering of vessels, small size

Webs, irregular flapsWebs, irregular flaps

CalcificationCalcification

Chronic PEeccentric wall thickening, obtuse anglesChronic PEeccentric wall thickening, obtuse angles

Chronic PEcalcified organized thrombusChronic PEcalcified organized thrombus

Chronic PEwebChronic PEweb

Acute on Chronic PEAcute on Chronic PE

Pulmonary infarcts with mosaicoligemiaPulmonary infarcts with mosaicoligemia

False Positive DiagnosisFalse Positive Diagnosis

ArtifactArtifact

Cardiac motion—stair step artifactCardiac motion—stair step artifact

Respiratory motionRespiratory motion

Volume averagingVolume averaging

Quantum mottleQuantum mottle

SVC streakingSVC streaking

Mucus pluggingMucus plugging

Chronic PEChronic PE

Hilar lymph nodesHilar lymph nodes

Veins poorly opacifiedVeins poorly opacified

Flow artifacts—unopacified blood entering from IVCFlow artifacts—unopacified blood entering from IVC

Mucous pluggingMucous plugging

Windowing is important!Windowing is important!

Positive for PE?Positive for PE?

“stair-step” artifact“stair-step” artifact

What’s new?What’s new?

D-dimer testingD-dimer testing

CT VenographyCT Venography

MRA?MRA?

D-dimerD-dimer

Doorkeeper testDoorkeeper test

Inexpensive, rapidInexpensive, rapid

Newer assays are quantitative, highly sensitiveNewer assays are quantitative, highly sensitive

High negative predictive valuesHigh negative predictive values

Negative test essentially precludes the presence ofDVT or PE.Negative test essentially precludes the presence ofDVT or PE.

Only in low or intermediate risk patientsOnly in low or intermediate risk patients

High risk patients may have PE even with negatived-dimer.High risk patients may have PE even with negatived-dimer.

Suggested protocol toinclude D-dimertestingSuggested protocol toinclude D-dimertesting

Patient with suspected PE

Low or intermediate risk

High risk

D-dimer

Proceed with

standard algorithm

No evaluation

for PE

CT VenographyCT Venography

Wait 2-3 minutes after CT PAgram.Wait 2-3 minutes after CT PAgram.

Scan every 4-5 cm from diaphragmto knees.Scan every 4-5 cm from diaphragmto knees.

Easy to identify most DVTEasy to identify most DVT

“one stop shopping” for PE andDVT evaluation“one stop shopping” for PE andDVT evaluation

Compares well in accuracy withDoppler USCompares well in accuracy withDoppler US

No additional contrast. Minimalextra time of exam.No additional contrast. Minimalextra time of exam.

Loud et al Radiology 2001;219:498-502Loud et al Radiology 2001;219:498-502

CT VenogramCT Venogram

IVC thrombus

Left iliac veinthrombus

MR AngiographyMR Angiography

SummarySummary

Initial test:Initial test:

US if sx of DVTUS if sx of DVT

Choice of V/Q or CTPA depends on yourinstitution.Choice of V/Q or CTPA depends on yourinstitution.

V/Q only for patients with normal CXR orcontraindication to CTPAV/Q only for patients with normal CXR orcontraindication to CTPA

Secondary test:Secondary test:

If initial test is non-diagnosticIf initial test is non-diagnostic

Repeat CTPARepeat CTPA

Catheter angiographyCatheter angiography

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