Imaging Pulmonary Embolism

Emily Willner, Willner,

HMS III

Gillian Lieberman, MD

Imaging Pulmonary

Embolism

New ways to look at a

diagnostic dilemma


HMS III


Core Radiology Clerkship, BIDMC

May 2001


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New approaches to imaging PE:

Agenda

1. Review two patients who had new

diagnostic modalities used for diagnosing

and/or treating PE

2. Review anatomy, differential diagnosis

and menu of tests available for PE

imaging.

3. Discuss algorithmic approach to use of

imaging modalities, and the strengths and

limitations of available tests.

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Patient J.R.: A classic story

64 year old man with recent diagnosis of

metastatic pancreatic CA. Known mets to the

liver.

Presents to the ED with acute onset of sharp, L-

sided pleuritic chest pain. Mild SOB for a few

days.

No cough or hemoptysis. hemoptysis.

No fevers or chills. No

leg symptoms

PMHx: PMHx:

Pancreatic CA. C4-5 C4 5 ruptured disc.

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J.R.: Physical Exam

Vitals: Afebrile, Afebrile,

HR 72, BP 121/64, RR18, Sat

98% RA

Thin man, mildly uncomfortable.

Chest clear.

Heart RRR, II/VI SEM, no rubs or gallops.

Mild abdominal tenderness, + hepatomegaly

Normal lower extremity exam

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J.R.: Chest X-ray X ray

Images from BIDMC PACS

Poor inspiratory effort, but otherwise clear lungs. No pneumothorax, pneumothorax,

no effusions.

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Ventilation

•Essentially Essentially

normal

Perfusion

• Shows possible

defect in LLL

J.R.: Ventilation/Perfusion Scan

RAO

LPO

RAO

LPO

Ant LAO

L Lat

Post RPO

R Lat

Ant LAO

L Lat

Post RPO

R Lat

Image from BIDMC PACS

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J.R.: Chest CT Angiogram w/

contrast showing embolus


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Embolus easier to visualize

scrolling through CT cuts


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Patient R.S.: An emergency on call

58 y.o. y.o.

man s/p cholecystectomy 2 weeks ago, re-

hospitalized for mental status changes

Abdominal/pelvic CT the day of admission

incidentally showed L femoral and ileac DVT;

heparin was started

The following day, he became acutely SOB, O2

sat 88%, tachy to 146, EKG: S1, Q3, T3.

Bedside echo: severe RV enlargement and

hypokinesis

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R.S.: CT on admission revealed

DVT in left iliac v.

Image from from BIDMC PACS

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R.S.: Chest X-ray while SOB


AP upright film: film:

Bilateral lower lung atelectasis. atelectasis.

Otherwise clear lungs.

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R.S.: Large saddle embolus in L

and R pulmonary arteries


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R.S.: Saddle embolus in R PA


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R.S.: Angiography and suction

thrombectomy

Pre-thrombectomy Post-thrombectomy

Large filling defect. Virtually

no flow to L lung.

After suction thrombectomy, flow

restored to L upper lung.


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Differential Diagnosis of chest

Respiratory: Respiratory:

PE,

pneumonia,

pneumothorax,

pneumothorax,

pulmonary edema,

asthma/COPD,

bronchitis, lung CA

Cardiac: Cardiac:

Pericarditis, Pericarditis,

angina, MI, aortic

dissection

pain with SOB

GI: GI:

GERD,

esophageal spasm,

cholecystitis

Musculoskeletal:

Musculoskeletal:

Muscle spasm, pulled

muscle, rib fracture,

costochondritis

Psychiatric: Psychiatric:

Anxiety

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Classic presentation of PE

Risk factors

Immobilization, surgery within 3 mo., trauma,

malignancy, CHF, MI, h/o VTE, postpartum or

hormone use

Symptoms

Pleuritic chest pain, dyspnea, dyspnea,

cough, hemoptysis, hemoptysis,

syncope

Signs

Tachypnea, Tachypnea,

rales, rales,

tachycardia, S4, loud P2, fever


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Lung Anatomy

Arteries run with Bronchi

Image from info.med.yale.edu/caim/ct/contents.html

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Pulmonary vasculature and bronchi

Bronchus

Pulmonary

trunk

Image from Digital Anatomist, http://www9.biostr.washington.edu/da.html

Pulmonary arterial

anatomy

Pulmonary trunk

2 Main pulmonary

arteries

Lobar arteries

Segmental arteries

Subsegmental arteries

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CT correlation and cross-

sectional anatomy T5-6

Aorta

Aorta

Aorta

Image from Digital Anatomist,

http://www9.biostr.washington.edu/da.html

Pulmonary artery

bifurcation

Mainstem

bronchus


bifurcation

Mainstem

bronchus


bifurcation

Mainstem

bronchus

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Imaging tests in suspected PE

Plain chest film: First

test; r/o other etiology

Ventilation/perfusion

scanning

Pulmonary

angiography: the “Gold

Standard” test

Helical CT scan/ CT

angiography

MR imaging/

angiography

Other: LE Venous

duplex Doppler US,

echocardiography

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Chest X-ray findings in PE

Most films (86%) are

abnormal. Common

findings are:

atelectasis

parenchymal opacity

pleural effusion

cardiomegaly

hemidiaphragm elevation

central pulmonary artery

prominence

Few show “classic PE”

findings:

Westermark’s sign = loss of

pulmonary vasculature distal to

central embolus.

Hampton’s hump= hump=

wedge- wedge

shaped, pleural based opacity

representing infarct

Fleischner's sign = regional

oligemia in the presence of an

ipsilateral enlarged pulmonary

artery

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Westermark sign

Image from Virtual Hospital, www.vh.org

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Hampton’s Hump

From www.med.virgina.edu/med-ed/rad

www.med.virgina.edu/med ed/rad

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Ventilation/perfusion scanning

Nuclear medicine test, IV

injection of 99Tc labeled

to albumin maps perfusion

Inhalation of radioactive

tracer shows ventilation

Read as high,

intermediate, low

probability, or normal

Normal perfusion r/o

embolus

High prob scan, 42%

have emboli; 96% if

correlated with high

clinical prob

Intermediate and low

prob scans =

indeterminate

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Ventilation

Perfusion

Normal V/Q scan

RAO

RAO

LPO

LPO

Ant

Post

Ant

Post

LAO

RPO

LAO

RPO

L Lat

R Lat

L Lat

R Lat


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Ventilation

•Few Few small

defects

Perfusion

• Multiple

Perfusion

Multiple

unmatched

perfusion

defects

High Probability V/Q scan

RAO

RAO

LPO

LPO

Ant LAO

L Lat

Post RPO

R Lat

Ant LAO

L Lat

Post RPO

R Lat


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Following up indeterminate V/Q

72% pts have indeterminate scan

Emboli detected in 30% of intermediate

scans and 14% of low prob scans

THUS, PIOPED recommends f/u with

PAgram in this group

Only 5% in this group have pulmonary

angiography!! angiography!!

Management is instead based

on clinical judgment.

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Diagnosing PE using V/Q scans:

No treatment

Normal perfusion

Nondiagnostic/

negative

Serial leg studies v.

angio

one algorithm

Clinically stable

Eval bilateral

lower extrem.

+ DVT

TREAT

V/Q Scan

Non-diagnostic

Pulmonary angiography

No PE

No treatment

Cinically unstable

PE present

TREAT

HIgh probability

TREAT

Chart adapted from UpToDate, UpToDate,

ATS guidelines 1999.

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Pulmonary Angiography

The “gold standard” test for PE

Trans-venous; Trans venous; mortality < 1%, morbidity 2-5% 2 5%

Interobserver variability: PIOPED found a 92%

concordance in PE cases

Least sensitive for subsegmental emboli

Diagnostic test can be combined with intervention

(Greenfield (IVC) filter, thrombolysis,

thrombolysis,

thrombectomy)

thrombectomy

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Normal Pulmonary Angiogram

To RML

To RLL

To RUL

Right PA

Left PA

To LUL

To LLL


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CT angiography in PE diagnosis

Helical CT with iodinated contrast bolus; 20-30 20 30

sec. scan, may be done in 2 breath-holds breath holds

Sensitivity: 86% for proximal vessels (main

through segmental a.); 53-100% 53 100% overall.

Specificity: 93% for proximal vessels; 81-100% 81 100%

overall.

CT has similar sensitivity to V/Q scanning, but a

negative CT is not as good as normal perfusion in

r/o PE

Should we re-think re think the algorithms? What is the

role for CTA?

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Diagnosing PE: an algorithm

using helical CT as the initial test

Normal

PE excluded

Low clinical

suspicion

D-dimer

Abnormal

CT angiography

Supect PE

Intermediate or

high clinical

suspicion

CT angiography

Other dx PE

No PE

Consider lower

extremity evaluation

Chart adapted from Ryu et. al., 2001.

• Consider V/Q scan if contraindication to IV contrast.

• V/Q has good utility as first test when patient has no pathology pathology

on CXR and no hx of cardiac or pulmonary disease

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Normal CTA

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Helical CT angio overview

Plus

Very fast

Evolving technology

faster faster scans and thinner

slices

May give alternate

diagnosis if negative for

PE

3-D D reconstructions

Negative scan scan safe to

withhold anticoagulation

Minus

Iodinated contrast

(renal insufficiency)

Radiation exposure

Poor visualization of

clots in subsegmental

arteries and obliquely

oriented vessels

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3-D CT reconstruction: R.S.


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CT in diagnosis of DVT: One stop

shopping?

Recent data has suggested that CT of the

lower extremities may be done at the same

time as chest CTA to yield greater

diagnostic accuracy

One contrast bolus and one scan

In future, possibly replace venous US in

patient already undergoing CT ?

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Role of MRA in diagnosis of PE

Plus

Excellent images

No iodinated contrast

Sensitivity and specificity

similar range to CTA

Real-time Real time reconstructions/

flow images

Future:, ventilation

scanning

Minus

Longer scan time

(minutes v. seconds)

Prolonged breath-

holding (30+ sec.)

Expensive

Poor sensitivity in

subsegmental a. clots

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Gadolinium contrast MRA

Normal

Image from www2.medical.philips.com/mri/Applications/

Cardiac/Angiography.asp

Cardiac/ Angiography.asp

MRA of a large embolus

Image courtesy of Dr. Thomas Vrachliotis

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Summary: Advances in imaging

CXR remains the initial test of choice.

V/Q scanning retains a role in healthier patients.

Helical CT is sensitive, specific, fast, and gives

alternate diagnoses. Potential for LE imaging. Needs

more investigation to fully delineate role.

Pulmonary angiography has a role especially in

patients who will need interventions.

MR is promising but currently scans too long and test

too expensive.

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References

American Thoracic Society. The diagnostic approach to acute venous venous

thromboembolism. thromboembolism.

ATS

guidelines. Am J Resp Critical Care Med 1999; 160: 1043.

Goodman LR, Lipchik RJ, Kuzo RS. Subsequent pulmonary embolism. Risk after negative helical

CT. Prospective comparison with scintigraphy.

scintigraphy.

Radiology 2000; 215: 535.

Kline JA, Johns KL, Colucciello SA, Israel EG. New diagnostic tests for pulmonary embolism. Ann

Emerg Med 2000; 35(2): 343.

Maki DD, Warren BG, Abass A. Emerging technology in clinical medicine: Recent advances in

pulmonary imaging. Chest 1999; 116(5): 1388.

PIOPED investigators. Value of ventilation/perfusion scan in acute acute

pulmonary embolism. JAMA

1990; 263: 2753.

Rathburn SW, Raskob GE, Whisett TL. Sensitivity and specificity of helical CT in the diagnosis of

pulmonary embolism: a systematic review. Ann Int Med 2000. 132(3): 227.

Ryu JH, Swensen SJ, Olson EJ, Pellikka PA. Diagnosis of pulmonary embolism with use of

computed tomography.

Thompson BT, Hales, CA. Clinical manifestations and diagnostic strategies strategies

for acute pulmonary

embolism. Up To Date 2001.

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Acknowledgements

Many thanks to Dr. Michelle Swire for her help with cases and images, images,

Dr. Lieberman for her ideas and suggestions, and to Dr. Thomas

Vrachliotis for his MR images.

Thanks to my Radiology classmates who made doing this presentation presentation

much more fun.

Thanks to Beverlee Turner for all her technical help.

Special thanks to Larry Barbaras and Cara Lyn D’amour,

our WebMasters.

WebMasters

41

Imaging Pulmonary Embolism

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