Pulmonary embolism and lung scans

Lungs ScansLungs Scans

Their role in diagnosis of Their role in diagnosis of Pulmonary EmbolismPulmonary Embolism

Suspect PE?Suspect PE?

Investigation of patients with suspected pulmonary emboli (PE) remains problematic and controversial

there are several ways to “rule in” and “rule out” the diagnosis (or, more importantly, to make a decision about anticoagulation or not)

At least 70% of patients with suspected PE don’t have it

PE is nearly always a complication of (proximal) DVT

Investigation of PEInvestigation of PE

Not every PE can (or needs to) be diagnosed. The clinical priorities in the investigation of patients with suspected PE include:

1. Diagnosis of extensive PE

2. Diagnosis of PE in patients with severe symptoms and/or poor cardiopulmonary reserve

3. Diagnosis of any PE when associated with symptomatic or asymptomatic proximal DVT

4. Diagnosis in patients presenting with possible recurrent PE

D-dimerD-dimer

Although most patients with PE and DVT have an elevated D-dimer result, D-dimer is also elevated in many other conditions

D-dimer raised in recent injury or surgery, cancer, inflammatory diseases, healthy elderly, etc

Therefore, a positive test result is not helpful. A negative result, using a sensitive D-dimer assay, helps to rule out PE.

Clinical Probability (Wells’) ScoreClinical Probability (Wells’) Score

Clinical symptoms and signs of DVT 3.0 No alternative diagnosis is more likely than PE 3.0 Heart rate > 100 beats/min 1.5 Immobilization or surgery previous 4 weeks 1.5 Previous DVT/PE 1.5 Hemoptysis 1.0 Malignancy (treated within previous 6 mos or palliative) 1.0

Total points ______

Clinical pretest probability of PE High >6 Moderate 2-6 Low <2

Wells PS, et al. Ann Intern Med 2001;135:98

Which scan?Which scan?

Choose V/Q 1. Normal CXR

2. Patient is otherwise healthy

3. CTPA is contraindicated because of contrast allergy Poor renal function

4. Young & pregnant patients

Choose CTPA1. Abnormal CXR2. Respiratory disease3. Critical care patient4. Suspect massive PE

If the CXR is normal the V/Q scan will be diagnostic >94% of the time

Anticipating the traps Anticipating the traps and pitfallsand pitfalls

<6% of V/Q scans are non-diagnostic >6% of V/Q scans are non-diagnostic without

background clinical data, CXR, etc V/Q scans do not help to identify an alternate

diagnosis in the large proportion of patients who don’t have PE.

Not as readily available

V/Q scan advantagesV/Q scan advantages

1. a normal V/Q scan rules out PE>99% negative predictive value

2. the radiation dose is low

3. iodine-based contrast is not used

SUSPECT PEClinical assessment

LOW

D-dimer

Intermediate or HIGH

HIGHNormal Non-diagnosticPOSITIVENegative

DVT Study

VQ scan and/or CTPA

PositiveNegative

PE Excluded

Treat

All clear now?

NORMAL SCAN

RPO: ant & lat basal segments RLL

RAO: inf lingula; ant segment RUL

POSITIVE SCAN

POSITIVE SCAN

NON-DIAGNOSTIC SCAN

V/Q lung scanV/Q lung scan

1. A normal perfusion scan rules out PE.2. Most patients with a positive V/Q scan (one or more,

segmental or larger, perfusion defects) have PE and they can be treated without further testing.

3. All other lung scan abnormalities are non-diagnostic. Modern imaging techniques and good clinical communication

can keep this number <10% Further testing is required in patients with this V/Q scan

pattern. (CTPA, doppler legs)

Recommended reference: Management of Suspected Acute Pulmonary Embolism in the era of CT Pulmonary Angiography. A Statement from the Fleischer Society. Remy-Jardin et al. Radiology 2007;245:315-329.

Thankyou