1. Lungs Scans
Their role in diagnosis of
Pulmonary Embolism

2. 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

3. Investigation 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

4. D-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.

5. Clinical 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

6. Which scan?
Choose V/Q Choose CTPA
2. Normal CXR 2. Abnormal CXR
3. Patient is otherwise 3. Respiratory disease
healthy 4. Critical care patient
5. Suspect massive PE
4. CTPA is contraindicated
 because of contrast allergy
 Poor renal function
5. Young & pregnant patients
If the CXR is normal the V/Q scan will be diagnostic >94% of the time

7. Anticipating the traps
and 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

8. V/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

9. SUSPECT PE
Clinical assessment
LOW Intermediate or HIGH
D-dimer VQ scan and/or CTPA
Normal Non-diagnostic HIGH
Negative POSITIVE
DVT Study
Treat
Negative Positive
PE Excluded

10. All clear now?

12. C AN
A LS
O RM
N

13. RPO: ant & lat basal segments RLL
RAO: inf lingula; ant segment RUL

14. C AN
E S
SITIV
PO

15. CAN
VE S
PO SITI

16. AN
IC SC
ST
NO
-DIAG
N ON

17. V/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)

18. Thankyou
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.