The document discusses the investigation and diagnosis of pulmonary embolism, noting that while CT pulmonary angiography and V/Q scans can diagnose or rule out PE, over 70% of patients suspected of having PE do not actually have it. It provides guidance on using clinical probability assessments, D-dimer testing, and choosing between CTA and V/Q scans to effectively diagnose PE while avoiding unnecessary additional testing for patients who are unlikely to have the condition.

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.