ElectricPE: The Diagnosis of Pulmonary Embolism: Case Study 5
Jeffrey R. Galvin, M.D. and James J. Choi, B.S.
Peer Review Status: Internally Reviewed
His PA and lateral chest X-ray was completely normal.
The perfusion scan demonstrated a minimal subsegmental defect in
left lung, seen only on the posterior view.
The ventilation scan was normal.
This scan was interpreted, at the time, as low probability for pulmonary embolus, although I think that some physicians might have placed it in the normal category.
A pulmonary arteriogram was normal. Multiple views of both lungs
were obtained. 
Case Assessment
This 27 year old presented with symptoms that, at first suggested a
cardiac origin. When that was ruled out, the clinicians turned their
attention to the possibility of pulmonary embolus.
The handling of patients with "low probability" scans continues to be controversial. It should be recognized, however, that the low probability category is, at best, not as reliable as either the "normal" or "high probability" categories. A diagnostic category is only as valid as its reproducibility and there is often substantial disagreement between readers of ventilation/perfusion scans when the abnormalities are small. If the scan cannot be read as either high probability or normal, then the clinician should strongly consider further work-up to rule out the diagnosis of pulmonary embolus.
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