Normal perfusion scintigraphy in pulmonary embolism - Causes and diagnostic alternatives

Diagnosing pulmonary embolism (PE) is a challenge for many physicians as it is a frequently occurring disease with nonspecific symptoms and signs. Ven tilation-perfusion (V/Q) scintigraphy is widely used as the first step in d iagnosing PE since it is non-invasive and highly sensitive. With a normal p erfusion scan, clinically relevant pulmonary thrombo-emboli are considered to be absent. In an ongoing study assessing the value of spiral CT in the d iagnosis of PE, we encountered a patient who had a normal perfusion scan wh ile a large partially occluding thrombus in the right lower lobe artery and its branches was depicted by spiral CT and pulmonary angiography. In this article, we discuss the significance of normal findings in perfusion scinti graphy, the causes of false-negative perfusion scans and the role of altern ative techniques such as spiral CT and pulmonary angiography. (C) 2000 Else vier Science B.V. All rights reserved.