Subsegmental pulmonary embolism – diagnosis and clinical significance

Overview

Pulmonary embolism (PE) remains a frequent and potentially fatal diagnosis that is easily missed. Multidetector computed tomographic pulmonary angiography (CTPA) has rapidly become the sine qua non for the workup of PE. In the USA, use of CT pulmonary angiography rose 14-fold while VQ scanning decreased by 52% from 2001 to 2008. The high resolution of CT pulmonary angiography makes it possible to detect filling defects in subsegmental arteries. However, there is evidence that some small clots do not need treatment. The significant increase in isolated subsegmental pulmonary embolism diagnosis by CTPA represented probably a subset of more benign disease, or accurate detection of a natural, benign “clearing” process of the lung vasculature. On the other hand, the risk of major bleeding from anticoagulation was 5.3 % but the risk of recurrent venous thromboembolism was only 0.7 %. Another risks of CTPA are nephrotoxic contrast and carcinogenic radiation. To avoid these problems is not simply to do less testing but to test (and subsequently treat) more selectively and to consider alternative tests such as VQ scanning and ultrasonography when appropriate. Clinicians should reserve CT pulmonary angiography for patients at intermediate to high risk of pulmonary embolism based on algorithms that combine clinical probability and D-dimer test results. Implementing policies to use pulmonary scintigraphy as the first line test for pulmonary embolism in stable patients with a normal x ray appearance can reduce use of CT pulmonary angiography and decrease detection of subsegmental pulmonary embolism without increasing deaths from pulmonary embolism.

Keywords:

subsegmental pulmonary embolism – CTPA – lung scintigraphy – diagnosis – Prognosis – treatment