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More Unsuspected PE Found on MDCT Scanning

January 10, 2008
Written by: , Filed in: Chest Radiology
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Background
Remarkable improvements have been made in CT imaging in the past decade. The new generation of multidetector CT (MDCT) scanners enables the entire thorax to be imaged with a single breath hold. With narrow collimation, visualization of opacified peripheral pulmonary arteries down to fifth order branches is now possible. A number of recent reports describe the detection of unsuspected pulmonary embolism (PE) by CT scanning.

Objective
The objective of a recent study was to evaluate the incidence of unsuspected PE in an inpatient population undergoing contrast-enhanced MDCT scanning of the thorax.

The results of this study would suggest that pulmonary emboli should be routinely searched for on all contrast-enhanced MDCT scans.

Methodology
In this prospective evaluation, during a 10-month study interval (January to October 2004), consecutive inpatients that underwent contrast-enhanced MDCT scanning of the chest for indications other than suspected PE were identified and their studies reviewed. Patients were excluded if they had known or suspected PE. CT pulmonary angiograms were not included.

The authors reviewed the reports generated from the day-to-day practice. Additionally, a thoracic radiologist unaware of the initial report reviewed the studies. The thrombus was recorded as central, lobar, segmental, or subsegmental.

Results
28 of the 487 scans showed PE (incidence, 5.7%). The incidence of unsuspected PE was 9.2% in patients aged >70 years and 16.7% in patients aged >80 years. Of the unsuspected PE cases, 30% were missed on the initial reading. Nine of the 28 patients with unsuspected PE were not diagnosed until the thoracic radiologist reviewed their scan. On these 9 scans, the emboli were in segmental vessels (n=6) and in subsegmental vessels (n=3).

Reviewer’s Comments
Unsuspected PE are not uncommon in inpatients undergoing contrast-enhanced MDCT of the thorax. In this study, the incidence of unsuspected PE was 5.7%.

Reviewer’s Comments
It is important to look for PE on any contrast-enhanced MDCT of the chest, regardless of the reason for obtaining the scan. When closer attention is paid to searching for PE, then more unsuspected emboli will be found. In this study, only 67% of emboli were seen on the initial review of the scan.

It should be noted that in 18 of the 28 positive cases, the emboli were located within the segmental and subsegmental levels. The truly vexing question that arises from reflecting on this study is “what to do with unsuspected PE,” particularly those that are confined to the segmental and subsegmental levels. Do all these emboli need treatment? Do all of these patients need anticoagulation?

Author: Richard A. Nusser, MD

Reference:
Ritchie G, McGurk S, et al. Prospective Evaluation of Unsuspected Pulmonary Embolism on Contrast Enhanced Multidetector CT (MDCT) Scanning. Thorax; 2007; 62 (June): 536-540

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