Incidental detection of pulmonary emboli on routine MDCT scans of the chest

OBJECTIVE. Theobjectivesofourstudyweretoassesstheprevalenceofpulmonaryem- bolism incidentally detected on routine MDCT of the chest and to determine whether the use of wide window settings can improve detection of unsuspected pulmonary embolism. MATERIALS AND METHODS. A retrospective review of routine contrast-enhanced MDCT scans of the chest obtained in 589 patients was undertaken. CT angiograms obtained for suspected pulmonary embolism or thoracic aorta disease were not considered. Image eval- uation was performed on a dedicated workstation during two separate review sessions using different window settings: standard, with a width of 400 H and level of 40 H; and wide, with a width of 600 H and level of 100–150 H. The quality of vascular enhancement was recorded. RESULTS. Eight examinations were excluded because of poor quality. Unsuspected pul- monary embolism was present in 20 (3.4%) of 581 patients with an inpatient prevalence of 4.0% (19/474) and outpatient prevalence of 0.9% (1/107). Fourteen patients (70.0%) with un- suspected pulmonary embolism had cancer. The proximal extent of pulmonary embolism in- volved the main pulmonary artery in five patients, a lobar artery in five, and a segmental artery in 10; isolated subsegmental thrombi were never found. The use of wide window settings al- lowed detection of pulmonary embolism in two more patients than did the standard settings. CONCLUSION. Unsuspectedpulmonaryembolismcanbefoundinasignificantnumber of patients undergoing a routine MDCT study of the chest, with a higher prevalence among in- patients with malignancy. The use of wide window settings is recommended when interpreting routine CT scans of the chest to improve detection of unsuspected pulmonary embolism.