Scott Robert Akers MD, PhD, Presenter: Nothing to Disclose

Harold Ira Litt MD, PhD, Abstract Co-Author: Research grant, Siemens AG Corporate Advisory Board, Siemens AG Speakers Bureau, Siemens AG Consultant, Bayer AG Research grant, VentriPoint Diagnostics Ltd

Filling defects in the left atrial appendage (LAA) can be seen on arterial phase imaging of the chest. It is important to differentiate between true thrombus and "pseudo-thrombus," i.e. a filling defect caused by layering of contrast and unopacified blood in the LAA. The purpose of this study was to analyze the characteristics of true and pseudothrombus in the LAA and describe quantitative measures which may allow discrimination between these two entitites.

1147 non-gated CT angiography studies of the chest performed on 16 or 64 slice machines were reviewed for LAA filling defects. Filling defects were classified as true trombus or pseudothrombus based upon resolution on delayed phase imaging or near simultaneous transesophageal echocardiography. Identified filling defects were classified on the basis of morphology/shape. The transition zone from filling defect to contrast enhancement was analyzed using a line profile drawn perpendicular to the transition. The length of the transition zone from the filling defect to contrast opacified region and the rate of change of attenuation at the transition zone normalized to overall degree of LAA enhancement were measured.

12 cases of filling defects were identified (1.05%), 2 of which represented true thrombus and 10 pseudothrombus caused by incomplete LAA contrast filling. The mean transition zone length was longer for pseudothrombus than true thrombus (11.96±4.76 mm vs. 5.25±0.35 mm, p=0.001). The mean normalized rate of change of attenuation at the transition zone was lower for pseudothrombus than true thrombus (0.097±0.038 vs 0.215±0.005, p<0.0001).

LAA filling defects are present in 1% of non-gated CT angiograms of the chest, and differentiation between true and pseudothrombus is of great clinical import in these cases. The transition zone from filling defect to opacified region occurs over a shorter distance and has a greater rate of change in attenuation for true vs. pseudothrombus. A normalized rate of change in attenuation of 0.17-0.2 may provide a useful discriminant value for prospective distinction between true thrombus and pseudothrombus on arterial phase CT angiograms of the chest.

The results of this study may provide a method for prospective discrimination between true and pseudothrombus on arterial phase CTA exams of the chest, without the need for delayed imaging or TEE.

Akers, S, Litt, H, Quantitative Differentiation between True and Pseudo-Thrombus in the Left Atrial Appendage on Nongated Arterial Phase CTA of the Chest.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6013895.html