The operator should be familiar with several pitfalls in the evaluation of possible aortic dissection:
• Artifacts mimicking intimal flaps are common in the ascending aorta25,27.
They are either side lobe or reverberation artifacts. A side lobe is a curvi-
linear echo along a sector arc and is not undulating. Side lobe artifacts are commonly caused by calcification of the aortic root, aortic valve, and sinotubular junction. A reverberation artifact is the duplication of a linear echo signal along the path of the ultrasound beam. Reverberation artifacts commonly originate from the left atrial wall, right pulmonary artery, and/or Swan-Ganz catheter. At times, fatty infiltration of the crista terminalis of the superior vena cava or an infusion catheter in the SVC can also produce side lobe artifacts. Applelbe et al. have demonstrated from a retrospective review that linear artifacts are more frequent when the aortic diameter is larger than the left atrium31. These artifacts can be easily recognized by using M-mode to assess their movement and color flow Doppler to assess the flow characteristics on either side of the linear echo. M-mode echo demonstrates the artifact to have the same motion as the structure from which it is originating. At times the primary structure's echo is not as obvious as its reverberation artifact. Color flow Doppler demonstrates normal homogeneous color on both sides of the curvilinear echo without communicating jets. Careful echo image parameter and frequency adjustments are necessary to avoid side lobe and reverberation artifacts from simulating an intimal flap. Recognizing the artifacts is es sential for correct diagnosis of dissection. Sensitivity and specificity are significantly impacted by appropriately recognizing such artifacts32.
• A limited arc of imaging due to the probe being very close to the anterior aortic wall may not permit thorough evaluation of a dilated tortuous descending thoracic aorta and may pose problems in differentiating a thrombus in an ectatic aorta from a thrombosed false lumen. Furthermore, it may not be possible to image the entire aortic segment.
• It is very difficult to optimally measure the true level of the imaging plane, and hence one should use the distance marks on the echo scope from the level of the incisors as well as relation to the cardiac structures themselves. For instance, by rotation of the probe from the position in the descending aortic rightward, one can determine the level of the aortic finding at the level of the left atrium or left ventricle, etc.
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