Rapid and accurate diagnosis of aortic dissection is a major determinant of patient outcome. Current methods of diagnosing type A aortic dissection include computed tomography angiography (CTA), magnetic resonance imaging (MRI), catheter-based arteriography, and transesophageal echocardiography (TEE). While each method has its merits, they all carry the risk for false-positive findings. We present the case of a patient diagnosed with presumed type A aortic dissection by CTA, subsequently ruled out by TEE investigation under general anesthesia. The patient provided written permission for publication of this report.
A 19-year-old man with no significant medical or surgical history presented to the emergency department after a sledding accident where he suffered blunt trauma to the anterior sternum after striking a tree trunk. He complained of continuous, nonradiating, sharp anterior and left-sided chest pain. Chest x-ray demonstrated a fractured sternum, but otherwise normal cardiopulmonary structures. A CTA was performed to assess for intrathoracic great vessel injury. Findings of the CTA suggested a dissection flap involving the ascending aorta and aortic arch (Figure 1). Based on CTA suggestion of aortic dissection, the patient was immediately taken to the operating room for surgical repair.
Before induction of general anesthesia, the left radial artery was cannulated under IV sedation with midazolam. Uneventful induction of general anesthesia, muscle paralysis, and endotracheal intubation were performed, after which a TEE probe (X7-2T Phillips probe; IE-33 machine; Phillips Healthcare, Inc, Andover, MA) was uneventfully placed. TEE images did not produce any evidence of dissection of the ascending aorta or aortic arch (Figure 2). A hyperechoic, curvilinear structure was visualized in the ascending aorta on TEE mimicking a dissection flap, but lack of independent movement on M-mode assessment and its continuation past anatomic planes when viewed in short-axis utilizing X-plane confirmed suspicion of an artifact (Figure 3). The lack of dissection flap in the distal aortic arch, lack of aortic regurgitation, and pericardial effusion were further evidence that a dissection was not present. Given discordant TEE and CTA findings, and no clear evidence of dissection by TEE, the planned operation was aborted after discussion by the cardiac surgeon and radiologist. The patient was transferred to the intensive care unit. Because of concern of CTA artifact on the initial scan, a gated CTA was performed, which demonstrated normal aortic anatomy without dissection. The patient was monitored and discharged in a stable condition on hospital day 3.
Arteriography has been replaced as the diagnostic method of choice for evaluating aortic injury by MRI, CTA, and TEE. A recent pooled analysis demonstrated near equivalency between the modalities for diagnosing type A aortic dissection.1 The Table reviews the benefits and pitfalls commonly encountered in each testing modality. MRI has the highest sensitivity and specificity and provides superior anatomical detail without need for contrast enhancement. However, its use in evaluating acute aortic injury is limited because of the length of time required to obtain images, its contraindication in patients with ferromagnetic devices, and safety concerns in unstable patients.2
The use of CTA as a first choice diagnostic modality is increasing. As many as 73% of hospitals evaluated in the International Registry of Aortic Dissection performed CTA as the initial study.3 In addition, given the emergent nature of type A aortic dissection and the need for a rapid and accurate test to initiate appropriate surgical or medical treatment, CTA is a reasonable first choice. While not equal in anatomic detail to MRI, CTA allows for the evaluation of underlying structures as well as assessment of effusions or tissue injury. The disadvantages of CTA include an increased risk for kidney injury and severe allergic reactions secondary to the use of contrasted agents. In addition, inappropriate timing of dye administration may impair adequate image acquisition.4,5 Finally, CTA does not detect aortic insufficiency and is prone to artifacts.
Artifacts reduce the sensitivity of CTA. They occur frequently due to cardiac or patient movement, patient positioning, and interference from mechanical or metallic devices. Motion artifacts may result in curvilinear artifacts that can suggest aortic injury.6 Streak artifacts are encountered when patient prostheses, devices, or high-contrast interfaces (as can occur between the pulmonary artery and aorta) cause beam displacement and impair image quality. Streak artifacts may result in appearance of lines, which can mimic tissue flaps. CTA artifacts are frequently confined to only 1 or 2 images.
In our patient, there was motion artifact during the initial, non-gated CTA that resulted in the suggestion of an aortic dissection. After additional review, the identification of the artifact was further verified by the appearance of a curvilinear structure in the pulmonary artery and extension of a “tissue flap” beyond anatomical planes (Figure 4). Furthermore, since the CTA study was not gated to our patient’s electrocardiogram, the chance of motion artifact was increased.7
While TEE has similar sensitivity (but lower specificity) to CTA and MRI, its use as the initial diagnostic modality has declined.1 This likely reflects time delay concerns and potential for hemodynamic compromise because of need for sedation and the potential for hemodynamic changes during manipulation of the echocardiographic probe. TEE is highly sensitive, but has decreased specificity compared to CTA and MRI in diagnosing type A aortic dissection because of artifacts and inability to visualize the entirety of the ascending aorta and arch. A review of TEE in patients presenting with suspected type A aortic dissection found that artifacts were present in the ascending aorta in 26% of patients, complicating the echocardiographic assessment.8
TEE views utilized to identify aortic dissection include the mid-esophageal long-axis plane, the mid-esophageal aortic valve short axis pulled up slightly to view the ascending aorta, upper esophageal aortic arch view, and scanning of the descending aorta from upper esophagus to the stomach. Aortic dissection is diagnosed or confirmed on TEE by a mobile dissection flap moving independent of the aortic wall and identification of this defect in more than 1 TEE plane.9 It is imperative that the echocardiographer be familiar with ultrasound artifacts and how to differentiate between true pathology versus artifact. Side lobe and reverberation artifacts appear as curvilinear structures and can mimic an aortic dissection. Unlike an aortic dissection, however, side lobe artifacts are displaced parallel to the aortic wall, lack independent movement compared to the aortic wall, may extend extraanatomically, and have similar blood flow velocities on both sides. M-mode and color flow Doppler are beneficial in identifying side lobe artifact.10 Reverberation artifacts require imaging with multiple planes to identify true anatomy.
In the absence of aortic dissection during TEE evaluation, it is important to rule out other pathology that present with similar clinical presentation of “aortic pain.” Other acute aortic syndromes include penetrating aortic ulcer, blunt aortic trauma, and aortic aneurysm rupture.9 Some aortic lesions that can result from blunt aortic trauma include intramural hematoma, lesion of the aortic branches, and subadventitial aortic rupture with or without complete circumferential extension. TEE findings in patients with blunt aortic injury include a crescent or circumferential thickening of the aortic wall, an abnormal aortic contour, dilation of the isthmus region, a pseudoaneurysm, intraluminal medial flap, or mobile linear echo densities attached to the aortic wall.9 It is important that the TEE operator has appropriate training and experience in identifying these lesions.
In summary, we report the case of an inaccurate diagnosis of type A aortic dissection attributed to motion artifact during CTA. While CTA is the preferred initial diagnostic method in most centers, it is important to consider its limitations and recognize artifacts. In patients where the clinical picture is not consistent with the CTA images, further workup with another testing modality or obtaining gated images is recommended.5 TEE should be considered as a reliable second method of assessment.
Name: Jeremy M. Bennett, MD.
Contribution: This author helped write the manuscript.
Name: Bantayehu Sileshi, MD.
Contribution: This author helpedcare for the patient, obtain transesophageal echocardiography images, and edit and contribute to the manuscript.
This manuscript was handled by: Hans-Joachim Priebe, MD, FRCA, FCAI.
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