Although highly sensitive for the diagnosis of AD’’’’ and disrupted aortic isthmus,’ the major widely acknowledged drawback of TEE is its relatively poor specificity. Interestingly, this relative lack of specificity has been predominantly reported for the diagnosis of Stanford type-A AD, whereas TEE diagnostic specificity is usually higher when the dissecting process is confined to the descending thoracic aorta. The presence of linear artifacts within the ascending aorta has been hypothesized to be responsible for most of the false-positive TEE results.
With the exception of one TEE study limited by suboptimal imaging quality, all inconclusive examinations encountered in protocol A of the current series (n = 24) were retrospectively attributed to the difficult interpretation of the presence of intra-aortic linear images. Of them, 21 images (87%) were linear artifacts, while only 3 images (13%) were related to the presence of an underlying intimal flap in the descending thoracic aorta. Interestingly, 13 of 21 linear artifacts (62%) were located in the ascending aorta. In this protocol, TEE diagnostic accuracy was similar to that reported in previous studies.’’’ The specificity of TEE for the identification of intimal flaps located within the ascending aorta was fairly higher than that reported by Nienaber et al. This discrepancy is presumably related to our larger cohort and the use of multiplane TEE probes in 37% of patients included in this protocol. In contrast with previous studies, we found a similar TEE diagnostic accuracy for the identification of intimal or medial flap in both the ascending and descending segments of the thoracic aorta (Table 3). Although in the latter anatomic segment of the aorta the incidence of linear artifacts was lower (7%), TEE has frequently been inconclusive when such images were encountered in patients with suspected TDA.
A false-positive diagnosis of intra-aortic flaps in the setting of patients who undergo a TEE for a suspected acute aortic condition may lead to unnecessary surgery, as shown in two of our patients from the retrospective series. Accurate identification of multiple-path artifacts is crucial in the presence of a linear image located in the ascending aorta, because surgical treatment of a dissection, or rarely a traumatic disruption, of this anatomic segment of the thoracic aorta is unequivocally advocated. In the present study, 21 of 64 patients (33%) sustaining a type-B AD also exhibited linear artifacts in the ascending aorta. As previously described, this image has been misdiagnosed as a true flap, resulting in unnecessary surgery in one patient who had a type-B AD rather than a type-A AD (Fig 6, left, A). In the setting of patients with severe blunt chest trauma, accurate diagnosis of linear artifacts within the descending thoracic aorta, as opposed to intraluminal medial flap, is also crucial because rapid surgery of subadventitial TDA is widely advocated to avoid lethal adventitial rupture. As in one of our patients (Fig 6, right, B), needless thoracotomy because of false-positive TEE results has been previously reported.
Importantly, the systematic use of strict TEE diagnostic criteria applied to intra-aortic linear images in protocol B substantially improved the specificity of this imaging modality for the identification of true flaps, within both the ascending and descending segments of the thoracic aorta (Table 3). Hence, no false-positive TEE results were encountered and no patient underwent unnecessary surgery during the prospective study. However, the learning curve during protocol A may also have contributed to the higher diagnostic accuracy observed in protocol B (Table 3).