Magnetic Resonance Imaging

The role of MRI in diagnostic evaluation of aortic diseases has been widely documented, resulting in comparative studies as one of the most accurate diagnostic techniques in the detection of acute and chronic aortic pathology55. A long examination time as well as difficult access to the patient has been considered the main limitation in acute aortic pathology. Although the development of fast MRI techniques has enabled the examination to be shortened to a few minutes, MRI has been underutilized in critically ill patients. For this reason, the use of MRI in traumatic aortic rupture for several years has been limited to case reports56, regardless of its potential. The value of MRI in detecting traumatic aortic rupture has been reported in a series of 24 consecutive patients in comparison with angiography and CT52. The diagnostic accuracy of MRI was 100%, 84% of angiography (two false negative, in two cases of limited partial lesion), and 69% of CT (two false negative and three false positive). Moreover, in almost all cases MRI was able to differentiate the type of lesion, according to Parmley's classification.

Because of the presence of methemoglobin, intimal hemorrhage has high signal intensity and is clearly detected by MRI spin-echo sequences. On the sagittal plane, the longitudinal visualization of the thoracic aorta allows one to distinguish a partial lesion, as a tear limited to the anterior or to the posterior wall (Figure 15.6), from a circumferential lesion, as a tear developing on the entire aortic circumference (Figure 15.7). This discrimination provides prognostic significance because circumferential lesions may have a greater risk of free rupture. The presence of periadventitial hematoma and pleural and medi-astinal hemorrhagic effusion, with high signal intensity, may also be considered to be a sign of instability of the lesion. The characteristic of MRI to detect the hematic content of a collection by its high signal intensity is widely useful in a polytraumatized patient. This is applicable to every traumatic lesion such as lung (Figure 15.6A), liver, or splenic hemorrhagic contusions, all characterized by high signal intensity, just like head hematoma. In the same sequence used to evaluate the aortic lesion, without any additional time, the wide field of view of MRI gives a comprehensive evaluation of chest trauma, such as lung contusion and edema, pleural effusion, and rib fractures. All this can compromise the result of emergency surgical repair, considering that respiratory insufficiency is the very common postoperative complication. In the subacute phase, MRI may be considered the ideal modality to monitor the aortic lesion before surgery because of its noninvasiveness, accuracy, and reproducibility of the parameters57. The development of fast techniques that reduce examination time to a few minutes and better accessibility to the patient may contribute to a feasible use of this powerful diagnostic tool in traumatic aortic rupture.

Figure 15.6. Sagittal oblique spin-echo MR image demonstrating a partial lesion of the isth-mic aorta. An intimal tear involving only the anterior wall is visible with associated pulmonary contusions, periaortic and bilateral pleural effusion. The sagittal plane provides a better visualization of the diverticular aneurysm.

Figure 15.6. Sagittal oblique spin-echo MR image demonstrating a partial lesion of the isth-mic aorta. An intimal tear involving only the anterior wall is visible with associated pulmonary contusions, periaortic and bilateral pleural effusion. The sagittal plane provides a better visualization of the diverticular aneurysm.

Figure 15.7. Sagittal oblique spin-echo MR image showing a circumferential aortic lesion. The involvement of both the anterior and posterior walls causes the development of a fusiform aneurysm. Note the invagination of the anterior and posterior aortic tears.

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