Minimal aortic injury of the thoracic aorta: imaging appearances and outcome Emerg Radiol, 2014 Harborview Medical Center, University of Washington

Introduction The use of computed tomography (CT) for the diagnosis of blunt thoracic aortic injury (BTAI) was first described more than 25 years ago. For the detection of BTAI, MDCT angiography has a sensitivity of 95–100 % and a negative predictive value is 100 %.

Several small case series have described generally favorable outcomes with conservative management of minimal aortic injury(MAI); However, the incidence, imaging appearance, management, and long-term natural history of these aortic injuries has not been well studied.

The purpose of this study was to describe the CT imaging appearances, management strategies, and outcomes of patients who presented with minimal aortic injury, to provide a basis for future MAI management recommendations.

Materials and methods Study population All patients from trauma center with a diagnosis of BTAI between 1 January 2004 and 31 December The electronic medical record (EMR) for each subject was reviewed for patient age, sex, mechanism of injury, injury severity score (ISS), the type and timing of BTAI management, time from initial presentation to the last recorded medical consultation in our EMR, and patient outcome (all-cause mortality, BTAI-AZ related mortality).

Image analysis All CT imaging and catheter angiography performed on the patients identified by the trauma registry and radiology information system(RIS) search. A radiologist with experience to determine the general type of aortic injury (MAI, non-MAI BTAI). The appearance and size of the aortic lesion and other nonvascular traumatic injuries were noted. The appearance of the aortic lesion on follow-up CTA and the time to follow-up imaging was also recorded.

CT imaging technique With one exception, all CTA examinations were performed on a 16 channel MDCT(GE LightSpeed 16 or GE LightSpeed 16 Pro). The helical acquisition of were acquired at a peak aortic enhancement (timing bolus peak plus 5 s) and reconstructed at 1.25 mm slice thickness. For one patient, the CTA was performed on a four- channel MDCT scanner with 5 mm slice reconstruction.

Statistical analysis Data analysis was performed using SPSS 18. Means, medians, standard deviations, and ranges were calculated for continuous variables. Frequencies were calculated for categorical variables. A Pearson Chi-square test was used to compare non- MAI and MAI groups. An independent samples t test was used to compare age and ISS between the non-MAI and MAI groups. A p value of <0.05 was considered significant.

Results Patient characteristics The demographics of these patients are summarized in Table 2.

MAI CT imaging appearances The most common imaging appearance of MAI, present in 78 % (18/23) patients, was a rounded or triangular intraluminal filling defect attached to the wall of the aorta (Fig. 1). Intramural hematoma was present in 9 % (2/23) (Fig. 2) Focal thin membrane-like filling defects without associated thrombus, thought to be intimal flaps, were present in 13 % (3/23) (Fig. 3). A large filling defect was noted in one patient (Fig. 4).

Fig.1 Fig.2

Fig.3 Fig.4

MAI follow-up CT scans No intervention was performed prior to follow-up CT imaging in 87 % (20/23) of MAI cases. Endovascular repair was performed prior to follow- up imaging in 13 % (3/23) of cases.

Median time to follow-up 3 days (range, 1–385 days), with 85 % (17/20) of follow-up CT’s performed within 1 week. On follow-up CT, the aortic abnormality had resolved or was smaller in 45 % (9/20) of cases, was stable in 40 % (8/20), and was larger in 10 % (2/20).

Of the two patients with enlarging filling defects on follow-up imaging, one was treated with immediate surgery. The other patient was management conservatively. Three of the eight patients with stable initial follow- up imaging had at least one additional follow-up CT angiogram which demonstrated resolution of the aortic abnormality.

Additional follow up imaging was not performed at our institution in the remaining five cases with a persistent, but stable, aortic abnormality on the first follow-up CT angiogram.

MAI clinical management The majority of patients with MAI were ultimately managed conservatively (83%, 19/23). Four patients were managed operatively. Three patients were treated with endovascular aneurysm repair (EVAR) and one with a hybrid surgical bypass and EVAR procedure.

MAI long-term outcome All patients but two were alive on follow-up. There was a mean clinical follow-up period of 464 days among the 21 survivors with MAI. In no patient was the MAI an isolated injury. No survivor was there evidence of long-term sequelae attributable to their minimal aortic injury. Only one of the two patient deaths in this group could be directly attributed to sequelae of the MAI.

MAI versus non-MAI Table 1 No significant difference in ISS, all-cause mortality, or mortality due to BTAI between the MAI and non-MAI groups. Significantly more patients were managed operatively in the non-MAI group than in the MAI group overall (22.4 % vs 0.0 % respectively, p<0.001)

Discussion Our retrospective series has described the CT appearance of a type of BTAI that can be treated conservatively and has a very good outcome. We have described the relative frequency of these injuries as a proportion of all BTAI. At our institution, the outcome of these aortic injuries is excellent with a mortality rate secondary to aortic injury of 4.4 %, even with conservative management in a large majority of cases.

Various authors have noted the increasing incidence of subtle aortic injuries as the use of screening MDCT of the aorta in the major trauma patient has increased. There are a few small case series in the literature assessing the natural history of these aortic injuries.

In the study, almost half of the patients, the aorta returned to a normal appearance by the first follow up CT angiogram and was stable in all but three of the remaining patients. The initial finding on CT was of a small intraluminal filling defect adherent to the internal wall of the aorta. we have no pathologic proof of the type of injury involved in these cases, we believe they are likely to be small endothelial or intimal injuries with adherent mural thrombus.

The poor outcome in the patient was not just due to the extent of injury but to complications of the combined open and endovascular repair. This raises the possibility that a better outcome may have been achieved with conservative management alone. That CTA is used for initial follow-up, despite concerns about radiation risk in these patients. The use of MRI and low-radiation dose CTA may be sufficient but was not specifically addressed here.

limitations 1.we did not re-examine all screening CT’s performed for suspected aortic injury, it is possible that these injuries were missed at the time of interpretation of the initial CT interpretation. 2.We under-estimated the incidence of minor aortic injury. 3.The CT scanners used in this study are somewhat dated(16- and 4-channel). But the majority of MAIs were located in the descending aorta where motion and pulsation artifact are small.

1.The mean follow-up period in patients managed conservatively was just 466 days. It is possible that intimal injuries could have progressed to pseudoaneurysms after that time and not been clinically apparent. 2.Differences in mortality rates between our MAI and non-MAI groups did not meet statistical significance (p=0.508). (For one death among 23 patients has a large effect on the mortality rate and the mortality rate of non-minimal BTAI at our institution is now low, 8.6 %. ).

The term “minimal aortic injury” are not necessarily minimal injuries, as demonstrated by the death of a patient in our series. Further research is needed to distinguish between minor injuries that are safe to manage conservatively or with simple observation and those that require surgery.

summary Minor aortic injuries represent approximately a quarter of BTAI at our institution and occur predominantly in the descending aorta. An excellent outcome can be expected in nearly all cases of minor aortic injuries when treated with antihypertensives, anticoagulation, and observation.