Imaging description

Patients who require staged thoracic aneurysm surgery may have an “elephant trunk” prosthesis placed during the first surgery. The proximal graft is sutured into the aortic arch, while the distal edges of the graft are freely mobile within the lumen of the descending thoracic aorta (Figures 69.1 and 69.2). Owing to the configuration, the free edges of the distal end of the graft can simulate an intraluminal dissection on axial CT. Correlation with surgical history and review of 2D MPRs and 3D renderings enables the radiologist to make the correct interpretation of a normal elephant trunk prosthesis. The surgical procedure and typical imaging appearance have been described in detail in the literature.

The free-floating graft serves to protect the descending thoracic aorta prior to the second surgery. It is then incorporated into either a surgical graft or endoluminal stent graft during repair of the descending aorta. Because the graft is positioned in the descending thoracic aorta, the second surgery can be performed at a distance from the first in unaltered anatomic planes; reoperating in the same location carries a high risk of hemorrhage. Patients may alternatively undergo endoluminal stent repair of the descending thoracic aorta. The elephant trunk graft has radiodense markers on the distal end (Figure 69.3), to enable localization during fluoroscopic endovascular stent placement.

It is important to distinguish the normal appearance from potential complications of this type of graft. These include graft entrapment in the patients with a residual dissection; the graft can migrate into one lumen and preferentially supply the blood flow to that lumen. Surgeons will excise the most cranial extent of the dissection to prevent this complication. Additionally, aneurysmal dilatation of the more distal aorta has been reported. Ideally, this graft is a temporary structure that is incorporated into the final repair in a timely fashion to prevent such complication.

Importance

Misdiagnosis of the normal elephant trunk prosthesis as a dissection of the descending thoracic aorta can lead to unnecessary patient anxiety, additional imaging examinations, and potentially inappropriate interventions.