Postoperative Aorta

An effective imaging evaluation of the postoperative aorta cannot be accomplished without an understanding of the surgical techniques utilized in aortic repair and the resultant alterations in aortic anatomy. A familiarity with those procedures most commonly employed at the specific institution and their imaging manifestations should allow for rapid distinction between a normal postoperative appearance and the development of a postoperative complication that requires intervention.

Two standard techniques are currently employed for the repair of aortic aneurysm and dissection [53]: (1) interposition graft and (2) inclusion graft. In interposition graft the diseased segment is excised and the graft is sewn end to end; tributary vessels are reimplanted. Inclusion graft consists of aor-totomy and insertion of the graft within the diseased aortic lumen, leaving a potential space between the graft and the native aortic wall. This potential space may thrombose or may contain clot and persistent blood flow in combination. A Cabrol procedure, whereby the perigraft space is decompressed into the right atrial appendage, is thought to prevent progression of pseudoaneu-rysm formation [54]. For patients with involvement of the aortic root, a composite graft that includes a prosthetic aortic valve may be utilized.

Non-contrast-enhanced CT of aortic grafts shows the graft as a ring of high attenuation (Fig. 17). While this ring will form the outer boundaries of the aorta when the graft is interposed, inclusion grafts will appear as a ring within a larger circle representing the native aortic wall. Many patients with inclusion grafts demonstrate a peripheral thrombosed space between the graft and the native aortic wall. Occasionally there will be flow in the perigraft space, a finding readily demonstrated on spiral CT. The vast majority of patients with repairs of acute Type A dissections will demonstrate a persistent intimal flap distal to the graft site on spiral CT [55]. One of the complications of aortic inclusion graft is aneurysmal dilatation of the aorta, which is easily depicted on spiral CT or MR (Fig. 17).

Endoluminal repair of aortic aneurysm and dissections is now possible with the use of endovascular stent grafts. These are placed at most institutions in a collaborative effort by interventional radiology and cardiovascular surgery. This procedure for the management of TAAs is predominantly limited

Figure 17 Aneurysm complicating aortic graft repair of ascending aortic aneurysm. (A) Unenhanced CT at level of main pulmonary artery shows an aortic graft (arrows) engulfed bv a large amount of soft tissue. (B) Following contrast enhancement, the lumen of the graft is opacified with enhancement of the perigraft space, representing an aneurysm of the ascending aorta due to graft leakage. Note marked compression of the right pulmonary artery (curved arrow) by the aneurysm.

Figure 17 Aneurysm complicating aortic graft repair of ascending aortic aneurysm. (A) Unenhanced CT at level of main pulmonary artery shows an aortic graft (arrows) engulfed bv a large amount of soft tissue. (B) Following contrast enhancement, the lumen of the graft is opacified with enhancement of the perigraft space, representing an aneurysm of the ascending aorta due to graft leakage. Note marked compression of the right pulmonary artery (curved arrow) by the aneurysm.

to patients who are poor operative candidates. Spiral CT has proven useful for both pre- and postoperative evaluation of stent graft repair of thoracic aortic aneurysms [56,57]. On spiral CT scans, the metallic portion of the stent-graft, most often a series of modified Z-stents, is easily identified [58]. Complications such as stent-graft migration, incomplete deployment or collapse, peri-graft leakage, branch vessel occlusion, and progressive aneurysmal dilatation are more easily detected on spiral CT than with conventional aortography [59].

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