MDCT and in particular multidetector computed tomographic angiography (MDCTA) is the first choice imaging modality for evaluation of the aorta. It is important to use a high flow of intravenous contrast and contrast material with high iodine content to ensure high quality results of the exam. For diagnosis of complications such as leaking, hemorrhage, graft infection, pseudoaneurysm, post-contrast images are mandatory. On the other hand, non-contrast images are important for differentiation of the hyperdense grafts and their morphology in comparison with the native aorta. Subsequent multiplanar reconstruction (MPR), maximum intensity projection (MIP) and volume rendering (VR) reconstructions are necessary for the precise evaluation of the aortic wall and its branches. [2, 3, 5] All our patients underwent contrast-enhanced MDCT and when necessary native series. We used a 320-detector CT scanner to obtain the images. Some post-treatment findings are easy to identify while others can mimic pathological conditions.
To recognise the normal appearance of the repaired aorta the radiologist should know the different surgical materials, components and techniques, used during the intervention.
- Surgical grafts are often used to fix the aortic wall and can also be used to repair vessels of the aortic arch. The diseased part of the native aorta is excised and the graft is placed and reanastomosed to the ends of the native aorta (interposition graft - the more common procedure). The other technique consists of wrapping the native aorta around the graft (inclusion grafts). Compared to the wall of the native aorta, grafts are hyperdense on unenhanced scans, therefore they are useful for easier differentiation. In these cases, unenhanced CT is important to distinguish the graft. On the other hand, circumferential calcifications on the vessel wall can mimic hyperattenuating grafts. As a result of their morphology, grafts have a straighter configuration, can lead to the formation of angulations and folds. The latter can be confused with an intimal flap. Grafts change the contour of the aorta - it is typical for the operated aorta to lack normal anatomic landmarks such as sinutubular junction and sinuses of Valsalva. [2, 4, 5]
Fig 1: Sagittal contrast-enhanced CT image shows graft fold in a patient with ascending aorta repair after DeBakey type I aortic dissection which can mimic intimal flap.
Fig 2: Coronal contrast-enhanced CT image shows the straighter configuration of the graft compared to the native aorta in a patient with thoracic aorta repair after DeBakey type I aortic dissection. - Felt rings are used to reinforce potential weak points during surgery such as sites of anastomoses. They appear as hyperattenuating linear structures on unenhanced and contrast-enhanced CT, which encircle the wall of the aorta and are helpful in identifying the proximal and the distal end of the surgical graft. Felt rings could be mistaken for pseudoaneurysm on contrast-enhanced CT. Other surgical materials could mimic pathological conditions on non-contrast CT such as intramural hematoma which shows a hyperdense crescent sign on native series. [2, 4]
Fig 3: Axial non contrast CT image shows semilunar hyperattenuating surgical material within the aortic wall in patient with aortic valve replacement and aortocoronary bypass which can mimic intramural hepatoma (a). Non-contrast CT image of another patient shows hyperdense crescent sign indicating intramural hematoma (b).
- Endovascular stent-grafts are made of a metal skeleton. This metal skeleton is easily visible on CT scans. The skeleton is covered with a polyester graft material that cannot be seen on CT scans. The stent-graft is placed in the aorta, and the native vessel wraps around it. This isolates the diseased part of the aorta from the systemic circulation. For a precise evaluation of the different parts of the stent-graft, MIP reconstructions are necessary. [1, 2]
Fig 4: Sagittal contrast-enhanced CT image shows the metal skeleton of the endovascular stent-graft in a patient with thoracic aorta repair after DeBakey type III aortic dissection.
Fig 5: 3D reconstruction shows the metal skeleton of the endovascular stent-graft in a patient with thoracic aorta repair after DeBakey type III aortic dissection. - Perigraft fluid and gas bubbles are common in the early post-treatment period in open surgical repair and they don’t require any specific treatment. It is difficult to distinguish the presence of infection only with diagnostic imaging. In case of suspicion of an infection, it is important to correlate the imaging results with the clinical laboratory and clinical symptoms of the patient. [2, 3, 4]
It is essential for the radiologist to quickly and accurately distinguish any pathological findings of the post-treatment aorta since some can be life-threatening. In these cases, imaging, especially MDCTA, plays a crucial role in establishing an accurate diagnosis and determining the subsequent treatment.
1. One of the common complications of endovascular is the presence of an endoleak. There are five types of endoleak.[3]
- Type I endoleak refers to an insufficient seal at the proximal or distal end of the graft, leading to blood leakage into the aneurysm sac. This type of endoleak does not resolve spontaneously.
- The vast majority of endoleaks are type II. They represent retrograde blood flow through branch vessels. For example in the chest this retrograde flow occurs from the intercostal arteries while in the abdomen - from the lumbar arteries, inferior mesenteric artery, internal iliac artery, accessory renal artery. This type of endoleak resolves spontaneously.
- Type III endoleak occurs due to a mechanical defect in the stent-graft and requires treatment.
- Type IV endoleak occurs when there is blood leakage due to the porosity of the graft, and it does not require any treatment.
- Type V endoleak refers to an expansion of the aneurysmal sac without any apparent site of leakage.
2. Pseudoaneurysms affect both the thoracic and abdominal part of the aorta. Aneurysms are dilations of arterial vessels consisting of three layers of the arterial wall, while pseudoaneurysms consist of only the outermost layer of the aortic wall (tunica adventitia). They are a common late complication of abdominal aortic aneurysm repair. Infection is one of the etiological factors responsible for the formation of pseudoaneurysms of the abdominal aorta. Open surgical repair is the most preferred method when managing pseudoaneurysms of the abdominal aorta. [3]
Concerning the ascending aorta the most common sites of postoperative pseudoaneurysms are the ends of anastomosis, the coronary artery anastomosis site, the aortotomy site, the aortic cannulation site and the needle vent site. Patients who have undergone surgical repair of the ascending aorta and are symptomatic should undergo MDCT with ECG gating to evaluate the structures of the aortic root precisely. If a pseudoaneurysm is present, graft replacement is the preferred option. [6]
3. Graft infection is a rare but life-threatening complication. Certain risk factors such as diabetes, malnutrition, chronic kidney disease, liver disease, radiotherapy or chemotherapy, autoimmune diseases can increase the risk of developing it. CT, especially CTA, is the first-choice modality for detecting suspicious graft infection. Some of the signs of graft infection on CT include fat stranding, increasing the perigraft fluid and gas collection over time. It is important to not forget that the minimal amount of gas in the proximity of the graft is a normal post-operative finding. Accurate diagnosis requires correlating clinical symptoms, elevated white blood cell count and markers of inflammation, to ensure proper interpretation of imaging results. If a timely diagnosis and treatment are not provided, there is a risk of developing a pseudoaneurysm. [3, 7]
