Imaging description

Following ascending thoracic aorta surgery, it is common to identify fluid collections that surround the ascending aortic graft. These fluid collections are most often seen in the recent post-operative phase, are low in attenuation, and can range in thickness from millimeters to several centimeters (Figure 71.1). [1,2]

Importance

Perigraft fluid collections are important to distinguish from clinically significant causes of mediastinal fluid accumulation, namely post-operative mediastinal abscess or graft anastomotic dehissence.

Typical clinical scenario

Perigraft fluid collections are found in the majority of patients after graft repair of the ascending aorta and are generally of no clinical consequence. These fluid collections will usually progressively decrease in size and resolve; however, in some patients they may persist indefinitely (Figure 71.2). The etiology of perigraft fluid collections is uncertain. In the immediate post-operative phase these collections have been postulated to represent evolving hematoma. Persistent collections may be due to an inflammatory response to graft material, something also noted in patients with prior open abdominal aneurysm repair.

Post-operative perigraft fluid collections should be distinguished from infected fluid collections or anastomotic dehissence. Thickened, enhancing walls surrounding the collection, inflammatory changes in the mediastinal fat, gas, or extension of the fluid into the sternal wound are signs of infection. Increasing size of a perigraft fluid collection is an important finding that should raise suspicion for infection, anastomotic dehissence, or both. Extensive air can also be seen in the setting of an aortoesophageal fistula (Figure 71.3). The presence of new extraluminal contrast or pseudoaneurysm within the perigraft fluid is a definitive sign of anastomotic break down (Figure 71.3). In cases of slow or intermittent leaks, obvious signs of extraluminal contrast may be absent; however, imaging will show a perigraft collection containing high- attenuation material due to hematoma.