What is the best way to diagnose an aortic graft infection?

Best Diagnostic Approach for Aortic Graft Infection

Computed tomography angiography (CTA) is the recommended initial imaging modality for diagnosing aortic graft infection, with a sensitivity of 85-100% and specificity of 85-94%. 1

Diagnostic Algorithm

Initial Imaging

• CTA should be the first-line imaging modality for suspected aortic graft infection due to its high sensitivity, rapid results, and ability to define precise anatomic location 1
• CTA can detect key diagnostic findings including:
  • Perigraft fluid collection (especially if present >3 months post-implantation) 1
  • Increasing perigraft gas volume on serial imaging 1
  • Perigraft gas present >7 weeks post-procedure 1
  • Presence of contrast material external to the interposition graft (indicating graft dehiscence) 1

For Indeterminate CTA Findings

• Magnetic resonance imaging (MRI) should be considered when CTA is nondiagnostic (sensitivity 68-85%, specificity 97-100%) 1
• MRI offers superior soft tissue resolution and can better differentiate between hematoma, inflammation, and infection 1
• MRI is particularly valuable in patients with renal impairment as it doesn't require iodinated contrast 1

Advanced Imaging Options

• For cases that remain indeterminate after CTA/MRI, consider:
  • 18F-FDG PET/CT (sensitivity 78-96%, specificity 70-93%) with an SUVmax >8 strongly suggesting infection 1, 2
  • Indium-labeled white blood cell scan (sensitivity 67-73%, specificity 87%) 1

Diagnostic Criteria by Graft Location

Intra-Abdominal Aortic Graft Infection

• In patients with suspected intra-abdominal VGI and gastrointestinal bleeding, both CTA and esophagogastroduodenoscopy are recommended 1
• Esophagogastroduodenoscopy can identify erosion or thrombus in the third or fourth portion of the duodenum overlying the graft 1
• CTA findings should be correlated with blood culture results (positive in 50-90% of cases) 1

Intrathoracic Aortic Graft Infection

• For suspected intrathoracic graft infection, a combination of echocardiography, CTA, and MRI is recommended 1
• Echocardiography helps define anatomy, valvular dehiscence, graft anastomotic disruption, and fistulae 1
• ECG-gated CTA is particularly important for the ascending aorta to minimize cardiac motion artifacts 1

CT Imaging Characteristics

• Key CT findings suggesting infection include:
  • Lobular, irregular, saccular shape (vs. fusiform in non-infected grafts) 1
  • Absent or minimal calcification 1
  • Uncommon mural thrombosis 1
  • Rapidly changing appearance on serial imaging 1
  • Periaortic soft tissue stranding, fluid, or concentric inflammatory response 1
  • Presence of periaortic gas (uncommon but highly specific) 1

Important Caveats and Pitfalls

• Timing considerations:

  • Perigraft fluid is normal in the early postoperative period (≤3 months) and should not be mistaken for infection 1
  • Indium scans can be falsely positive in the early postoperative period 1
  • Recent antimicrobial therapy can decrease the sensitivity of indium scans 1

• Diagnostic challenges:

  • CT may not differentiate between hematoma and low-grade inflammation 1
  • Metallic clips and spinal hardware can degrade CT image quality 1
  • PET/CT has limited experience in aortic graft infection diagnosis compared to other modalities 1

• Clinical correlation:

  • Laboratory findings (leukocytosis, elevated inflammatory markers) are nonspecific and must be correlated with imaging 1
  • Blood cultures should be obtained and are positive in 50-90% of cases 1