What is the treatment for a suspected mycotic aneurysm, presenting as a saccular posterior outpouching of the thoracic aorta measuring up to 3.8 cm at the level of the pulmonic valve?

Treatment of Suspected Mycotic Aneurysm of the Thoracic Aorta

For a suspected mycotic aneurysm presenting as a saccular posterior outpouching of the thoracic aorta measuring 3.8 cm at the level of the pulmonic valve, in situ reconstruction with antimicrobial therapy is the recommended treatment approach. 1

Initial Management

Diagnostic Confirmation

• CT angiography is the preferred imaging modality for detailed assessment of the aneurysm morphology, extent, and involvement of branch vessels
• Blood cultures (at least 3 sets) must be obtained before initiating antimicrobial therapy
• Inflammatory markers (ESR, CRP) should be measured to assess infection severity

Immediate Interventions

• Hospital admission with close hemodynamic monitoring
• Broad-spectrum IV antibiotics should be started immediately:
  • Vancomycin (to cover gram-positive organisms including MRSA)
  • PLUS
  • Piperacillin-tazobactam or meropenem (for gram-negative coverage including Salmonella)
• Adjust antimicrobial therapy based on blood culture results and sensitivities
• Aggressive blood pressure control with IV medications (target SBP <120 mmHg)

Definitive Treatment

Surgical Management

The 2022 ACC/AHA guidelines provide specific recommendations for mycotic aneurysm management 1. For a thoracic mycotic aneurysm at the level of the pulmonic valve, the options include:

1. In situ reconstruction (preferred for thoracic location):

   • Advantages: More versatile, higher patency rates, lower recurrent infection rate
   • Technique: Debridement of infected tissue followed by reconstruction with:
     • Rifampin-soaked or silver-coated polyester grafts
     • Cryopreserved arterial allografts (when available)

2. Endovascular repair (TEVAR):

   • Role: Primarily as a bridge procedure in unstable patients
   • Advantages: Less invasive, avoids aortic cross-clamping
   • Disadvantages: Higher long-term morbidity and mortality with device retention
   • Note: Generally requires eventual device explantation and definitive reconstruction

3. Extra-anatomic reconstruction:

   • Not feasible for thoracic location according to guidelines 1

Antimicrobial Therapy

• Targeted antimicrobial therapy based on culture results for 6-8 weeks
• Consider lifelong suppressive antibiotics in high-risk patients or those with retained prosthetic material
• Regular follow-up blood cultures and inflammatory markers to assess treatment response

Specific Considerations for This Case

• The saccular morphology increases rupture risk even at smaller diameters 2
• Location at the pulmonic valve level (proximal thoracic aorta) makes in situ reconstruction the preferred surgical approach 1
• The 3.8 cm diameter is below typical intervention thresholds for non-infected aneurysms, but the suspected mycotic etiology mandates intervention regardless of size due to high rupture risk 3, 4

Post-operative Management

• Early post-operative imaging (within 1 month)
• Regular surveillance imaging:
  • CT angiography at 3,6, and 12 months
  • Then annually if stable
• Continued antimicrobial therapy as guided by infectious disease specialists
• Aggressive cardiovascular risk factor modification

Potential Complications and Pitfalls

• Delayed diagnosis increases mortality risk significantly
• Blood cultures may be negative in up to 25-30% of mycotic aneurysms
• Risk of reinfection is higher with prosthetic material
• Endovascular repair alone without subsequent open reconstruction carries high risk of persistent infection and late complications

The decision between surgical options should be made by a multidisciplinary team including vascular surgery, infectious disease, and cardiac anesthesiology, but in situ reconstruction remains the gold standard for definitive treatment of thoracic mycotic aneurysms 1.