Which vertebrae are most commonly involved in a psoas abscess?

Most Common Vertebrae Involved in Psoas Abscess

The lumbar vertebrae are most commonly involved in psoas abscess, particularly L2-L4 vertebrae, as these are anatomically adjacent to the psoas muscle where infection can directly spread.1, 2

Pathophysiology and Anatomical Relationship

• The psoas muscle originates from the transverse processes and lateral aspects of the vertebral bodies of T12 through L5, with the majority of its bulk adjacent to the lumbar spine, making these vertebrae most susceptible to infection spread 1
• Psoas abscesses can be classified as primary (hematogenous or lymphatic seeding) or secondary (direct spread from adjacent structures) 3
• Secondary psoas abscesses frequently originate from spinal infections, particularly spondylodiscitis of the lumbar vertebrae 1
• The spine should always be considered as a primary source of infection in cases of psoas abscess, especially in patients with back pain or history of spinal surgery 1

Clinical Presentation and Diagnosis

• Patients with psoas abscess often present with hip or low back pain, limited mobility, and may maintain an antalgic posture with hip flexion 4
• Diagnosis is frequently delayed due to nonspecific symptoms that can mimic arthritis, joint infection, or urologic/abdominal disorders 1, 5
• Laboratory findings typically include leukocytosis, elevated C-reactive protein, and positive blood cultures, most commonly for Staphylococcus aureus in primary cases 3, 6
• MRI is the imaging modality of choice for definitive diagnosis, showing abnormal enhancement of the vertebral bodies and psoas muscle 5, 2

Imaging Considerations

• CT scan with contrast is highly effective for diagnosis, revealing enlargement of the psoas muscle with multiple bacterial foci 4, 2
• MRI without and with IV contrast is the preferred imaging modality for suspected spine infection with sensitivity of 97% and specificity of 93% 2
• Nuclear imaging such as gallium scans can be valuable when other imaging is inconclusive, especially in cases of fever of unknown origin 5
• Radiographs have low sensitivity in early disease process, as 30-40% of bone destruction is needed before radiographic changes become apparent 2

Treatment Approach

• Management includes surgical drainage of the abscess and appropriate antibiotic therapy 1, 6
• In patients with high operative risk and uniloculated abscess, CT-guided percutaneous drainage may be sufficient 1
• Treatment must address both the abscess and the primary infectious focus in the spine 1
• Continuous antibiotic therapy is recommended for 2-3 weeks after normalization of infectious parameters 1, 6

Special Considerations

• In cases of vertebral involvement with spinal instability, surgical consultation is essential to assess the need for surgical intervention 2
• Surgical procedures may be required for bony lesions that produce spinal instability, spinal cord or nerve root compression, or significant sequestered paraspinal abscess 2
• Multiple surgical approaches (anterior, lateral, posterior, or posterolateral) may be considered depending on the location and extent of infection 2
• The incidence of spine-associated psoas abscesses has increased with more frequent invasive procedures of the spine and recurring tuberculosis in industrialized countries 1