The Batson Plexus and Spondylodiscitis
The Batson plexus is a valveless, low-pressure venous network that provides a direct hematogenous route for bacteria to reach the vertebral endplates, making it the primary anatomical pathway for the development of spondylodiscitis in adults, particularly in immunocompromised patients and those with recent spinal surgery.
Anatomical Basis of Hematogenous Spread
The Batson plexus (also called the vertebral venous plexus) is a valveless venous system that connects the pelvic, abdominal, and thoracic veins directly to the vertebral column without passing through the pulmonary circulation. This anatomical feature is critical because:
Bacteria bypass normal filtration: The valveless nature allows bidirectional blood flow, enabling bacteria from distant infection sites (endocarditis, urinary tract infections, pulmonary infections) to reach vertebral structures directly without pulmonary or hepatic filtering 1.
Low-pressure system facilitates seeding: The low-pressure environment in this venous plexus allows bacteria to settle and colonize the highly vascularized vertebral endplates, which are the initial site of infection in adult spondylodiscitis 1.
Pathophysiology of Vertebral Infection via Batson Plexus
Initial Endplate Seeding in Adults
Adults develop infection at the vertebral endplate first: Unlike children who develop primary discitis, adults experience initial bacterial seeding at the vertebral endplate via arterial end-arteries that communicate with the Batson plexus 1.
The infection then spreads to the adjacent disc: From the endplate, bacteria invade the avascular intervertebral disc, creating the classic pattern of two adjacent vertebral bodies with intervening disc involvement (osteomyelitis-discitis complex) 2.
High-Risk Populations
The Batson plexus route is particularly relevant in:
Immunocompromised patients: HIV, diabetes mellitus, hepatic or renal failure, rheumatologic disease, or immunosuppression increase susceptibility to bacteremia and subsequent vertebral seeding 1.
Post-spinal surgery patients: Surgical manipulation can introduce bacteria directly into the vertebral structures or create conditions for hematogenous seeding via the Batson plexus, with these patients at risk for multilevel disease 1, 3.
IV drug users: Repeated bacteremia episodes provide multiple opportunities for bacterial seeding through the Batson plexus, often resulting in multilevel or multifocal spine infection 1.
Extension Patterns After Initial Seeding
Once bacteria establish infection via the Batson plexus at the endplate:
Posterior extension into epidural space: Infection spreads posteriorly creating epidural abscesses that compress nerve roots and spinal cord at multiple levels, occurring in approximately 20% of contiguous multilevel cases 2.
Lateral extension into paravertebral tissues: Infection spreads laterally forming paravertebral abscesses that compress exiting nerve roots in neural foramina 2.
Multilevel disease patterns: The Batson plexus can deliver septic emboli to multiple non-contiguous spinal levels simultaneously, explaining why 10% of cases present with non-contiguous multilevel infections and 20% with contiguous multilevel disease 3, 4, 2.
Clinical Implications for Diagnosis
Understanding the Batson plexus mechanism guides diagnostic approach:
Assess the entire spine: Because the Batson plexus can seed multiple levels, imaging must evaluate the complete spine—30% of cases involve multiple levels (20% contiguous, 10% non-contiguous) 4, 2.
MRI with contrast is essential: Sagittal MRI views identify the full extent of involvement, epidural abscess formation, and paravertebral soft tissue extension with 96% sensitivity and 94% specificity 3, 4.
Consider PET/CT for multilevel disease: [18F]FDG PET/CT is particularly valuable for detecting multilevel disease resulting from multiple septic emboli through the Batson plexus 4, 2.
Critical Pitfall to Avoid
Never assume single-level disease: The Batson plexus anatomy means that any patient with spondylodiscitis, especially those who are immunocompromised or post-surgical, requires complete spinal imaging to exclude multilevel involvement that would alter surgical planning and antibiotic duration 4, 2.