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E1461. Extradural Spinal Infections: A Case-Based Pictorial Review
Authors
  1. Archana Sachedina; Harbor UCLA Medical Centre
  2. Brandon Gisi; Harbor UCLA Medical Centre
  3. Anton Mlikotic; Harbor UCLA Medical Centre
  4. Sanjaya Viswamitra; University Of Arkansas Medical Sciences
Background
Vertebral osteomyelitis and discitis, while responsible for only 2 to 7% of musculoskeletal infections, are associated with a high morbidity and mortality. Initial clinical symptoms are often insidious and nonspecific, leading to a delay in diagnosis. This delay and the subsequent sequelae place a huge burden on health care resources. Early and correct identification on imaging studies is crucial for managment of the infection, and prevention of devastating neurological symptoms. The purpose of our exhibit is to review the pathophysiology of spinal infections, provide information about different imaging modalities commonly used for evaluation of spinal infections, and characterize imaging findings on each modality.

Educational Goals / Teaching Points
1. Review pathophysiology of common and uncommon extradural spinal infections 2. Discuss application of different imaging modalities 3. Characterize common imaging findings

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Key anatomic and pathophysiologic issues: There are three common routes through which infection occurs. While hematogenous spread is the most common, infection can also occur by contiguous spread from adjacent sites, as well as direct inoculation from intervention or trauma. Bacteria (predominantly staphylococcus aureus) are the most common offending organisms. Other less common pathogens include tuberculosis, fungi or rarely, parasites. Pathogenesis and imaging characteristics can be explained by the unique vascular anatomy of the disc and vertebral body. Imaging techniques and findings can be summed as follows: 1. Plain films - Changes not evident until 2 to 8 weeks after onset of symptoms. Early findings – subchondral lucency, loss of endplate definition, loss of disc height. Late findings – endplate destruction, loss of vertebral height. Role in resource poor facilities. 2. CT scan - Bony changes appreciated earlier than on plain radiographs. Neural tissue and soft tissue changes not as well appreciated as on MRI. Valuable tool for guided biopsy. 3. MRI - Modality of choice for initial imaging diagnosis. Useful for therapeutic follow up. Sequences – T1w, T2w, post contrast T1w, fat suppression of T2w and post contrast T1W. Increasing use of DWI to differentiate from reactive bone marrow edema. 4. Nuclear scintigraphy - 3 phaseTc99m MDP – Specificity decreased in bone altered by degeneration and instrumentation. In111 and Tc99m Radiolabeled leukocytes – limited use in discitis-osteomyelitis, often cold. Ga67 – in conjunction with bone scan or with SPECT-CT, 18F FDG PET-CT – useful when MRI contraindicated or indeterminate or in low grade infection

Conclusion
Identification of spinal infections on imaging studies is crucial for early diagnosis and treatment to prevent severe neurological complications. While MRI remains the modality of choice for initial imaging diagnosis, understanding the role of each imaging modality is useful, especially in facilities with limited available resources, and in patients where MRI may not be feasible. Being aware of imaging characteristics commonly associated with certain pathogens helps guide the clinician's next steps.