Epidural Abscess¶

Definition¶

A spinal epidural abscess (SEA) is a collection of purulent material in the epidural space that can compress the spinal cord or cauda equina. It is a surgical emergency when causing neurological compromise, as delays in decompression lead to irreversible deficits. Staphylococcus aureus is the causative organism in approximately 60–70% of cases.

Etiology¶

• Hematogenous spread — Most common route (50%); from skin/soft tissue infections, endocarditis, UTI, or IV drug use
• Direct extension — From adjacent spondylodiscitis or paravertebral abscess
• Direct inoculation — Post-surgical, epidural injection, lumbar puncture

Imaging Findings¶

MRI (Modality of Choice)¶

• Location — The abscess is typically posterior in the thoracolumbar spine, extending over multiple vertebral segments
• T1-weighted — Iso- to hypointense collection in the epidural space displacing the thecal sac
• T2-weighted — Hyperintense collection
• Post-contrast T1 with fat saturation — Rim enhancement of the abscess capsule is the hallmark finding. The center of the abscess (pus) does not enhance, while the peripheral capsule enhances avidly.
• DWI — Restricted diffusion within the abscess (bright on DWI, dark on ADC) — helps distinguish abscess from other epidural collections
• Cord compression — Evaluate for displacement, compression, and signal change within the cord
• Associated spondylodiscitis — Present in 50–80% of cases

CT¶

• Epidural soft tissue collection with rim enhancement
• Less sensitive than MRI, particularly for phlegmon (early pre-abscess stage)
• CT myelography if MRI is contraindicated

Stages¶

1. Phlegmon — Early inflammatory stage without a drainable collection. MRI shows diffuse epidural enhancement without a rim-enhancing cavity. May respond to antibiotics alone.
2. Abscess — Mature collection with a capsule. MRI shows rim enhancement with a non-enhancing center. Typically requires surgical drainage.

Management¶

• Emergency surgical decompression — Laminectomy and drainage for neurological deficit or progressive symptoms
• Antibiotics — Prolonged IV antibiotics (4–8 weeks minimum)
• Medical management alone — May be considered for small abscesses without neurological deficit (phlegmon stage) with close serial monitoring
• Timing — Outcomes correlate strongly with preoperative neurological status and time to decompression

Key Points¶

• Spinal epidural abscess is a surgical emergency when causing cord compression
• S. aureus is the organism in 60–70% of cases
• Rim enhancement on post-contrast MRI is the hallmark — distinguishes abscess from phlegmon
• DWI showing restricted diffusion supports the diagnosis
• Typically posterior in the thoracolumbar spine, often spanning multiple levels
• Associated spondylodiscitis is present in 50–80%
• Neurological outcome depends on preoperative deficit severity and time to decompression

References¶

1. Darouiche RO. Spinal epidural abscess. N Engl J Med. 2006;355(19):2012-2020. https://pubmed.ncbi.nlm.nih.gov/17093252/
2. Hall WA, Munakomi S, Mesfin FB. Spinal Epidural Abscess. In: StatPearls. Treasure Island (FL): StatPearls Publishing; updated 2025 Nov 8. https://www.ncbi.nlm.nih.gov/books/NBK441890/
3. Expert Panel on Neurological Imaging, Ortiz AO, Levitt A, Shah LM, et al. ACR Appropriateness Criteria® Suspected Spine Infection. J Am Coll Radiol. 2021;18(11S):S488-S501. https://pubmed.ncbi.nlm.nih.gov/34794603/
4. Numaguchi Y, Rigamonti D, Rothman MI, Sato S, Mihara F, Sadato N. Spinal epidural abscess: evaluation with gadolinium-enhanced MR imaging. RadioGraphics. 1993;13(3):545-559. https://pubmed.ncbi.nlm.nih.gov/8316663/
5. Eastwood JD, Vollmer RT, Provenzale JM. Diffusion-weighted imaging in a patient with vertebral and epidural abscesses. AJNR Am J Neuroradiol. 2002;23(3):496-498. https://pubmed.ncbi.nlm.nih.gov/11901028/
6. Dumont RA, Keen NN, Bloomer CW, et al. Clinical Utility of Diffusion-Weighted Imaging in Spinal Infections. Clin Neuroradiol. 2019;29(3):515-522. https://pubmed.ncbi.nlm.nih.gov/29582111/
7. Sharfman ZT, Gelfand Y, Shah P, et al. Spinal Epidural Abscess: A Review of Presentation, Management, and Medicolegal Implications. Asian Spine J. 2020;14(5):742-759. https://pmc.ncbi.nlm.nih.gov/articles/PMC7595828/
8. Spinal epidural abscess. Radiopaedia.org. https://radiopaedia.org/articles/spinal-epidural-abscess

Related Articles¶

• Pyogenic Spondylodiscitis
• Paravertebral Abscess
• Spinal Epidural Hematoma