Spinal Epidural Abscess (SEA)

Diagnosis Definition

• Spinal epidural abscess (SEA) is an infection of the epidural space, located between the spinal dura mater and the vertebral periosteum
• Diabetes and intravenous drug use are the most significant risk factors for SEA
• Symptomatic patients most commonly present with back pain, fever, and severe focal tenderness
• SEA most often results from 1) hematogenous dissemination of microbes from a remote infection, 2) contiguous spread of infection, such as from adjacent vertebral discitis-osteomyelitis (VDO), or 3) direct inoculation, such as from penetrating trauma, discography/biopsy/other surgical procedures, and spinal anesthesia

Imaging Findings

• MRI is 91% – 100% sensitive for SEA, most often showing a soft tissue mass with tapering edges in the spinal epidural space with mass effect on the thecal sac and spinal cord
• SEA appears isointense to the spinal cord on T1-weighted images and hyperintense to cord on T2/ STIR scans
• Postcontrast enhancement can be thin and peripheral, heterogeneous, or diffuse and smooth
• Bright signal on diffusion-weighted imaging (DWI), confirmed by low values on apparent diffusion coefficient (ADC) mapping within the abscess represents abnormal restricted diffusion, a feature of SEA
• A low signal area on T1 that is high signal on T2 and shows no central area of enhancement is consistent with a liquid abscess that is amenable to surgical drainage

KEY IMAGES

Pearls

• SEA can appear similar to a phlegmon; the distinction is critical as SEA often requires surgical treatment
• Paralysis, which can result from spinal compression or ischemia secondary to septic thrombosis, requires urgent intervention
• Differential diagnostic considerations include vertebral metastases (with extradural extension), epidural hematoma, extruded or migrated lumbar disc, and postoperative spinal seroma

References

1. Laur O, Mandell JC, Titelbaum DS, Cho C, Smith SE, Khurana B.  Acute nontraumatic back pain: infections and mimics. RadioGraphics. 2019; 39(1): 287-288
2. Reihsaus E, Waldbaur H, Seeling W.  Spinal epidural abscess: a meta-analysis of 915 patients. Neurosurg Rev. 2001; 23(4):175-204