Spinal epidural abscess is a neurospinal emergency characterized by purulent material (pus) collection in the epidural space of the spinal canal. The most common pathogen is S.aureus (60-90%) and hematogenous spread is the main route of infection. The posterior epidural space is more commonly involved than anterior due to the rich venous plexus. MRI is the gold standard: epidural collection shows T1 low-isointense, T2/STIR hyperintense signal, and rim enhancement (ring sign) on contrast-enhanced sequences is pathognomonic — inner surface is smooth, outer surface is in contact with peridural fat. Marked diffusion restriction on DWI confirms purulent content and differentiates from reactive fluid or phlegmon. Clinically, the triad of fever + severe back/spine pain + progressive neurological deficit is diagnostic but the complete triad is present in only 10-15% of patients. IVDU, diabetes, immunosuppression, spinal procedure history, and chronic renal failure are major risk factors. Emergency surgical decompression + drainage is the gold standard when neurological deficit is present; IV antibiotic therapy with close monitoring may be used without deficit. Time to surgery is the most critical prognostic factor — delay beyond 24-36 hours increases permanent neurological damage risk.
Age Range
30-70
Peak Age
55
Gender
Male predominant
Prevalence
Rare
Spinal epidural abscess develops through three main mechanisms. First is hematogenous spread (50%): during bacteremia, pathogens (most commonly S.aureus) reach the epidural space via Batson's vertebral venous plexus — this valveless venous system provides free communication between pelvis, abdomen, and thorax, allowing infection from distant foci (skin abscess, IV drug use, endocarditis, urinary infection) to spread to the spine. Second is contiguous spread (33%): direct extension from spondylodiscitis, paravertebral abscess, or psoas abscess. Third is iatrogenic inoculation (15%): after spinal surgery, epidural catheter, or lumbar puncture. Once bacteria establish in the epidural space, they rapidly multiply and trigger the inflammatory cascade — neutrophils, proteases, cytokines together lead to purulent material (pus) formation. Pus accumulation increases epidural pressure and damages the spinal cord through two pathways: (1) direct mechanical compression — cord is compressed, axonal conduction is disrupted, and myelopathy develops, (2) vascular compromise — epidural pressure compresses spinal arteries and coronal venous plexus, ischemia → infarction develops. Rim enhancement (ring sign) on MRI results from neovascularization in the granulation tissue of the abscess capsule — new vessels have defective endothelial barrier and contrast agent leaks into the capsule. Central purulent content is completely avascular and does not enhance. Marked diffusion restriction on DWI results from restricted free movement of water molecules due to high cellularity (neutrophils), protein, and fibrin in pus — critical for abscess-phlegmon differentiation.
Granulation tissue of abscess capsule enhances in epidural collection, central purulent area does not — pathognomonic for neurospinal abscess.
On contrast-enhanced T1, epidural collection shows rim enhancement — abscess capsule enhances intensely with smooth rim, central purulent area does not enhance. This ring sign is the most specific MR finding of epidural abscess.
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A collection showing rim enhancement in the posterior/anterior epidural space at ...-... levels, consistent with epidural abscess.
Epidural collection shows markedly bright signal on DWI — low signal on ADC map (0.4-0.9 × 10⁻³ mm²/s). Confirms purulent content.
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Marked diffusion restriction in the epidural collection on DWI (ADC: ... × 10⁻³ mm²/s), favoring purulent collection (abscess).
T2/STIR shows hyperintense epidural collection. Cord compression and myelopathy signal (T2 hyperintensity within cord) may accompany.
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Hyperintense epidural collection on T2/STIR at ...-... levels with/without accompanying spinal cord compression and myelopathy signal.
Contrast-enhanced CT may show epidural hypodense collection with rim enhancement. CT is less sensitive than MRI but is alternative when MRI is contraindicated.
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Epidural hypodense collection with rim enhancement at ...-... levels on CT; suggestive of epidural abscess, further evaluation with MRI recommended.
T1 shows low-isointense epidural collection. Posterior epidural fat is compressed or displaced. Mild T1 signal increase may be seen in high-protein abscesses.
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Low-isointense collection in the posterior/anterior epidural space at ...-... levels on T1.
STIR sequence reveals paravertebral soft tissue edema and inflammation surrounding the epidural abscess. This finding indicates spread of infection from the epidural space to paraspinal tissues, and periosteal inflammation of posterior spinal elements (lamina, spinous process) may be present. Edema in dorsal subcutaneous fat may indicate sinus tract formation. The extent of paravertebral involvement is important for planning the surgical approach and determining the duration of antibiotic therapy.
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Paravertebral soft tissue edema and inflammation accompanying the epidural collection at ...-... levels on STIR; suggestive of paraspinal extension of infection.
Criteria
Rapid onset, high fever, rapid neurological deterioration. Prominent rim enhancement on MRI.
Distinct Features
High surgical urgency, mortality 5-15%
Criteria
Insidious onset, low-grade fever, gradual neurological decline. Granulation tissue predominant.
Distinct Features
Thick capsule, better organized, may respond better to antibiotics
Criteria
Early stage, organized abscess not yet formed. Diffuse epidural enhancement, no rim. Minimal DWI restriction.
Distinct Features
May resolve with antibiotics (surgery may not be needed), no rim enhancement, DWI critical for differentiation
Distinguishing Feature
Spondylodiscitis shows end-plate and disc involvement; isolated epidural abscess shows no vertebra/disc involvement (may accompany as complication)
Distinguishing Feature
Spinal TB shows vertebral destruction, cold abscess, disc preserved, subligamentous spread; epidural abscess shows no vertebral destruction (in isolated form)
Distinguishing Feature
Ependymoma is intramedullary, solid enhancement, cap sign; epidural abscess extramedullary, rim enhancement, DWI restriction, clinical infection
Urgency
emergentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralSpinal epidural abscess is a neurospinal emergency. Emergency surgical decompression + drainage is gold standard with neurological deficit — delay beyond 24-36 hours dramatically increases permanent paraplegia risk. IV antibiotic therapy (4-8 weeks) with close clinical and MRI monitoring may be used without deficit. Blood culture (60-80% positive) and surgical material culture for pathogen isolation are important. Vancomycin should be started for MRSA-suspect S.aureus.
Spinal epidural abscess is a neurospinal emergency — untreated carries risk of permanent neurological damage (paraplegia) and death. Emergency surgical decompression and drainage is the gold standard in the presence of neurological deficit. IV antibiotic therapy with close clinical and MRI follow-up may be used if no neurological deficit. The most important prognostic factor is time from symptom onset to surgery — delay beyond 24-36 hours increases permanent damage risk.