Epidural Abscess Workup

Updated: Nov 11, 2022
  • Author: Mark R Wallace, MD, FACP, FIDSA; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Laboratory Studies

Routine tests

The CBC count may reveal leukocytosis, left shift, thrombocytopenia, and anemia. Only about two thirds of patients who present with spinal epidural abscess have leukocytosis at the time of initial evaluation.

The ESR and CRP are almost invariably elevated; this is a nonspecific finding.

Always obtain blood cultures prior to antibiotics, as they are positive in 60% of cases. [1, 2, 7, 10]

Abscess fluid/operative material

Perform Gram staining and routine aerobic and anaerobic cultures on all aspirated or surgically obtained abscess fluid.

Special stains and cultures for mycobacteria and fungi are indicated.

PCR studies for bacteria, and in some cases fungi and/or mycobacteria, are often of great value. Treating epidural abscesses without identifying the offending pathogen(s) is extremely challenging, and PCR studies often save the day. 

Consider Brucella cultures and serologies when this is a possibility; alert laboratory personnel that Brucella may be involved so they can take precautions.



Imaging Studies

MRI is the cornerstone of diagnosis in both intracranial epidural abscess and spinal epidural abscess. MRI has the greatest diagnostic accuracy and is the method of first choice in the diagnostic process. [1, 22, 23] The sensitivity of MRI is 90%-95%, and its specificity also exceeds 90%. In some cases, MRI findings are indeterminate, necessitating a repeat of the study. Gadolinium enhancement increases sensitivity for detecting spinal epidural abscess, even in the absence of contiguous bony infection, and enables better differentiation between abscess and surrounding neurological structures. Always image the entire spine (cervical, thoracic, lumbar) when spinal epidural abscess is a consideration.

CT scanning with intravenous contrast may demonstrate fluid collections in the epidural space (see image below). CT scanning is the procedure of choice when MRI cannot be performed but may miss abscesses readily appreciated on MRI.

CT scan showing a lenticular-shaped intracranial e CT scan showing a lenticular-shaped intracranial epidural abscess.

When combined with myelography, CT scanning is a fairly sensitive tool to diagnose spinal epidural abscess, but it carries considerable risk, including introduction of infection, bleeding, nerve injury, and spinal shock. Myelography may underestimate the length of a spinal epidural abscess and carries a risk of paralysis.

Plain radiographs may demonstrate osteomyelitis or vertebral collapse. While these should be performed in all cases, they are never enough to establish the diagnosis.



Make every effort to establish a microbiological diagnosis. Blood cultures are positive in 60% of patients with spinal epidural abscess and are essential. [2, 7]

CT-guided needle aspiration may be used to obtain material for analysis.

Surgical specimens must be stained and cultured appropriately (see Causes). PCR studies are often helpful, especially in the culture negative epidural abscess situation.

Lumbar puncture generally is not indicated in spinal epidural abscess and carries the risk of spreading the bacteria into the subarachnoid space, with consequent meningitis. It is contraindicated in intracranial epidural abscess because of the high risk of cerebellar tonsillar herniation due to increased intracranial pressure. When obtained in spinal epidural abscess, lumbar puncture usually reveals a nonspecific parameningeal infection picture, with elevated protein levels, normal or slightly depressed glucose levels, and modest pleocytosis. Results may also be normal or indicative of frank bacterial meningitis. Culture results may be positive in up to 25% of cases, but almost all these patients have positive blood cultures. [2]




A staging system for the progression of spinal epidural abscess exists and may be of some diagnostic value, but it must be stressed that not all patients move sequentially through the stages, and that deterioration may be rapid. [1]

  1. Back pain, tenderness, and fever
  2. Radicular pain, reflex abnormalities
  3. Sensory abnormalities, motor weakness, bowel and bladder problems
  4. Paralysis, which rapidly becomes permanent without surgical intervention