Infections of the Spine: A Review of Clinical and Imaging Findings

Vikram K. Sundaram, MD; Amish Doshi, MD

Disclosures

Appl Radiol. 2016;45(8):10-20. 

In This Article

Epidural Abscess

Pathophysiology

Like pyogenic spondylodiscitis, epidural abscesses are often due to hematogenous spread of bacteria through the arterial network, and can also be a result of direct inoculation. Typically, primary epidural abscesses almost always appear at the posterior aspect of the spinal canal, while anterior collections are more likely to be related to concomitant vertebral body infections.[2] Due to the multilevel anastomotic arterial arcades, epidural abscesses can affect multiple vertebral bodies, and can also affect non-contiguous vertebral bodies as "skipped lesions."

Clinical Findings

Many epidural abscesses will eventually need surgical drainage of some form for resolution of disease, and will otherwise require close imaging follow-up to track the response to medical treatment over time. A review in 2014 suggests that patients with elevated CRP above 115, leukocytosis above 12.5, bacteremia, and diabetes have a 76.9% chance of medical failure, while having three of the aforementioned characteristics implies a 40.2% chance of medical failure.[3] For these reasons, localizing all foci of infection is imperative to decrease morbidity and mortality for patients. A second lesion may not be clinically apparent on initial presentation, since the presenting symptom for many patients often includes site-specific pain or pain related to a recent surgical procedure. The presence of other infectious processes, such as pyogenic spondylodiscitis, meningitis, and distant infections, may also mask the symptoms of multiple epidural abscesses.

K. Ju et al suggested a method for stratifying the likelihood of a patient having skipped lesions of epidural abscess. Patients with delayed presentation beyond 7 days, who also have concomitant infection outside the spine and paraspinal regions, and who have an ESR greater than 95, have a 73% chance for the presence of a skipped lesion.[18] Patients with the highest chance of having skipped lesions would benefit from MRI scan of the entire spinal column, rather than just at the focus of initial symptoms.

Imaging Findings

Plain Radiographs and CT. The search for a primary epidural abscess is very limited on plain radiography, except in cases where findings of concurrent spondylodiscitis are evident. CT imaging with contrast can demonstrate enhancement at paraspinal tissues, such as extension of disease to the psoas muscles. To demonstrate the spinal canal, intrathecal contrast would be necessary for the most accurate imaging and to overcome beam-hardening artifacts. This method sees limited use with improved MRI techniques, as there is a risk of spread of infection from the myelography spinal tap needed to introduce intrathecal contrast.

MRI. An epidural abscess presents as a soft tissue mass that can encroach upon the thecal sac, spinal cord, and/or spinal nerve roots. Characteristically they appear as an epidural fluid collection with hypointense T1 signal abnormality and concurrent hyperintense T2 and STIR signal abnormalities. Along with rim-enhancement with IV contrast, high T2 signal intensity abnormalities can be seen both at the abscess itself and within the adjacent spinal cord, indicating edema from cord compression (Figure 7). Evaluation of the craniocaudal extent of the abscess is optimized on sagittal views of the spine. Similar to pyogenic spondylodiscitis, non-contiguous lesions can occur given the vast anastomotic channels of the spinal column. On occasion, a single lesion can "spiral" from posterior to anterior in the craniocaudal dimension, giving the appearance of multiple separate foci of infection. On axial slices, the radiologist can determine the lateral extension of epidural infection and the severity of intraspinal involvement and compression.

Figure 7.

T1 postcontrast (A) and T2 (B) sagittal sequences of the thoracolumbar spine of a 26-yr-old man with multifocal segmental disease of the thoracic spine, including prevertebral (A and B, arrow), paravertebral, and epidural extension (A and B, dotted arrows), indicating multilocular abscesses. Along with relative sparing of the disc spaces, this pattern is more indicative of tuberculous spondylitis or fungal spondylitis. There is severe cord compression at T2-T4 and T10-T11.

Follow-up Imaging

Similar to bacterial spondylodiscitis, follow-up imaging can be obtained focally to document decrease in extent or resolution of disease, in which case site-specific imaging with CT, MRI, or bone scan would be sufficient for comparison to pre-treatment studies. On the other hand, in cases of persistence or worsening of disease extent or symptomatology, imaging of the entire spine should be obtained with at least MRI or bone scan for potential detection of distant infectious foci, including skipped epidural abscesses or the development of vertebral osteomyelitis.

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