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Case 35 - Discitis, Osteomyelitis

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Classic history. Fever, back pain, IV drug abuser.

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Here we see on the T1-weighted scan,

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T2-weighted scan and STIR imaging,

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the imaging features of discitis and osteomyelitis.

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We see on the T1-weighted scan dark signal intensity

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in the endplates, as well as the disc.

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On the T2-weighted scan, high signal intensity in the

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disc, as well as the endplates.

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This is not as well seen on the T2-weighted scan as the STIR

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image because with the STIR image, we suppress

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the fat of the normal vertebral bodies.

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But the edematous vertebral bodies is not able

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to be suppressed because of the fluid content.

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So you notice that the L4 vertebra and the

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L5 vertebra are both high in signal intensity

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on the STIR image. The disc is also bright in signal intensity.

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You also see irregularity of the inferior endplate of

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the L4 vertebra and the superior endplate.

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So this irregularity and erosion is yet another finding that will

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help us to distinguish between degenerative changes,

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which may cause bone edema.

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Remember,

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we have the modic type changes which are bright on

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T2 and dark on T1 in modic type 1 changes.

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But this irregularity of the endplate is one

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of the helpful findings. In addition,

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we want to look at the post-gadolinium scans.

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Let's look at the gadolinium-enhanced

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image of the same patient.

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You notice that on this gadolinium-enhanced image, you

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see marked enhancement of the intervertebral disc.

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This would not be occurring in the

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typical degenerative category.

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Once we've looked at the diagnosis and the endplates

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in the disc, we have discitis/osteomyelitis complex,

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or what some people will refer to as the

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DOI, Disguised Osteomyelitis Infection.

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We want to look at the epidural space and this

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is best seen on the sagittal and the axial scans.

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We're going to look at the axial post contrast scans.

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Here we have the axial post contrast scans.

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And as we scroll down to the level in which

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there is the abnormal infection,

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you will see that there is soft tissue anterior to the thecal sac,

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which is demonstrated along the back of the vertebral

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body of L4 representing epidural infection.

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When we look at the scan along the paraspinal soft tissue,

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you see that there is enhancement in the

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medial aspect of the psoas muscle,

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both on the left side as well as the right side,

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as well as this inflammatory epidural collection that's

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compressing the thecal sac, just at the L4-L5

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level. So this is discitis/osteomyelitis with epidural phlegmon,

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epidural abscess,

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as well as paraspinal involvement

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extending into the psoas muscles.

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In order to confirm that this is enhancement

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and not fat in the psoas muscle,

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you might want to look at the T2-weighted scans.

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On the T2-weighted scans,

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one would expect the edema of the infection to be bright

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in signal intensity as opposed to the muscle,

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which is usually very dark in signal intensity.

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So let's confirm that.

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We're going to scroll through the axial T2

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weighted scans, and as we get down to the L4-L5 level,

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we can see some of the bright signal intensity in the medial

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aspect of the psoas muscle representing the inflammation.

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Now, this is not a psoas abscess.

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We're not seeing necrosis within the psoas musculature,

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but we are seeing the inflammation

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in the paraspinal soft tissues.

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So these are the findings that we're going

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to rely on in a patient who has

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suspected fever, back pain for discitis/osteomyelitis.

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Sometimes, if I'm a little bit unsure about whether it

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represents degenerative change and modic type endplate

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changes versus an infection, I will specifically say

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in the impression of the report, "Recommend correlation

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with the patient sed rate, C-reactive protein,

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and white blood count. Because discitis/osteomyelitis usually elicits a

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pretty active elevation of the erythrocyte sedimentation

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rate and the C-reactive protein levels,

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as well as elicits an elevated white blood count.

Report

Faculty

David M Yousem, MD, MBA

Professor of Radiology, Vice Chairman and Associate Dean

Johns Hopkins University

Tags

Neuroradiology

Head and Neck

Emergency

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