Presentation: 

42-year-old female. Hx of IVDU, now with back pain and weakness.

Key findings:

• Evidence of discitis-osteomyelitis involving the C4-C6 vertebral levels (T1 hypointense marrow signal spanning the discs). Here's a great example of how important the T1 is.
• There's adjacent epidural abscess (best seen on diffusion-weighted imaging). This is really subtle/indistinguishable on the pre-contrast T1 sequence.
• The epidural abscess causes severe central canal stenosis and cord deformity (best seen on post-gadolinium axial T1 fat saturated images).
• There is transforaminal extension into the left greater than right paravertebral soft tissues with left vertebral artery contact.
• Prevertebral swelling/signal abnormality without definite abscess anterior to the C2-C5 vertebral bodies. This involves the prevertebral musculature and may represent infection/phlegmon.
• Incidental enhancing peripheral nodular consolidations within the visualized lung apices, which may represent septic emboli.

Diagnosis: 

Discitis-osteomyelitis (spondylodiscitis)

Highest-yield Sequences:

• T1 pre-contrast images show hypointensity of the vertebral marrow signal abutting the disc, as well as the disc itself.
• There's typically an adjacent, poorly defined hyperintense fluid signal which is most conspicuous on fat-saturated T2 or STIR images.
• The disc and bone marrow typically enhance on the post-gadolinium t1 fat-saturated images unless they're necrotic.
• The abscess itself will be isointense to muscle on T1 and hyperintense on DWI.

Discussion: 

Here's the most common discitis-osteomyelitis scenario: Staph aureus gains access to the bloodstream, gets lodged in a vertebral endplate capillary, and then spreads into the vertebra, the adjacent disc, and the vertebra across the disc. That’s a functional model for how patients commonly end up with discitis and osteomyelitis involving two adjacent vertebrae (together, sometimes called one vertebral unit). Of course, it’s possible to have just discitis or vertebral osteomyelitis, but most of the HMC cases we reviewed showed both conditions. In the majority of these, there’s a paraspinal and/or epidural phlegmon or abscess, which can result in cord compression. Progressive infection eventually leads to disc collapse and necrosis of the vertebrae. The post-gadolinium fat-suppressed images will show intense enhancement of the disc, bone, and the adjacent soft tissues, as you’d expect with any infection.

Management: 

Cord compression requires a neurosurgery consult to determine if emergent decompression is needed. If not, conservative management with IV antibiotics may suffice.

Helpful Videos

• From our illustrious colleagues at CTisus, "Discitis-Osteomyelitis" https://www.youtube.com/watch?v=4wN8djZdlHg
• From some other dude on YouTube, "Spinal epidural abscess is easy to miss. T1 images are key." https://www.youtube.com/watch?v=_ayjMZPdpCM

Resources:

• https://pubs.rsna.org/doi/full/10.1148/rg.292085137
• https://app.statdx.com/document/discitisosteomyelitis/7a39be36-8b89-47a0-9ebb-6fd7630cecfd
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5007384/