Transverse Myelitis
- Transverse myelitis is inflammation cutting across the spinal cord — a band of swollen, irritated cord that knocks out everything traveling through that level.
- On MRI you're hunting for a long, swollen, T2-bright stripe in the cord, often centered in the gray matter, with the cord looking a little plumped up.
- The shape and length matter: a long lesion spanning many vertebral segments points one direction, a short one points another. The pattern is the diagnosis.
- It's a clinical-plus-MRI diagnosis, and the radiologist's real job is sorting "inflamed cord" from the things that mimic it — compression, infarct, and tumor.
- This is an urgent workup, not a "come back Thursday" finding. Acute cord dysfunction is an emergency until proven otherwise.
Imagine the spinal cord as a thick bundle of phone cables running down a building, carrying every signal between your brain and your body. Transverse myelitis is what happens when one floor of that building catches a small electrical fire. The fire doesn't have to be big — it just has to sit across the whole cable bundle at one level, and suddenly everything below that floor stops answering the phone. Weakness, numbness, a bladder that won't cooperate, a sensory "level" the patient can point to like a belt around their middle.
That word "transverse" is doing real work: it means the inflammation goes across the cord, not lengthwise down a single tract. That's the whole vibe of the disease in one prefix.
What's actually going on
"Myelitis" just means inflammation of the spinal cord — the myel- part comes from the Greek for marrow, the old word for the cord tucked inside the spine. The cord gets inflamed, swells, and the local wiring stops conducting. Sometimes there's an obvious culprit (a recent viral illness, an autoimmune condition, a known demyelinating disease), and sometimes the workup comes back shrugging and we call it idiopathic. Either way, the imaging question is the same: is this inflamed cord, and how much of it?
What you're looking for on MRI
MRI is the entire ballgame here. CT looks at the cord the way you'd appreciate a painting through a frosted window — technically you're aimed the right direction, but the soft-tissue detail just isn't there. So we reach for MRI of the spine, with and without contrast.
The classic appearance is a swollen, T2-hyperintense segment of cord — a bright stripe where the normally quiet cord lights up because inflammation means water, and water is bright on T2. The cord is often a touch expanded, like a garden hose with a kink that's bulging just upstream. On the axial images, the bright signal frequently favors the central gray matter, sometimes giving that butterfly or H-shaped pattern across the cord's core.
Contrast enhancement is variable — some lesions enhance (often patchy or peripheral), some don't, and the pattern can hint at the underlying cause rather than nail it. Don't expect a tidy rule; expect a clue.
The two features to describe in your report: how long the bright segment is (count the vertebral body segments) and how much of the cord's cross-section it occupies. Those two numbers steer the entire differential.
Length is a fingerprint
Here's the part that makes radiologists feel clever. The length of the lesion is one of the most useful sorting tools you have.
| Pattern | What it suggests |
|---|---|
| Long segment (spanning roughly three or more vertebral bodies) | "Longitudinally extensive" disease — think conditions like neuromyelitis optica spectrum disorder, among other causes. |
| Short segment (one to two segments), often peripheral | More in keeping with classic multiple sclerosis plaques in the cord. |
This isn't a magic spell that hands you a single answer, but it genuinely narrows the field, and it's the kind of observation that makes a clinician trust your read.
The mimics — this is the real job
Calling something "myelitis" is the easy part. Making sure it isn't one of the dangerous look-alikes is the part that earns your paycheck.
Before you commit to "inflammation," rule out the cord being squeezed. A disc, a mass, or a collection pressing on the cord can cause swelling and bright T2 signal that masquerades as myelitis — but the treatment is completely different and often time-critical. Always check whether something is physically deforming the cord.
The big three to consciously exclude:
- Compression. Always look outside the cord first. Cord compression from disc, bone, mass, or blood needs a different (often surgical) answer, and you do not want to call it inflammation.
- Infarct. Cord infarct comes on suddenly (minutes, not days), often favors specific vascular territories, and may restrict on diffusion. The clinical tempo is your best tell.
- Infection / abscess. Discitis-osteomyelitis with epidural abscess can inflame and compress the cord at once. Look at the disc and bone, not just the cord.
Acute weakness, a sensory level, and new bladder or bowel trouble is a cord emergency. The imaging is urgent, and "non-compressive" must be actively confirmed, not assumed. Missing a compressive cause buys the patient a permanent deficit.
The takeaway
Transverse myelitis is a band of angry, swollen cord that interrupts everything passing through one level. On MRI it's a bright, plumped-up segment — often centered in the gray matter — and your two most powerful descriptors are how long it is and how much of the cord it fills. But the single most important habit is reflexive: before you write "inflammatory," prove to yourself the cord isn't being crushed, starved, or infected. Get that order right and you'll be right.