Approach to Spine MRI
- Spine MRI is just a stack of slices through a bony stovepipe; you read it the same way every time so you never miss the cord.
- The workhorses are sagittal and axial T1 and T2. T1 shows you anatomy and fat; T2 shows you water — and trouble usually shows up as extra water.
- Read in passes: alignment, bones and marrow, discs, the canal and cord, then the exit ramps (foramina) where nerves leave.
- The two things you cannot miss are cord compression and infection — both change management today, not next week.
- "Degenerative changes" are nearly universal on adult spine MRI. The skill is deciding which of them actually matters.
The spine is one of the most satisfying things in radiology to read, because it rewards a routine. It's a long, repetitive tube — the same vertebra-disc-vertebra sandwich stacked twenty-some times — so once you have a system, you can run it top to bottom and trust that nothing slipped past you. The danger is the opposite: it's so repetitive that your eyes glaze over around the fourth disc and you cruise right past the thing that brought the patient in.
So let's build the routine. First, the sequences.
The sequences, in plain English
If MRI weighting is still fuzzy, take two minutes on T1, T2, and weighting first — everything below leans on it. The short version for spine:
- T1 is your anatomy map. Fat is bright, so the normal fatty bone marrow glows and the cord sits as a comfortable gray ribbon. T1 is where you notice when marrow that should be bright suddenly isn't.
- T2 is your trouble detector. Water is bright. The cerebrospinal fluid (CSF) around the cord lights up white, edema lights up, and most pathology — tumor, infection, cord injury — shows up as too much bright signal where it doesn't belong.
- Fat-suppressed T2 (often STIR) is T2 with the bright fat turned off, so a subtle bright spot of edema in the marrow stops hiding behind the normal fat glow. This is the sequence that makes a sneaky compression fracture or early infection jump out.
Think of it like turning off the kitchen lights to find which appliance has a glowing standby LED. Suppress the fat, and the one abnormal bright thing finally announces itself.
Most spine MRI is done without contrast. You add gadolinium when you're hunting for tumor, infection, or scar versus recurrent disc in a post-operative back — anything where enhancement (tissue lighting up after contrast) tells you something is vascular and active.
Sagittal first: the big midline picture
I always start on the sagittal stack — the slices cut head-to-toe down the midline, giving you the whole spine in one elegant column. Scroll through it like flipping a book sideways.
Run these passes on the sagittals, in order:
| Pass | What you're checking | The "uh-oh" |
|---|---|---|
| Alignment | Is the column a smooth curve? | A vertebra slipped forward on its neighbor (spondylolisthesis) |
| Bones & marrow | Is marrow uniformly bright on T1? | A dark vertebra on T1 — think tumor or infection |
| Discs | Normal height, normal T2 brightness? | Dark, collapsed discs; one bulging backward |
| Canal & cord | Is CSF a continuous bright stripe around the cord? | The bright stripe pinched off — that's compression |
That last row is the whole game. The bright CSF should completely wrap the cord like water around a hot dog in a bun. The moment that water gets squeezed out at one level, something is pressing on the cord — and you stop browsing and start measuring how bad it is.
Axial next: confirm and localize
Now jump to the axial images — the doughnut-shaped cross-sections — at any level the sagittals flagged. The axials are where you confirm where and how much. A disc that looked like a vague backward bump on sagittal reveals itself on axial as a herniation shoving to one side, crowding a specific nerve. The axial also shows the neural foramina — the little exit ramps on each side where nerve roots leave the spine — and whether bone or disc has narrowed them.
Sagittal tells you which level is abnormal. Axial tells you which side and which nerve. You need both to write a useful report; one without the other is half a sentence.
The two things you cannot miss
Everything else can wait for the morning. These two cannot.
Cord compression. If the cord itself is squashed and especially if it's developing bright T2 signal within it (the cord saying "I'm getting hurt"), that's an urgent finding. Go deeper on cord compression — it's the kind of read where you pick up the phone, not just the dictaphone.
Infection. Discitis-osteomyelitis classically lights up a disc and the two endplates hugging it on fluid-sensitive sequences, sometimes with an epidural abscess pressing on the cord. Miss it and a treatable infection becomes a catastrophe.
Almost every adult lumbar spine MRI shows some degenerative change — dark discs, little bulges, mild stenosis. That does not make it the answer. Match the imaging level to the patient's actual symptoms before you blame a bulge. A scary-looking disc on the wrong side from the pain is a red herring.
Putting it together
Pick a starting sequence (sagittal T2), run your passes top to bottom, jump to the axials wherever something looked off, and always — always — confirm the CSF wraps the cord at every level. Same order, every study. The routine is boring on purpose: boring is what keeps the one emergency from slipping past your fourth-disc glaze.