Intramedullary Tumors
- "Intramedullary" means the tumor is growing inside the spinal cord itself — not pressing on it from outside, but part of the cord's own substance.
- The cord usually looks fat and swollen wherever one of these lives, and the lesion is bright on T2 (cord tissue waterlogged) and dark-ish on T1.
- The two big adult players are ependymoma and astrocytoma; in von Hippel–Lindau, think hemangioblastoma.
- Cysts, swelling, and a syrinx love to tag along, so the abnormal cord segment is often longer than the tumor.
- MRI with and without gadolinium is the whole ballgame — these are an MRI diagnosis, full stop.
The spinal cord is basically a wet rope of nervous tissue running down a bony tube, and an intramedullary tumor is a knot that grows within the strands of that rope. That "within" is the entire point. Most spine tumors politely push on the cord from the outside; these ones move in, unpack their bags, and swell the cord from the inside out.
Where exactly is it? (The compartment game)
Before you name any spine tumor, you answer one question: which of the three boxes is it in? Radiologists are obsessed with this, and for once the obsession is justified — the box tells you the likely diagnosis before you've even looked at the tumor.
| Compartment | Where it sits | Classic suspects |
|---|---|---|
| Intramedullary | Inside the cord | Ependymoma, astrocytoma, hemangioblastoma |
| Intradural-extramedullary | In the sac, but outside the cord | Meningioma, nerve sheath tumors |
| Extradural | Outside the dural sac entirely | Metastases, marrow lesions |
The tell for intramedullary disease is cord expansion. The cord, which should be a slim, smooth cylinder, gets locally pudgy — like a snake that swallowed something it shouldn't have. The dressing on the outside (the cerebrospinal fluid space around it) gets squeezed thin, but the trouble is clearly internal. For the neighboring compartments, see intradural-extramedullary tumors.
What it looks like on MRI
Nearly everything in the cord follows the same boring-but-reliable signal recipe: bright on T2 (it's swollen, watery tissue), iso-to-dark on T1, and then you give gadolinium and watch what lights up. The enhancement pattern is where the personality shows.
A few features travel with these tumors so often they're worth hunting for on purpose:
- A syrinx or tumor cysts. Fluid pockets at the top or bottom of the mass, like air bubbles at the ends of a sausage. (More on the fluid-filled cousin in syringomyelia.)
- Extensive T2 edema. The bright signal usually runs well beyond the actual enhancing tumor, so don't mistake the swelling for the lesion's true size.
- Hemorrhage, which can leave a dark hemosiderin rim — a real clue for certain tumors.
Cord expansion + a centrally bright T2 lesion + abnormal enhancement = intramedullary tumor until proven otherwise. The enhancement pattern then narrows the field.
The usual suspects
Ependymoma is the most common intramedullary tumor in adults. It tends to be central — sitting right down the middle of the cord like the pit in an avocado — and well-marginated, often with crisp enhancement and that dark hemosiderin "cap" at its edges from prior bleeding. Because it's central and tidy, surgeons sometimes get a clean plane around it.
Astrocytoma is the more common one in kids, and it behaves more like a stain than a marble: eccentric (off to one side), infiltrating, with fuzzy borders and patchy enhancement. The edges blur into normal cord, which is exactly why it's a harder surgical customer.
Hemangioblastoma is the show-off. It's a small, intensely enhancing nodule that often hugs the surface of the cord and can drag along a disproportionately huge cyst or syrinx — a tiny tumor throwing a big party. When you see one (or several), think von Hippel–Lindau and go looking for friends elsewhere.
Multiple intramedullary enhancing nodules, especially with prominent cysts, should make you say "von Hippel–Lindau" out loud and recommend screening the rest of the neuraxis and the abdomen.
The mimic that ruins your day
Here's the trap. A swollen, T2-bright, enhancing cord segment is not automatically a tumor. Inflammation and infarction can produce a near-identical picture, and they don't need a scalpel — they need steroids or a stroke workup.
A long, T2-bright, swollen cord can be tumor, demyelination/transverse myelitis, or cord infarct. Tumors tend to expand the cord more, enhance in a mass-like way, and evolve over weeks; inflammation and cord infarct come on faster and behave differently over time. When unsure, the clinical tempo and a short-interval follow-up MRI are your friends — don't send a myelitis to the operating room.
Why the compartment is the whole story
If you remember one thing, make it this: intramedullary means the tumor is part of the cord, so the cord itself gets fat, and your job is to spot that expansion, characterize the enhancement, and respect the mimics. Get the compartment right and the differential almost writes itself; get it wrong and you've sent yourself chasing meningiomas that were never there.