Carotid/Vertebral Dissection
- A dissection is a tear in the inner lining of an artery wall, letting blood burrow into the wall itself instead of staying in the lumen where it belongs.
- That blood-in-the-wall (a mural hematoma) narrows the channel, throws clots downstream, or both — which is why dissection causes stroke in young people who otherwise look healthy.
- The classic targets are the cervical carotid and vertebral arteries; trauma, neck manipulation, or sometimes nothing obvious sets it off.
- On imaging you're hunting for the crescent of blood in the wall and a narrowed, tapering lumen — best seen on fat-suppressed T1 MRI and CTA.
- Most heal on their own; the imaging job is to catch it early because the treatment is anticoagulation or antiplatelets, not a scalpel.
Imagine the lining of a garden hose starts to peel. Water sneaks in between the layers of rubber, balloons the wall outward, and pinches the actual channel down to a trickle. Now imagine that hose is feeding your brain. That, in one slightly alarming sentence, is an arterial dissection.
The thing that makes dissection sneaky — and a favorite exam topic — is who it hits. We expect strokes in older folks with decades of plaque buildup. Dissection is the plot twist: it's a leading cause of stroke in people who are young, fit, and absolutely not expecting it.
What's actually happening in the wall
An artery wall has layers, like plywood. The smooth inner layer (the intima) is supposed to be a seamless tube. In a dissection, the intima tears, and pressurized blood dives through the gap into the wall, forming a mural hematoma — a pocket of clotting blood sandwiched in the layers.
This causes trouble two ways. First, the hematoma bulges inward and squeezes the true channel, so less blood reaches the brain. Second, the torn, roughed-up surface is a magnet for clots, which can break off and sail downstream to plug a vessel — an ischemic stroke by remote control. The stroke is usually embolic, not just from the narrowing itself, which surprises people.
Sometimes the blood burrows outward toward the outer wall instead of inward. If it balloons the outer surface, you get a pseudoaneurysm — an outpouching that wasn't there before. Same disease, different direction of digging.
Carotid vs. vertebral: same idea, different real estate
The two cervical workhorses are the internal carotid arteries (front of the neck, feeding most of the cerebrum) and the vertebral arteries (running up through little bony tunnels in the cervical spine, feeding the back of the brain).
Carotid dissection has a signature trio worth knowing: neck or face pain, a partial Horner syndrome (a droopy lid and small pupil on that side, because the dissection bothers nearby sympathetic nerve fibers), and stroke symptoms that may show up hours to days later. Vertebral dissection tends to announce itself with posterior headache or neck pain and back-of-brain (posterior circulation) symptoms like dizziness and double vision.
How it starts
Sometimes there's an obvious culprit — a car crash, a sports collision, vigorous neck manipulation, even a violent coughing fit. Sometimes there's nothing dramatic at all, and an underlying connective-tissue weakness in the wall is suspected. Honestly, plenty of cases are filed under "we're not totally sure," and that's an accurate thing to teach rather than a gap to paper over.
Finding it on imaging
This is where the radiologist earns lunch. You're looking for blood where it shouldn't be — inside the wall.
The MRI money shot is fat-suppressed T1 through the neck. Fresh-ish wall blood lights up bright, and because you've turned the surrounding fat dark, that bright crescent of hematoma jumps out hugging the vessel wall. It's one of those findings that's genuinely satisfying once you've seen a couple.
On CT angiography (CTA), you don't see the hematoma color, but you see its consequences: a smoothly tapered narrowing of the lumen (often described as a flame or tapering shape rather than the abrupt cutoff of an embolus), an eccentric crescent of wall thickening, an enlarged outer vessel diameter, or a pseudoaneurysm pouch. CTA is fast and widely available, so it's frequently the first test in the acute setting.
| Modality | What it shows | Best for |
|---|---|---|
| Fat-suppressed T1 MRI | Bright crescent of wall hematoma directly | Confirming the diagnosis, dating the bleed |
| CTA neck | Tapered lumen, mural thickening, pseudoaneurysm | Fast acute workup, bony detail for vertebral |
| MRA / time-of-flight | Narrowed flow, sometimes the hematoma | Adjunct, often paired with the T1 |
A dissection can masquerade as a plain old embolic occlusion, and vice versa. The tell is the shape of the narrowing: dissection usually tapers smoothly like a melting candle, while an embolus tends to stop abruptly with a meniscus. When the patient is young with neck pain, bias yourself toward dissection and go looking for the wall crescent.
Why catching it matters
Here's the reassuring part: most dissections heal on their own as the wall remodels over weeks. The reason we hustle to diagnose isn't to rush someone to surgery — it's that the treatment is medical (anticoagulation or antiplatelet therapy to stop clots from launching toward the brain) and timely treatment heads off the stroke that hasn't happened yet.
If a young patient has neck pain plus stroke symptoms — or a partial Horner syndrome — think dissection and get vessel imaging. The findings are subtle, but the bright wall crescent and the smoothly tapering lumen are the two clues that crack it open.
So when you're staring at neck vessels, don't just check that contrast is flowing — check the wall. Dissection is the disease that hides one millimeter outside where you're looking. If the anatomy of these vessels feels fuzzy, a quick refresher on the approach to brain MRI sequences will make that bright crescent click into place.