Cerebral Venous Sinus Thrombosis
- Cerebral venous sinus thrombosis (CVST) is a clot blocking the brain's drainage pipes — the venous sinuses — not its arterial supply.
- Because the plumbing backs up, brain swelling and bleeds can appear in places that don't respect the usual arterial stroke territories.
- The direct sign is clot inside the sinus; the indirect signs are venous infarcts and hemorrhage downstream of the blockage.
- The single best confirmatory test is a dedicated venogram (CT venography or MR venography) — you have to image the veins on purpose.
- It loves young patients, pregnancy/postpartum, and anyone in a hypercoagulable state, and the headache can be sneaky.
Most of what you learn about stroke is about arteries — the pipes bringing fresh blood in. CVST is the plot twist where the drains clog instead. Same organ, opposite direction, and a whole different set of rules for where things go wrong.
The plumbing, and why a clogged drain is bad
Picture your brain as a sink. Arteries are the faucet, pouring blood in. The veins and dural venous sinuses are the drain, carrying it back out toward the heart. Normally the drain keeps up with the faucet and everything flows.
Now jam a clot into the drain. The faucet keeps running, but the water has nowhere to go, so pressure builds backward into the sink. In the brain that backed-up pressure does two nasty things: it forces fluid out into the tissue (swelling, also called edema — fancy word for waterlogged brain), and if the pressure gets high enough, small veins burst and you get bleeding. That's a venous infarct, and unlike the usual arterial stroke, it's often hemorrhagic from the start.
The big takeaway: arterial strokes follow neat, predictable territories (one artery, one chunk of brain). Venous problems follow the drainage map instead, which is why a venous infarct can sit in a weird spot — like both sides of the midline, or a region that no single artery would ever produce. A "stroke that doesn't make arterial sense" should make you think veins.
What you're hunting for on imaging
There are two flavors of clue: the clot itself (direct) and the downstream mess it causes (indirect).
On a plain non-contrast head CT, a fresh clot in a sinus can look subtly too white — denser than the flowing blood around it. In the superior sagittal sinus seen end-on, this dense triangle is the classic dense triangle sign (sometimes called the dense clot sign). It's easy to talk yourself into or out of, so treat it as a prompt to look harder, not a final answer.
The cleaner direct sign comes with contrast. When you opacify the veins, flowing blood lights up but the clot doesn't, leaving a filling defect. In the superior sagittal sinus on contrast-enhanced imaging, the enhancing sinus wall surrounding a non-enhancing central clot creates the empty delta sign — a little dark triangle wearing a bright outline, like a donut that forgot its filling.
Don't get faked out by normal anatomy. The dural sinuses have normal variants — an asymmetric or hypoplastic (small from birth) transverse sinus is extremely common and can mimic a clot on a venogram. Granulations and septations inside sinuses cause filling defects that aren't thrombus either. Before calling CVST, ask whether the "clot" might just be a small or absent sinus the patient was born with — and correlate with the parenchyma and the clinical picture.
The indirect signs: read the room, not just the pipe
Sometimes the clot is subtle but the consequences are loud. Look for brain swelling and, especially, hemorrhage that sits next to a draining sinus or cortical vein rather than in an arterial territory. A bleed in the temporal lobe, or swelling/hemorrhage straddling the midline near the top of the brain, should make you check the sinuses before you sign off.
Any hemorrhage or area of swelling that doesn't fit a normal arterial stroke territory deserves a hard look at the venous sinuses. The parenchymal finding is often what tips you off to go hunting for the clot.
Confirming it: image the veins on purpose
Here's the catch that trips people up: a standard contrast CT or routine brain MRI can miss CVST because they aren't optimized to show the venous channels. You usually need a dedicated venogram.
| Test | What it shows | Notes |
|---|---|---|
| Non-contrast CT | Dense sinus (direct), swelling/bleed (indirect) | Fast, first-line, but normal CT does not rule it out. |
| CT venography (CTV) | Filling defect in the opacified sinus | Excellent, quick; the empty delta lives here. |
| MR venography (MRV) | Absent flow signal in the blocked sinus | No radiation; great in pregnancy and follow-up. |
| Brain MRI | Clot signal + venous infarct + edema | Sensitive for the downstream brain injury. |
MR is especially handy in the patients CVST loves — younger people and pregnancy/postpartum — where you'd rather skip the radiation. If you want a refresher on why different sequences make a clot look different over time, the common MRI sequences page is a good detour.
Why it matters clinically
CVST is treatable, and treatment is often the opposite of your instinct: the mainstay is anticoagulation (blood thinners) to stop the clot from growing — even when there's already some venous hemorrhage. That's a counterintuitive, attending-level point, and it's exactly why the diagnosis has to be right.
The headache is the great pretender. CVST can show up as a new, worsening, or just plain weird headache, sometimes with seizures or signs of raised pressure — and the head CT can look near-normal early on. In a young patient, a pregnant or postpartum patient, or someone with a clotting tendency, a stubborn unexplained headache is a reason to think about imaging the veins, not a reason to relax.
If you remember one thing: when the brain's findings don't follow the arterial map, stop and check the drains. That single habit catches CVST that everyone else walks past.