Suspected cerebral venous sinus thrombosis

AHA CVT scientific statement (2024); ACR AC Cerebrovascular Diseases-Stroke (2024)

A diagnosis that a routine unenhanced head CT misses in a substantial minority of cases, so the vetting job is to convert a plain CT request into a dedicated venographic study — by MR or by CT, which perform comparably.

Headache that is progressive rather than thunderclap, often with seizures, focal deficit, papilloedema or an unexplained parenchymal haemorrhage, in a patient with a prothrombotic context such as pregnancy, the puerperium, oral contraception, dehydration or malignancy.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

GCS

Focal neurological deficit

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

MR Venogram Head

What we'd amend, and why

Thrombus in a dural sinus is a filling defect, and demonstrating a filling defect requires an acquisition designed around venous flow or venous opacification. The combined study also shows the parenchyma, which matters because venous infarction and cortical haemorrhage are what actually harm the patient, and because the alternative diagnoses for this presentation are parenchymal. It avoids ionising radiation and iodinated contrast in a population weighted towards young women and pregnancy.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayadult — Adults
rulerule-mr-device-screening — MR safety screening for implants and foreign bodies; checked by Radiographer at the scanner
rulerule-contrast-reaction-premed — Prior contrast reaction and elective premedication; checked by Nurse before the scan
rulerule-gadolinium-renal — Kidney function and gadolinium-based contrast; checked by Radiographer at the scanner
rulerule-pregnancy-gadolinium — Gadolinium in known or possible pregnancy; checked by Radiographer at the scanner
rulerule-iv-access — Intravenous access adequate for the planned injection; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(2)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

MR safety screening for implants and foreign bodies
Complete the MR safety questionnaire, verify implant labelling and its stated conditions of use against this scanner and this protocol, and ensure no ferromagnetic object enters Zone IV.
Radiographer at the scannerBefore the scan
Flags back if: An implant or retained foreign body that is MR Unsafe, unlabelled, or cannot be identified; or an MR Conditional device whose stated conditions this scanner or the requested protocol cannot satisfy; or a credible unexcluded intraocular metallic foreign body history.
Device screening runs in parallel with booking, not in front of it. Where an unidentified implant would genuinely delay the MR study by more than a few hours, CT venography is the equivalent test and should be substituted rather than waiting.
Intravenous access adequate for the planned injection
Site and test a cannula that supports the protocol flow rate, preferring an antecubital or large forearm vein, and observe the injection for extravasation. A 20-gauge or larger cannula is preferred for flow rates of 3 mL/s or more.
Radiographer at the scannerAt the scanner
Flags back if: No cannula can be sited that supports the protocol flow rate — for example only a 22-gauge hand or foot cannula for a CT angiogram needing 4–5 mL/s; or the only available access is a central line or port that is not labelled power-injectable; or an extravasation occurs.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Focal deficit or depressed consciousness — venography tonight, by whichever route is quickest

Role	Study & protocol	Why this answers the question
First line	MR Venogram Head MR Venogram Head usually appropriate	A deficit or a falling conscious level in this presentation means the parenchyma has already been injured — venous infarction, cortical haemorrhage, or the mass effect that precedes herniation — and MR remains the study that shows the thrombus and its consequences together, which is what the treating team needs before anticoagulating a patient who is also bleeding. The preference is unchanged; the tolerance for waiting is not.
First line	CT Venogram — Cerebral CT Venogram — Dural Venous Sinuses	Co-equal here rather than an alternative, because the argument that ranked MR above it — radiation avoidance in a young, often pregnant population — is an elective argument, and this patient is not elective. Accuracy for the major sinuses is comparable, it can be delivered in minutes on a scanner that is already free, and it tolerates an agitated or ventilated patient that a twenty-minute venographic acquisition does not. A referrer who has worked out that the MR cannot be delivered tonight and asks for the CT venogram is right, and telling them to wait for the better test is how the diagnosis gets made in the morning.
Second line	CT Head CT Head — Unenhanced	Worth doing on the way past in a deteriorating patient, because it takes seconds and it identifies the haemorrhage, established venous infarct or hydrocephalus that changes what happens in the next hour. It still cannot exclude the diagnosis, and a normal unenhanced scan here does not close the question.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	MR Venogram Head MR Venogram Head usually appropriate	Thrombus in a dural sinus is a filling defect, and demonstrating a filling defect requires an acquisition designed around venous flow or venous opacification. The combined study also shows the parenchyma, which matters because venous infarction and cortical haemorrhage are what actually harm the patient, and because the alternative diagnoses for this presentation are parenchymal. It avoids ionising radiation and iodinated contrast in a population weighted towards young women and pregnancy.
Reasonable alternative	CT Venogram — Cerebral CT Venogram — Dural Venous Sinuses	Comparable accuracy to MR venography, and genuinely preferable when the patient has a non-conditional device, cannot tolerate a long acquisition, or when MR cannot be obtained within a clinically useful time. It is also the natural completion of an unenhanced CT that already showed a suspicious hyperdense sinus.
Second line	CT Head CT Head — Unenhanced	Useful as a rapid triage study for the complications — haemorrhage, established venous infarct, hydrocephalus — and it occasionally shows a dense cord or dense sinus that clinches the diagnosis. It cannot exclude the condition: a normal unenhanced CT is reported in a substantial minority of confirmed cases, so accepting a plain CT request as the whole answer is the characteristic error here.

Pitfalls

Accepting a plain CT head as the whole answer: it cannot exclude venous sinus thrombosis, being normal in a substantial minority of proven cases.
Calling a hypoplastic or atretic transverse sinus a thrombosis. Correlate with the bony groove on any available CT and with the parenchyma.
Arachnoid granulations produce round filling defects that mimic thrombus, characteristically in the transverse sinus.
Missing the diagnosis in a patient whose presentation was a seizure or an isolated headache rather than a focal deficit, which is how a large share of cases actually present.
Deferring venous imaging in a pregnant or postpartum patient over contrast or radiation concerns. The unenhanced MR venogram needs neither, and a missed sinus thrombosis in this group is the harm the caution was meant to avoid.
Failing to escalate an unexplained parasagittal or temporal haemorrhage that does not fit an arterial territory to venous imaging.

Priors — what to pull first

Any prior venous study establishes whether an apparent occlusion is new or a chronically thrombosed or congenitally hypoplastic segment.
Hypoplasia of a transverse sinus is common and is the single commonest reason a venogram is over-called.

What makes a good request

MR venography and CT venography have broadly similar accuracy; the choice is driven by availability, speed, pregnancy, renal function and device status rather than by diagnostic superiority.
MR has the advantage of showing the parenchymal consequences — venous infarction, cortical haemorrhage — in the same sitting, and avoids ionising radiation in the young and pregnant patients who make up much of this population.
A haemorrhage that does not respect an arterial territory, particularly parasagittal or temporal, is the parenchymal sign that should prompt venous imaging even when it was not the original question.
Pregnancy and the puerperium are the population this diagnosis concentrates in, and neither is a reason to withhold the study. An unenhanced time-of-flight or phase-contrast MR venogram is diagnostic for the major sinuses and needs no gadolinium and no ionising radiation, which makes it the study of choice in pregnancy; gadolinium is reserved for the case where the unenhanced venogram is equivocal and the answer would change management. Where MR cannot be delivered in a clinically useful time, CT venography is still done — the fetal dose from a head acquisition with the abdomen out of the primary beam is negligible against an untreated sinus thrombosis.

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

MR Venogram Head CT Venogram — Dural Venous Sinuses CT Head — Unenhanced

Confirm locally

MR Venogram Head: timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.