Introduction
Cerebral venous thrombosis (CVT) refers to thrombosis within the dural venous sinuses and/or cerebral cortical and deep veins. It can present with a wide spectrum of symptoms—ranging from headache to seizures, focal deficits, or even coma—and requires high clinical suspicion and imaging confirmation.
Early diagnosis through neuroimaging is crucial to prevent infarction, hemorrhage, and long-term disability.
Imaging Modalities
1. Non-contrast CT (NCCT) Head
Often the first investigation in the emergency setting.
Key Findings:
- Dense Triangle Sign: Hyperdensity in the thrombosed superior sagittal sinus.
- Cord Sign: Hyperdense thrombosed cortical vein (less common).
- Hemorrhagic Venous Infarcts:
- Frequently bilateral or in atypical locations (e.g. parasagittal, temporal lobes).
- Not restricted to arterial territories.
- Cerebral Edema: Hypodense areas in affected brain parenchyma.
Limitations:
- Normal in 25–30% of early CVT cases.
- Cortical vein thrombosis can be subtle or missed.
2. CT Venography (CTV)
Performed after IV contrast injection with venous-phase imaging.
Key Findings:
- Empty Delta Sign: Classic sign on contrast-enhanced CT—filling defect in superior sagittal sinus surrounded by enhancing dura.
- Non-visualization or filling defect in one or more dural sinuses.
- Collateral venous channels: Seen in chronic CVT.
Advantages:
- Widely available, fast, and good spatial resolution of large sinuses.
- Can detect associated hemorrhages or infarcts.
3. MRI and MR Venography (MRV)
MRI with MRV is the most sensitive and specific modality for CVT. It allows detailed evaluation of the thrombus, the brain parenchyma, and venous flow.
A. MRI Sequences
i. T1-weighted images
- Acute thrombus: Isointense.
- Subacute thrombus: Hyperintense due to methemoglobin.
- Loss of normal flow void in thrombosed sinuses or veins.
ii. T2-weighted images
- Thrombus may appear hypointense (acute) or hyperintense (subacute).
- Associated edema or venous infarcts seen as hyperintensities.
iii. FLAIR
- Shows parenchymal edema, infarcts, and subtle hemorrhagic changes.
- Helpful in identifying secondary effects of thrombosis.
iv. DWI (Diffusion-Weighted Imaging)
- Differentiates cytotoxic edema (restricted diffusion) in infarction from vasogenic edema (no restriction).
- Helps identify venous infarcts, which often show mixed diffusion patterns.
v. GRE/SWI (Gradient Echo/Susceptibility Weighted Imaging)
- Blooming artifacts due to paramagnetic deoxyhemoglobin or hemosiderin in thrombus or hemorrhage.
- Best for detecting hemorrhagic transformation and small thrombi.
B. MR Venography (MRV)
Essential to confirm CVT and identify extent.
Techniques:
- Time-of-Flight (TOF) MRV: Non-contrast, flow-dependent technique. May overestimate thrombosis due to flow artifacts.
- Contrast-enhanced MRV: More accurate. Shows absent or reduced enhancement in thrombosed sinuses or veins.
- Phase contrast MRV: Used less commonly.
MRV Findings:
- Non-visualization or abrupt cutoff of a venous sinus or cortical vein.
- Narrowed or irregular sinus lumen.
- Collateral venous channels in chronic or subacute cases.
Commonly Involved Sites
- Superior sagittal sinus (most common)
- Transverse and sigmoid sinuses
- Straight sinus
- Internal cerebral veins and vein of Galen (deep CVT—more severe)
Associated Parenchymal Findings
- Venous infarction: Edema and hemorrhage in atypical, non-arterial territories.
- Intracerebral hemorrhage: May occur due to venous congestion.
- Mass effect and midline shift: If infarct is large.
Differential Diagnosis
- Intracranial hypotension (mimics meningeal enhancement)
- Dural sinus hypoplasia
- Arterial infarcts
- Tumors or meningiomas near sinuses
Teaching Points
- CVT can be missed on non-contrast CT; always consider advanced imaging (CTV/MRV).
- MRI is superior for evaluating extent, age of thrombus, and parenchymal changes.
- GRE/SWI helps detect hemorrhage, while DWI assesses infarction severity.
- Use contrast-enhanced MRV to confirm sinus involvement.
- Imaging is crucial for treatment planning and follow-up.
Conclusion
MRI with MRV is the imaging modality of choice for detecting cerebral venous thrombosis due to its superior sensitivity in identifying thrombus and parenchymal changes. CT and CTV remain useful for initial and rapid assessment. A combination of imaging findings guides accurate diagnosis and management.
