Dense Venous Sinus.

19-year-old female with thrombosis (arrow) of the left transverse sinus (LTS) (A) and superior sagittal sinus (C), confirmed by CT venography in sagittal (B) and axial (D) reconstruction. Average attenuation inside the LTS was 83.6 HU (HU unit is valiable above 64 HU).

A) Anatomy:

Anatomy

B) When to think of venous thrombosis:

C) Radiological Signs:

Normally veins are slightly denser than brain tissue and in some cases it is difficult to say whether the vein is normal or too dense .
In these cases a contrast enhanced scan is necessary to solve this problem.

Visualization of a thrombosed cortical vein that is seen as a linear or cord-like density, is also known as the cord sign.
Another term that is frequently used, is the dense vessel sign.

Images of a patient with a hemorrhagic infarction in the temporal lobe (red arrow).
Notice the dense transverse sinus due to thrombosis (blue arrows).

The empty delta sign is a finding that is seen on a contrast enhanced CT (CECT) and was first described in thrombosis of the superior sagittal sinus.
The sign consists of a triangular area of enhancement with a relatively low-attenuating center, which is the thrombosed sinus. 

 A case of thrombosis of the right transverse sinus and the left transverse and sigmoid sinus (arrows).
There is enhancement surrounding the thrombosed hypoattenuating veins.

A T2-weighted image with normal flow void in the right sigmoid sinus and jugular vein (blue arrow).
On the left there is abnormal high signal as a result of thrombosis (red arrow).

Bilateral almost par sagittal symmetrical area of infarction due to sagittal sinus thrombosis.

Venous infarction

The other sign that can help you in making the diagnosis of unsuspected venous thrombosis is venous infarction.
Venous thrombosis leads to a high venous pressure which first results in vasogenic edema in the white matter of the affected area.
When the proces continues it may lead to infarction and development of cytotoxic edema next to the vasogenic edema.
This is unlike in an arterial infarction in which there is only cytotoxic edema and no vasogenic edema.
Due to the high venous pressure hemorrhage is seen more frequently in venous infarction compared to arterial infarction.

Since we are not 

that familiar with venous infarctions, we often think of them as infarctions in an atypical location or in a non-arterial distribution. 

However venous infarctions do have a typical distribution, as shown on the figure above.

Since many veins are midline structures, venous infarcts are often bilateral.
This is seen in thrombosis of the superior sagittal sinus, straight sinus and the internal cerebral veins.

The most frequently thrombosed venous structure is the superior sagittal sinus.
Infarction is seen in 75% of cases.
The abnormalities are parasagittal and frequently bilateral.
Hemorrhage is seen in 60% of the cases.

On the left bilateral parasagittal edema and subte hemorrhage in a patient with thrombosis of the superior sagittal sinus.

Another typical venous infarction is due to thrombosis of the vein of Labbe.
On the left images demonstrating hypodensity in the white matter and less pronounced in the gray matter of the left temporal lobe.
There is a broad differential diagnosis including arterial infarction, infection, tumor etc.
Notice that there is some linear density within the infarcted area.
This is due to hemorrhage.
In the differential diagnosis we also should include a venous infarct in the territory of the vein of Labbe.
The subtle density in the area of the left transverse sinus (arrow) is the key to the diagnosis.
This is a direct sign of thrombosis and the next step is a CECT, which confirmed the diagnosis (not shown).

There is a combination of vasogenic edema (red arrow), cytotoxic edema and hemorrhage (blue arrow).
These findings and the location in the temporal lobe, should make you think of venous infarction due to thrombosis of the vein of Labbe.
The next examination should be a contrast enhanced MR or CT to prove the diagnosis.

A FLAIR image demonstrating high signal in the left thalamus.
When you look closely and you may have to enlarge the image to appreciate this, there is also high signal in the basal ganglia on the right.
These bilateral findings should raise the suspicion of deep cerebral venous thrombosis.
A sagittal CT reconstruction demonstrates a filling defect in the straight sinus and the vein of Galen (arrows).

A young patient with bilateral abnormalities in the region of the basal ganglia.
Based on the imaging findings there is a broad differential including small vessel disease, demyelinisation, intoxication and metabolic disorders.
Continue with the T1-weighted images in this patient.

Notice the abnormal high signal in the internal cerebral veins and straight sinus on the T1-weighted images, where there should be a low signal due to flow void.
This was unlike the low signal in other sinuses.
The diagnosis is bilateral infarctions in the basal ganglia due to deep cerebral venous thrombosis.

MR Venography:

The MR-techniques that are used for the diagnosis of cerebral venous thrombosis are:
Time-of-flight (TOF), phase-contrast angiography (PCA) and contrast-enhanced MR-venography:

• Time-of-Flight angiography is based on the phenomenon of flow-related enhancement of spins entering into an imaging slice.
  As a result of being unsaturated, these spins give more signal that surrounding saturated spins.
• Phase-contrast angiography uses the principle that spins in blood that is moving in the same direction as a magnetic field gradient develop a phase shift that is proportional to the velocity of the spins.
  This information can be used to determine the velocity of the spins. This image can be subtracted from the image, that is acquired without the velocity encoding gradients, to obtain an angiogram.
• Contrast-enhanced MR-venography uses the T1-shortening of Gadolinium.
  It is similar to contrast-enhanced CT-venography.

Right transverse sinus thrombosis.

When you use MIP-projections, always look at the source images.

A lateral and oblique MIP image from a normal contrast-enhanced MR venography.
Notice the prominent vein of Trolard (red arrow) and vein of Labbe (blue arrow).
Every MR techniques has its own pitfalls as we will discuss in a moment.
Contrast-enhanced MR venography has the disadvantage that you need to give contrast, but has less pitfalls.

an illustration of the territories of the venous drainage.
There is great variation in these territories and the illustration should be regarded as a rough guide.

Reference