0:01

I want to alert you to one of the potential

0:04

pitfalls of the analysis of sagittal sinus

0:07

thrombosis using MR and MR venogram.

0:11

This is a sagittal T1-weighted scan, and what

0:15

you see on this sagittal T1-weighted scan is

0:17

bright signal intensity in the superior sagittal

0:20

sinus in the vast majority of the vessel.

0:26

Now, this patient underwent MR venography,

0:30

and what you see on the MR venography is

0:33

that the vessel appears to be patent.

0:38

This is a reminder that time-of-flight MR

0:41

venography is a T1-weighted sequence,

0:44

and therefore, if you have a clot on a T1-weighted scan

0:49

that is already bright, it will superimpose,

0:54

as if it is a patent vessel, despite the

0:59

fact that this is a clotted vessel.

1:01

In other words, the bright signal on this time-

1:03

of-flight venogram is not because of flow,

1:07

it's because of subacute methemoglobin in the vessel.

1:12

So, it's not flow; it's T1 shine-through.

1:18

In other words, it's bright on T1 from the clot,

1:21

and it looks like it's flow, but it really is not.

1:24

The way to get around this, if you are worried,

1:27

is to do something called a phase contrast

1:30

MR venogram. On a phase contrast venogram,

1:34

it is not a T1-weighted sequence, and therefore,

1:37

the absence of demonstration of the superior

1:41

sagittal sinus on this phase contrast MRV

1:45

shows that the vessel is thrombosed with

1:50

bright signal intensity subacute

1:51

32 00:01:52,875 --> 00:01:56,565 clot. With regard to sinus thrombosis,

1:56

remember that the likelihood of a venous infarction

2:00

is around 70%, and the likelihood of hemorrhage in

2:05

association with venous infarction is around 70%.

2:09

So, you can have sinus thrombosis without

2:12

having an infarct, and you can have

2:15

infarcts without having hemorrhage,

2:18

but the majority of them will be hemorrhagic.

2:22

The sinus that is thrombosed most commonly is the

2:26

superior sagittal sinus, and it seems, if I see

2:29

that most commonly in children and young adults,

2:33

whereas the transverse sinus or sigmoid sinus

2:36

thrombosis, I see more commonly in individuals

2:40

who have inflammatory disease of otomastoiditis.

2:46

These will also show a high rate of

2:49

thrombosis. With regard to the deep veins,

2:53

usually, the internal cerebral vein is the most

2:55

common deep vein as opposed to a sinus,

3:00

and that is more common than the vein of Galen.

3:04

Again, you may have normal parenchyma

3:07

on the MRI scan, suggesting that you can have either deep

3:11

vein thrombosis or sinus thrombosis without parenchymal

3:16

injury, and within the parenchyma, it is variable

3:20

as to whether this is vasogenic or cytotoxic edema.

3:26

Cytotoxic meaning a stroke with dead cells, vasogenic

3:30

meaning just a backup of pressure, which leads to edema.

3:36

So, this is from an article looking at

3:39

the DWI patterns with venous thrombosis.

3:43

And what you see is that you can have heterogeneous

3:46

signal intensity, bright and dark on the ADC value—

3:51

on the ADC maps, which suggests both restricted diffusion

3:56

because of cytotoxic edema, as well as enhanced

4:01

diffusion from vasogenic edema.

4:04

Similarly, you may have high

4:07

signal intensity on the DWI scan.

4:10

That is purely a stroke that is low

4:14

on ADC maps, and you can have the clot

4:17

itself, which may be bright on the DWI.

4:21

This, again, may or may not be associated

4:23

with a parenchymal abnormality.

4:27

So, high signal intensity on DWI has a

4:29

lower signal sensitivity but a higher

4:32

specificity than high signal intensity on T2

4:34

for diagnosing cortical vein thrombosis.

4:39

So, in other words, while if you do see the dark

4:42

signal on the ADC map, it does imply cytotoxic edema.

4:47

There are cases of sinus thrombosis

4:51

where you merely have vasogenic edema.

4:54

Not only that, but there are examples

4:57

where that restricted diffusion may

5:01

reverse when you have sinus thrombosis.