CEREBRAL VENOUS THROMBOSIS

BY DR. ANILESH1styear PGRD

INTRODUCTION

Cerebral venous thrombosis is located in descending order in the following venous structures:oMajor dural sinuses: Superior sagittal sinus, transverse,straight and sigmoid sinuses.oCortical veins: Vein of Labbe, which drains the temporal lobe. Vein of Trolard , which is the largest cortical vein that drains into the superior sagittal sinus.oDeep veins:Internal cerebral and thalamostriate veins.oCavernous sinus.

• Clinically patients with cerebral venous thrombosis present with variable symptoms ranging from headache to seizure and coma in severe cases.• In neonates shock and dehydration is a common cause of

venous thrombosis.• In older children it is often local infection, such as mastoiditis,

or coagulopathy.• In adults, coagulopathies is the cause in 70% and infection is

the cause in 10% of cases.• In women, oral contraceptive use and pregnancy are strong

risk factors.

NOTE:-Clinically patients with venous thrombosis often present with seizures, which is not a symptom in patients with an arterial infarction.

Dense clot sign• Direct visualization of a clot in the

cerebral veins on a non enhanced CT scan is known as the dense clot sign.• It is seen in only one third of cases.• 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 (see pitfalls).• 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 thedense vessel sign. Dense clot sign in a thrombosed cortical vein.

• On the right images of a patient with a hemorrhagic infarction in the temporal lobe (red arrow).

• Notice the dense transverse sinus due to thrombosis(blue arrows).

Empty delta sign

• 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.• The likely explanation is

enhancement of the rich dural venous collateral circulation surrounding the thrombosed sinus, producing the central region of low attenuation.

• In early thrombosis the empty delta sign may be absent and you will have to rely on non-visualization of the thrombosed vein on the CECT.• The sign may be absent after two

months due to recanalization within the thrombus.

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

Absence of normal flow void on MR

• On spin-echo images patent cerebral veins usually will demonstrate low signal intensity due to flow void.• Flow voids are best seen on T2-weighted

and FLAIR images, but can sometimes also be seen on T1-weighted images.• A thrombus will manifest as absence of

flow void.• Although this is not a completely reliable

sign, it is often one of the first things, that make you think of the possibility of venous thrombosis.• The next step has to be a contrast

enhanced study. On the right a T2-weighted image with normalflow void in the sigmoid sinus and jugularvein (blue arrow) and abnormal high signal as aresult of thrombosis (red arrow).

• The images on the left show abnormal high signal on the T1-weighted images due to thrombosis.• The thrombosis extends from the

deep cerebral veins and straight sinus to the transverse and sigmoid sinus on the right.• Notice the normal flow void in the

left transverse sinus on the right lower image.• Absence of normal flow void on MR-

images can be very helpful in detecting venous thrombosis.• Slow flow can occur in veins and

cause T1 hyperintensity

Venous thrombosis with absence of normal flow void on T1-weighted image

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.

Venous infarction - Superior sagittal sinus thrombosis

• 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 subtle hemorrhage in a patient with thrombosis of the superior sagittal sinus.

Bilateral infarction in superior sagittal sinusthrombosis

Venous infarcts - 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

Venous infarct in Labbe territory

• On the left images of a patient with hemorrhage in the temporal lobe.• When the hemorrhagic

component of the infarction is large, it may look like any other intracerebral hematoma with surrounding vasogenic edema.• The clue to the diagnosis in this

case is seen on the contrast enhanced image, which nicely demonstrates the filling defect in the sigmoid sinus (blue arrow).

Hemorrhagic venous infarct in Labbe territory

• On the far left 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).

Venous infarction - Deep cerebral veins

Venous thrombosis of vein of Galen and straightsinus

Venous infarction - Edema

• In some cases of venous thrombosis the imaging findings can resolve completely.• On the left a patient with a subcortical

area of high signal intensity.• The first impression was that this could

be a low grade glioma.• On a follow up scan the abnormalities

had resolved completely.• In retrospect a dense vessel sign was

seen in one of the cortical veins and the diagnosis of venous thrombosis was made.• The high signal intensity can be

attributed to vasogenic edema due to the high venous pressure that resulted from the thrombosis

Imaging in suspected thrombosisCT-venography:-

• CT-venography is a simple and straight forward technique to demonstrate venous thrombosis.• In the early stage there is non-

enhancement of the thrombosed vein and in a later stage there is non-enhancement of the thrombus with surrounding enhancement known as empty delta sign.

On the left some images of a CT-venography demonstrating thrombosis in many sinuses

• 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.

MR-venography:-

Transverse MIP image of a Phase-Contrastangiography.The right transverse sinus and jugular vein have no signal due to thrombosis

• Contrast-enhanced MR-venography uses the T1-shortening of Gadolinium. It is similar to contrast-enhanced CTvenography

On the left a lateral and oblique MIP image froma normal contrast-enhanced MR venography.Notice the prominent vein of Trolard (red arrow)and vein of Labbe (blue arrow).

DSA

• Angiography is only performed in severe cases,when an intervention is planned.• On the left images of a patient

with venous thrombosis, who was unconsious and did not respond to anticoagulant therapy.• There is thrombosis of the

superior sagittal sinus (red arrow), straight sinus (blue arrow) and transverse and sigmoid sinus (yellow arrow).

Venous territories