Cerebral Venous Thrombosis

Dr.NIJALINGAPPA PG IN RADIOLOGYDEPARTMENT OF RADIO DIAGNOSISJJMMC DAVANGERE

DEPARTMENT OF RADIO DIAGNOSIS

The syndrome of intracranial venous and sinus thrombosis - termed as cerebral venous thrombosis(CVT)

DEFINITION:

5-8 per 1 million population Increased frequency of diagnosis since advent

of DSA, CT & MRI/V.

< 2% of all strokes Male/female ratio = 1.29/1 Males uniform age distribution Females 61% CVT in 20-35 age group 75% of adult patients are women (ISCVT

study) Accounts for up to 50% of strokes during

pregnancy and puerperium

INCIDENCE

Superior sagittal sinus 72% Lateral sinus 70%

Right 26%Left 26%Both 18%

Straight sinus 14.5% Cavernous sinus 2.7% Cerebral veins 38%

Superficial 27%Deep 8%

Cerebellar veins 3%

FREQUENCY OF VENOUS SITES(OFTEN MULTIPLE)

One sinus only 23% Superior sagittal sinus 13% Lateral sinus 9% Straight sinus 1% Deep veins only 1% Isolated cortical veins 1%

FREQUENCY OF VENOUS SITES(SINGLE SITE)

Causes of and Predisposing Factors for Cerebral Venous Thrombosis

Local conditionsBrain and skull damageIntracranial and local regional infections(eg;mastoiditis)

Systemic conditionsHormonal (pregnancy or puerperium, estroprogestativeand steroid therapy)Surgery, immobilizationHematologic and hypercoagulable disordersConnective tissue diseaseMalignancySystemic infectionDehydration

Idiopathic causes (25%)

ETIOLOGY

Chronic Headache 75% Papilledema 49% Motor or sensory deficit 34% Seizures 37% Drowsiness, mental changes,confusion, or coma

30% Dysphasia 12% Multiple cranial nerve palsies 12% Cerebellar incoordiantion 3% Nystagmus 2% Hearing loss 2% Bilateral or alternating cortical signs 3%

Clinical Manifestations

Thrombosis and endogenous thrombolysis and recanalization may occur concurrently, the clinical manifestations may fluctuate in as many as 70% of patients, adding to clinical uncertainty.

Intracranial hypertension occurs in 20%–40% of patients with cerebral venous thrombosis and should be excluded in patients with the specific complex of symptoms

1.Thrombosis of cerebral veins Local effects caused by venous obstruction, oedema

of brain (both cytotoxic and vasogenic) and infarction due to elevated venous and capillary pressure complicated by haemorrhage – may be multiple and bilateral, and not respect arterial vascular territories

2. Thrombosis of major sinusesobstruction leads to impaired absorption of CSF and

intracranial hypertension

1/5 of patients with sinus thrombosis have intracranial hypertension only without signs of cortical vein thrombosis

Pathogenesis

1. CT

2. MRI/V

3. DSA

4. TCD

5. OTHERS: EEG, CSF, CRANIOTOMY, isotope

brain scanning

INVESTIGATIONS – DIAGNOSTIC

Normal Venous Anatomy

Normal sinovenous anatomy.(a, b) Axial MIP CT image (a) and 3D volume-rendered image from CT venography (oblique anterosuperior view) (b) show the internal cerebral veins (ICV), basal veins of Rosenthal (BVR), vein of Galen (VOG), and straight sinus (StrS). On the volume-rendered image, note the asymmetric appearance of the torcular herophili (TH), which is formed by the union of the superior sagittal sinus (SSS),straight sinus, and transverse sinuses (TS).The volume-rendered image also shows the sigmoid sinus (SS) and superficial middle cerebral vein (SMCV). (c) Sagittal MIP CT image shows the inferior sagittal sinus (ISS), as well as the internal cerebral vein, superior sagittal sinus, straight sinus, and vein of Galen.

Normal sinovenous anatomy. Three-dimensional integral image from CT venography (lateral view) shows the anastomotic vein of Trolard (AVOT) draining into the superior sagittal sinus (SSS), the anastomotic vein of Labbe´ (AVOL) draining into the transverse sinus (TS), and the superficial middle cerebral vein (SMCV).

Normal sinovenous anatomy. Axial MIP CT image shows asymmetric transverse sinus(TS). The sigmoid sinuses (SS) begin where the transverse sinuses leave the tentorial margin. The right cavernous sinus (CS) is also demonstrated.

MIP image from contrast-enhanced MR venography, with a color overlay, demonstrates the superiordural sinuses. They include the superior sagittal sinus (green), inferior sagittal sinus (light blue), straight sinus(dark purple), confluence of the sinuses (orange), transverse sinuses (dark blue), and sigmoid sinuses (yellow). The internal jugular veins and bulbs (light purple) also are depicted. (2)lateral MIP image from contrast-enhanced MR venography, with editing of the deep veins to improve the visibility of the ascending veins that drain into the superior sagittal sinus from the lateral hemispheric cortex (the frontopolar [1], anterior frontal [2], and posterior frontal [3]veins; Trolard vein [superior anastomotic vein] [4]; and anterior parietal veins [5]) and the larger named veins on thelateral surface of the cerebrum (the superficial sylvian vein [superficial middle cerebral vein] [6], which typically drains into the sphenoparietal sinus or the cavernous sinus, and the Labbe´ vein [7], which drains into the transverse sinus).

Axial MR image series with a coloroverlay represents the major superficial cortical venous drainage territories according to Meder et al. Most of the superior cerebrum (green) is drained primarily into the superior sagittal sinus,which also receives drainage from the parasagittal cortical regions at lower levels. The sylvian veins drain blood from the peri-insular region (yellow) into the basal dural sinuses.The transverse sinuses receive blood from the temporal, parietal, and occipital lobes (blue).The Labbe´ vein, if dominant,may drain much of this territory. Parenchymal abnormalities such as hemorrhage or edema in this territory may be indicative of thrombosis of the transverse sinus or Labbe´ vein.

DENSE CLOT SIGNDirect 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 .In these cases a contrast enhanced scan is necessary to solve this problem

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

CORD SIGN

Thrombosis of the left transverse sinus in a 42-year-old woman. (a, b) Axial unenhanced CT images show left cerebellar and temporal hematoma with increased attenuation in the left transverse sinus (cord sign) (* in a). (c) On a 3D MIP image from CT venography, the left transverse sinus is not visible.

EMPTY DELTA SIGNThe 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 empty delta sign is seen in 25%–75%

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 empty delta sign can disappear in chronic stages with enhancement of organized clot or due to recanalization within the thrombus

Two cases of empty delta sign due to thrombosis of the superior sagittal sinus.

On the left 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

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

ABSENCE OF NORMAL FLOW VOID ON MR

On the left 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).

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, but there are some pitfalls . Slow flow can occur in veins and cause T1 hyperintensity.

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 process 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. 

VENOUS INFARCTION

However venous infarctions do have a typical distribution

Since many veins are midline structures, venous infarcts are often bilateral and hemorrhagicThis 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.

Bilateral infarction in superior sagittal sinus thrombosis

Superior sagittal sinus thrombosis

reconstructed sagittal CT-images in a patient with bilateral parasagittal hemorrhage due to thrombosis of the superior sagittal

sinus.The red arrow on the contrast enhanced image indicates the filling

defect caused by the thrombus.

Another typical venous infarction is due to thrombosis of the vein of Labbé. 

On the left images demonstrating hypodensity in the white matter and less pronounced in the gray matter of the left temporal lobe. .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,

Venous infarct in labbé 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 demonstrates the filling defect in the sigmoid sinus (blue arrow).

On the left a similar case on MR.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 Labbé.The next examination should be a contrast enhanced MR or CT to prove the diagnosis.

Hemorrhagic venous infarct in Labbe territory

Venous infarction in Deep cerebral veins

On the far left a FLAIR image demonstrating high signal in the left thalamus.When you look closely the image, 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 thrombosis of vein of Galen and straight sinus

Bilateral infarctions in the basal ganglia due to deep cerebral venous thrombosis

On the left 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.

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, as discussed before.

Unlike MR, CT-venography virtually has no pitfalls.The only thing that you don't want to do, is to scan too early, i.e. before the veins enhance or too late, i.e. when the contrast is gone.Some advocate to do a scan like a CT-arteriography and just add 5-10 seconds delay.To be on the safe side we advocate 45-50 seconds delay after the start of contrast injection. We use at least 70 cc of contrast.

IMAGING IN SUSPECTED THROMBOSIS

CT-venography

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.

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

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

MR-VENOGRAPHY

Transverse MIP image of a Phase-Contrast angiography.The right transverse sinus and jugular vein have no signal

due to thrombosis.

Acute thrombus in a 35-year-old woman with a severe headachefor 5 days. (a, b) Axial T2W MR image (a) and axial T1W MR image (b) show a thrombus in the left sigmoid sinus (arrows). The signal in the thrombus, compared with that in the normal brain parenchyma, is

hypointense in a and iso- to hyperintense in b. (c) Frontal MIP image from coronal TOF MR venography shows a lack of flow in the distal portion of

the left transverse sinus and the sigmoid sinus (arrows).

On the left images of a patient with venous thrombosis, who was unconscious 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).

DSAAngiography is only performed in severe cases, when an intervention is planned.

PITFALLS IN CT

Arachnoid granulations

Arachnoid granulations of Pacchioni play a major role in the resorption of cerebrospinal fluid. They are most commonly found within the lacunae laterales of the superior sagittal sinus

Arachnoid granulations can also protrude directly into the sinus lumen, adjacent to venous entrance sites, and should not be mistaken for sinus thrombosis. Arachnoid granulations are present in the superior sagittal sinus, transverse sinus, cavernous sinus, superior petrosal sinus, and straight sinus in decreasing order of frequency

Arachnoid granulations produce well-defined focal filling defects within the dural venous sinuses and measure 2–9 mm in diameter. They are isoattenuating (one-third) or hypoattenuating (two-thirds) relative to brain parenchyma

Arachnoid granulations of Pacchioni in the venous sinuses. (a) Sagittal 2D MIP image from CT venography show arachnoid granulations (arrows) in the superior sagittal sinus and straight sinus. (b) Axial contrast-enhanced CT image shows a well-limited lobulateddefect (arrow) in the right transverse sinus.

Classic appearance of arachnoid granulations.(a) Photograph from an anatomic dissection ofthe right transverse sinus demonstrates focal protuberances consistent with arachnoid granulations (arrows). Intrasinus septa (chordae willisii)(arrowheads) also are depicted. (b, c) Axial contrast-enhanced CT image (b)and superoinferior MIP image from contrast-enhanced MR venography (c) show well-defined focal filling defects consistent with arachnoid granulations in the lateral part of the transverse sinus (arrow), the most common site of such findings.

Pseudodelta signThe dense triangle sign can be mimicked in infants by the combination of the hypointensity of the unmyelinated brain and the physiologic polycythemia resultig in high density of the blood in the sagittal sinus. A pseudodelta sign can also be seen in patients with hyperattenuating acute subarachnoid hemorrhage around the sinus or subdural empyema or in patients with a posterior parafalcine interhemispheric hematoma.In these cases, administration of contrast material should opacify the sinus, obliterating the lucent center of the pseudodelta

(a) AnteroposteriorMIP image from TOF MR venography shows a high bifurcation of the superior sagittalsinus (arrow). (b) On the axial contrast-enhanced CT image, the early bifurcation of the sinusproduces a pseudo empty delta sign (arrow), mimicking sinus thrombosis.

Anomalous location of the superior sagittal sinus bifurcation

Normally veins are slightly denser than brain tissue and in some cases it is difficult to say whether it is normal or too dense.In these cases a contrast enhanced scan is necessary to solve this problem.On the left an image of a thrombosed transverse sinus and next to it a normal transverse sinus.

Normal transverse sinus (lt) Thrombosed transverse sinus(rt).

Three images of a patient with venous thrombosis in the superior sagittal sinus. On the far left we see a dense vessel sign on the unenhanced CT. In the middle an image made 25 seconds after the start of the contrast injection. There is arterial enhancement and it looks as if the superior sagittal sinus enhances, but in fact what we see is the shine through of the dense thrombus. Only on the image on the right, which was made 45 seconds after contrast injection there is an empty delta sign, which proves the presence of a thrombus in the sinus.

Wrong bolus timing

Hematoma simulating venous thrombosis

Usually there is no problem in differentiating a hematoma from a thrombosed sinus. On the left a patient with a peripheral intracerebral hematoma, that on first impression simulates a thrombosed transverse sinus.

POTENTIAL PITFALLS IN MRIVariants of normal venous anatomy

that may mimic sinus thrombosis have been well describedThese can be subdivided into venous anatomic variants that mimic occlusion (sinus atresia or hypoplasia), asymmetric or variant sinus drainage (occipital sinuses, sinus duplication),and normal sinus filling defects (arachnoid granulations, intrasinus septa).

Hypoplastic transverse sinus

The transverse sinuses are commonlyasymmetric, with the right transverse sinusbeing dominant in the majority of cases. Aunilateral atretic posteromedial segment of

theleft transverse sinus is also common

On the left a case that demonstrates that you cannot fully rely on phase contrast imaging.The signal in the vein depends on the velocity of the flowing blood and the velocity encoding by the technician.On the far left a patient with non visualization of the left transverse sinus.This could be hypoplasia, venous thrombosis or slow flow.On the contrast enhanced T1-weighted image it is obvious that the sinus fills with contrast and is patent.

Flow gaps most commonly appear in the nondominant transverse sinus and are correlated with a normal but small sinus as depicted at conventional angiography. The combination of a small sinus size, a slow or complex flow pattern, and an image acquisition plane that is not perpendicular to the sinus likely results in this finding . A close assessment of the source images is mandatory to accurately evaluate venous structures and reduce the potential for diagnostic error. The lack of a thrombus signal within the sinus on MR images is a helpful clue for avoiding this pitfall. Flow gaps are a much less common problem with the use of contrast-enhanced MR venographic or CT venographic techniques

Flow Gaps at TOF MR Venography

Transverse sinus flow gap. (a) Coronal image from TOF MR venographyshows an apparent interruption of flow in the medial part of the left transverse sinus (arrows).(b) Oblique MIP image from contrast-enhanced MR venography shows enhancementindicative of normal flow in the medial part of the left transverse sinus (arrow).

An intrasinus thrombus in the subacute stagemay have markedly increased signal intensity onMR images that may be misinterpreted as evidenceof flow on TOF MR venograms. A close evaluation of MR venographic source images usually allowsdifferentiation, as the thrombus signal is typicallynot as intense as the flow related signal. T1-weighted MR images in such cases depict anabnormal increase in signal intensity within thesinus.

Thrombus Signal Shine-Through at TOF MR Venography

T1-shortening shine-through in a patient with thrombosis of the superior sagittal sinus and transverse sinuses. Lateral MIP image from coronal TOF MR venography shows an area of thrombosiswith a signal of intermediate intensity (arrows) resembling that of normal sinus flow but less intense than that in patent cortical veins (arrowheads).

Flow void on contrast-enhanced MR

On the contrast enhanced T1 images on the left there is an area of low signal intensity within the enhancing transverse sinus. This could easily been mistaken for a central thrombus within the sinus.This however is the result of flow void.

On the phase contrast images it is obvious that the transverse sinus is patent.

We can conclude that MRI has many false positives and negatives in the diagnosis of venous thrombosis. Contrast enhanced MR-venography is the most reliable MR technique. CT-venography is even more reliable, because it is easy and less sensitive to pitfalls

Cerebral venous thrombosis is a relatively uncommonbut serious neurologic disorder.Imaging plays a primary role in diagnosis. Prompt and appropriate medical therapy is important becausebrain parenchymal alterations and venous thrombusformation are potentially reversible. MR imaging,TOF MR venography, contrast-enhancedMR venography, and CT venography are themost useful techniques for diagnosis of this condition.Knowledge of normal venous variations andpotential pitfalls related to image interpretationare important for achieving an accurate diagnosis.

SUMMARY;

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