are in the Department of Medical Imaging at the Toronto Hospital,
Western Division, in Toronto, Ontario, Canada.
ascular diseases of the venous system in the central nervous system
(CNS) are less well understood than the arterial disorders, and
often, venous disorders are considered late in the differential
diagnosis. The onset of venous diseases often is insidious. With
the ability to recognize the signs of venous abnormalities on
imaging, the radiologist may be the first to suggest the
appropriate diagnosis. Commonly encountered venous disorders in
clinical practice which have radiological significance are venous
occlusive disease and venous thrombosis, Sturge-Weber syndrome,
dural arteriovenous fistula and venous congestive encephalopathy,
cavernomas, and developmental venous anomalies (DVAs).
Venous occlusive disease
Occlusive disease of the cerebral veins or sinuses may be the
result of trauma, invasion by tumor, infection or thrombosis in
hypercoagulable states; occasionally no cause is discernible.
Cerebral vein thrombosis is a frightening event because of the
clinical manifestations and the high mortality rate, estimated to
be 5 to 30%.
Clinically, the disease can have a variable presentation ranging
from a subtle headache to impaired consciousness. Broadly speaking,
the symptoms are either related to raised intracranial pressure
(ICP), taking the form of headache, nausea and vomiting, and
papilledema, or are due to a venous infarct and/or bleed within the
Depending on the location of the infarct and/or bleed, the
clinical presentation may be focal neurological deficit, seizure,
or altered level of consciousness. Most often, presentation is
acute, with symptoms present for less than 7 days. Rarely, however,
a subacute or chronic presentation is seen in the form of benign
intracranial hypertension (pseudotumor cerebri). Common
predisposing conditions include infection (such as mastoiditis
which most often results in transverse sinus thrombosis),
polycythemia, malignancy, peurperium, dehydration, oral
contraceptive use, inflammatory bowel disease, head injury, and
In clinical practice, the most commonly seen conditions are
peurperium and dehydration. These two groups of patients also
represent the group in which the disease is obviously preventable
in most situations. No predisposing factor can be found in
approximately 30% of patients.
Diagnosis often is based on imaging, and in this scenario the
radiologist would be the first person to consider the condition.
Findings of venous occlusive disease, although subtle, are quite
characteristic on CT. These include the presence of hyperdense
venous sinuses or the "cord sign" on a noncontrast CT scan. On a
post-contrast scan, the "empty delta sign" is seen in cases of
superior sagittal sinus thrombosis, which represents the enhancing
menin geal venous tributaries and other collateral venous channels
around the non-enhancing sinus.
Another common manifestation is the presence of hemorrhagic
infarcts. These typically have a non-arterial distribution, and may
be bilateral in cases of thrombosis of midline structures such as
the superior sagittal sinus (bilateral parasagittal infarcts) or
straight sinus (bilateral thalami) (figure 1). Also, venous
hemorrhagic infarcts typically are associated with significant
perifocal edema and mass effect. Consequently, venous infarcts may
simulate hemorrhage within a tumor (figure 2A).
Maintaining a high index of suspicion, correlating with the
clinical scenario, and obtaining additional investi-
gations such as MRI may be useful in differentiating venous
infarcts from other causes of hemorrhages. The location of the
lesion may be another indicator of a venous infarct. For example,
the presence of a hemorrhagic lesion within the lateral part of the
temporal lobe should raise the suspicion of transverse sinus
thrombosis, as this part of the brain drains into the transverse
sinus via the vein of Labbe (figures 2-4).
MR allows direct visualization of the major venous channels and
is now the imaging modality of choice for suspected venous
thrombosis. Thrombus often is visualized on spin-echo MR imaging
within the vascular channels (figures 3A,3B,4C). An MR venogram
allows excellent visualization of the major sinuses (figure 4D).
Detection of cortical vein thrombosis in the absence of involvement
of the sinuses may be difficult on MR; however, the diagnosis of a
venous infarct may be suggested on the basis of imaging
Angiography, although still considered the gold standard, is
rarely performed. Indications for angiography include suspected
cortical vein thrombosis or when therapeutic intervention is
planned. Findings on angiography include filling defects within the
veins, venous occlusion, presence of venous collaterals, and a
pseudophlebitic pattern of the veins draining the normal brain
parenchyma (figure 2C). In cases of chronic thrombosis, there may
be evidence of recanalized sinuses which demonstrate an irregular
The first line of management for venous occlusive disease is
hydration and administration of heparin (even in the presence of
hemorrhage on imaging). Thrombolysis should be considered only if
there is deterioration of the clinical status despite therapeutic
levels of heparin. Patient selection criteria for thrombolysis are
difficult to determine, as the outcome of the disease is variable
and dependent on the location of thrombosis. For example, extension
into the deep venous system and into the cerebral veins is a poor
Conversely, in one series, 71% of patients with cerebral venous
thrombosis affecting the dural sinuses made a complete recovery and
there was a 10% mortality rate.
In another series of 28 patients presenting with deep vein
thrombosis, 37% made a full recovery, 26% had deficits, and 37%
In a series of seven patients who failed a trial of medical
therapy, direct thrombolytic therapy resulted in clinical
improvement in six patients.
Sturge-Weber syndrome is most frequently a sporadic,
noninherited abnormality consisting of a facial venular
malformation (port-wine stain), letomen ingeal venous angiomatosis,
seizures, dementia, hemiplegia, hemianopsia, buphthalmos, and
glaucoma. The topography of the facial malformation does not
predict the cerebral lesion. The cortical lesion arises from an
early thrombosis of the medullary veins, leading to a congestive
post-ischemic venous atrophy and eventually calcification.
CT imaging of this disorder demonstrates atrophy and linear
gyral calcification (tramtrack on plain films). The findings are
more classical on MR, although calcification may be difficult to
identify. Typical findings include presence of cerebral atrophy,
typically found in the occipital/parietal lobes with T2 darkening
(hemosiderin staining), and pial and leptomeningeal enhancement or
Cranial dural arteriovenous fistula and venous congestive
Although intracranial dural arteriovenous fistulas (DAVFs) are
not strictly considered venous vascular disease, their clinical
presentation, as well as the decision regarding patient management
options, are most often a result of the venous expression of the
disease. Presentation of benign DAVFs often relates to the location
of the fistula and includes tinnitus, cranial nerve palsies, and/or
signs related to venous hypertension in the orbit.
Imaging features of DAVFs are variable and are dependent on the
location of the fistula, the resultant effect on the veins, and on
the drainage of the surrounding normal brain parenchyma. CT often
is nondiagnostic and may show only the effects of the disease, such
as parenchymal hematoma, proptosis, or dilated venous channels,
rather than the disease itself. Presence of a dural arteriovenous
malformation (AVM) usually is obvious on MR by the presence of
multiple flow voids in the vicinity of the fistula (figure 5A).
Manifestation of venous drainage may be proptosis with a dilated
superior ophthalmic vein in the case of cavernous sinus DAVMs, or
may be hydrocephalus and an acquired Chiari malformation in
posterior fossa fistulae. In patients with neurological deficits
due to DAVFs with venous congestive encephalopathy (VCE), MR may
show diffuse edema in the white matter in addition to the flow
voids (figure 5B).
These patients may present with nonspecific symptoms such as
dementia. Rarely, the congested brain may show diffuse enhancement
after administration of gadolinium which is different from the
enhancement pattern of many neoplasms (figure 6A).
When MR findings suggest a DAVF, selective angiography,
including all dural branches, is mandatory. The value of a good
quality angiogram performed by an experienced angiographer with
selective injection into every dural branch cannot be overstressed.
If the clinical suspicion of a DAVF is high, angiography should be
performed, even in the absence of MR abnormality.
Intracranial dural arteriovenous fistulae have been grouped into
two categories--benign or aggressive--based on the presence or
absence of retrograde leptomenin-
geal venous drainage (RLVD) (figures 5C,6B,6C).
Aggressive DAVFs with RLVD may have a similar presentation to the
benign type, or they may present with an intracranial bleed,
progressive neurological deficit, or seizure.
In 1986, Lasjaunias and coworkers demonstrated that focal
neurological deficits are related to the territory of the venous
Awad and coworkers, in their review of 360 cases from the
literature prior to 1990, found that RLVD, venous ectasia, and
Galenic venous drainage correlated with intracerebral hematoma
(ICH) and nonhemorrhagic neurological deficit (NHND) at
A comprehensive classification of DAVFs based on
angioarchitecture was first proposed by Djindjian et al in 1977.
In 1995, this scheme was modified by Cognard et al in a review of
their own series of 205 patients. Cognard was able to show a
relationship between type and presentation;
a similar but simplified version of this classification was
proposed by Borden et al in 1995.
In 1996, Davies et al confirmed the validity of these
classification systems by showing a highly significant correlation
between either the Borden type or the Cognard type and presentation
with either ICH or nonhemorrhagic neurological deficit.
In DAVFs, aneurysmal venous drainage has a higher incidence of
bleeding on presentation compared to those without aneurysmal
Sinosal drainage with retrograde flow in the venous sinuses but no
cortical venous drainage can result in raised intracranial
Davies et al, in their study of the natural history of the DAVF,
confirmed the benign course of those DAVFs that have sinosal
drainage only and the aggressive course of those with cortical
The presence or absence of retrograde leptomeningeal venous
drainage is an important determinant in treatment planning. The
sine qua non in management of DAVFs is that those with RLVD must be
cured and those without may be followed clinically or partially
treated for symptom palliation.
Treatment involves either surgical disconnection of the refluxing
vein or obtaining the same result by the endovascular route. The
most commonly used embolic agents include polyvinyl alcohol (PVA)
and N-butyl cyanoacrylate (NBCA).
Cavernomas are the only true venous malformations. Their
incidence is 0.4% and they can be found in the brain or spinal
About 80% are supratentorial, with the frontal and temporal lobes
being the most frequent sites.
They are angiographically occult, except in rare instances at the
time of a bleed where venous "puddling" has been demonstrated.
Cavernomas have a strong association with developmental venous
Fundamentally stable, they can grow by confluence of vascular
spaces often related to intralesional bleeds or thrombosis. In the
familial forms, which are often multiple, an anomaly of endothelial
growth factor has been identified. Additionally, there is an
autosomal dominant inheritance.
MR has been found to be a sensitive tool in the diagnosis of
cavernomas. They typically are seen as well-defined, lobulated
lesions with a central core of reticulated, mixed signal intensity
surrounded by a rim of signal hypointensity (figures 7-9). Use of
the correct imaging sequences is key to the diagnosis. A
gradient-echo sequence which enhances the magnetic susceptibility
effects should be a part of the imaging protocol of every patient
with a bleed. On this sequence, cavernomas are seen as black
lesions. Size measurement is inaccurate on this sequence due to the
"blooming effect" (figure 10).
Cavernomas produce symptoms either by hemorrhage (figure 11) or
thrombosis. Hemorrhage outside the cavernoma generally is not
observed at surgery, even in the face of a perilesional bleed
evident at MR. Subacute blood seen outside the hemosiderin ring on
MR is found, at surgery, to be contained by a thin capsule.
Hemosiderin staining in the adjacent parenchyma has been found at
autopsy, suggesting diapedesis or "slow ooze" of blood products
through the endothelial lining. The presence of significant mass
effect indicates either leaking of blood into potential spaces
within the cavernoma or acute thrombosis. Perilesional bleeds may
result from extravasation into the potential crevasses in the
periphery of the lesion; perilesional edema is likely related to
the sudden expansion of the lesion, compromising local blood
Turjman et al demonstrated the value of MR in identifying a
cavernoma as the underlying cause of an intracerebral hematoma.
It is not our present practice to perform angiography when
cavernomas are discovered on MR. Serial MR images demonstrate that
cavernomas can be dynamic lesions with active and regressive
changes. Additionally, serial MR images are helpful in cases of an
acute intracerebral hematoma, wherein the cavernoma may be seen on
a follow-up study though it was completely obscured by the bleed in
the original study.
Zabramski grading has alerted us to the various morphologies of
From our analysis, however, this grading has not been useful in
predicting future bleeds.
Gender or multiplicity was not associated with higher bleeding
rates. In our series we did find a high bleeding rate (10.9%) in
the posterior fossa.
Therapeutic options, as of now, are limited to surgery.
Endovascular techniques have no established role, and radiation,
including stereotactic radiotherapy, has not proven to be
Developmental venous anomalies (DVAs)
DVAs originally were classified as malformations and often were
referred to as venous angionias. It has become clear that DVAs
represent extreme variations of the venous drainage of the cerebral
or cerebellar hemispheres. They drain normal brain, and the
circulation time is normal. Their association with cavernomas is
well known, and the cavernomas may account for the symptomatology
seen when these entities are discovered.
A recent study described the prospective hemorrhage rate of 0.34%
per year for DVAs.
The authors felt that this represented a complication of an
underlying but as yet undetected cavernoma.