Chapter 14 Cerebral Venous Thrombosis

Cerebral venous thrombosis (CVT) was first described by Ribes in the early 19th century on the basis of postmortem examination.¹ For a long time, CVT was seen as a rare and severe illness resulting in seizures, focal deficits, and often death. Its association with sinus infections was well described,² but other predisposing conditions were not yet recognized. However, advances in vascular neuroimaging have led to a renewed appreciation of this disorder, which is more common, more variable, and less uniformly severe than previously assumed.^3–6

Cerebral sinus venous thrombosis is estimated to account for 0.5% of all strokes in adults,³ but its true incidence is unknown, and frequent underrecognition is suspected.⁷ Initially asymptomatic venous sinus thrombosis has been implicated in the etiology of idiopathic intracranial hypertension.^8,9 Indeed, studies have demonstrated that the most common symptom of CVT is headache (80%–90%) and the most common sign papilledema (50%–60%).¹⁰ Other clinical signs include focal deficits and partial seizures, and alteration of consciousness. Headache may be the only clinical symptom of CVT.^11,12 Approximately one quarter of all patients have completely normal examination.³

Multiple causes and risk factors for CVT have been identified.⁵ The list comprises genetic and acquired prothrombotic conditions (the latter most prominently including pregnancy, puerperium, and combination of hormonal contraceptives and smoking), infections (particularly sinusitis, otitis, mastoiditis, and meningitis), systemic inflammatory illnesses (such as systemic lupus erythematosus, sarcoidosis, and inflammatory bowel disease), hematological disorders (e.g., polycythemia, leukemia, thrombocythemia, paroxysmal nocturnal hemoglobinuria), systemic cancer, severe dehydration, and head trauma. The threshold for obtaining brain imaging to exclude CVT should be lower in the presence of these conditions.

Current neuroimaging techniques have greatly enhanced our ability to diagnose CVT.^3,13 Magnetic resonance imaging (MRI), particularly in combination with MR venography (MRV), provides excellent diagnostic yield in cases of thrombosis of dural sinus or deep cerebral veins (Figure 14-1).^13,14 It is worth reemphasizing that noninvasive imaging modalities are allowing us to learn the broad spectrum of CVT. Although once the diagnosis was only suspected after severe intracranial hypertension or venous infarctions had occurred, today the possibility of CVT must be considered in the differential diagnosis of patients with new headaches and benign intracranial hypertension. Often CVT can be timely diagnosed only by keeping a low threshold for its clinical suspicion. A delayed or missed diagnosis of CVT, unfortunately still a common occurrence in practice, cannot be justified now that we have reliable and extremely safe means to reach the diagnosis.

Figure 14-1 Example of normal gadolinium-enhanced magnetic resonance venography. Refer to Figure 14-3 for anatomical details.

Although MRI/MRV is the most proved and widely used set of tests for the identification of CVT, computed tomography (CT)/CT venogram (CTV) represent a valuable alternative when MRI is contraindicated or unavailable. The main disadvantage of CTV is the requirement for administration of iodinated contrast material.

Case Vignette

A 23-year-old woman presented during her puerperium for evaluation of new severe headaches. They had developed soon after child delivery and had worsened over the previous several days. She described them as bifrontal and pulsating. They were not accompanied by nausea or vomiting, but photophobia was intense. Soon after initial evaluation, the patient experienced increasing vomiting and developed right facial weakness and double vision on right lateral gaze. She did not have any significant medical history except for several early miscarriages and heavy smoking. She had recently begun using an oral hormonal contraceptive.

On examination at the hospital, the patient was drowsy, had bilateral papilledema, right VI nerve palsy, and peripheral right facial nerve palsy. Otherwise the examination was unremarkable. She underwent MRI and MRV of the brain that demonstrated extensive thrombosis of the posterior two thirds of the superior sagittal sinus and the proximal transverse sinuses (Figure 14-2). Thrombophilia workup was negative.

Figure 14-2 Time-of-flight magnetic resonance venography (anteroposterior projection on the left and lateral projection on the right) showing extensive venous sinus thrombosis affecting the posterior two thirds of the superior sagittal sinus and bilateral proximal transverse sinuses (arrows).

The patient improved gradually after initiation of anticoagulation. Anticoagulation was continued for 1 year, and she was advised to avoid contraceptives and stop smoking.

Knowledge of the normal anatomy of the cerebral venous system and its variations is essential to interpret the vascular images effectively. Hence we begin by illustrating and summarizing basic anatomical information.

ANATOMY OF THE VENOUS SYSTEM

The cerebral venous system consists of dural venous sinuses, superficial veins, and deep veins. The dural venous sinuses are venous channels devoid of valves situated between the two layers of the dura, and thus they are not collapsible. They constitute the major draining pathways of the cerebral venous circulation. Cerebral veins are also devoid of valvular structures and have a very thin wall with no muscular tissue. They empty into the dural sinuses but may reverse their flow in cases of dural sinus occlusion. Venous anatomy is illustrated on angiographic pictures shown in Figure 14-3.

Figure 14-3 Normal venous anatomy on conventional angiography. Upper left: Frontal (anteroposterior) view, venous phase. Upper right: Lateral view, venous phase. Lower left: Frontal (anteroposterior) view, late venous phase. Lower right: Lateral view, late venous phase.

Dural Sinuses

The major dural sinuses are the superior and inferior sagittal sinuses; cavernous and intercavernous sinuses; superior and inferior petrosal sinuses; occipital sinus; and straight, transverse, and sigmoid sinuses.

The major superficial sinus is the superior sagittal sinus, which is located in the convex margin of the falx cerebri. It runs from the foramen cecum to the torcula Herophili, where it merges with the transverse sinuses. It receives blood from cortical parasagittal veins on the cortical surface.

The inferior sagittal sinus is much smaller and is contained in the posterior half or two thirds of the free margin of falx cerebri. It terminates at the falcotentorial apex by joining with the great cerebral vein (vein of Galen) to form straight sinus. It receives blood from the falx, corpus callosum, cingulum, and medial cerebral hemispheres. The occlusion of this sinus is rarely clinically significant.

The straight sinus is situated at the line of the junction of the falx cerebri with the tentorium cerebelli. After a descending course, it terminates at the internal occipital protuberance, usually emptying into the left transverse sinus. It receives venous blood flow from the great vein of Galen and superior cerebellar veins, thus participating in the deep venous drainage. Occlusion of this sinus usually produces venous infarcts in the deep basal ganglia.

The transverse sinuses are contained within the attachment of the tentorial leaves to the calvarium. At the posterior border of the petrous temporal bone, the transverse sinuses receive the superior petrosal sinus to become the sigmoid sinuses. Transverse sinuses receive blood from the superior sagittal sinus and straight sinus, as well as bridging veins from cerebellum, inferolateral surfaces of the temporal and occipital lobes, and tentorium. It also receives blood from the cortical vein of Labbé. In more than half of cases, the right transverse sinus is larger than the left.^15,16 In up to 20% of the cases, a narrowed or atretic segment can be identified in at least one of the transverse sinuses.¹⁶

The sigmoid sinuses begin where the transverse sinus leaves the tentorial margin and drain into the jugular bulb, thus becoming the internal jugular veins. There are numerous anastomoses between sigmoid sinuses and the vertebral plexus, muscular, and scalp veins.

The superior petrosal sinuses extend from the cavernous sinus to the sigmoid sinus, running along the attachment of the tentorium to the dorsal ridge of the petrous temporal bones. They receive venous drainage from the pons and upper medulla, lateral mesencephalic vein, cerebellar veins, and veins draining the inner ear.

The inferior petrosal sinuses lie in a groove between the petrous apex and the clivus, extending posterolaterally along the petrooccipital fissure. They have multiple anatomical variations but usually terminate draining into the jugular bulb. On their way, they form multiple anastomoses with deep venous plexuses.

The cavernous sinuses lie on either side of the sphenoid body. They are formed by numerous small veins with multiple interconnections that constitute a trabeculated space. They extend from the superior orbital fissure to the petrous apex. They contain the cavernous segment of internal carotid artery and cranial nerve VI. Cranial nerves III, IV, and V1 branch of trigeminal nerve are located in the lateral wall of the sinus. This sinus receives venous drainage from superior and inferior ophthalmic veins, intercavernous sinus, and multiple deep venous plexuses. They drain into the superior and inferior petrous sinuses.

Arachnoid granulations are present along venous sinuses and often protrude into their lumen. They can be confused with areas of restricted flow on imaging studies when they are prominent (most frequently the case in the transverse and superior sagittal sinus).

Superficial Cerebral Veins

Cortical veins are highly variable in number, location, and configuration. Three larger superficial veins are most constant and recognizable:

The superficial middle cerebral (Sylvian) vein runs along the surface of the Sylvian fissure. It collects blood from multiple cortical veins that drain opercular areas and drains into the cavernous or sphenoparietal sinus.

The inferior anastomotic vein (vein of Labbé) courses over the temporal lobe along the occipitotemporal sulcus and connects the superficial middle cerebral vein to the transverse sinus.

The main superior anastomotic vein (vein of Troland) courses in a posterior-superior direction from the Sylvian fissure over the midhemispheric convexity. It connects the superficial middle cerebral vein to the superior sagittal sinus.

Deep Cerebral Veins

Deep venous drainage is variable, although major basal veins are relatively constant. The deep venous system drains the inferior frontal lobe; most of the white matter of the frontal, temporal, and parietal lobes; basal ganglia; thalamus; corpus callosum; and upper brainstem. Small medullary veins are responsible for draining blood from the deep cerebral white matter and basal ganglia into the subependymal veins of the lateral ventricles. Those veins form the thalamostriate veins, which unite with septal veins to form the internal cerebral veins. The internal cerebral veins are the largest deep veins. They are paired and originate behind the foramen of Monro. After collecting venous drainage from deep white matter and basal ganglia, they join to form the vein of Galen.

The basal veins of Rosenthal arise deep within the Sylvian fissure. They course posteriorly around the cerebral peduncles and across the tectum to join the vein of Galen. The anterior and deep middle cerebral veins as well as veins from the insula and cerebral peduncles drain through this system.

The great cerebral vein of Galen arises under the splenium of the corpus callosum from the junction of the internal cerebral veins and basal veins of Rosenthal. It usually runs a short trajectory before joining with inferior sagittal sinus to form the straight sinus.

This complex anatomical composition can be simplified by knowing the major venous drainage territories. Four general pathological patterns can be identified in cases of CVT:

1. A superficial pattern in which major dural sinuses and adjacent cortical veins are occluded.

♦ The superior sagittal sinus is the most common site of occlusion, followed by transverse, sigmoid, and cavernous sinuses.

♦ Extensive edema and cortical venous infarcts may occur in the parenchyma adjacent to the occlusion.

♦ It is the most common pattern of CVT.

2. A deep central pattern results from thrombosis of the internal cerebral veins, sometimes extending into the great vein of Galen and the straight sinus.

♦ Bilateral thalamic infarcts are the most characteristic finding.

♦ Edema and infarction may also involve the basal ganglia and adjacent white mater and upper midbrain.

♦ This pattern accounts for about 10% of cases of CVT.

3. A deep basal pattern is caused by cavernous sinus thrombosis.

♦ Manifestations are mostly related to ocular venous hypertension and cranial nerve compression and ischemia leading to ophthalmoplegia.

♦ Parenchymal involvement is rare.

♦ Represents less than 5% of CVT cases.

4. The fourth pattern is isolated cortical venous thrombosis.

♦ Venous infarcts usually are associated with parenchymal hemorrhage.

♦ It represents less that 1% of cases of CVT (in the absence of venous sinus occlusion).

♦ It is difficult to diagnose because of the anatomical variability of cortical veins.

IMAGING CHARACTERISTICS OF CVT

Computed Tomography

♦ CT scan is less sensitive than MRI for the detection of the venous thrombus.

♦ CT is highly sensitive for acute hemorrhagic infarctions, but it does not allow differentiation between edema and infarction and may not allow visualization of early edema.

♦ Usefulness increases enormously when combined with helical CTV.

Signs of Venous Thrombosis

♦ Noncontrast CT scan may disclose the delta sign (Figure 14-4), a dense triangle that represents an acute thrombus at the end of the superior sagittal sinus or torcula. However, this sign is insensitive and lacks specificity. It is present in less than a quarter of cases of superior sagittal sinus thrombosis¹⁷ and may be mimicked by blood hyperviscosity (e.g., dehydration, erythrocytosis), sinus calcification, or adjacent subarachnoid or subdural hemorrhage.¹³

♦ Contrast CT scan may demonstrate the empty delta sign (Figure 14-5), caused by lack of contrasted flow in the occluded sinus but enhancement of the sinus wall. It is slightly more sensitive than the delta sign and may be present in close to 30% of cases of superior sagittal sinus thrombosis.¹⁷ This sensitivity may be substantially greater when thin sections of helical CT scan are carefully reviewed.¹³ The empty delta sign is probably produced by rich dural venous collateral circulation (from meningeal venous tributaries) and a vascular mesh of cavernous spaces within the dural wall.¹⁷

♦ The specificity of the empty delta sign may be far from optimal, especially in the pediatric population.¹⁸

♦ High or asymmetric junctions between transverse and superior sagittal sinuses (normal anatomical variants) may produce “pseudo–empty delta signs.”¹³

♦ The appearance of an empty delta sign in delayed CT scans performed more than 30 minutes after injection of contrast material (the so-called delayed empty delta sign) is not a reliable sign of sinus thrombosis, unless seen in combination with the dense delta sign on the noncontrast scan.¹⁹

♦ The presence of the delta and empty delta signs in the appropriate clinical setting should prompt further evaluation with noninvasive venography, especially when both signs are present together. However, their absence does not exclude the possibility of CVT, because they are not apparent in more than two thirds of patients with CVT involving the superior sagittal sinus.

Figure 14-4 Nonenhanced computed tomography scan of the brain showing the delta sign at the level of the torcula (dark arrows) and hemorrhagic infarctions on the parasagittal frontal lobes (light arrows) in a case of superior sagittal sinus thrombosis.

Figure 14-5 Contrast-enhanced computed tomography scan of the brain demonstrating the empty delta sign (arrow) on a patient with superior sagittal sinus and transverse sinus thrombosis.

Signs of Parenchymal Involvement

♦ Parenchymal changes in CVT may be caused by extracellular (vasogenic) edema and infarction. CT scan does not allow reliable differentiation between these two abnormalities, except when venous infarctions have a hemorrhagic component. Edema and infarction are most often combined. Thus, in the absence of blood, one should refrain from interpreting areas of low attenuation on CT scan as infarctions.

♦ Signs of parenchymal edema without changes in attenuation, such as sulcal effacement, may be observed on CT scan, but they are better visualized on MRI.^13,20

♦ Areas of focal low attenuation do not respect arterial territories. These lesions are most commonly cortical-subcortical, and the characteristic locations are parasagittal and superior convexities in superior sagittal sinus occlusion, posterior temporal lobe in transverse sinus occlusion, and thalami in deep venous thrombosis. Bilateral lesions, especially in close proximity to the sinuses, should be considered highly suspicious for cerebral venous infarction.

♦ Venous infarctions are characterized by their tendency to develop early hemorrhagic transformation and the presence of marked perilesional edema. Hemorrhage may be observed in more than 20% of patients at the time CVT diagnosis¹⁰ and occurs in more than 30% of patients during the acute phase of the disease.^13,21 Hemorrhages are typically cortical with subcortical extension, but purely subcortical hemorrhages have been described in cases of isolated cerebral vein thrombosis.²²

Magnetic Resonance Imaging

♦ MRI, especially in conjunction with MRV, is the most sensitive and specific imaging modality for the diagnosis of CVT.^{13,20,23–25}

♦ Timing of the venous thrombus is possible with MRI (Table 14-1).

♦ It allows accurate distinction between vasogenic edema and infarction.

TABLE 14-1 Temporal changes of signal intensity of intraluminal venous thrombus imaged by MRI.

Signs of Venous Thrombosis

♦ Acute venous occlusion (0–5 days) most often appears isointense on T1-weighted and hypointense on T2-weighted sequences, making it difficult to detect without concomitant MRV. The absence of flow void in a cerebral sinus, as evidenced by the empty delta sign on the contrast T1-weighted images shown in Figure 14-6, should make one suspicious of the possibility of venous thrombosis. Conversely, gadolinium enhancement of the sinus does not exclude sinus thrombosis because slow flow through dural or intrathrombus collateral channels may mimic normal sinus flow.²⁶

♦ During the subacute phase (6–15 days), MRI characteristics of the clot change, becoming hyperintense on T1-weighted and shifting from iso- to hyperintense (Figure 14-7) on T2-weighted sequences as the clot ages. Hence, MRI is sensitive for the detection of the sinus thrombosis after the first week.

♦ After approximately 2 weeks, the thrombus appears similarly hyper- to isointense on T1-weighted and T2-weighted sequences. The appearance of chronic thrombosis with partial recanalization can be variable on MRI, and MRV is necessary for adequate determination of sinus patency.

♦ Fluid-attenuated inversion recovery (FLAIR) sequence can also demonstrate the clot in the cerebral sinus, following the temporal signal changes described for the T2-weighted sequence (Figure 14-8).

♦ Gradient-recalled echo (GRE) and echo planar T2* susceptibility-weighted imaging can demonstrate a blooming artifact on the thrombosed sinus, and it increases the sensitivity of MRI during the acute phase.^27,28 These sequences may also allow recognition of cortical vein thrombosis even in patients with no visible occlusions on MRV.²⁷

♦ Diffusion-weighted imaging (DWI) may depict the intrasinus thrombus as a hyperintense signal with matching reduction of the apparent diffusion coefficient (ADC) (Figure 14-9).²⁹ Diffusion abnormalities were noted in more than 40% of patients with sinus thrombosis, especially during the subacute stage, and correlated with lower chances of recanalization in one study,²⁹ but the sensitivity and significance of this finding remains to be firmly validated.

Figure 14-6 Contrast enhanced T1-weighted sequence of brain magnetic resonance imaging (left, coronal view; right, sagittal view) displaying the empty delta sign (arrows) in a case of superior sagittal sinus thrombosis.

Figure 14-7 Noncontrast T1-weighted sequence of brain magnetic resonance imaging (sagittal view) showing a hyperintense signal in the superior sagittal sinus indicative of subacute thrombus (left panel). This diagnosis is confirmed by the findings on the time-of-flight (TOF) magnetic resonance venography (right panel), which disclosed extensive occlusion of the superior sagittal sinus and left transverse sinus.

Figure 14-8 Fluid-attenuated inversion recovery sequence of brain magnetic resonance imaging (left) showing a hyperintense signal in the left transverse sinus consistent with late subacute thrombosis. Time-of-flight magnetic resonance venography (right) confirms the left transverse sinus occlusion but also discloses occlusion of the left sigmoid sinus and superior sagittal sinus.

Figure 14-9 Diffusion-weighted imaging sequence displaying a bright signal in the area of the torcula (arrow) in a case of early subacute superior sagittal sinus thrombosis.

Signs of Parenchymal Involvement

♦ Acute ischemic infarction can be detected by its hyperintense signal on DWI with corresponding reduction of ADC (dark signal)^30–32 (Figure 14-10). Areas of infarction are often patchy, intermixed with regions of vasogenic edema (bright on DWI and ADC), which often predominate³³ and do not respect arterial perfusion territories. DWI also allows timing of parenchymal lesions as diffusion restriction is present only during the first 7 to 10 days following the infarction.³¹ Although areas of decreased ADC almost invariably become infarcted, resolution of lesions with reduced ADC has been reported in patients with CVT.³⁴

♦ The extent of parenchymal signal changes (infarction and vasogenic edema) is displayed with excellent definition by T2-weighted and FLAIR sequences.

♦ In addition, subtle changes produced by swelling are accurately visualized on MRI, including mild effacement of sulci and subarachnoid cisterns, and slight compression of the lateral ventricles. These changes sometimes help explain the apparent discrepancy between symptoms and radiological appearance.

♦ Hemorrhages, especially when small, are best demonstrated by susceptibility-weighted sequences (GRE/T2*) showing signal loss in the presence of hemoglobin breakdown products with paramagnetic properties, such as deoxyhemoglobin and methemoglobin.

♦ There is little reported experience with the use of perfusion MRI in cases of CVT.^30,35 As expected, there is no evidence of hypoperfusion in areas of vasogenic edema.³⁰ Prolongation of mean transit time in the absence of diffusion restriction or changes in cerebral blood volume may indicate reversible degrees of compromised perfusion.³⁵

Figure 14-10 Diffusion restriction (bright diffusion-weighted imaging on the left and dark signal on apparent diffusion coefficient map on the right) in the left thalamus and putamen in a case of acute deep venous sinus occlusion.

Angiographic, Magnetic Resonance, and Computed Tomography Venograms

♦ A partially thrombosed sinus is characterized by intraluminal filling defects.

♦ A completely occluded sinus appears as an empty channel devoid of contrast.

♦ The occluded sinus might be surrounded by dilatated collateral venous channels.

♦ The most frequently used venographic techniques are nonenhanced time-of-flight (TOF) MRV, gadolinium-enhanced MRV, and helical CTV.

♦ Catheter angiography is typically not necessary to confirm the diagnosis.

MR Venography

♦ Nonenhanced (two- or three-dimensional) TOF MRV is the most commonly used radiological modality for the diagnosis of CVT. It provides good definition of the vascular anatomy and is sensitive to slow flow.

♦ Its main pitfall is that venous flow in the plane of image acquisition may produce saturation and annul venous signal, giving the incorrect impression that the venous channel is occluded. Careful review of the various planes of image acquisition (coronal, axial, sagittal, oblique) and source images is crucial to reduce false-positive readings.¹³ Transverse sinus flow gaps on the coronal views of TOF MRV are seen in up to 30% of patients without CVT; thus this finding should be interpreted with particular caution.³⁶

♦ Gadolinium-enhanced three-dimensional MRV affords better visualization of smaller venous channels and may also improve assessment of sinus flow compared with TOF MRV,¹⁴ which is more susceptible to artifacts from flow turbulence.^37,38 Flow gaps are much less common in contrast-enhanced MRV.

♦ Novel techniques, such as fourfold accelerated two-dimensional sensitivity encoding (FFA 2D SENSE) MRV may increase spatial resolution and improve visualization of small deep cerebral veins and superficial cerebral veins.³⁹

CT Venography

♦ Helical CTV provides a reliable and rapid alternative to MRV for the detection of sinus thrombosis.⁴⁰ Anatomical definition is excellent, and flow gaps are seldom a problem. Its accuracy has been shown to be comparable to that of TOF MRV.⁴¹

♦ Because of delays and technical challenges inherent to the reconstruction of maximum intensity projection images, the acute diagnosis is based on the assessment of source images and multiplanar reformatted images.

♦ Exposure to iodine is the major disadvantage of this technique.

Conventional Angiography

♦ Conventional cerebral angiography should be strongly considered when isolated cortical venous thrombosis is suspected.⁴² However, even conventional angiograms often fail to provide conclusive evidence for this elusive diagnosis.

SINUS OCCLUSION SYNDROMES

Severe headache often associated with papilledema is the most common presentation of venous sinus thrombosis.^3,5 The headache typically worsens for hours to a couple of days before reaching its maximal intensity, but thunderclap headache can also be the first manifestation of CVT.⁴³ Cranial nerve deficits, especially abducens nerve palsy, can be accompanying signs. Complex partial seizures and focal neurological deficits may occur; they usually correlate with parenchymal lesions on brain imaging but sometimes are generated by milder degrees of swelling, which only cause subtle radiological changes. Rapid development of coma may be the presentation of deep venous thrombosis with bilateral thalamic damage.

Several characteristic clinical patterns have been recognized: (1) acute to subacute onset of focal neurological deficits and seizures; (2) isolated intracranial hypertension associated with headaches, papilledema, and unilateral or bilateral VIth nerve palsy; (3) generalized encephalopathy or coma without major focal neurological deficits, a pattern that is more common in deep vein thrombosis; and (4) acute proptosis, chemosis, and painful ophthalmoplegia in cases of cavernous sinus thrombosis.⁴ However, atypical presentations are not exceptional.³ The onset of clinical manifestations varies substantially; subacute onset (within a month) occurs in about 50% of the cases, acute presentation in 30%, and chronic presentation in 20%.⁴⁴ Symptoms may progress or fluctuate with extension of the thrombosis, opening of collateral draining channels, and recanalization from endogenous thrombolysis.⁶

In the following paragraphs, we present the characteristic features and radiological examples of the most common types of CVT.

Superior Sagittal Sinus

♦ Intracranial hypertension with headache, vomiting, and papilledema without any focal neurological deficits may be the only manifestation of extensive superior sagittal sinus thrombosis. Focal deficits may appear when brain edema or venous infarctions develop as a consequence of progressive venous hypertension.

♦ Venous infarctions, often associated with hemorrhagic transformation, tend to occur in the parasagittal frontal lobes (Figure 14-11), resulting in paraparesis (often asymmetric), hemiparesis, and fluctuating unilateral or bilateral sensory symptoms. Progression of the thrombosis into the cortical veins or severe venous hypertension in the superficial venous system may result in aphasia.

Figure 14-11 A 42-year-old woman with history of recurrent deep venous thrombosis presented with depressed level of consciousness and bilateral proximal leg weakness for 1 day. She had been complaining of progressive headache and blurred vision for the previous 3 to 4 days. Nonenhanced head computed tomography (CT) scan (upper left) shows high attenuation in the torcula and left transverse sinus, indicating acute thrombosis. Higher cuts of the CT scan (upper right) show bilateral hemorrhagic infarctions in the frontal lobes. Magnetic resonance imaging obtained that same day is also shown: T2-weighted sequence (middle left) shows hypointense signal in the torcula (indicative of acute thrombus) and edema surrounding the hemorrhagic lesions; gradient-recalled echo sequence (middle right) demonstrates the blooming effect induced by acute breakdown products of hemoglobin; and diffusion-weighted imaging (DWI) sequence (lower left) shows areas of restricted diffusion (i.e., cellular edema) within the frontal lesions, confirming the diagnosis of venous infarctions (areas of bright signal on DWI were mostly matched by dark signal on the apparent diffusion coefficient map, not shown). Time-of-flight magnetic resonance venography (lower right) proves the presence of extensive dural sinus thrombosis involving the superior sagittal sinus as well as both transverse sinuses and upper sigmoid sinuses.

Transverse Sinus Thrombosis

♦ The most common presentation of transverse sinus thrombosis is headaches and papilledema, even in cases with extensive thrombosis extending into the sigmoid sinus and internal jugular vein (Figure 14-12). In our experience, some of these patients may also exhibit cognitive and behavioral changes in the absence of parenchymal changes on neuroimaging.

♦ Venous infarction might affect superior temporal lobe with resulting aphasia and often partial seizures that may generalize.

♦ Venous infarctions due to transverse sinus occlusion may produce large temporal hematomas (Figure 14-13). They characteristically spare the temporal pole but risk for uncal herniation nonetheless exists.

Figure 14-12 A 36-year-old woman presented with unrelenting headache for 2 to 3 days. Examination revealed bilateral papilledema, worse on the right, and bilateral deficits of eye abduction. Noncontrast computed tomography scan of the brain (upper left) showed high attenuation in the area of the right transverse sinus, prompting further evaluation with magnetic resonance imaging. T2-weighted sequence (upper right) showed hypointense signal in that area, supporting the diagnosis of acute sinus thrombosis. Sagittal views of the T1-weighted sequence display the absence of flow signal replaced by an isointense thrombus (middle left) and the empty delta sign after gadolinium administration (middle right). Time-of-flight magnetic resonance venography at the time demonstrated complete occlusion of the right transverse sinus, right sigmoid sinus, and right internal jugular vein (lower left). Repeat time-of-flight MRV 3 months later disclosed persistent occlusion of the right transverse sinus but recanalization of the sigmoid sinus and internal jugular vein (lower right).

Figure 14-13 Computed tomography scan of the brain before and after contrast administration (upper left and upper right, respectively), T2-weighted magnetic resonance imaging (MRI) sequence (middle left), and gradient-recall echo sequence (middle right), showing a subacute left posterosuperior temporal hematoma. Sagittal view of nonenhanced T1-weighted MRI sequence allows visualization of bright signal corresponding to late subacute clot in the torcula (lower left, arrow). Time-of-flight magnetic resonance venography confirms the diagnosis of left transverse sinus occlusion extending into the most posterior aspect of the superior sagittal sinus.

Cavernous Sinus Thrombosis

♦ The cavernous sinuses receive blood from the facial veins and pterygoid plexus via the inferior and superior ophthalmic veins. Infections of the face including the nose, orbits, tonsils, and soft palate can spread to the cavernous sinus by this route.

♦ Cavernous sinus thrombosis is rare, but when it occurs, it is often septic because of aggressive bacterial or fungal sinusitis.⁴⁵

♦ The clinical presentation includes marked chemosis and proptosis, ophthalmoplegia (from affected III, IV, and VI nerves) and upper facial hypoesthesia (from involvement of the ophthalmic division of the V nerve).

♦ The cavernous sinus may not be well visualized in normal angiograms. Close examination of head imaging for signs of sinusitis is crucial to reach the diagnosis.

♦ Cavernous-carotid fistula must always be excluded in these patients.

Deep Vein Thrombosis

♦ Deep venous thrombosis most often provokes bilateral thalamic damage. Lenticular nuclei are also frequently involved, and the lesions may extend into the upper midbrain.

♦ Bilateral thalamic edema or infarction (Figure 14-14) may cause symptoms and signs ranging from inattention, spatial neglect, and amnesia, to akinetic mutism and apathy, or even sudden coma.

♦ The severity of clinical manifestations depends on the degree of venous hypertension, which in turn varies according to the extent of thrombosis in the deep venous system, the draining territory of the vessels involved, and the sufficiency of the venous collaterals.⁴⁶ Occlusion of internal cerebral veins sparing the basal veins of Rosenthal may produce relatively mild deficits.⁴⁶

♦ High attenuation changes in thrombosed deep veins can occasionally be seen on CT scan (“chord sign”).⁴⁷ Signal changes on MRI depend on the age of the clot,⁴⁷ as discussed in cases of dural sinus occlusion.

Figure 14-14 Magnetic resonance imaging of the brain obtained for evaluation of coma preceded by a rapid decline in level of consciousness. Nonenhanced axial T1-weighted sequence shows loss of differentiation of the margins of thalami and lenticular nuclei bilaterally (upper left). Nonenhanced sagittal T1-weighted image (upper right) demonstrates a hyperintense signal in the straight sinus (magnified view shown in lower left panel, arrows). Fluid-attenuated inversion recovery sequence (middle row, left and right) better depict the extension of the deep parenchymal changes. Time-of-flight magnetic resonance venography (lower right) confirms the diagnosis of deep venous thrombosis.

Cortical Vein Thrombosis

♦ Thrombosis of superficial veins is often extraordinarily difficult to document because of the marked variations in the normal anatomical distribution of the superficial venous system.

♦ Clinical manifestations are caused by superficial infarctions involving the cortex and subjacent white matter (Figure 14-15). They are typically hemorrhagic and do not conform to arterial territory boundaries.⁴⁸

♦ CT or MRI can sometimes demonstrate signal change in a cortical vein (the “chord sign”).

♦ Thrombosis of the vein of Labbé causes infarction of the underlying superior temporal lobe, and occlusion of the vein of Trolard affects the parietal cortex.⁴⁹

♦ Partial seizures, with or without secondary generalization, are the most common presenting feature.⁴⁸ Hemiparesis, incomplete hemianopia, and aphasia, may occur and often fluctuate over days.

Figure 14-15 Patient evaluated for new complex partial seizure with right upper quadrantanopsia on examination. Fluid-attenuated inversion recovery sequence of his brain magnetic resonance imaging is featured. Note hyperintense signal in the torcula (arrows) and lesion surrounded by edema in the left posterior-superior temporal lobe (lower right panel presents a magnified view of the lesion and does not show definitive evidence of a thrombosed vein). Venographic studies revealed that all major sinuses were patent, but the left vein of Labbé was not visualized. Patient was diagnosed with cortical vein thrombosis, with the diagnosis supported by the finding of homozygous factor V Leiden mutation on testing for thrombophilia.

Atypical Presentations

♦ Atypical presentations are not uncommon in cases of CVT. Intermittent headaches with migrainous features, transient ischemic attack–like episodes, isolated cranial nerve palsies, transient amnesia, fever with ear pain and tinnitus (expressions of underlying mastoiditis; Figure 14-16), and subarachnoid hemorrhage (Figure 14-17) are among the initial manifestations that could announce CVT.

Figure 14-16 Axial (upper left) and coronal (upper right) T2-weighted magnetic resonance imaging of the brain showing changes consistent with right mastoiditis (arrows). Abnormal flow signal in the right transverse sinus is noted on the axial cuts. Time-of-flight magnetic resonance venography demonstrated proximal occlusion of the right transverse sinus (lower left). Recanalization is observed on a follow-up time-of-flight MRV obtained after a full course of antibiotics.

Figure 14-17 Nonenhanced computed tomography scan of the brain showing subarachnoid hemorrhage in the sulci of the right hemispheric convexity (upper left, arrow). High attenuation changes were visible in the area of the right transverse sinus (upper right, arrow). Cerebral angiography obtained to investigate the source of the bleeding demonstrated right transverse sinus occlusion (venous phase shown, lateral view on the lower left and anterior-posterior view on the lower right).