CEREBRAL VENOUS THROMBOSIS

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CHAPTER 46 CEREBRAL VENOUS THROMBOSIS

Gian Luigi Lenzi, Alessio Mercurio, Marta Altieri

Cerebral vein and sinus thrombosis (CVST) is a rare event in comparison with arterial stroke, accounting for less than 1% of all strokes. CVST occurs in all age groups, peaking in incidence among neonates and young adults. Clinical diagnosis is difficult, because of the wide spectrum of clinical symptoms of CVST. The achievements of neuroimaging since the 1970s have been fundamental for diagnosing and treating CVST and for a better understanding of its pathogenesis. Early diagnosis of CVST is crucial, because therapy, based mainly on anticoagulation, reduces the risk of fatal outcome and severe disability.1,2

ANATOMY OF THE INTRACRANIAL VENOUS SYSTEM

Cortical Cerebral Veins

These veins drain blood from the superficial part of the brain (cortex and the adjacent white matter) and are composed of three systems:

1. The dorsomedial system drains into the superior sagittal sinus (SSS) and the inferior sagittal sinus (ISS), receiving blood from the convexity and the midline of the brain.
2. The posteroinferior system drains into the lateral sinus, receiving blood from the temporo-occipital areas.
3. The anterior system drains into the cavernous or the pterygoid venous plexus through sylvian veins, receiving blood from the frontal pole, the inferior part of the frontal lobe, and the anterior part of the temporal lobe.

These systems show variations among the population: Any of the three major components may be missing or hypoplastic. In these cases, the other components are hypertrophic. Cortical veins are connected to the dural sinuses by the so-called bridging veins.

Deep Cerebral Veins

These veins drain the deepest parts of the white matter, the basal ganglia, and the diencephalon. The septal and thalamostriate veins, called the subependymal veins, are the most important and drain into the internal cerebral vein.

1. The septal veins receive blood from the genu of the corpus callosum, from the septum pellucidum, and from the anterior part of the caudate nucleus, and they drain into the thalamostriate veins.
2. The thalamostriate veins receive blood from the basal ganglia and from the internal and external capsules; they pass through the roof of the third ventricle, cross in the interventricular foramen of Monro, and end in the internal cerebral veins.
3. The posterior choroidal veins drain blood from the pineal gland and from the choroid plexus of the lateral ventricles and end in the thalamostriate veins.
4. The internal cerebral veins run parallel beneath the choroidal vein of the third ventricle to join their counterpart and form the vein of Galen.
5. The vein of Galen, unique and median, runs from the posterior part of the diencephalon up to the straight sinus, between the cerebellum and the splenium of the corpus callosum; early in its course, it receives the paired basal veins of Rosenthal.
6. The basal veins of Rosenthal drain the bottom parts of the basal ganglia; the bottom parts of the temporal, frontal, and occipital lobes; and the medial parts of the insula and the temporal lobe. These veins originate in correspondence to the anterior perforated substance near the confluence of two vessels—the anterior limbic vein and the deep middle cerebral vein (or insular vein)—and then they “tie” into a bow around the mesencephalon before ending in the vein of Galen. Sometimes they receive the posterior limbic veins, the hippocampal veins, and the middle superior cerebellar veins.
7. The anterior limbic veins drain the cingulate circumvolution. In correspondence with the genu and the rostrum of the corpus callosum, they bend to reach the basis of the brain, in order to join the deep middle cerebral vein on the same side and to form the homolateral basal vein of Rosenthal.

Posterior Fossa Veins

The venous drainage of the posterior fossa is highly variable. Four main systems can be outlined:

1. The posterosuperior system drains the dorsal cerebellum, vermis, and the upper portion of the brainstem into the vein of Galen. The most important vessels of this group are the superior cerebellar hemispheric veins and the superior vermian veins.
2. The anteromedial system is formed by the anterior pontomesencephalic vein, which drains into the basal vein of Rosenthal on both sides.
3. The anterolateral system is formed by the petrosal veins, which drain the ventral cerebellum and the upper part of the brainstem, and by the choroidal vein of the fourth ventricle, which drains the lower part of the brainstem.
4. The posteroinferior system is formed by the inferior cerebellar hemispheric veins, which are tributaries of the transverse sinus, and by the bilateral posterior spinal vein, which ends in the inferior retrotonsillar vein; this vein and the superior retrotonsillar vein form the inferior vermian vein. This vessel is finally a tributary of the ISS.

Dural Sinuses

The dural sinuses are situated between the leaves of the falx and the tentorium and are triangular in section. They drain blood from the cortex, the meninges, and the scalp (through the calvarian veins) and deliver it to the internal jugular veins. They are connected with the extracranial veins in the scalp by the emissary veins. This may explain dural involvement after cutaneous contusions or infections (Fig. 46-1).

1. The SSS begins at the foramen cecum, before the crista galli, and runs along the curve of the inner table of the skull to reach the torcular Herophili, where it converges with the straight sinus. Their combined flows drain into the transverse sinus. The SSS receives blood from frontal, parietal, and occipital superior regions of the cortex. The SSS, and other sinuses, contains the arachnoid villi and granulations in which the absorption of cerebrospinal fluid takes place. There is a direct dependency of cerebrospinal fluid pressure on the intracranial venous pressure, which explains the frequent increase in intracranial pressure in CVST. The dura mater adjacent to the sinus contains important venous plexuses, which represent a potential alternative drainage route when a sinus is occluded; this explains the “empty-delta” sign, which is visible on computed tomographic (CT) scan in occlusion of the SSS.
2. The straight sinus is formed by the junction of the tentorium, falx cerebri, and falx cerebelli and receives blood from the vein of Galen and from the ISS. It ends in the torcular Herophili or in the left transverse sinus.
3. The ISS runs parallel to the SSS in correspondence to the free margin of the cerebral falx, receiving blood from the middle regions of the brain that drains into the SSS through the venous vessels of the cerebral falx.
4. The lateral sinus connects the torcular Herophili with the internal jugular veins on both sides and is formed by two components: the transverse sinus, which lies in the peripheral margin of the tentorium cerebelli, and the sigmoid sinus. The transverse sinuses are frequently of unequal size; the left one, which receives blood from the SSS, is usually larger. Atresia or agenesis of the transverse sinus is related to alternative filling of the sigmoid sinus by the vein of Labbé. The sigmoid sinus starts at the end of the transverse sinus and reaches the jugular vein; agenesis and atresia of this sinus are very uncommon.
5. The cavernous sinuses are situated on the sphenoid bone, laterally to the sella turcica. Their walls contain the cranial nerves III, IV, V2, and V3 of both sides, whereas the cranial nerve V1, the intracavernous tract of the internal carotid artery, and the pericarotid sympathetic plexus are contained in their lumen. They drain the ophthalmic veins, the anterior and middle cranial fossa, and the sphenoparietal sinus (the medial extension of the superficial sylvian vein). Blood drains posterolaterally along petrosal sinuses to the lateral sinus and the jugular vein through the inferior petrosal sinus. The two cavernous sinuses are connected by the intracavernous sinus, which lies on the clivus behind the sella turcica: this strict anatomical connection explains their frequent simultaneous involvement (Fig. 46-2).
6. The petrosal sinuses are four in number, two for each side (superior and inferior). The first one is the anterior continuation of the transverse sinus and corresponds to the oblique insertion of the tentorium on the rocca petrosa, ending in the cavernous sinuses. The second begins at the inferior part of the intercavernous sinus to end, together with the sigmoid sinus, in the jugular vein.
7. The occipital sinus is located at the insertion of the falx cerebelli on the occipital bone, and it drains blood from the dorsal regions of the cerebellum vermis.
image

Figure 46-1 A, Anatomy of the deep venous circulation of the brain. B, Anatomy of the superior sagittal sinus. C, Anatomy of the lateral sinus (divided into its components: transverse sinus and sigmoid sinus) and the straight sinus.

image

Figure 46-2 Anatomy of the cavernous sinus.

Venous Anastomoses

The intracranial venous system has no valves and therefore allows reversals of the blood flow direction, following pressure gradients. The most important vessels of this system are (1) the great anastomotic vein of Trolard that runs from the sylvian fissure to the SSS, thus forming an anastomosis between the SSS and the petrosal sinuses, and (2) the little anastomotic vein of Labbé, which connects the superficial sylvian vein with the transverse sinus or connects the SSS with the transverse sinus (depending on interindividual variability). There are also other, less important links, such as those between the little cortical veins and the adjacent sinuses or those between the basal vein of Rosenthal and the cortical veins. Transcerebral veins are virtual vessels that, when necessary, connect superficial and deep veins, crossing the cerebral parenchyma. The dural sinuses also communicate with the meningeal, diploic, and calvarian veins through the emissary veins.1–5

EPIDEMIOLOGY

CVST may manifest with such a wide spectrum of clinical signs and symptoms that it goes unrecognized in quite a few patients. It follows that epidemiological studies are difficult to perform. On the basis of retrospective trials, CVST accounts for about 0.1% to 9% (mean, about 1%) of all deaths for stroke, with great geographic and ethnic variabilities.1,2,6–8 In industrialized countries, the incidence of CVST is estimated between 1.5 and 2.5 cases per 100,000 per year.6 Although these numbers, based on CT scan or magnetic resonance imaging (MRI) findings, are remarkably higher than those observed before the neuroimaging era, they still account for only patients who present with the more severe consequences of CVST: namely, hemorrhagic or ischemic venous strokes. As the frequency of venous stroke ranges from 30% to 80% of all cases, the prevalence of patients who develop symptoms related to intracranial hypertension might be considerably higher.6,9–12

In a multicenter prospective observational study, 624 patients with CVST were enrolled. Female gender was prevalent (74.5%); the mean age was 39 years. Patients were predominantly white (79.2% versus 9.3% Hispanic, 5% black, 3.4% Asian, and 3.1% other races). Ischemic venous infarction was present in 46.5% patients, and hemorrhagic lesions were detected in 39.3% patients. Ischemic and hemorrhagic infarcts coexisted in some patients; the cumulative rate of parenchymal lesions at neuroimaging was 62.9%. The SSS was the most frequently involved (62%), followed by the left lateral sinus (44.7%), the right transverse sinus (41.2%), the straight sinus (18%), the choroidal vein (17.1%), and the jugular veins (11.9%). The deep venous system was involved in 10.9% of patients, and the cavernous sinuses in 1.3%. A posterior fossa vein thrombosis was reported in only 0.3%.13

In one study, researchers have investigated the distribution of risk factors and clinical features of CVST among white and African-Brazilian patients. The female/male ratio was higher among the African-Brazilian patients than among the white patients (4.75 versus 1.36), whereas the mean ages were similar. African-Brazilian patients had higher rates of focal deficits (60.8% versus 46.1%) and decreased consciousness (47.8% versus 27%); however, these differences were not significant.7

A high incidence of CVST in young women, especially during pregnancy and the puerperium, has been reported in several studies.6,11,12 As a matter of fact, estimates of CVST associated with pregnancy and the puerperium range from 2 to 60 per 100,000 deliveries in western Europe and North America and from 200 to 500 per 100,000 in India.1,2 The use of oral contraceptives appears to be a risk factor for CVST.1,2,6,10–13

PATHOPHYSIOLOGY

The causal factors leading to CVST are essentially four: (1) prothrombotic state; (2) venous stasis; (3) direct involvement of the venous wall; and (4) abnormal blood viscosity.14 Symptoms of sinovenous occlusion may arise directly from the primary or underlying process, venous obstruction, vascular inflammation, or secondary complications. Venous obstruction causes a rise of venous and parenchymal pressure in its competence territory, which leads to venous distension and edema. Many of the clinical consequences of CVST arise from brain swelling and increased intracranial pressure caused both by venous engorgement and by decreased cerebrospinal fluid absorption secondary to venous hypertension. Furthermore, in the majority of cases, thrombosis involves multiple dural sinuses or both sinuses and veins.1,2,13,15

Experimental studies have contributed to a better definition of the pathological features of CVST. A subacute occlusion of SSS provokes clinical manifestations only when the occlusion spreads to cortical or bridging veins.16–20 SSS occlusion is usually associated with brain swelling, an increase in intracranial pressure, and diffuse cellular damage.16–21 On the other hand, occlusion of bridging and cortical veins produces a localized well-shaped venous infarction, with both ischemic and hemorrhagic features, surrounded by brain swelling and edema.19–23 In cats, the ligature of SSS provokes a stroke only when located after the confluence between this sinus and the rolandic vein, because the anterior third of the sinus is well compensated by collateral vessels. What is remarkable is that ischemic/hemorrhagic lesions are absent at 2 hours but present at 24 hours; this demonstrates that the acute occlusion of a dural sinus, at least in experimental conditions, is related not to an acute infarction but only to a subacute one.19 This observation could also apply to humans, inasmuch as the majority of patients with dural sinus involvement exhibit a subacute onset of the CVST signs and symptoms. Also remarkable is that neither the site nor the extent of a sinus occlusion is indicative of the final site and size of the corresponding ischemic lesion. On the contrary: The thrombosis of a cortical vein produces a definite area of infarction in the gray and superficial white matter. As a consequence, patients with cortical and deep vein thrombosis show the worst clinical outcome,22 because the deep vein thrombosis produces a widespread lesion that involves the thalamus, the deep white matter, and the upper parts of the brainstem.1,2,24

DIAGNOSIS AND CLINICAL FEATURES

CVSTs manifest with a wide spectrum of signs and symptoms; therefore, the differential diagnosis should account for a number of possible conditions. The variability of clinical features of CVST is high in relation to the site and extent of thrombosis, the rate of propagation of the occlusion, the age of the patient, and the underlying pathology. Spinal cord venous involvement in these thrombotic processes is also possible, but it is very rare and related mostly to the propagation of an infectious thrombophlebitis of the pelvic veins.

Headache is the most frequent presenting symptom and the most common complaint (75% of cases).1,2,12,25 The headache is usually diffuse and progressive, with no typical clinical characteristics or temporal profile. In the 2004 International Classification of Headache Syndromes, headache associated with CVST is classified as follows: (1) any new headache, with or without neurological signs, that fulfills the second and third criteria; (2) headache with neuroimaging evidence of CVST; (3) headache (and neurological signs, if present) that develops in close temporal relation to CVST.26

Despite its polymorphism, the most frequent clinical features of CVST can be grouped into three syndromes, according to their physiopathology: (1) intracranial hypertension syndrome (IHS); (2) stroke-related syndrome; and (3) encephalopathic syndrome.

Intracranial Hypertension Syndrome

Headache is the most common clinical symptom of IHS, reported in 75% to 95% of patients.6 It represents the inaugural symptom in 70% to 75% of cases and is often the unique clinical manifestation of IHS.6–27 The headache may be any grade of severity, diffuse or localized, and persistent or intermittent. The onset is usually subacute (2 to 30 days) but can also be acute (>2 days) or chronic (>30 days).1,2 Attacks may mimic migraine or may be interpreted as a subarachnoid hemorrhage manifesting as a thunderclap-type headache, with instantaneous onset and coming on very quickly.27 Papilledema is observed in about 50% of affected patients.11 Only 20% to 40% of patients have the complete syndrome of isolated IHS with headache, nausea, vomiting, papilledema, transient visual obscurations, and eventually cranial nerve VI palsy. The involvement of other cranial nerves is very rare.6 IHS resulting from CVST should be differentiated by the idiopathic intracranial hypertension or pseudotumor cerebri, with a complete neuroradiological workup. IHS is more frequently caused by the occlusion of the dural sinuses, particularly the SSS.1,2,27

Stroke-Related Syndrome

This syndrome is typically related to the occurrence of a venous infarction that can be both ischemic and hemorrhagic. In the majority of cases, the pattern is represented by multiple small intraparenchymal hemorrhages, surrounded either by normal parenchyma or by ischemic areas. Its clinical features are ill-defined and differ from those of an arterial stroke, which is more sharply outlined and wedge-shaped. The abundance of collateral vessels and anastomosis of the venous circulation, in comparison with the arterial circulation, is responsible for the lack of topographic localization of the lesions. Focal neurological signs (sensory and motor deficits, speech disturbances, hemianopia) are present in 40% to 60% of all cases.6 Headache, vomiting, and ataxia with acute onset are the most frequent symptoms in patients with cerebellar vein thrombosis, which is always associated with a concomitant effect on the lateral sagittal sinus and SSS.6

Encephalopathic Syndrome

This condition is the least frequent manifestation of CVST but also the most severe. It is typically related to the involvement of the deep venous system, with diffuse damage of the white matter, basal ganglia, thalamus, and mesencephalon. Parenchymal damage may be related to necrosis, hemorrhages, and brain swelling.1,2,28 The clinical syndrome is characterized by generalized seizures, psychiatric disturbances, confusion, and variable levels of consciousness, disorders of which range from stupor to coma.1,2,6,10,11,25 Major cognitive impairments are reported in only 15% to 19% of cases.6

Focal or generalized seizures are present in more than 40% of patients with CVST2 and may occur in every related clinical syndrome. During the puerperium, the incidence is even higher (76%).6,12 Among the focal forms, the jacksonian type is the most common and is characteristically associated with Todd’s postconvulsive paresis, which is rare in idiopathic epilepsy.6,12,29 Nonetheless, only a few cases progress to epilepsy.29

Cavernous sinus thrombosis provokes a peculiar neurological syndrome characterized by any combination of unilateral chemosis, proptosis, and eyelid edema (caused by inadequate ocular venous drainage from the ophthalmic vein), with diplopia resulting from the involvement of the oculomotor nerves. Myosis and ptosis may also be present as a result of involvement of the third cranial nerve, as may mydriasis, caused by the involvement of the pericarotic sympathetic plexus. Retro-orbital and/or frontotemporal pain and anesthesia in the territories of the first and second branches of the trigeminus may also be present, constituting the so-called painful ophthalmoplegia. In the case of slow occlusion of the sinus, the only clinical manifestation may be limited to the sixth nerve palsy accompanied with pain. The thrombosis may extend to the contralateral sinuses. The differential diagnosis should take into consideration other causes of painful ophthalmoplegia such as the Tolosa-Hunt syndrome, which is an idiopathic granulomatous inflammation of the dural wall of the cavernous sinuses; giant cells arteritis; sarcoidosis; local or general neoplasm; pseudotumor orbitae; and infectious thrombophlebitis caused by the propagation of a septic process from the face or neck into the cavernous sinuses.30

DIAGNOSTIC METHODS

Venous angiography was the first instrumental technique used to diagnose CVST. Today, its clinical use is limited to dubious cases because of its excellent sensitivity. Angiography shows venous thrombosis as an interruption of flow that may be differentiated by sinus aplasia by the presence of a tortuous collateral circulation, consisting of “corkscrew vessels.”1,2 These vessels cannot be visualized by any other technique, and thus angiography remains the most important diagnostic tool in these cases.31

CT scan is usually the first investigation performed in the emergency department6; thus, it plays an important role in differential diagnosis, allowing the clinician to rule out disorders that may mimic CVST, such as tumors, encephalitis, brain abscesses, and subarachnoid hemorrhage.32 However, CT scans may be normal in 25% to 30% of patients.6

On CT scan, CVST may show direct and indirect signs. Direct signs are as follows:

1. The empty delta sign is the most frequent direct sign of CVST, being detected in 25% to 30% of patients with CSVT.6 Visible only after injection of contrast material, it appears as a hypodense area, because of the presence of a clot in the torcular Herophili, surrounded by a hyperdense triangular (delta-shaped) image, because of the enhancement of collateral vessels developed in the context of the dural wall.1,

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