17 Cerebral Venous Thrombosis and Occlusion
Abstract
Cerebral venous sinus thrombosis (CVST) and cerebral venous occlusion (CVO) are rare forms of ischemic stroke that often pose significant challenges to the treating physician with regard to diagnosis and/or management. Given the high morbidity and mortality associated with these lesions, expeditious clinical evaluation, diagnosis, and treatment are essential. While the mainstay of treatment remains medical therapy with therapeutic anticoagulation, surgical and neuroendovascular therapies may be considered in a select group of patients. In this chapter, the authors describe the epidemiology, clinical presentation, pathophysiology, imaging characteristics, evaluation, and management/treatment options for CVST/CVO.
Introduction
While large artery occlusion in the anterior circulation has garnered much attention in the literature given the recent clinical trials showing a benefit for mechanical thrombectomy in acute ischemic stroke, thrombosis of the cerebral dural sinuses and veins plays an important—and often underappreciated—role in neurovascular disease. Cerebral venous sinus thrombosis (CVST) and cerebral venous occlusion (CVO) are uncommon forms of ischemic stroke, accounting for 0.5 to 1.0% of all strokes. The overall incidence of this disease in adults is 13.2 per 1 million people per year. While CVST/CVO may occur at any age, the highest incidence is in the second to third decade of life. Women are typically more affected than men (3:1 ratio).
Historically, CVST/CVO has been a source of diagnostic intrigue given its myriad presenting clinical signs and symptoms and elusive appearance on standard imaging modalities. A high index of suspicion is required on the part of the neurovascular specialist to establish the diagnosis based on clinical history, presenting signs and symptoms, and radiographic evaluation. Prompt treatment is essential, as significant morbidity and mortality accompanies the natural history of untreated CVST/CVO.
Major controversies in decision making addressed in this chapter include:
Optimal medical treatment of CVST/CVO.
Medical versus surgical treatment for CVST/CVO.
Indications for endovascular intervention in CVST/CVO.
Whether to Treat
Considerations: Factors influencing the decision to treat patients with CVST/CVO—either medically and/or surgically—include variables related to the patient and the disease process. Patient factors include age, medical comorbidities, clinical presentation, neurological condition, and estimated life expectancy. For some patients, the disease process underlying the hypercoagulable state may be so significant (e.g., widely disseminated systemic malignancy) that conservative therapy, or palliative care, should be considered (see Conservative Management section, below). In general, however, given the young age of the majority of patients affected with this disease, aggressive medical and surgical therapy should not be withheld ( 1 in algorithm ).
Overall, while our understanding of the natural history of CVST/CVO remains incomplete, the preponderance of evidence suggests that these lesions carry a high rate of morbidity and mortality if left untreated ( 2–6 in algorithm ). Acute anticoagulation with either low-molecular-weight heparin (LMWH) or unfractionated heparin (UFH) (followed by oral anticoagulation) should be given in all patients without a major contraindication (level I evidence), even in the setting of intracerebral hemorrhage (ICH) ( 6, 8, 9 in algorithm ). If patients fail to improve, or deteriorate, on medical therapy alone and have malignant intracranial hypertension and a poor neurological exam, surgical management (cerebrospinal fluid [CSF] diversion, decompressive hemicraniectomy [DHC], endovascular intervention) may be considered ( 7, 10, 11 in algorithm ).
Conservative Management
For some patients (e.g., advanced age; extreme medical comorbidities [e.g., widely disseminated neoplasm causing systemic hypercoagulable state]; moribund neurological exam; short life expectancy; inability to tolerate medical or surgical therapy; small, asymptomatic, incidentally discovered thrombus; or patient preference), it is reasonable to consider conservative therapy only. However, these patients must be counseled regarding the natural history of untreated CVST/CVO and may need to be followed clinically for symptom progression and radiographically with noninvasive neuroimaging.
Anatomical Considerations
Cerebral venous system is a complex network of anastomotic channels with much interindividual variability. In general, the venous system may be organized into superficial and deep components, both of which drain into the dural venous sinuses (▶ Fig. 17.1 ). The superficial cerebral veins drain the cortex and subcortical white matter in a centrifugal manner; these include the middle cerebral veins (draining into the sphenoparietal sinus and then cavernous sinus), superior anastomotic vein of Trolard (draining into the superior sagittal sinus [SSS]), and the inferior anastomotic vein of Labbé (draining into the junction of the transverse/sigmoid sinus). The deep cerebral veins drain the deep gray and white matter in a centripetal manner; these include the paired internal cerebral veins and basal veins of Rosenthal. The deep cerebral veins coalesce into the great cerebral vein of Galen under the splenium of the corpus callosum. The vein of Galen, in turn, empties into the straight sinus, torcula (confluence of sinuses), transverse sinuses, sigmoid sinuses, and internal jugular veins.
The most commonly involved dural venous sinuses include the SSS (62%), transverse/sigmoid (41–45%), straight sinus (18%), jugular vein (12%), and deep venous system (11%). The location of brain edema and/or hemorrhage on neuroimaging studies resulting from CVST/CVO typically maintains a close spatial relationship with the area of venous stenosis/occlusion. For example, a CVST of the SSS or CVO of a cortical vein may manifest as hemorrhage or edema in the frontal, parietal, or occipital lobe. Temporal lobe pathologies suggest involvement of the transverse sinus, sigmoid sinus, or vein of Labbé. Pathology involving deep nuclear brain structures (e.g., bilateral thalamus) may be caused by CVO of a deep cerebral vein. ICH or edema that is atypical, lobar, bilateral, or does not conform to a specific arterial territory strongly suggests a venous etiology.
Pathophysiology
The pathophysiology of CVST/CVO involves an imbalance in the equilibrium between prothrombotic and antithrombotic states. Not surprisingly, in a large, multicenter, prospective study on CVST/CVO (the International Study on Cerebral Vein and Dural Sinus Thrombosis; ISCVT), an underlying thrombophilia or exposure to known prothrombotic agents (e.g., oral contraceptives) were associated with 34 and 54% of cases, respectively.
In general, it is important to distinguish between two distinct pathological mechanisms—(1) thrombosis/occlusion of major dural venous sinuses and (2) thrombosis/occlusion of cerebral veins—since dichotomizing these two pathologies is important for patient diagnosis and treatment. In the former situation, a thrombus/occlusion develops within a dural venous sinus (most commonly the SSS). The SSS harbors high concentrations of arachnoid granulations, which serve as the main conduit through which CSF is reabsorbed into the venous system. Following thrombus formation, the affected venous sinus will redirect flow through anastomotic channels such that venous outflow, venous pressure, and CSF reabsorption remain constant. However, if the clot burden is significant—or if the collateral circulation is insufficient—then venous outflow obstruction can occur with resultant venous hypertension. Elevated venous pressures may interfere with the reabsorption of CSF into the dural sinuses, ultimately leading to CSF obstruction and intracranial hypertension. This process can culminate in diffuse vasogenic and/or cytotoxic edema (with failure of ATP-dependent ionic pumps), refractory elevations in intracranial pressure (ICP), and cerebral venous infarction with or without venous hemorrhage. In contradistinction, CVO directly obstructs the egress of venous blood from surrounding brain tissues. This can cause an elevation in venous and capillary pressure, local breakdown of the blood–brain barrier, and ischemia/infarction/hemorrhage to the brain areas receiving drainage by that vein.
Workup
Clinical Evaluation
Every patient warrants a detailed history and neurological examination. The medical history should focus on patient comorbidities and medications that might predispose to a hypercoagulable state. A complete neurological exam should be performed including funduscopic exam to assess for papilledema. In stable patients, a neuro-ophthalmologic analysis (including visual acuity and field testing) should be performed.
Clinical signs and symptoms vary considerably and are dependent on the location and burden of the thrombosis/occlusion. These may include headache (present in 90% of cases), visual changes/loss, focal neurological deficits, aphasia, coma, seizures (present in 40% of cases), and death. Potential etiologies of CVST/CVO are numerous and include neoplasms, infection, puerperium, pregnancy, acquired and hereditary thrombophilia, systemic inflammatory diseases, anemia, dehydration, head trauma, mechanical factors, and certain medications (particularly oral contraceptives and some chemotherapeutic agents). In up to 30% of cases, however, no underlying cause can be identified.
A complete biochemical laboratory evaluation should be performed in each patient with CVST/CVO to assess for metabolic derangements and/or an occult coagulopathy including acquired and hereditary prothombotic conditions.
Imaging
Head computed tomography (CT): Head CT is useful for detecting cerebral edema, intraparenchymal hemorrhage, and infarction. A normal head CT does not exclude the diagnosis of CVST/CVO. On occasion, unenhanced CT may depict a hyperattenuating thrombus within the affected dural sinus (▶ Fig. 17.2a , arrowhead). CVO can also manifest as a homogenous hyperattenuation along the affected vein. A significant number of patients with CVST/CVO (30–50%) experience ICH. ICH, if present, is typically seen as a large area of edema with patchy/punctate areas of hyperdense blood products that do not correspond to a particular arterial territory (▶ Fig. 17.2a ). An unexpected degree of edema often supports a venous etiology relative to other common causes of ICH. Smaller hemorrhages without significant edema (e.g., juxtacortical hemorrhages) may also be observed at the junction between the superficial and deep venous systems.
Computed tomographic venography (CTV): CTV is a rapid, facile, and accurate technique for detecting CVST/CVO. It has a reported sensitivity of 95%. The resolution of CTV is superior to that of conventional magnetic resonance venography (MRV) time-of-flight imaging. A central intraluminal filling defect surrounded by contrast-enhanced dural collateral venous channels (empty delta sign) is highly suggestive of CVST/CVO (▶ Fig. 17.2d , arrowhead).
Magnetic resonance imaging (MRI): MRI is an excellent modality for assessing a filling defect in a dural venous sinus or cerebral vein. On T1-and T2-weighted MR studies, the thrombus appearance can vary significantly depending on its age. As the thrombus evolves, signal intensity variations will occur that depend on the state of the blood products. T2*, gradient echo, and susceptibility-weighted MR sequences are particularly useful for detecting ICH and thrombosed dural sinuses/veins. Vasogenic and cytotoxic edema can be seen as hyperintense areas on T2-weighted and fluid attenuation inversion recovery (FLAIR) sequences.
MRV: Nonenhanced (time-of-flight) MRV is the most commonly used method for diagnosis of CVST/CVO. Similar to CTV, this modality may demonstrate a central filling defect within a dural sinus. Contrast-enhanced MRV is a superior technique (e.g., higher resolution) and may circumvent some of these issues.
Cerebral catheter angiography: Catheter-based digital subtraction angiography (DSA) is the gold standard study for detecting CVST/CVO. DSA allows for dynamic vascular imaging, which includes early, mid, and late arterial phases, capillary phase, and early, mid, and late venous phases. A complete study should include ample views of the anterior and posterior circulation. Adequacy of venous anastomoses and collaterals should be assessed. In CVST/CVO, venous congestion, enlarged cortical veins, or reversal of normal venous flow may be seen. Catheter-based venography affords superior resolution of the cerebral venous system and can be performed with pressure readings at various points along the dural venous sinuses.
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
