Venous Infarction and haemorrhage
Parenchymal oedema with venous infarction and haemorrhage, complicates about10-50% of cases, principally affecting the cortex and adjacent white matter.1 Haemorrhagic infarcts are included in bad prognostic indicators of CVST by 'International Study on Cerebral Vein and Dural Sinus Thrombosis (ISCVT)'.2
The Pathophysiology of venous infarction is thought to be primarily due to elevated venous and capillary pressure caused by the persistence of thrombosis.3 Extensive collateral circulation within the cerebral venous system allows for a significant degree of compensation in the early stages of venous occlusion. Elevated cerebral venous pressure due to cerebral venous occlusion can result in a spectrum of phenomena including a dilated venous and capillary bed, development of interstitial oedema, increased cerebrospinal fluid production, decreased cerebrospinal fluid absorption and rupture of venous structures (haematoma). All of these pathophysiological changes may explain the clinical observation that cerebral venous occlusion, if promptly diagnosed and adequately managed, contains reversible alterations and need not always lead to venous infarction.
The rate of thrombosis is also an important factor in the evolution of venous infarction.4 It may be acute and stroke-like or it may be gradual, allowing time for the development of collateral venous circulation, which may protect against venous infarction or limit its extension.
The infarction due to CVST is frequently haemorrhagic with accompanied bleeding in subarachnoid and subdural spaces as discussed in detail later. The reason behind this haemorrhagic predisposition is probably the same elevated venous and capillary pressure due to persistent thrombus. Pale venous infarcts may occur, which do not conform to an arterial territory. Because of the increased venous pressure, there is early swelling of the infarct and adjacent brain.
CVST particularly thrombosis of internal cerebral veins is also a potential risk factor for neonatal intraventricular haemorrhage and periventricular leukomalacia, particularly when the infant is near term and has bilateral haemorrhagic lesions as described by Ehlers H, Courville CB (1936).5
The treatment of venous haemorrhagic infarct differs from its arterial counterpart over the issue of the use of anticoagulants.
After the separate trials conducted by Einhaupl6 and De Bruijn7 there is general agreement that intravenous heparin should be the first-line treatment of CVST, even in the presence of haemorrhagic infarction, provided there are no general contraindications to its use.
Rapidly Progressive Illness and coma
This is a very rare occurrence, usually associated with the extensive involvement of deep cerebral venous system.15 The classic picture is that of a child with an acute coma associated with decerebrate decortication, extra-pyramidal hypertonia, signs of raised intracranial pressure, papillary changes, and rise in blood pressure leading to death in a few hours or days. Similar cases are reported in adults. When patients survive, severe sequelae, such as akinetic mutism, mental retardation, dementia, bilateral athetoid movement, hemi-paresis, vertical gaze palsy, and dystonia are common.
Rapidly progressive state can also arise due to extension of thrombosis leading to complete occlusion of the superior sagittal sinus (SSS) and right transverse/sigmoid sinus complex.16 The presentation is usually a history of several days of illness with severe headache and photophobia that changes its course to a rapid deterioration and coma.
If large unilateral infarcts or haemorrhages compress the diencephalons and brain stem; patients may become comatose or die from cerebral herniation if untreated. Other causes of coma are involvement of the thalamus and generalized seizures.17
ISCVT regards coma as one of the poor prognostic indicators and involvement of deep cerebral veins as variable indicating dependency and increase risk of death.2
Due to poor prognosis, aggressive measures are favoured in this setting. In the rare patient who develops coma, fixed and dilated pupils, and brain herniation, early intervention by emergency decompressive craniectomy may be helpful.18
Surgical thrombectomy or microsurgical revascularization with venous bypass for aseptic lateral sinus thrombosis and superior sagittal sinus thrombosis may be considered in patients with a rapidly progressive course despite appropriate medical therapy. Use of attractive techniques like Microsnare, AngioJet, intravascular laser and intravascular ultrasound for thrombus disruption are still experimental.4
One additional method of clot disruption is to perform balloon angioplasty within the clot to disrupt it and facilitate the effect of the thrombolytic agent.4,16 This technique may be helpful in patients with rapid clinical worsening and extensive thrombosis. The balloon may also be inflated in the clot and used to pull the clot into the jugular vein, such as is done in peripheral vascular diseases (Fogarty technique).
Development of AV fistula
Development of AV fistula is the most interesting though rare chronic complication of CVST.23 There is a clear-cut association between CVST and dural arteriovenous fistulas, although it may be difficult in some cases to ascertain if the thrombosis was a primary or secondary event. According to Tripathi et al.24, DAVFs can be classified into two major groups: cavernous sinus DAVFs (CS-DAVFs) and noncavernous sinus DAVFs (NCS-DAVFs). Approximately 30% of symptomatic intracranial DAVFs involve the transverse and sigmoid sinuses. Tsai et al.23 in his analysis of 69 patients of DAVFs states that out of 69, the most frequent location of Dural AVF was the cavernous sinus (21 (30%)), followed by the skull base (13 (19%)), transverse sinus (12 (17%)), Dural convexity (8 (12%)), sigmoid sinus (7 (10%)), torcular Herophili (5 (7%)), and superior sagittal sinus (3 (4%)). Symptoms depend upon the location of AV fistulas.
DAVFs due to CVST are uncommon in young children with atypical clinical presentation representing with prematurity and delayed milestones with childhood hemiplegia as described by Tripathi in a case report. Confusion can be created by the possibility of a sequel of hypoxic-ischemic encephalopathy or a TORCH infection.24
Two hypotheses have been proposed for the pathogenesis of Dural AVF.23 The first is based on the physiological arteriovenous shunts between the meningeal arterial networks and the dural venous sinuses. An increase in sinus and venous pressure-for example, by the obstruction of venous outflow by CVST, may open these channels to create Dural AVFs. The second hypothesis, as shown in the rat model, suggests that venous hypertension induced by an obstruction to venous outflow may reduce cerebral perfusion and lead to ischemia, followed by angiogenesis. The aberrant angiogenic activity of the Dural blood vessels would then result in arteriovenous shunting. In both, CVST may be the primary event that caused the venous hypertension. The occurrence of secondary thrombotic event is also a possibility probably because of the turbulent flow into the venous sinus due to DAVFs.
Hung-Yi et al. in a case study described Serial Venous Transcranial Color-Coded Sonography as a useful technique for detecting disturbance of cerebral venous circulation and for follow-up of patients with cerebral venous sinus thrombosis.25 Valuable information such as flow direction and changes in the Doppler flow waveform, which cannot be routinely obtained by time-of-flight MR angiography, can be recorded easily and noninvasively with venous TCCS. Although TCCS cannot examine all the intracranial venous structures, it can serve as a complementary examination technique, providing hemodynamic information on venous circulation.
Regarding treatment of DAVFs, it is a highly challenging subject. Intrasinus stenting can be helpful for relieving elevated sinus pressure but may lead to a greater arteriovenous pressure gradient and shunt flow. Arterial embolization of a DAVF without relief of venous hypertension can give rise to another fistula.
Techniques like, intermittent carotid arterial compression25, Percutaneous intraarterial embolization using detachable balloons26, isobutylcyanoacrylate, or polyvinyl alcohol particles, transvenous embolization with coils or liquid adhesives27, and surgeries like venous bypass using saphenous vein28 and gamma knife stereotactic surgery25 are used in different cases.
Controlled hypotension can also become an alternative for treatment of DAVF in high-risk patients or when there is no chance for embolization.29
Recurrence of CVT is infrequent. Preter et al15. reported only 12% recurrence in a series of 77 patients followed for a mean of 78 months. Recurrences have been mostly reported in hospitalized -patients, or in patients with an underlying prothrombotic condition.
Amberger et al. describe a unique case in which third occurrence of CVST took place in a short span of time.35 The underlying cause was thrombophilia due to antiphospholipid syndrome.
Most authors recommend using oral anticoagulation for 3 to 6 months at which time they should be reevaluated with MRI/MRV. Prolonged anticoagulation may be required for refractory cases or for patients with an identified prothrombotic state. In the above-described case life long anticoagulation was started.
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