Intracranial venous thrombosis
Thrombosis in the dural sinuses and/or cerebral veins is much less common than cerebral arterial thromboembolism, and leads to a number of rather different clinical syndromes which are seldom like ‘a stroke’ (Bousser and Ross Russell 1997). However, intracranial venous thrombosis shares some of the same causes as ischaemic stroke, which these days are far less frequently ‘septic’ than in the past (Southwick et al. 1986). No cause at all is found in something like 20 per cent of cases. Although it was originally regarded as a rare condition which was commonly fatal, nowadays with heightened awareness of mild cases and more sophisticated imaging, it is clearly a more common condition which is rarely fatal.
Causes of intracranial venous thrombosis
Local conditions affecting the cerebral veins and sinuses directly:
- Head injury (with or without fracture)
- Intracranial surgery
- Local sepsis (sinuses, ears, mastoids, scalp, nasopharynx)
- Subdural empyema
- Bacterial meningitis
- Dural arteriovenous fistula (Section 27.4.8)
- Tumour invasion of dural sinus (malignant meningitis, lymphoma, skull base secondary, etc.)
- Catheterization of jugular vein
- Lumbar puncture
- Pregnancy and the puerperium
- Oral contraceptives
- Haematological disorders
- Inflammatory vascular disorders
- Congestive cardiac failure
- Inflammatory bowel disease
- Androgen therapy
- Antifibrinolytic drugs
- Non-metastatic effect of extracranial malignancy
- Nephrotic syndrome
Thrombosis in a dural sinus can be relatively restricted when it tends to cause raised intracranial pressure and the syndrome of benign intracranial hypertension without any neurological deficit (Section 17.1.4). On the other hand, thrombosis in cerebral veins, with or without dural sinus thrombosis, is more likely to cause widespread and multiple ‘venous’ infarcts which are congested, oedematous, and often haemorrhagic.
There are several clinical syndromes, so intracranial venous thrombosis enters into the consideration of patients with benign intracranial hypertension, diffuse encephalopathies, sometimes strokes, and rarely subarachnoid haemorrhage (Bousser et al. 1985b; Enevoldson and Ross Russell 1990).
In perhaps one-quarter of ‘benign intracranial hypertension’ patients the cause is dural sinus thrombosis, which should be particularly considered in males and non-obese females (Tehindrazanarivelo et al. 1992). In these cases, there is seldom propagation of thrombosis into the cerebral veins with venous infarction and focal neurological features. Indeed, the clinical picture seems identical to that of idiopathic benign intracranial hypertension. The prognosis is very good, although a few patients may be left blind due to optic atrophy.
The other common presentation is with an encephalopathy coming on over days, a week or two, or sometimes months. Headache is almost universal and other common features include partial and generalized epileptic seizures, confusion, declining conscious level, papilloedema, and sometimes focal neurological deficits such as hemiparesis and dysphasia. The differential diagnosis is therefore wide, and includes encephalitis, cerebral abscess, subdural empyema, and cerebral vasculitis, as well as metabolic and toxic encephalopathies. In this situation there is widespread and often propagating thrombosis in cerebral veins, as well as, usually, the dural sinuses. Mortality and morbidity are high, although some patients recover spontaneously, even to normal. The main difficulty is to think of the diagnosis at all, often because it may be confused by features which suggest infection (e.g. fever, raised ESR, neutrophil leucocytosis, etc.).
‘Strokes’ are seldom due to intracranial venous thrombosis, but on occasion a more or less sudden focal neurological deficit can occur as a result of cortical vein thrombosis. There may be progression and fluctuation, more headache than usual for an arterial stroke, rather typically seizures, any infarct on brain imaging is seldom in a typically ‘arterial’ pattern, and the patients are ‘too young’ for an ordinary stroke. Migraine and glioma are frequent misdiagnoses. There is a good prognosis (Jacobs et al. 1996).
Sudden headache, often with blood in the CSF, is a very rare presentation and clearly can be confused with spontaneous subarachnoid haemorrhage due to aneurysmal rupture (de Bruijn et al. 1996). Even isolated cranial nerve palsies have been described with transverse sinus thrombosis (Kuehnen et al. 1998).
Cavernous sinus thrombosis is a restricted form of intracranial venous thrombosis, usually due to sepsis spreading from the veins in the face, nose, orbits, or sinuses. In diabetics and immunocompromised hosts, fungal infection can be responsible, particularly mucormycosis. The presentation is with unilateral orbital pain, periorbital oedema, chemosis, proptosis, reduced visual acuity, and papilloedema. The third, fourth, sixth, and upper two divisions of the fifth cranial nerves may be involved. Thrombus may propagate to the other cavernous sinus to cause bilateral signs. Septic meningitis and epidural empyema are occasional complications. The patients are generally severely toxic and ill (Clifford Jones et al. 1982; Southwick et al. 1986). The differential diagnosis includes severe facial and orbital infection, and carotico-cavernous fistula.
Diagnosis and investigations
Is it intracranial venous thrombosis? So often the diagnosis is not quickly considered but is stumbled on, particularly on brain MRI, after others have been considered and then excluded. The CSF can be normal but usually there is a modest increase in cells (lymphocytes, red blood cells, and perhaps polymorphs) and protein, and almost always an increase in pressure if the venous sinuses are occluded: these changes are, however, very non-specific. There are no oligoclonal bands. The EEG may be slowed bilaterally (even when the clinical picture is unilateral or asymmetrical), with or without epileptic discharges, but again that is hardly specific.
Brain CT is the most helpful initial investigation because, although it can be normal (particularly with the ‘benign intracranial hypertension’ presentation), there is often evidence of brain swelling, small ventricles, and rarely there is intensification of the dural sinuses or a cerebral vein (Chiras et al. 1985). Low-density areas of infarction, but not in the usual arterial territories, may appear and also single or multiple areas of high-density haemorrhagic infarction. There is often a lot of early swelling beyond the boundaries of the hypodense infarct. Sometimes there is subarachnoid blood, which is most unusual in either arterial infarcts or primary intracerebral haemorrhage (Bakac and Wardlaw 1997). After intravenous contrast there may be gyral, falcine or tentorial enhancement and, occasionally, the ‘empty delta’ sign (hypodensity in the middle of the posterior part of the superior sagittal sinus representing an area of no filling due to thrombus). Unfortunately, CT is neither sensitive nor specific enough by itself, so if there is any possibility of intracranial venous thrombosis either cerebral angiography or MR must be done, or both.
Cerebral angiography with late venous views is the definitive investigation. There should be total or partial occlusion of at least one dural sinus on two projections. Often there is also occlusion of cerebral veins, late venous emptying, and evidence of venous collateral circulation. A lack of filling of a transverse (lateral) sinus is not due to congenital hypoplasia if there is an appropriate sinus groove and jugular foramen on the plain skull X-ray, or if magnetic resonance venography (MRV) is diagnostic. In obscure subacute encephalopathies, cerebral angiography or MR (see below) should always be done to rule out intracranial venous thrombosis before resorting to brain biopsy.
Fig.4. Lateral view of the venous phase of a carotid angiogram showing lack of filling of the superior sagittal sinus.
Magnetic resonance imaging and venography can now provide a definitive diagnosis in most patients, although attention to technique and exclusion of artefacts are essential. MRI can visualize thrombus in the sinuses, less often in the cerebral veins, and is more sensitive than CT in displaying brain parenchymal changes (Bousser and Ross Russell 1997).
Fig.5 MRI showing venous thrombosis of the sagittal sinus .
What is the cause of the intracranial venous thrombosis? Once the diagnosis of venous thrombosis is made, it is important to consider all the possible causes listed in Table 27.36 and to investigate the patient appropriately. It is probably always worth checking for thrombophilia as a predisposing cause even when a more obvious ‘cause’ (such as oral contraceptives, pregnancy, etc.) is present (clotting screen, protein C, protein S, antithrombin III, activated protein C resistance (Factor V Leiden), lupus anticoagulant, etc.) (Deschiens et al. 1996).
The general principles of stroke treatment apply. In addition, it seems that immediate and full heparinization is not only surprisingly safe, even in the presence of haemorrhage on brain CT, but also improves the prognosis (Einhaupl et al. 1991). However, a recent Dutch trial did not confirm this result (de Bruijn and Stam 1999). Local thrombolytic infusion into the occluded veins is said to be dramatically effective but no real trials have been done and no doubt any disasters have not been published (Kasner et al. 1998).
Once the patient is clearly improving, warfarin can be started or substituted for the heparin, and continued for several months. If after withdrawal of warfarin the patient relapses, or has a venous or arterial thrombosis in another site, both of which are unusual, then re-anticoagulation should probably be lifelong. Naturally, any underlying cause should be treated on its merits; for example, patients with a definite thrombophilia should probably be anticoagulated for life, oral contraceptives should never be used again, but a further pregnancy may be safe (Preter et al. 1996).