Cerebral venous thrombosis (CVT) refers to occlusion of venous channels in the cranial cavity, including dural venous thrombosis, cortical vein thrombosis and deep cerebral vein thrombosis. They often co-exist and the clinical presentation among them is very similar and nonspecific. Furthermore, the diagnostic imaging features can be subtle.
Demographics of affected patients reflects underlying predisposing factors, which are identified in the majority of cases (87.5%) with many patients having more than one coexistent risk factors 2:
- oral contraceptive pill: very common cause in female patients <50 years of age 2
- prothrombotic haematological conditions: 35% 2
- e.g. prothrombin 20210 (factor II) mutation 7
- local factors
- systemic illness
- dehydration: e.g. gastroenteritis
- connective tissue disorders
- idiopathic: ~12% 2
Unlike most other intracranial vascular conditions, the presentation can be highly variable and range from essentially asymptomatic to coma and death, and can also mimic a host of conditions 1.
- decreased/altered conscious state
- decreased/altered vision
CVT pathogenesis remains poorly understood 5. There is an extensive list of known risk factors, already mentioned above.
The lesion volume is related to the development of collateral veins in the affected venous segment. Venous hypertension from a poor outflow can lead to oedema, cerebral venous infarction (~50% of cases 1) and even haemorrhage.
Superior sagittal sinus or the dominant transverse sinus thrombosis can affect the arachnoid granulations absorption of cerebrospinal fluid, a consequent increase of cerebral swelling may occur 1.
Unenhanced CT is usually the first imaging investigation performed given the nonspecific clinical presentation in this cases.
Non-contrast CT, when not associated with venous haemorrhage or infarction can be a subtle finding, relying on hyperdensity of the sinus being identified 1,5. Thrombus can appear as a hyperdense vein or sinus for the first 7-14 days; this is an accurate sign when present 6.
With contrast administration, especially with a CT venogram, a filling defect in a sinus is sought. When in the sagittal sinus it is referred to as the 'empty delta sign'. CTV has a reported sensitivity of 95% compared to DSA as the gold standard 1.
Filling defects should not be confused with Pacchionian bodies (arachnoid granulations) which can be seen in essentially all dural sinuses and are especially common in the superior sagittal sinus and transverse sinus.
MRI is able to both visualise the clot as well as the sequelae.
The clot acutely is isointense on T1 and hypointense on T2 (this can mimic a flow void), with subacute clot becoming hyperintense on T1.
Cerebral oedema can be identified even in the absence of neurological dysfunction or infarction 1.
MRV will demonstrate a lack of flow. 2D time of flight (TOF) venography is routinely performed in suspected cases. Contrast MR venography is more sensitive in detecting dural venous sinus thrombosis than TOF venography. Hypoplastic dural sinuses and low flow areas remain a major problem with 2D TOF.
Although digital subtraction angiography has historically been the gold standard, the relative lack of experienced interventionalist and invasive nature of the examination has led to a dramatic decline in its use as a primary mode of diagnosing cerebral venous thrombosis.
Treatment and prognosis
In approximately 50% of cases, cerebral venous thrombosis progresses to venous infarction 1. Unlike arterial infarcts, venous infarcts usually present after some days 1:
- <2 days of symptom onset: 30%
- 2-30 days: 50%
- >30 days: 20%
The mainstay of treatment is heparin, even in the setting of haemorrhagic venous infarction 2,4. The natural history of cerebral venous thrombosis is highly variable, with some patients having minimal or no symptoms and an uneventful recovery (~65%), whereas others have a fulminant course culminating in extensive venous infarction and dependency or death (~20%) 2.
Interventional neuroradiologists can perform catheter directed thrombolysis by using targeted thrombolytics in the affected sinuses.
Not surprisingly coma, haemorrhagic venous infarcts and co-existing malignancy correlate with poor outcome 2. Deep cerebral venous thrombosis also has a negative impact on prognosis due to the usually bilateral involvement of the thalami 3.
Dural arteriovenous fistula and increased CSF pressure have been reported as possible complications after cerebral venous thrombosis.
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