Venous anatomy of the brain is covered in the section 'Vascular Neuroanatomy.'
The diagnosis of CVST is challenging. Dedicated imaging of the venous sinuses is required to 'rule out' the diagnosis. Increasing awareness and the treatable nature of the disorder have lead to an increased demand for this imaging. The disorder remains relatively uncommon though, in contrast to misinterpretation of imaging which seems frequent!
CVSTs may present with headache or focal neurological symptoms. Given a large number of neurological problems can present in this way CVST should be considered when: - Procoagulant factors are identified - Neuroimaging is suspicious for CVST - Papilloedema
Prothrombotic factors include: - Pregnancy - Pueperium - Oestrogen-containing contraceptives - Infections - Malignancy
In addition, CVST can occur after traumatic brain injuries (TBI). Local expertise suggests that CVST in the context of TBI is more benign than non-traumatic CVST. This is somewhat lucky given that this can be a risky cohort of patients with respect to anticoagulation.
Venous sinus imaging is the gold standard for identifying CVST but a non-contrast CT head may be abnormal: - Intraparenchyma haemorrhage is seen in around a third of cases. Lesions at the grey-white matter function are characteristic. - A hyperdense clot containing venous sinus is seen in around a third of cases.
The investigation of CVST can be considered in two parts: 1) Confirmation of the diagnosis 2) Identification of precipitating factors
Confirmation of the diagnosis is centred around neuroimaging. While the D-dimer plays a role in other disorders caused by venous thrombosis a negative D-dimer is not felt to be sufficient to exclude cerebral venous thrombosis.
The density of normal venous sinus on an unenhanced CT brain is in the region of 45-53 HU. An attenuated sinus resulting from clot is in the region of 61-66 HU. Adjusting these thresholds for haematocrit improves diagnostic yield, but this is not foolproof.
CVST is not the only thing that can lead to apparent obstruction of the venous sinuses. Two common causes of apparent obstruction are: - Hypoplastic venous sinus - Arachnoid granulations
A number of tests are reasonable to perform in all people with a newly identified CVST: - A physical examination - seeking evidence of systemic infection or neoplasia which are associated with pro-thrombotic states - Urine dip - seeking protein that might necessitate further investigation for nephrotic syndrome
Solid phase anti-phospholipid syndrome (APS) assays should be sent acutely as they alter management. This assay includes tests for anti-cardiolipid and anti-Beta2-glycoprotein antibodies.
Platelets are also important. Thrombocytosis should prompt testing for JAK mutations.
At this point, the diagnosis of CVST should have been confirmed and other common differentials such as a hypoplastic venous sinus should have been considered. Next, consideration needs to be given to whether the obstruction is likely to be acute or chronic.
Patients with CVST can become extremely unwell. Venous thrombosis can lead to venous infarction, seizures, hydrocephalus, increased intracranial pressure and coma. Patients should be monitored closely while anticoagulation is initiated.
Low molecular weight heparin (LMWH) or unfractionated heparin are generally used as first line management. LMWH is generally preferable because of its ease of use. Unfractionated heparin may be used in situations where there is concern about the potential for bleeding. It should be noted though that even when LMWH is used in the setting of intracerebral haemorrhage secondary to CVST, outcomes are better than when anticoagulation is not used. Unfractionated heparin may be reserved for situations in which there is significant haemorrhage.
It is known that recannalisation occurs in a portion of patients with CVST. There is ongoing debate about whether repeat neuroimaging is useful. One study suggested that failure of recannalisation is associated with poor outcome so repeat scanning may aid decisions regarding the duration of anticoagulation. Some feel that a follow up scan after anticoagulation can be useful for establishing the new baseline of a patient so that should they return with headaches in the future the scan can be used to provide a point of reference for a time they were 'well.' Others believe there is no high quality evidence indicating rescanning is useful for guiding management and therefore do not routinely undertake this.
The rarity of the disease makes it hard for these questions to be conclusively answered with clinical trials.