Answers

Short answers

1 The head computed tomogram shows a subarachnoid haemorrhage in the left sylvian fissure and overlying convexity.

2 The most common causes of non-traumatic subarachnoid haemorrhage are ruptured intracranial aneurysms and arteriovenous malformations.

3 A filling defect throughout the left transverse and sigmoid sinuses can be seen on the digital subtraction angiogram, which is suggestive of venous sinus thrombosis.

4 The treatment for venous sinus thrombosis is anticoagulation with heparin and subsequently warfarin.

Long answers
1 Diagnosis of subarachnoid haemorrhage
Unenhanced computed tomography of the brain is the investigation of choice for the assessment of acute haemorrhage and bony injury. A good quality non-contrast high resolution computed tomogram can be used to detect subarachnoid haemorrhage within 12 hours of occurrence (the "ictus") in more than 98% of cases.¹ Blood within the cisterns or fissures shows up as hyperdense (white) on the computed tomogram. Associated hydrocephalus might also be present and occurs acutely in about a fifth of patients with aneurysmal subarachnoid haemorrhage.² The sensitivity of computed tomography for subarachnoid haemorrhage declines over time to only about 50% a week after the ictus.³ Therefore, if a subarachnoid haemorrhage is clinically suspected but computed tomography is not diagnostic, a lumbar puncture is mandatory. Following subarachnoid haemorrhage, red blood cells that have entered the cerebrospinal fluid undergo lysis and liberate oxyhaemoglobin, which is subsequently converted to bilirubin. To give time for this process, lumbar puncture should be delayed until 12 hours after the ictus. The presence of xanthochromia, as assessed by spectrophotometry, is the most sensitive marker of subarachnoid haemorrhage—almost 100% sensitive at 12 hours after the ictus and about 70% sensitive four weeks after.⁴

2 Causes
The most common cause of subarachnoid haemorrhage is trauma. Traumatic subarachnoid haemorrhage is usually associated with moderate and severe head injuries, but can occur with mild head injury (initial Glasgow coma score 13-15).⁵ In the absence of trauma, subarachnoid haemorrhage is most often caused by the rupture of an intracranial aneurysm (75-80% of cases) or by a cerebral arteriovenous malformation (5%).⁶ A number of other aetiologies of subarachnoid haemorrhage exist, however, including vasculitis, tumour, cerebral artery dissection, rupture of a small superficial artery, coagulation disorders, and dural sinus thrombosis.

Computed tomography can provide clues to the aetiology of subarachnoid haemorrhage. If the history is at all unclear, it is essential to first review the imaging results for any associated skull fractures that suggest trauma. The location of subarachnoid blood can also be informative. In this patient, blood within the left sylvian fissure suggested a left middle cerebral artery aneurysm. Equally, blood predominantly in the anterior interhemispheric fissure suggests an anterior communicating artery aneurysm, and blood within the third and fourth ventricles suggests a posterior communicating artery aneurysm. Subarachnoid blood in the presence of parenchymal lesions (damage within the grey and white matter of the brain itself) and blood in the cerebral convexities (that is, along the outer surface of the brain) sparing the basal cisterns may suggest non-aneurysmal causes.

View larger version (84K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 3 Unenhanced axial computed tomogram of the brain demonstrating subarachnoid haemorrhage in the left sylvian fissure (arrow in left image) and the associated anatomy (right image)

 
3 Venous sinus thrombosis
The definitive diagnosis of an underlying vascular abnormality requires angiography. The gold standard is conventional digital subtraction cerebral angiography, during which a catheter is placed in the carotid arteries and contrast medium is introduced. The resulting image is "subtracted" from the pre-contrast image to visualise the cerebral vasculature. Non-invasive methods of angiography—such as computed tomography angiography and magnetic resonance angiography—are approaching similar sensitivity to conventional digital subtraction cerebral angiography.¹ Regardless of the modality chosen, it is crucial that imaging is performed early (generally within 24 hours of admission) so that subsequent management can be planned. In this patient, digital subtraction cerebral angiography demonstrated a filling defect throughout the left transverse and sigmoid sinuses, suggestive of venous sinus thrombosis. This case shows the importance of reviewing carefully the venous phase of a digital subtraction cerebral angiogram when no aneurysm or arteriovenous malformations are identified.

View larger version (80K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 4 Digital subtraction angiography (venous phase) demonstrating filling defect in the left transverse and sigmoid sinuses (arrow in top image) and the associated anatomy (bottom image)

 
Venous sinus thrombosis is an uncommon condition that can affect men and women of any age. Diagnosis is often delayed as the symptoms of headache, seizure, and focal neurological deficits mimic other conditions. The key to diagnosis of venous sinus thrombosis, therefore, is clinical suspicion in patients with these symptoms and appropriate imaging. In hindsight, our patient’s presentation with a generalised tonic clonic seizure and dysphasia preceded by recent otitis media (characterised by ear pain and nausea) was entirely consistent with a diagnosis of venous sinus thrombosis. The patient’s non-enhanced computed tomogram showed blood localised at the cerebral convexity but sparing the basal cisterns, suggesting a non-aneurysmal cause of subarachnoid haemorrhage. Other features of venous sinus thrombosis that can be seen with non-enhanced computed tomography are parenchymal venous infarcts with haemorrhagic transformation and, occasionally, direct features of venous sinus thrombosis such as the "triangle sign" (a solid white triangle at the location of the superior sagittal sinus), which represents fresh thrombus in the superior sagittal sinus.⁷ Computed tomography venography, which can be combined with a computed tomography angiography during the investigation of subarachnoid haemorrhage, can be useful in identifying venous pathology such as the "empty delta sign" (an empty white triangle at the location of the superior sagittal sinus), which represents enhancement of collateral veins in the superior sagittal sinus wall surrounding a non-enhancing thrombus. Magnetic resonance venography, however, is usually the investigation of choice in patients with suspected venous sinus thrombosis as this technique may exclude significant alternative diagnoses and demonstrate cerebral venous infarction complicating venous occlusion.⁸

4 Treatment for venous sinus thrombosis
The immediate management of a patient with venous sinus thrombosis consists of general measures to stabilise their airway, breathing, and circulation; to minimise further injury; and to prevent secondary complications. There is a consensus, based on two randomised controlled trials,^{9 10} that venous sinus thrombosis itself should be treated with anticoagulation, even in the presence of haemorrhage (National Institute for Health and Clinical Excellence and European Federation of Neurological Societies guidelines^{11 12}). The duration of treatment is usually six months, although patients with recurrent venous thrombosis (including deep vein thrombosis and pulmonary embolism) should be treated for their entire lives.¹² Local thrombolysis can be offered to the small proportion of patients who deteriorate despite adequate anticoagulation in the acute setting.

Around 40% of patients with venous sinus thrombosis will present with seizures. These individuals should be treated with antiepileptic drugs, particularly if they also have venous infarction.¹³

Raised intracranial pressure can cause papilloedema, which, if threatening vision, can be treated with lumbar puncture or cerebrospinal fluid diversion procedures such as shunting. Life threatening raised intracranial pressure may require decompressive craniectomy, but this situation is rare.¹⁴

Identification and management of any precipitating causes of venous sinus thrombosis should not be forgotten. Multiple risk factors exist, including genetic and acquired prothrombotic states (such as pregnancy and the post-partum period), infections (such as otitis media), inflammatory diseases, haematological conditions, drugs (such as oral contraceptives), and mechanical trauma.

The prognosis of venous sinus thrombosis is generally favourable, with a 30 day case fatality of only 3.4%.¹⁵ One study showed a higher mortality at six months (16%), yet 77% of patients regained independence and only 7% required help.¹⁶ Our patient responded well to anticoagulation and now has only a subtle expressive dysphasia.

Cite this as: BMJ 2009;339:b3204