Headache (Adult)

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Red Flags

• Most patients that present with headache in the primary care setting will not have a serious underlying condition but those with any of the ‘red flag’ features should probably be imaged with CT 1
• A number of the ‘red flags’ have been based on the US Headache Consortium Evidence-Based Guidelines for Neuroimaging in patients with non-acute headache 1, 2
• These features are mostly based on small retrospective studies and do not have sufficient sensitivity or specificity to rule out intracranial pathology 2, 3
• An abnormal neurological examination finding increases the likelihood of a significant abnormality on neuroimaging 4-6
• Two studies have shown a trend towards more significant abnormalities on CT with older patients 4, 7
• One study has shown an increase in the likelihood of significant pathology, most commonly a Chiari malformation, with headaches that worsen with the Valsalva maneuver 4
• CT is generally not indicated in suspected meningitis unless there are clinical signs which predict for abnormal radiological findings (e.g. age >60 years, immunocompromised, history of CNS disorder, associated new onset seizures, mental state changes or focal neurological deficits). If CT is required, blood cultures and antibiotics should not be delayed 8, 9

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Computed Tomography (CT)

• Generally considered the initial investigation of choice for headache 5
• There have been very few studies comparing CT and MRI in the investigation of headache. One study showed MRI to be more sensitive in the detection of white matter lesions but in general CT is favoured because it is less expensive and more widely available 10

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Temporal Arteritis

• Imaging has a limited role in the diagnosis of temporal arteritis. It is usually diagnosed on a combination of clinical suspicion, elevated ESR and temporal artery biopsy 11
• One small study found the presence of a dark halo around the lumen of the temporal artery on ultrasound had 100% specificity for the diagnosis of temporal arteritis. 11
• However another study found it only had a specificity of 79%, although it did increase to 93% if the halo was at least 1mm thick 12

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Trigeminal Neuralgia

• The aim of imaging patients with symptoms of trigeminal neuralgia is to detect those with a structural cause for their symptoms such as a demyelinating lesion, mass lesion in the cerebellopontine angle or an ectatic vessel 13
• Precise indications for imaging in patients with typical symptoms of trigeminal neuralgia are not clear 14
• One retrospective study failed to find any features on history or examination that could reliably predict high risk patients and concluded it may be prudent to consider MRI for all patients with trigeminal neuralgia to exclude structural lesions 15
• Several studies have shown that approximately 10-15% of cases of trigeminal neuralgia are secondary to a tumour or other structural lesion 13, 15, 16

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Carotid and Vertebral Artery Dissection

• Once thought to be a rare cause of ischaemic stroke. However, dissection is a major cause of stroke in young and middle aged patients, accounting for 10-25% of cases. (18) The overall incidence is 2-2.5 per 100 000 for spontaneous carotid artery dissection, and 1-1.5 per 100 000 for vertebral artery dissection in US and French populations 17
• Spontaneous dissection of the carotid & vertebral arteries usually arise from an intimal tear. Blood enters the wall of the artery forming an intramural haematoma, which may result in stenosis of the arterial lumen resulting in an ischaemic insult to the brain or brainstem 18
• Clinical features that may suggest arterial dissection include 17, 19
  • Carotid artery dissection: Initial presenting symptom is pain. Typically pain is unilateral facial, orbital or neck (upper anterolateral). It may present gradually or acutely, and is generally a constant steady ache. After several days (median 4), patients may develop neurological symptoms such as partial Horner's syndrome (miosis, ptosis), cranial nerve palsies of the lower cranial nerves (particularly hypoglossal), pulsatile tinnitus or transient ischaemic attacks
  • Vertebral artery dissection: Pain is the initial presenting symptom. Pain is less distinct than with carotid artery dissection and can often be mistaken for musculoskeletal pain. Pain may be localised to the back of neck or occiput, unilaterally or bilaterally. Nature of pain can be steady or throbbing. After (median) 2 weeks, patients may develop neurological symptoms such as lateral medullary syndrome, unilateral pain or weakness of an arm
• Conventional angiography has long been the gold standard for diagnosing arterial dissections. However, it has some important limitations. It is an invasive test, and carries additional risks compared with non-invasive imaging. Also, it cannot demonstrate intramural haematomas 19, 20
• Non-invasive imaging (particularly MRI and CT) is commonly used to investigate headaches and partially accounts for the increased recognition and diagnosis of craniocervical arterial dissections 19
• There are a few small head-to-head studies comparing MRI/MRA to MDCT/CTA for evaluating craniocervical arterial dissections. Elijovich et al. used a retrospective series of 7 patients, and found that 7/7 dissections were diagnosed on CTA vs 5/7 for MRI/MRA. 21 Vertinsky et al. used 18 retrospective cases and found that MDCT was able to visualise more features of cervical & vertebral artery dissection and was generally preferred over MR imaging by the reviewing neuroradiologists 20
• A review of 21 studies by Provenzale et al. suggested that MRI/MRA and CTA had similar test characteristics, and concluded that there was limited evidence to suggest the superiority of one technique over the other 22

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Cerebral Venous Thrombosis (CVT)

• Has a highly variable and non specific presentation from thunderclap headache to symptoms of raised cerebral venous pressure such as headache, vomiting and papilloedema 23
• Imaging findings can be direct when the thrombus is visible within the cerebral venous system or indirect when there are ischaemic changes related to the venous outflow obstruction 23, 24
• The combination of MRI and magnetic resonance venography (MRV) is the imaging modality of choice for the investigation of suspected CVT 9, 25, 26
• CT Venography (CTV) is a viable alternative to MRV in the examination of patients with suspected dural sinus thrombosis especially in acute settings 27
• The CTV is not affected by flow-related artefacts and is considered superior to MRV in identification of cerebral veins (particularly smaller ones with slow flow) and sinuses and at least equivalent to MRI/MRV in the diagnosis of of cerebral venous sinus thrombosis (CVST) 26, 27
• CTV also has the advantage that it may be used in the uncooperative patient as acquisition times are only approximately 1 min and is useful when MRI is contraindicated 9
• MR techniques have the benefit of avoiding intravenous contrast and ionising radiation and are more sensitive than CT to cerebral parenchymal changes 9, 28 which are present in 40-70% patients with CVST 29
• On pre-contrast CT the acute thrombus may be visible as an elongated high attenuation lesion within the dural sinus or cortical vein - the cord sign or dense triangle sign 24
• On post-contrast images a filling defect may be seen as the dura enhances but the thrombus does not - the empty delta sign 24
• On MRI acute thrombus is isointense to brain on T1-weighted images and hypointense on T2-weighted images. Between 3 and 7 days after thrombus formation the clot becomes hyperintense on T-1 weighted images and is easier to recognize but this may interfere with time of flight MRV studies 23, 24
• MRI is also sensitive to the parenchyma and haemorrhagic changes of venous infarction. High signal intensity lesions on fluid-attenuated inversion-recovery sequence and T2-weighted imaging that do not correspond to an arterial territory may suggest CVT 30

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