RED FLAGS 

Most patients do not have serious secondary headache. Red flags indicate the need for urgent assessment to exclude a secondary cause. The most consistent indicators for serious secondary causes for headache are: 

1. Thunderclap (sudden onset) headache (consider SAH and its differential) 
2. New focal neurological deficit on examination (e.g. hemiparesis) 
3. Systemic features (considering GCA, infection such as meningitis or encephalitis, etc) 
4. New progressive headache in a patient over 50 (most headaches presenting in patients over 50 are benign, but there is an increased risk of secondary pathology with increasing age) 

Headache suggesting the possibility of a brain tumour 

1. New headache plus sub-acute progressive focal neurology 
2. New headache plus seizures 
3. New headache with personality or cognitive change not suggestive of dementia, with no psychiatric history and confirmed by witness 

Features that may indicate a secondary cause but may also be seen in primary headaches: 

1. Changes in headache intensity with changes of posture (upright consider low pressure / headache when lying flat consider high pressure) 
2. Worsening/Triggering headache with Valsalva (e.g. coughing, straining) 
3. Atypical aura (duration >1 hour or including motor weakness) 
4. Progressive headache (worsening over weeks or longer) 
5. Head trauma within the last month 
6. Previous history of cancer or HIV 
7. Re-attendance to A&E or GP surgery with progressively worsening headache severity or frequency 

Consider a secondary cause if any of these are present 

Features that do not help to differentiate primary from secondary headaches are: 

1. Severity  
2. Treatment response  

Features that are supportive of a diagnosis of primary headache: 

1. Recurrent episodic headache, particularly with features of migraine 
2. Long history of daily headache 

If there are no concerning features then it is appropriate to manage these patients for migraine. Other features that are pointers to migraine include a previous migraine history and a family history of migraine. 

GP open access CT scan for Headache (where available) should be available for: 

• Adult patients above the age of 16 years 
• No red flags  
• Normal neurological examination 

Patients should not be routinely imaged for migraine 

Patients with red flags should be referred as emergency / urgently to secondary care for appropriate assessment / investigation 

Patients with amber flags should be considered for urgent referral to secondary care for investigations, unless the primary care physician decides that a GP open access CT is more appropriate 

If there is diagnostic uncertainty or concern about a secondary cause, at this point consider open access CT as an alternative to secondary referral. For some patients, CT may not be the most appropriate investigation e.g. ESR/CRP/Plasma viscosity in GCA and LP (after appropriate imaging) in Idiopathic Intracranial Hypertension. 

There must be a clear local pathway for management of patients who have an abnormality detected on their GP open access CT scan.  

The overall prevalence of incidental brain findings in 2000 asymptomatic volunteers aged 46-97 using high resolution MRI was more than 10%. Asymptomatic brain infarcts were present in 7.2% and brain aneurysms in 1.8%. Benign tumours (mostly meningiomas) were present in 1.6%, arachnoid cysts in 1.1% and Chiari malformations in 0.9% 

A further metaanalysis subdivided incidental findings on MRI scans in 19559 participants into  

Potentially symptomatic or treatable abnormalities 

• Neoplasms 
• Cysts 
• Structural vascular abnormalities 
• Inflammatory lesions 
• Others – chiari malformations, neoplasms 

Markers of cerebrovascular disease 

• White matter abnormalities 
• Silent brain infarcts 
• Brain microbleeds 

The meta-analysis reported an incidental abnormality pickup rate of 1.7% using low resolution MRI and 4.3% using high resolution MRI. The age range of patients was 3-97 which perhaps explained the lower pick up rate. They also reported an age related increase in white matter hyperintensities and brain infarcts and also in all neoplastic incidental brain findings. 

CT 

In a study of 1111 patients with headache who were scanned, 10.8% scans were abnormal, the majority in patients above the age of 40. This included 4% with a brain infarct and 1.6% with a primary neoplasm 

In a study looking at direct access CT brain scan for patients with a chronic headache, abnormal findings were reported in 10.5% 

MRI 

The HUNT study reported that patients with any headache disorder did not have a higher incidence of any intracranial abnormality as compared to the non-headache population except for non-specific white matter changes.