Other Headache Types That Require Imaging
There are a host of relatively rare conditions that can present with headache, of which two will be discussed by the authors. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a hereditary angiopathy that is an important cause of stroke in young patients. Migraine with aura (MA) occurs in 20–40% of these patients, and when present is usually the first symptom. In practice, a suggestive family history associated with MA, or transient ischemic attack and/or stroke in a young patient, should prompt consideration of this condition. Imaging is an essential component of the diagnostic work-up, and may demonstrate multiple ischemic strokes incongruous to the patients age and cardiovascular risk profile. Anterior temporal lobe involvement is particularly characteristic of this condition.
The syndrome of mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) is an inherited multisystem disorder caused by mutations in mitochondrial DNA that can present with migraine-like headaches. The phenotype is quite heterogeneous, but typically manifests in childhood with recurrent bouts of vomiting and/or migraine. Those patients at the less severe end of the spectrum and without a suggestive family history or signs, such as loss of hearing, may only be diagnosed after presenting with a stroke. MRI abnormalities can be transient, tend to localize to grey matter, and do not conform to a vascular territory.
Primary headache is a common condition; migraine causes much of the morbidity in this population. The decision to order an MRI brain scan is a common dilemma facing clinicians, and should only be contemplated when there is clinical suspicion of a secondary cause of headache, usually indicated by the presence of one of the 'red flags'. Studies demonstrate that there is no appreciable difference in the frequency of pathological and incidental findings in common headache populations compared with the general community. Imaging is therefore not routinely required where a primary headache diagnosis can be made, except in special cases outlined above, such as the TACs. Clinicians must be aware of the risk of manufacturing morbidity in diagnosing a patient with incidental, nonsignificant imaging changes.