Structural imaging in the dementias

European and US guidelines suggest that all patients with dementia should have brain imaging performed as part of the diagnostic work-up. Whilst computer tomography (CT) may be sufficient to exclude the majority of ‘treatable causes’ such as tumours or other mass lesions, magnetic resonance imaging (MRI) allows for a much more detailed assessment of brain structure and white-matter integrity, may be performed serially to assess change over time, and avoids ionizing radiation. MRI is increasingly being used to help distinguish both the various dementias from one another, and early dementia (mild cognitive impairment) from normal ageing; such distinctions will become increasingly important as specific disease-modifying agents become available. Pattern of atrophy, best seen on T1-weighted volumetric sequences, may help to differentiate the neurodegenerative dementias. Thus Alzheimer’s disease is typically associated with prominent, symmetrical and early medial temporal lobe atrophy; frontotemporal dementia with asymmetric frontal lobe atrophy and an anterior > posterior gradient; semantic dementia with (dominant) temporal lobe atrophy; and progressive non-fluent aphasia with dominant hemisphere peri-Sylvian atrophy and inferior frontal/anterior temporal lobe atrophy. T2-weighted or FLAIR MR sequences are useful for assessing vascular disease, and may aid diagnosis in a range of rarer forms of dementia, such as those associated with prion disease, infection or inflammation. A potentially exciting development has been that of novel amyloid-binding PET ligands, which may prove to be useful in the early diagnosis of Alzheimer’s disease.