The Additional Value of PET in the Assessment of Cerebral Small Vessel Disease.

The diagnosis of cerebral small vessel disease (SVD) is difficult because there is no consensus on clinical criteria, and therefore imaging is important for diagnosis. Most patients undergo brain imaging by CT, which is able to detect ischemic strokes, hemorrhages, and brain atrophy and may also indicate white matter changes. MRI remains the key neuroimaging modality and is preferred to CT in vascular cognitive impairment (VCI) because it has higher sensitivity and specificity for detecting pathologic changes. These modalities for imaging morphology permit detection of vascular lesions traditionally attributed to VCI in subcortical areas of the brain, single infarction or lacunes in strategic areas (thalamus or angular gyrus), or large cortical-subcortical lesions reaching a critical threshold of tissue loss. In SVD, multiple punctuate or confluent lesions can be seen in the white matter by MRI and were called leukoaraiosis. Another major neuroimaging finding of SVD in VCI are microhemorrhages. However, whereas CT and MRI are able to detect morphologic lesions, these modalities cannot determine functional consequences of the underlying pathologic changes. PET can support the clinical diagnosis by visualizing cerebral functions in typically affected brain regions. In SVD, 18F-FDG PET can clearly differentiate scattered areas of focal cortical and subcortical hypometabolism that differ from the typical metabolic pattern seen in Alzheimer dementia (AD) with marked hypometabolism affecting the association areas. Additional PET tracers can further support the diagnosis of a type of dementia and also yield information on the underlying pathophysiology.