Crossed cerebellar diaschisis
Crossed cerebellar diaschisis (CCD) refers to a depression of blood flow and metabolism affecting a cerebellar hemisphere occurring as a result of a contralateral focal supratentorial lesion, classically an infarct.
Other than neurological deficits and other clinical features associated with the contralateral supratentorial lesion, this condition is generally asymptomatic 1.
Diaschisis in the brain, by definition, refers to an acute inhibition of function and metabolism produced by a focal disturbance in a portion of the brain at a distance from the original site of injury but connected via white matter tracts 1. Although initially defined as caused by an acute lesion, many sources in the literature employ a more liberal definition and refer to it being related to a lesion of any temporal duration 1.
When affecting the cerebellum, it is a well-recognized phenomenon following cerebral infarction 2-4, although it can be a sequela of any significant supratentorial lesion (e.g. tumors 1, intracerebral hemorrhage 5, encephalitis 5, Dyke-Davidoff-Masson syndrome 6, radiation necrosis, etc). The most likely mechanism is thought to be interruption of cortico-ponto-cerebellar white matter tracts, which then results in deafferentation and hypometabolism of the contralateral cerebellar hemisphere 2.
By definition, nuclear medicine should be performed to formally detect hypometabolism in the contralateral cerebellar hemisphere 1, however other imaging modalities may be useful if interpreted in the correct clinical context.
CT perfusion / MRI perfusion
CT perfusion performed during an acute stroke may show a contralateral perfusion abnormality in about 20% of cases 4. In particular, CBF and CBV maps show only mild-to-moderate reduction in these parameters, which are not low enough to classify as infarctions 7. MR perfusion can also play a similar role 3,4. In chronic stages, there can be associated volume loss to the contralateral cerebellar hemisphere, known as crossed cerebellar atrophy 1,2.
FDG PET shows hypometabolism in affected cerebellar hemisphere, which is diagnostic of this condition 1.