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crossed cerebellar diaschisis ( ccd ) is a matched depression of blood blow or metabolism in the cerebellar hemisphere contralateral to a focal supratentorial lesion . in acute brain disorders such as infarct , limitation of the excitatory output from an injured brain region
ct scan of the brain showed ischemic stroke involving the left middle cerebral artery territory .
mri of the brain showed altered signal intensity in the left parietal , temporal cortices and left basal ganglia [ figure 1 ] .
mri of the brain ( a ) showing altered signal intensity in the left parietal , temporal cortices and left basal ganglia . both cerebellar hemispheres ( b ) are normal patient was planned for stem cell transplant for stroke and underwent fdg pet / ct as part of routine evaluation .
pet / ct of the brain revealed reduced fdg uptake in the frontal , parietal and temporal cortices and basal ganglia on the left side [ figure 2 ] .
correlative ct revealed a hypo - dense lesion in the medial part of the left basifrontal lobe , in the left putamen extending superiorly to the left para - ventricular white matter and around the frontal horn of the left lateral ventricle .
additionally , right cerebellum showed reduced fdg uptake without any morphologic abnormality [ figures 3 and 4 ] .
transaxial sections at basal ganglia level ( a ) pet ( b ) ct ( c ) fused pet / ct showing fdg hypometabolism in the frontal , parietal and temporal cortices and basal ganglia on the left side region corresponding to a well defined hypodense area on ct transaxial sections at the cerebellar level ( a ) pet ( b ) ct ( c ) fused pet / ct showing diffuse fdg hypometabolism in the right cerebellar hemisphere with ct showing no morphological abnormality maximum intensity projection image showing right cerebellar hypometabolism
the term  diaschisis  defined as a reversible , functional phenomenon without any structural change was introduced by von monakow in 1914 .
the underlying mechanism of ccd is the interruption of the corticopontocerebellar tract by the infarct causing deafferentation and transneural metabolic depression of the contra - lateral cerebellar hemisphere .
baron in 1980 using pet imaging demonstrated matched reduction in cerebral blood flow and oxygen extraction fraction in the contralateral cerebellum in patients with supratentorial ischemic stroke .
the finding has been subsequently seen with spect perfusion imaging in many settings including : internal capsule / basal ganglion infract , brain tumor , spinocerebellar degeneration , alzheimer 's disease , wada test in epilepsy , and progressive supranuclear palsy .
cerebral gliomas cause a reduction of glucose metabolism in the cerebellum contralateral to the tumor side ccd .
ccd was reportedly higher in malignant than in low - grade gliomas and increasing tumor size increased ccd values .
although acute - stage ccd has no prognostic value independent of acute - stage hypoperfusion volume , it might indicate the proportion of nutritional to non - nutritional perfusion at the infarct site , and hence , be useful in the evaluation of reperfusion therapies in the acute stage .
spect has been used to evaluate ccd in acute ( 530 hours ) , early sub - acute ( 5 - 15 days ) , and chronic ( 1356 days ) stages .
several series of stroke have reported frequency of ccd after infarct greater than 60%.[810 ] ccd has been demonstrated on f18-fdg - pet up to 20 years after a cerebro - vascular accident indicating the irreversibility of the lesion once the acute phase is over .
it is of particular significance to the nuclear medicine physician as it is most often clinically and anatomically occult yet may frequently seen with cerebral perfusion studies . in summary , we present a unique case of ccd on f-18 fdg pet / ct scan whose abnormal findings reflect decreased glucose metabolism with ct showing normal morphology .
diaschisis is the inhibition of function produced by focal disturbances in a portion of the brain at a distance from original site of injury . 
 many studies using brain spect ( single - photon emission computed tomography ) have demonstrated crossed cerebellar diaschisis ( ccd ) in patients with cerebral cortical infarct . 
 we report a case of cerebrovascular accident involving the left middle cerebral artery territory . 
 pet / ct performed one month after stroke showed hypometabolism in the left cerebral hemisphere with hypometabolism of the contralateral cerebellum . 
 the finding of diminished glucose metabolism in the contralateral cerebellum represents ccd .