Glucose metabolism in the human cerebellum: anatomical-functional correlations

Cerebellum-specific 18F-FDG PET analysis for the detection of subregional glucose metabolism changes in spinocerebellar ataxia

The cerebellum (CB) consists of complex anatomical and functional subregions. To better investigate the complicated functional anatomy, a detailed subregional analysis and/or a precise spatial normalization of the fluorine-18 fluorodeoxyglucose (F-FDG) PET imaging data are essential. Here, the 28 MRIcron CB volumes of interests (VOIs) template merged into eight cerebellar subregional VOIs (bilateral anterior, superior, and inferior posterior lobes of the CB cortex, and the superior and inferior vermis) on mean F-FDG PET templates. We also developed a new spatial normalization method using a study-specific and CB-specific template (CBSST) to better localize the VOIs and to minimize interparticipant differences for the locations of whole and subregional CB VOIs, as well as to increase the accuracy of the subregional mean F-FDG uptake. Using VOIs of individual F-FDG PET images normalized to the F-FDG template, we analyzed subregional cerebellar glucose metabolism in patients with spinocerebellar ataxia, a representative disease involving the spinocerebellum, and compared them with age-matched and sex-matched healthy normal controls. We achieved significant improvement over the Montreal Neurological Institute template in spatial normalization accuracy using our CBSST approach for CB VOI location agreement increases (79 vs. 90%) and VOI uptake error decreases in many CB subregions. We also found significant decreases in the anterior/posterior ratio of F-FDG uptake in patients with spinocerebellar ataxia (0.45) compared with those in normal controls (0.73) only using our CBSST approach. Therefore, we established an accurate CB subregional VOI analysis framework, and this may be useful for understanding and differentiating many of the cerebellar ataxia diseases.

Language organization in patients with early and late left-hemisphere lesion: a PET study

Functional neuroimaging studies have shown enhanced right-hemisphere language activations in adults with left-hemisphere damage. We hypothesized that this effect would be stronger in patients with lesion occurring early in development. Using [15O]-water PET, we studied eight normal adults and 23 patients with unilateral left lesion during rest, listening to sentences, and sentence repetition. Thirteen patients had lesions with early onset (< 5 years) and ten had lesions with late onset (> 20 years). For listening to sentences, frontotemporal blood flow increases were significantly stronger in the left than in the right hemisphere in normal adults. This normal asymmetry was reduced in patients with late lesion and reversed in those with early lesion. For sentence repetition, analogous group differences were significant for the basal ganglia, but failed to reach significance for the (pre)motor and insular regions. We conclude that left lesion leads to alterations in the asymmetry of language activations (in and beyond the perisylvian areas). In addition, rightward shifts of language activation tend to be stronger as a consequence of early (as compared to late) lesion. Finally, postlesional reorganization appears to reflect a coexistence of 'additive' and 'subtractive' effects, i.e., activation in some regions that are not normally involved in language processing and lack of activation in other (undamaged) regions that are normally activated by language tasks.

Cerebellar reorganization following cortical injury in humans: effects of lesion size and age

OBJECTIVE

The authors investigated chronic cerebellar reorganization following unilateral cortical lesions in children and adults using PET to measure benzodiazepine receptor (BZR) binding with [11C]flumazenil (FMZ) and glucose metabolism with 2-deoxy-2[18F]fluoro-D-glucose (FDG).

BACKGROUND

Crossed cerebellar diaschisis (CCD) is defined as decreased metabolism or blood flow in the cerebellum contralateral to a cortical insult measured by functional neuroimaging, and is typically seen in adults with large frontal or parietal lesions. The authors previously reported that CCD of glucose metabolism was not as prominent in children as in adults, and that some children showed a paradoxical pattern of increased glucose utilization in cerebellar cortex contralateral to the cortical lesion. The current study investigated whether CCD is associated with alterations in the gamma-aminobutyric acid (GABA(A))/BZR complex.

METHODS

Patients with frontal lesions alone or with parietal lesions were compared with patients with temporal lesions, which are typically not associated with CCD.

RESULTS

Children with lesion onset before 1 year of age showed significantly higher glucose utilization in contralateral posterior quadrangular and superior semilunar lobules of cerebellar cortex than did adults. Two patterns of change in cerebellar BZR binding were seen in children: 1) Five of 10 children showed increased BZR binding in the dentate nucleus contralateral to the lesion, and 2) the remaining five children showed no increase in dentate nucleus BZR binding but showed increased binding in the lateral lobules of the cerebellar cortex contralateral to the lesion. Adults showed increased binding only in contralateral dentate nucleus and not in cerebellar cortex. The size and severity of the supratentorial lesion, as well as age at the time of injury, were important factors in these findings.

CONCLUSIONS

Reorganization of GABA-mediated mechanisms and glucose metabolism in cerebellum following cortical injury differs with size of lesion and age at the time of injury.

Brain organization of language after early unilateral lesion: a PET study

Neuropsychological studies suggest that good long-term language outcome is possible following extensive early left-hemisphere damage. We explored the brain organization for language in children with early unilateral lesion, using [15O]-water PET. In 12 patients with left lesion (LL) and 9 patients with right lesion (RL), cerebral blood flow changes during listening to sentences and repetition were studied. A rightward shift of language activations in the LL group was found in perisylvian areas and multiple other, mostly temporo-parietal, regions. The hypothesis of intrahemispheric reorganization in the LL group found only limited support. The number of activated regions was overall greater in the RL group. Unexpected findings included a stronger subcortical and cerebellar language involvement in the RL group. We suggest that (a) early left lesion is associated with enhanced language participation of the right hemisphere in and beyond the classical language areas, and (b) postlesional effects are in part additive (recruitment of noncanonical areas), in part subtractive (functional depression in areas normally involved in language).

Glucose metabolism in the human cerebellum: an analysis of crossed cerebellar diaschisis in children with unilateral cerebral injury

Using high-resolution positron emission tomography (PET), we have recently described the normal pattern of glucose utilization in 11 anatomical regions of the human cerebellum. In the present study, we evaluated the phenomenon of crossed cerebellar diaschisis in 40 patients (mostly children) with unilateral cerebral injury sustained at various periods of brain development. Diaschisis refers to a functional impairment at a remote site following injury to an anatomically connected area of brain and, presumably due to a loss of afferent input to the remote site. Of the 40 patients, 11 had sustained their cerebral injury prenatally, 7 in the perinatal period (+/- 24 hours of birth), and 22 postnatally (1 day to 15 years). Crossed cerebellar hypometabolism was seen in 22 patients; symmetric cerebellar metabolism was found in 16 subjects. The presence of crossed cerebellar hypometabolism was typically associated (75% of cases) with a postnatal injury, while symmetric cerebellar metabolism was seen only in patients with injury occurring prior to 4 weeks of age (13 of the 16 had prenatal or perinatal insults). A third pattern of cerebellar metabolism, consisting of paradoxical crossed cerebellar hypermetabolism, was seen in two patients; both had sustained their cerebral injury at 4 months of age. These findings suggest the presence of considerable plasticity, which is dependent on age at injury, in the cerebrocerebellar pathway of developing brain.