Abstracts

RATIONALE: We examined crossed cerebellar diaschisis on SPECT as a possible predictor of laterality of seizure foci in pediatric patients with refractory epilepsy. Participants should be able to discuss the possible implications of crossed cerebellar diaschisis seen on SPECT in this patient population.
METHODS: As part of a pre-surgical evaluation for epilepsy surgery, 22 patients with refractory epilepsy underwent SPECT studies using 99m-Tc. These were patients in whom clinical localization by history and/or MRI and/or EEG suggested a focal onset of epilepsy. All patients had interictal SPECT performed, and eight patients had both ictal and interictal studies. Other patients who had SPECT studies performed but who did not have historical, MRI, or EEG evidence of focality were not included in this anaylsis.
Crossed cerebellar diaschisis (CCD) was characterized by ictal crossed cerebellar hyperperfusion or interictal crossed cerebellar hypoperfusion. The SPECT studies were evaluated visually for CCD, and cross-sectional histograms across the cerebellar hemispheres were used to establish asymmetry indices. Asymmetry indices of ten percent or greater were considered positive.
We evaluated whether or not CCD corresponded to the clinical localization as well as to the laterality seen on SPECT in the cortices of the patients.
RESULTS: Crossed cerebellar diaschisis was observed, with asymmetry indices of ten percent or greater, in 10 of the 22 patients (45 percent). In eight of these 10 patients (80 percent), CCD correctly corresponded to clinical and cortical SPECT lateralization of seizure foci.
Examining the interictal SPECT studies alone, nine of the 22 patients (41 precent) had CCD. Among the nine, there were seven (78 percent) in whom CCD corresponded to clinical localization and therefore correctly predicted laterality.
Ictal SPECT was performed in seven of the above 22 patients. Only two (29 percent) had CCD. In one case, the ictal crossed cerebellar hyperperfusion corresponded to interictal crossed cerebellar hypoperfusion. However, in the other case the ictal CCD was contralateral to the interictal CCD. Of the five patients with ictal SPECTs negative for CCD, three also had interictal SPECTs negative for CCD, one had interictal SPECT positive for CCD that corresponded to clinical localization, and one had interictal SPECT positive for CCD that did not correspond to clinical localization.
The patients included had temporal and extra-temporal foci in the left and right hemispheres by MRI and EEG. The predictability of CCD did not correlate with either hemisphere or any particular location in the cortex.
CONCLUSIONS: Crossed cerebellar diaschisis on interictal and ictal SPECT may be used in conjunction with clinical data to predict lateralization of seizure foci in patients with refractory epilepsy. When present, CCD on interictal SPECT was more closely associated with clinical localization and cortical SPECT abnormalities and may be more predictive as well as easier to obtain than ictal studies.
Our study suggests that the cerebellum and its connections may have a role in the pathophysiology of epilepsy that is yet to be elucidated.