Crossed cerebellar diaschisis on F-18 FDG PET/CT and MRI/Functional MRI

Objectives: Crossed cerebellar diaschisis (CCD) refers to a depression of blood flow and metabolism affecting the cerebellar hemisphere occurring as a result of a contralateral focal, supratentorial lesion. The mechanism of CCD is the interruption of the corticopontocerebellar tract by the infarct causing deafferentation and transneural metabolic depression of the contralateral cerebellar hemisphere. CCD is appreciated on PET/CT imaging as reduced uptake in the contralateral cerebellum as the insult whether it is malignancy or infarct. Studies have shown the improvement in CCD to be a potential prognostic indicator but primarily in stroke patients. This study aims to evaluate CCD seen on PET/CT with the nature of the insult, corresponding findings on functional or conventional MRI, whether the findings change over time and the clinical signficance.

Methods: Our study includes 26 patients between 2001 and 2016. Of these, 11(42%) had metastatic tumor to the brain, 10 (38%) had a primary brain tumor and 5 (19%) had remote infarct in the MCA territory. All 26 patients had at least one PET/CT and one MRI including functional MRI (3 had conventional MRI alone). We identified the cases with CCD on PET/CT and correlated it to findings on MRI (regular or functional). We then followed these cases to examine if the CCD improved or remained the same and the duration based on the primary cause (tumor or infarct).

Results: Out of the 26 patients, only 2/26 (7.6%) showed improvement of CCD on followup PET/CTs over 5-18 months. One of these patients had bilateral metastasis (left frontal and right occipital) status post resection of the left frontal metastasis and ensuing improvement of the right CCD. The other patient had a unilateral supratentorial metastasis. Another 2/26 (7.6%) showed complete resolution over 3-10 months, one of them had remote stroke and the other one had metastasis. All 26 MRI cases were reviewed by a board-certified neuroradiologist focusing on blood flow, signal abnormalities and morphologic changes in the cerebellum and found no evidence of abnormalities to suggest CCD.

Conclusion: CCD is likely to be permanent while a small percentage (15%) showed improvement or even complete resolution regardless of the causative insult (tumor or infarct). While MRI is the study of choice in evaluating the brain, it was not able to detect any evidence of abnormal morphology, signal or blood flow in the cerebellum of patients who have a supratentorial insult. Given the small number of cases with improvement of CCD, the clinical significance has yet to be determined. Research Support: None