Remote regional cerebral blood flow consequences of focused infarcts of the medulla, pens and cerebellum

The aim of this study was to evaluate regional and remote diaschisis of inferior brain stem or cerebellar infarcts in 25 patients presenting with relatively limited lesions. Patients presented with medullary, pontine or cerebellar infarction. Methods: Lesions were evaluated on MRI (0.5 T). Regional cerebral blood flow (rCBF) was assessed by means of SPECT, after injection of Tc-99m-hexamethyl propyleneamine oxime (HMPAO) and, when possible, inhalation of Xe-133 in the same session. For each method, asymmetry indices (Als), comparing contralateral to ipsilateral rCBF values, were calculated in four areas of each cerebral hemisphere and in the cerebellum and later compared with values obtained in healthy subjects (P = 0.05). Results: Higher rCBF values were observed in the contralateral cerebellum in 2 of 7 patients with selective lateral medullary lesions, and cerebellar Als were significantly increased. When a cerebellar infarct was associated with a lateral medullary lesion, the cerebellar and contralateral hemispheric asymmetries were more severe. Unilateral paramedian pontine infarcts had more frequent consequences on the cerebellum (2 of 3 cases), with rCBF or tracer uptake being reduced in the ipsilateral or the contralateral lobe. Inverse cerebral hemispheric asymmetry could then be observed. Bilateral pontine lesions were difficult to evaluate. Using (TC)-T-99m-HMPAO, discrete cerebellar asymmetry was observed in 3 of 6 cases. Pure cerebellar infarcts in the posterior inferior cerebellar artery territory were always associated with a severe ipsilateral flow drop in the cerebellum, and contralateral hemispheric diaschisis was frequent (3 of 4 patients), predominating in the frontotemporal cortex and subcortical structures. This was also more obvious using Tc-99m-HMPAO than 133Xe. Variance analysis showed that hemispheric diaschisis was more severe in mixed brain stem and cerebellar infarcts than in pure cerebellar or brain stem lesions. Furthermore, cerebellar and hemispheric Al values were not correlated with measurements of clinical deficits, disability or handicap. Conclusion: Unilateral and limited inferior brain stem lesions can have ipsi- or contralateral consequences on the cerebellum and cerebral hemispheres rCBF. These remote effects are related to lesions of the main pathways joining these structures, resulting in deactivation and, in some cases, overactivation. Contrary to what has been suggested, consequences' on cerebral hemispheres are more severe in mixed cerebellar and brain stem infarcts than in pure cerebellar lesions.