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 inf erior brain stem or cerebellar infarcts in 25 patients presenting with rela tively limited lesions. Patients presented with medullary, pontine or cereb ellar 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, inhal ation of Xe-133 in the same session. For each method, asymmetry indices (Al s), comparing contralateral to ipsilateral rCBF values, were calculated in four areas of each cerebral hemisphere and in the cerebellum and later comp ared with values obtained in healthy subjects (P = 0.05). Results: Higher r CBF values were observed in the contralateral cerebellum in 2 of 7 patients with selective lateral medullary lesions, and cerebellar Als were signific antly increased. When a cerebellar infarct was associated with a lateral me dullary lesion, the cerebellar and contralateral hemispheric asymmetries we re more severe. Unilateral paramedian pontine infarcts had more frequent co nsequences on the cerebellum (2 of 3 cases), with rCBF or tracer uptake bei ng reduced in the ipsilateral or the contralateral lobe. Inverse cerebral h emispheric asymmetry could then be observed. Bilateral pontine lesions were difficult to evaluate. Using (TC)-T-99m-HMPAO, discrete cerebellar asymmet ry was observed in 3 of 6 cases. Pure cerebellar infarcts in the posterior inferior cerebellar artery territory were always associated with a severe i psilateral flow drop in the cerebellum, and contralateral hemispheric diasc hisis was frequent (3 of 4 patients), predominating in the frontotemporal c ortex and subcortical structures. This was also more obvious using Tc-99m-H MPAO than 133Xe. Variance analysis showed that hemispheric diaschisis was m ore severe in mixed brain stem and cerebellar infarcts than in pure cerebel lar or brain stem lesions. Furthermore, cerebellar and hemispheric Al value s were not correlated with measurements of clinical deficits, disability or handicap. Conclusion: Unilateral and limited inferior brain stem lesions c an have ipsi- or contralateral consequences on the cerebellum and cerebral hemispheres rCBF. These remote effects are related to lesions of the main p athways joining these structures, resulting in deactivation and, in some ca ses, overactivation. Contrary to what has been suggested, consequences' on cerebral hemispheres are more severe in mixed cerebellar and brain stem inf arcts than in pure cerebellar lesions.