Cerebral blood flow in lateral medullary infarcts.

Objective: The aim of this study was to evaluate the diaschisis phenomenon in patients presenting with lateral medullary infarct (Wallenberg's syndrome).

Methods: We examined all patients admitted between 1991 and 1993. The localization of lesions was evaluated by MRI. Single-photon emission computed tomographic technique was used to assess cerebral blood flow by two methods (133Xe and hexamethylpropyleneamine oxime) on five slices of brain tissue. Flow values were calculated in 11 regions of interest in each cerebral hemisphere and in the cerebellum and were compared with those obtained in 20 control subjects.

Results: Three patients had selective lateral medullary infarct: Relative reduction of flow (133Xe) and of tracer uptake (HMPAO) were observed in one patient in the ipsilateral cerebellum and contralateral hemisphere; in two patients, hemispheric flow values were relatively low, without significant asymmetry. Two patients also presented with cerebellar infarct: Flow drop was severe in the ipsilateral cerebellum, and contralateral reduction in the brain hemisphere was observed in both cases.

Conclusions: Lateral medullary infarct can be associated with ipsilateral reduction of flow in the cerebellum, but this phenomenon is inconstant. Severe flow drop suggests infarction in the territory of the posterior inferior cerebellar artery. Contralateral hemispheric flow reduction can also be observed. These phenomena of cerebellar and crossed hemispheric diaschisis are probably related to lesions of tracts from the olivary and reticular nuclei.