Although there have been attempts to make clinical-MRI correlation in patients with lateral medullary infarction (LMI), studies with a large number of patients are unavailable. In this study, clinical features, MRI findings and angiogram results of 130 acute, consecutive patients with pure LMI were studied and correlated. MRI-identified lesions were classified rostro-caudally as rostral, middle and caudal, and horizontally as typical, ventral, large, lateral and dorsal. The distribution of horizontal subtypes was significantly different (P <0.001) among three rostro-caudal lesions in that rostral lesions tend to be ventral types and caudal lesions are lateral types. Patients with rostrally located lesions had dysphagia, facial paresis (P < 0.01, each) and dysarthria (P < 0.05) significantly more often, and severe gait ataxia and headache (P < 0.05, each) less often than those with caudal lesions. The frequencies of dysphagia (P < 0.01), dysarthria (P < 0.01) and bilateral trigeminal sensory pattern (P < 0.05) were significantly different among horizontal subtypes in that these symptoms were frequent in patients with "large type" as compared with those with lateral type lesions. Angiograms performed in 123 patients showed vertebral artery (VA) disease in 67% and posterior inferior cerebellar artery (PICA) disease in 10%. The presumed pathogenetic mechanisms included large vessel infarction in 50%, arterial dissection in 15%, small vessel infarction in 13% and cardiac embolism in 5%. Dissection occurred more often in patients with caudal (versus rostral) lesions (P < 0.01), whereas dorsal type infarcts (versus other types) were related more often to cardiogenic embolism and normal angiogram findings (P < 0.05, each). Patients with isolated PICA disease (versus those with VA disease) more often had cardiogenic embolism (P < 0.05) and less often had dissection (P < 0.01). It is concluded that rostro-caudal and horizontal classification of MRI helps us to understand the clinical and, partly, the aetiopathogenetic aspect of the heterogeneous LMI syndrome.

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