Pure midbrain infarction - Clinical, radiologic, and pathophysiologic findings

Objective: To describe the clinical features, MRI findings, and the pathogenesis of the pure midbrain infarction. Methods: Forty patients with infarcts limited to the midbrain were studied. MRI and angiography (mostly MR angiography) were performed in all patients. Results: Clinical manifestations included gait ataxia in 27 (68%) patients, dysarthria in 22 (55%), limb ataxia in 20 (50%), sensory symptoms in 17 (43%), third nerve palsy in 14 (35%), definitive limb weakness (<= IV/V) in nine (23%), and internuclear ophthalmoplegia in five (13%). According to MRI findings, the lesions were categorized into four groups. The anteromedial group (n = 18) was characterized by oculomotor disturbances (89%), ataxia (89%, bilateral in 17%), and sensory changes (39%) usually restricted to the perioral and hand areas. Lesions restricted to the subcortical area (n = 10) were usually related to small vessel disease (SVD) (78%), whereas those involving the medial surface (n = 8) were caused by large vessel disease (LVD) (78%). The anterolateral group (n = 11) was characterized by ataxia (70%) and definitive hemiparesis (30%) usually caused by LVD (82%). The combined group (n = 6) had frequent oculomotor disturbances (83%), definitive hemiparesis (67%), and ataxia (50%) and was usually associated with LVD (67%). The lateral group (n = 2) was characterized by prominent sensory symptoms. The prognosis was generally good except for one patient with a bilateral lesion. Conclusion: Clinical-radiologic correlation study yields four distinct subgroups: anteromedial, anterolateral, combined, and lateral. Large vessel disease and small vessel disease are usual pathogenic mechanisms, whereas cardiogenic embolism is rare.