Differential diagnosis of T2 hyperintense brainstem lesions: Part 1. Focal lesions.

Brainstem lesions can be classified as focal or diffuse. Magnetic resonance imaging is the most suitable imaging modality for evaluating these lesions. As a rule, focal lesions are not large and have well-defined margins. Causes include tumors, vascular malformations, demyelinating diseases, brain abscesses, hypertrophic olivary degeneration, and dilated Virchow-Robin spaces. Differential diagnoses of these numerous entities mandates a review of magnetic resonance imaging findings in conjunction with epidemiologic aspects, clinical features, and other medical test results.