Magnetic resonance imaging of occult vascular malformations of the brain stem.

A characteristic appearance of occult cerebrovascular malformations (OCVMs) on high-field spin-echo magnetic resonance imaging (MRI) has been described previously. The authors report a series of 21 of these lesions located in the brain stem and examine the clinical and MRI characteristics. Most of these lesions display a prolonged, fluctuating clinical course, which suggests multiple sclerosis or brain-stem glioma. Although the possibility of hemorrhagic neoplasms mimicking the MRI appearance of OCVMs has been emphasized recently, distinguishing between these two groups of lesions should be possible in most cases. MRI should allow the diagnosis to be made with sufficient certainty to avoid unnecessary intervention for OCVMs in this delicate location.