Unilateral cortical dysplasia associated with contralateral hyperplasia of the brainstem.

Magnetic resonance imaging of a patient with unilateral frontotemporal cortical dysplasia is described. The brainstem showed ipsilateral hypoplasia, a usual but subjective radiological finding reportedly associated with unilateral cortical dysplasias, which inherently may cause underestimation of contralateral brainstem changes. In this patient contralateral hyperplasia of the brainstem was also present, evidenced especially by apparent hyperplasia of the pyramid of the medulla oblongata, where the corticospinal tract runs. Such hyperplasia of the brain stem may reflect a compensation reaction in order to increase the number of fibers in the corticospinal tract within the normal hemisphere, which are actually deficient (hypoplastic) in the contralateral, diseased hemisphere.