A group of neurologic syndromes caused by brainstem lesions (e.g., due to ischemia, neoplasms, demyelination, or infections). Because most cranial nerves (other than CN II & IV) do not decussate while most of the body’s motor and sensory fibers cross the midline in the medulla, brainstem strokes are characterized by ipsilateral cranial nerve deficits accompanied by contralateral hemiparesis or hemisensory loss (ie, crossed signs).