The brainstem is a very important structure of the central nervous system. The respiratory and circulatory centers are located in the brainstem, and there are 12 pairs of cranial nerves, 10 of which are connected to the brainstem. When the brainstem is damaged, crossed paralysis occurs clinically, i.e., damage to the ipsilateral cranial nerve and damage to the contralateral pyramidal tract. For example, if the right side of the brainstem is damaged, there may be damage to the right facial nerve, causing facial palsy on the right side and central paralysis of the left limb. When this occurs, the primary cause of the damage should be clarified, which can be cerebral infarction, cerebral hemorrhage, or brain tumor. The prognosis differs with different etiologies, for example, brainstem tumors have a poor prognosis. If brainstem infarction or brainstem hemorrhage is present, the prognosis is still quite good with timely hospital consultation and comprehensive treatment.