“…Such lesions may also arise secondarily from the effects of hypoxic brain injury, posttraum atic edema, posttraum atic vasospasm, or, most dramatically, trans tentorial herniation [24], It has generally been observed that primary brainstem lesions, in the absence o f signifi cant complicating factors such as tentorial herniation, consist o f small hemorrhages most commonly dis tributed from the caudal mesencephalon to the mid pons. Lesions tend to occur laterally in the basis pontis and lateral mesencephalic sulcus, as well as periventricularly from the colliculi to the pontine tegmentum [2,22,30,31,36]. There is microscopic evidence to suggest that lateral hemorrhages arise from small arterial and possibly capillary tears, whereas the periventricular lesions may be a result of venous disruption [26].…”