Snapshot A 67-year-old man is brought to the emergency department by his son due to abnormal behavior. The son reports that the patient appeared to be confused and had left-sided weakness. Approximately 5 days prior to presentation the patient fell and hit his head; however, he decided to not seek medical care. On physical examination, the left pupil is unresponsive to light and there is 2/5 left-sided weakness. A computerized tomography (CT) scan of the head is shown. (Uncal herniation with Kernohan's phenomenom) Introduction Clinical definition login to view 3 more bullets ETIOLOGY Pathogenesis login to view 4 more bullets Herniation Syndromes Three Clinically Important Brain Herniation SyndromesHerniation SyndromeMechanismClinical FindingsTranstentorial herniationThe medial temporal lobe (especially, theuncus) herniatesthrough thetentorial notchUncal herniation triadipsilateral unresponsive("blown")pupilhemiplegiatypically contralateral; however,if midbrain is compressed on the opposite side it can result inipsilateral hemiplegia(Kernohan's phenomenon)decreased level of consciousness secondary tocompression of the midbrain reticular formation and can progress tocomaCentral herniationThebrainstem becomes downwardly and centrally dispacedUnilateral or bilateral lacteral rectus palsyin cases ofmild central herniation that compresses theabducens nerveBilateral uncal herniation in cases ofsignificant central herniationTonsillar herniationcerebellar tonsils herniates through the foramen magnum that can result incompression of the midbrain that leads torespiratory arrestcardiovascular instabilitydeathSubfalcine herniationThe cingulate gyrus (as well as other structures) herniates under the falx cerebriAt times this can lead to anterior cerebral artery compression under the falx cerebri resulting ininfarction TREATMENT Prevention login to view 6 more bullets