Papilledema or paralysis of cranial nerves III or VI in a patientwith depressed consciousness is strong evidence of elevatedICP, a medical and neurosurgical emergency. Herniations occur under the falx, through the tentorial notch, or into theforamen magnum (Table 184-2). Recognition of the signsassociated with the major herniation syndromes can be lifesaving, if emergent neuroimaging and treatment are initiated.Uncal herniation implies displacement of the mesial temporal lobe over the tentorial edge, producing a unilateral third
Transtentorial Unilateral Supratentorial mass lesions, Downward displacement of supratentorial Headache (uncal) or bilateral diffuse brain swelling, brain tissue into infratentorial compartment Altered consciousness focal edema, or acute (below tentorium), compressing the cerebral Dilated ipsilateral pupil hydrocephalus peduncles, midbrain, third cranial nerve, and Cranial nerve III palsy posterior circulation Hemiparesis Decerebrate posturing Cushing triad Respiratory arrest nerve palsy (“blown pupil”) and hemiparesis (which can beipsilateral, because of compression of the contralateral cerebralpeduncle, or contralateral if the uncus compresses the ipsilateral peduncle). Transtentorial (or central) herniation occurs with gradual downward pressure from the diencephalonthrough the tentorium, resulting in compression of the brain-stem (first midbrain, then progressing to pons and medulla). Aprogressive loss of consciousness accompanied by a characteristic progression of motor, oculomotor, pupillary, and respiratory signs indicates incipient transtentorial herniation.
Evaluation is guided by the history and physical examination(see Table 184-1). Computed tomography (CT) remains thepreferred imaging technique in emergency situations because itcan be performed rapidly and accurately identifies acute hemorrhages, large space-occupying lesions, edema, and shifts ofthe midline. The initial head CT scan is done without contrast to identify blood and calcifications. Contrast can be administered to identify inflammatory and neoplastic lesions, but is notusually required for identification of major lesions. Several metabolic derangements (hepatic encephalopathy, Reye syndrome,hyponatremia, lead encephalopathy, diabetic ketoacidosis, andhypoxic-ischemic injury) may give rise to severe elevations of ICPwithout producing obvious CT abnormalities. Lumbar puncture (LP) in a patient with elevated ICP can result in transtentorial herniation, so imaging should be performed before LP ifelevated ICP is suspected, especially if there are any focal neurological deficits on exam. If trauma or immersion injuries aresuspected, neck manipulation should be avoided until cervicalspine imaging excludes vertebral fracture or subluxation.
Examination of the cerebrospinal fluid (CSF) may establishthe cause of the alteration of consciousness. Appropriate neuroimaging should be performed to ensure that no added injury islikely to be inflicted with LP. The presence of red blood cells inthe CSF may suggest primary subarachnoid hemorrhage, parenchymal hemorrhage, or hemorrhagic infection (herpes simplexvirus), or it may be due to a traumatic procedure. White bloodcells in the CSF usually denote infectious meningitis or meningoencephalitis but may also be associated with vasculitis or parainfectious syndrome. Elevated CSF protein is seen in patientswith meningeal inflammation or tumors, and abnormal CSFglucose levels are also markers of infection and inflammation.