in the cerebellum present with combinations of ataxia, vertigo, nausea, occipital headache, and resistance to neck flexion Coma is an unusual early sign of infarction of cerebral structures but becomes more common as lower anatomic centers are affected Occlusion of the basilar artery may result in upper brainstem infarction, resulting in rapid onset of coma, as does hemorrhage or infarction of the pons Posterior reversible encephalopathy syndrome (PRES, a.k.a reversible posterior leukoencephalopathy syndrome [RPLS]) causing ALOC is associated with autoimmune disease, sepsis, nephrotic syndrome, or immunosuppressive agents Cerebrospinal Fluid Shunt Problems Children with congenital or acquired hydrocephalus as a result of prematurityrelated hemorrhage, neoplasm, or trauma depend on the continued function of an intraventricular shunt to drain CSF and maintain normal ICP (see Chapter 122 Neurosurgical Emergencies ) The most common shunt type is ventriculoperitoneal (VP), draining CSF from a lateral cerebral ventricle through a small skull burr hole and valve with an attached reservoir into the peritoneum via subcutaneous tubing running through neck, chest, and abdomen CSF shunts may malfunction for many reasons, including shunt infection, tubing blockage, rupture, disconnection, or valve malfunction The risk of failure is greatest during the first months after shunt placement or revision Systemic Abnormalities The second major category of disorders causing coma listed in Table 17.2 arise in organs other than the CNS and affect the brain diffusely These abnormalities alter neuronal activity by a variety of mechanisms, including decreasing metabolic substrates required for normal function (e.g., hypoxia, hypotension, hypoglycemia, other electrolyte abnormalities), altering the rate of intracellular chemical reactions (e.g., hypothermia, hyperthermia), and introducing extraneous toxins into the CNS Children with autoimmune disease such as systemic lupus erythematosus, Behỗet disease, multiple sclerosis, and acute disseminated encephalomyelitis (ADEM, a.k.a postinfectious encephalitis) may present with ALOC due to inflammation of brain parenchyma Hypoxia Oxygen delivery to the brain may be adversely affected by disorders that compromise a patient’s airway, breathing, or circulation Neurons are the cells most sensitive to oxygen deprivation, and they will cease to function within seconds after being deprived of adequate levels of oxygen Hypoxic coma may