Hydrocephalus from congenital abnormalities or due to an intracranial mass is typically characterized by a slowly evolving syndrome of increased ICP extending over weeks or months. CSF is continuously produced by the choroid plexus within the lateral, third, and fourth ventricles. CSF flows from the lateral ventricles through the intraventricular foramen of Monro to the third ventricle, then passes through the cerebral aqueduct to the fourth ventricle. CSF exits the fourth ventricle from the foramen of Magendie and foramina of Luschka. Sub-arachnoid flow occurs superiorly to the cisterns of the brain and inferiorly to the spinal subarachnoid space. Absorption of CSF is accomplished predominantly by the arachnoid villi into the large dural sinuses. Hydrocephalus is due to the obstruction of CSF flow anywhere along its course (see Table 1846). Obstructive hydrocephalus is caused by a block before the CSF flows to the subarachnoid space, usually within the fourth ventricle or at the level of the aqueduct. Impairment of CSF flow within the subarachnoid space or impairment of
Hydrocephalus Infarction with edema Hemorrhage Tumor Abscess Cyst Inflammatory mass Arterial ischemic stroke Intracranial venous sinus thrombosis
Hyponatremia Diabetic ketoacidosis Dialysis dysequilibrium syndrome Reye syndrome Fulminant hepatic encephalopathy Pulmonary insufficiency with hypercarbia Lead intoxication
Idiopathic intracranial hypertension (pseudotumor cerebri) Drugs Withdrawal of long-term steroid administration Endocrinologic disturbance Obesity
Obstruction of CSF Intraventricular foramina (Monro) pathways obstruction Parasellar mass (craniopharyngioma, germinoma, pituitary tumor) Intraventricular tumor (ependymoma) Tuberous sclerosis with subependymal giant cell astrocytoma Aqueduct of Sylvius (cerebral aqueduct) obstruction Aqueductal stenosis Midbrain or pineal region tumor Postinfectious or postinflammatory Posthemorrhagic Impaired flow from the fourth ventricle foramina of Luschka and Magendie Basilar impression Platybasia Dandy-Walker malformation Arnold-Chiari malformation Bone lesions of the cranial base (achondroplasia, rickets)
Overproduction of Choroid plexus papilloma CSF
Defective Hypoplasia of the arachnoid villi reabsorption of CSF Postinfectious or posthemorrhagic (extraventricular destruction of arachnoid villi or obstruction or subarachnoid fibrosis communicating Extensive cerebral sinovenous thrombosis hydrocephalus)
CSF, Cerebrospinal fluid.
absorption is known by the misnomer communicating hydrocephalus, where there is actually extraventricular obstruction of CSF flow (external hydrocephalus). Hydrocephalus caused by overproduction of CSF without true obstruction is seen in choroid plexus papillomas, which account for 2% to 4% of childhood intracranial tumors.
Bacterial meningitis may produce increased ICP by blockage of CSF pathways, toxic cerebral edema, increase in cerebral blood flow, or multifocal cerebral infarctions (Chapter 100). Most children with bacterial meningitis can undergo LP safely because the brain swelling is diffuse and distributed evenly throughout the brain and spinal CSF compartments. A few patients with meningitis, however, develop transtentorial herniation within a few hours of LP. Focal neurologic signs, poorly reactive pupils, and a tense fontanelle are contraindications to LP in a patient with suspected bacterial meningitis.