About 150 ml of CSF is present in the ventricles at any time. About 700 ml of CSF is produced each day. Normal CSF pressure is about 100-180 mm of H2O (8-15 mm Hg) with the patient lying on the side, and 200-300 mm with the patient sitting up. Intracranial pressure is lower in infants and children.
Raised intracranial pressure (ICP), sometimes described as increased intracranial “tension,” can be due to brain tumors, aneurysms, hydrocephalus, intracerebral hemorrhage, meningitis, head injury, etc. The combination of headache, papilloedema, and vomiting is generally considered indicative of raised ICP.
Pressure headaches are often described as throbbing or bursting. They’re exacerbated by factors that further increase ICP, such as coughing, sneezing, recumbency, or exertion. Cushing’s reflex (bradycardia and hypertension) occurs in response to raised ICP. Classically, the headache of raised ICP is worse in the morning.
Papilledema is seen due to elevated ICP. Ophthalmoscopy shows a swollen optic disc with blurring of disc margins. Raised ICP can lead to intracranial herniation with catastrophic results. The tentorium is a dural structure that separates the cerebrum from the brainstem and cerebellum. The midbrain passes through the tentorial incisura, which is an opening in the tentorium. Lumbar puncture should be avoided in patients with raised ICP, as it may precipitate herniation of brain structures.
Uncal herniation (most common)
Subfalcine herniation
Tonsillar herniation (coning)
The term hydrocephalus is derived from the Greek words “hydro” meaning water and “cephalus” meaning head. It’s a condition in which the primary feature is excessive accumulation of CSF in the brain, causing dilation of the ventricles and often (but not always) increased intracranial pressure.
Hydrocephalus can be either primary or secondary.
In primary hydrocephalus, there is an actual increase in CSF volume along with elevated intracranial pressure. In secondary hydrocephalus, there is a compensatory increase in CSF without an increase in intracranial pressure due to cerebral atrophy. Secondary hydrocephalus is seen in Alzheimer’s disease and is called “hydrocephalus ex-vacuo.” In this setting, the brain parenchyma is thinned and the ventricles are dilated.
Types of primary hydrocephalus:
i) Obstructive or non-communicating hydrocephalus: This type is due to obstruction of CSF flow out of the ventricles. It is seen in congenital stenosis of the cerebral aqueduct of Sylvius, Arnold-Chiari malformations, etc., or it may be acquired due to tumors, hemorrhages, etc., that block CSF flow.
ii) Non-obstructive or communicating hydrocephalus: In communicating hydrocephalus, CSF can flow from the ventricles to the subarachnoid space. It occurs due to overproduction or reduced absorption of CSF, such as in choroid plexus papillomas, scarring post-meningitis, SAH, dural sinus thrombosis, etc.
In the early stages of hydrocephalus, the periventricular white matter loses myelin and axons. If pressure is not relieved, permanent atrophy occurs - initially in white matter, followed by grey matter. This can cause spastic paralysis, loss of bladder function, and dementia. In young children (before closure of the fontanelles), hydrocephalus increases head circumference. In adults, head circumference does not change.
Normal pressure hydrocephalus or NPH: NPH is an abnormal increase of cerebrospinal fluid that may result from a subarachnoid hemorrhage, head trauma, infection, tumor, or complications of surgery. Most cases are idiopathic. It presents with a wide based gait, urinary incontinence, and dementia. Patients may complain of general slowing of movements or that their feet feel “stuck.” CSF pressure is normal. Removal of CSF relieves symptoms, including dementia. Imaging shows dilated ventricles and atrophy of sulci.
Pseudotumor cerebri or benign intracranial hypertension: Pseudotumor cerebri literally means “false brain tumor.” Intracranial pressure is high due to buildup or poor absorption of CSF, but the ventricles are not dilated. The disorder is most common in women between the ages of 20 and 50.
Symptoms of pseudotumor cerebri include headache, nausea, vomiting, and pulsating sounds within the head, and they can closely mimic symptoms of large brain tumors. Obesity, hypothyroidism, and some medications (such as oral contraceptives, steroids, tetracyclines, all-trans retinoic acid, and tamoxifen) can cause pseudotumor cerebri. Repeated ophthalmologic exams are required to monitor for changes in vision. Weight loss (through dieting or weight loss surgery) and stopping predisposing drugs may lead to improvement. Therapeutic shunting is done in resistant cases. Flattening of the posterior lobe is seen on MRI.
Cerebral edema is swelling of the brain. It can be vasogenic, cytotoxic, or interstitial.
Vasogenic edema is caused by cerebral infarcts, contusions, tumors, etc., which increase the net filtration pressure across the vessel. Cytotoxic edema results from hypoxia or toxins that cause direct damage to cells. Interstitial edema occurs when excess fluid (e.g., from hydrocephalus) crosses the ependymal lining and accumulates in the periventricular white matter.
As edema develops, intracranial pressure rises. On gross examination, the brain looks swollen with flattened gyri and narrowed sulci.
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