the foramen magnum some are congenital and some are acquired B There are four

the foramen magnum; some are congenital, and some are acquired. B. There are four types, although types 1 and 2 most common C. Cerebellar tonsillar herniation is the most common type D. Surgery is usually the treatment of choice HYDROCEPHALUS I. Definition A. Hydrocephalus is a condition in which an excessive amount of CSF accumulates within the cerebral ventricles. 1. The human brain makes approximately 500 ml of CSF per day, most of which is generated by the choroid plexus within the ventricular system. a. CSF circulates around the brain and spinal cord and is reabsorbed in the venous system. B. Hydrocephalus is a common neurosurgical problem that leads to changes in cerebral blood flow caused by displacement, deformation, stretching, or decrease in the caliber of cerebral vessels. 1. Change in the vessels causes a change in vascular resistance and cerebral perfusion pressure, which is important for cerebral microcirculation. C. Normal pressure hydrocephalus is an unusual cause of dementia. 1. Although the cause is often idiopathic, it may occur as a late complication of intracerebral infection, Alzheimer’s disease, or SAH. CSF opening pressure is usually 5-18 mmHg (70-245 mm H20). 2. The syndrome develops subacutely for a few weeks; in some patients, no predisposing reason is identified. II. Etiology A. Oversecretion/overproduction of CSF B. Obstruction of CSF (lesions or tumors) C. Impaired absorption D. Normal pressure hydrocephalus may follow head injury, SAH, or meningoencephalitis. III. Classification A. Communicating 1. Ventricles are patent; obstruction occurs beyond the fourth ventricle. 2. Caused by impaired absorption or overproduction

3. Usually occurs 4-20 days after aneurysmal rupture, although it may occur at any time B. Noncommunicating 1. Obstruction occurs within or next to the ventricular system, preventing CSF made in the lateral and third ventricles from circulating normally; thus, this fluid no longer communicates with the subarachnoid space. 2. It is related to lesions or tumors IV. Signs/symptoms (adults) A. Acute hydrocephalus 1. Papilledema 2. Headache 3. Nausea and vomiting 4. Gait change 5. Upgaze B. Normopressure hydrocephalus 1. Classic triad a. Dementia b. Gait disturbance c. Urinary incontinence V. Management A. Acute: external ventricular drain B. Chronic: ventricular shunt C. Endoscopic third ventriculostomy (Mixter surgery) has been used in noncommunicating hydrocephalus to enable the surgeon to control the condition without the need for ventricular shunting and without long-term complications associated with shunts. 1. The advantage of endoscopic surgery is that, when feasible, it can be performed withminimal disruption of neural tissue, thus frequently allowing patients to become mobilized rapidly, resulting in shorter hospitalizations and reduced costs.

BRAIN TUMORS (SPACE OCCUPYING LESIONS) I. Definition A. Brain tumors consist of primary neoplasms (originating in the brain) or secondary neoplasms (originating from sites other than the brain, such as the lung, the breast, the genitourinary tract, and the gastrointestinal tract) located within the intracranial vault.