Hydrocephalus can be defined broadly as a disturbance of formation, flow, or absorption of cerebrospinal fluid (CSF) that leads to an increase in volume occupied by this fluid in the central nervous system (CNS). This condition also could be termed a hydrodynamic disorder of CSF. Acute hydrocephalus occurs over days, subacute over weeks, and chronic over months or years. Conditions such as cerebral atrophy and focal destructive lesions also lead to an abnormal increase of CSF in CNS. In these situations, loss of cerebral tissue leaves a vacant space that is filled passively with CSF. Such conditions are not the result of a hydrodynamic disorder and therefore are not classified as hydrocephalus. An older misnomer used to describe these conditions was hydrocephalus ex vacuo.
Normal pressure hydrocephalus (NPH) describes a condition that rarely occurs in patients younger than 60 years. Enlarged ventricles and normal CSF pressure at lumbar puncture (LP) in the absence of papilledema led to the term NPH. However, intermittent intracranial hypertension has been noted during monitoring of patients in whom NPH is suspected, usually at night. The classic Hakim triad of symptoms includes gait apraxia, incontinence, and dementia. Headache is not a typical symptom in NPH.
Benign external hydrocephalus is a self-limiting absorption deficiency of infancy and early childhood with raised intracranial pressure (ICP) and enlarged subarachnoid spaces. The ventricles usually are not enlarged significantly, and resolution within 1 year is the rule.
Communicating hydrocephalus occurs when full communication exists between the ventricles and subarachnoid space. It is caused by overproduction of CSF (rarely), defective absorption of CSF (most often), or venous drainage insufficiency (occasionally).
Noncommunicating hydrocephalus occurs when CSF flow is obstructed within the ventricular system or in its outlets to the arachnoid space, resulting in ventricular/subarachnoid space noncommunication.
Obstructive hydrocephalus results from obstruction of the flow of CSF (intraventricular or extraventricular). Most hydrocephalus is obstructive, and the term is used to contrast the hydrocephalus caused by overproduction of CSF.
Arrested hydrocephalus is defined as stabilization of known ventricular enlargement, probably secondary to compensatory mechanisms. These patients may decompensate, especially following minor head injuries.
Normal CSF production is 0.20-0.35 mL/min; a majority is produced by the choroid plexus, which is located within the ventricular system, mainly the lateral and fourth ventricles. The capacity of the lateral and third ventricles in a healthy person is 20 mL. Total volume of CSF in an adult is 120 mL.
Normal route of CSF from production to clearance is the following: From the choroid plexus, the CSF flows to the lateral ventricle, then to the interventricular foramen of Monro, the third ventricle, the cerebral aqueduct of Sylvius, the fourth ventricle, the 2 lateral foramina of Luschka and 1 medial foramen of Magendie, the subarachnoid space, the arachnoid granulations, the dural sinus, and finally into the venous drainage.
ICP rises if production of CSF exceeds absorption. This occurs if CSF is overproduced, resistance to CSF flow is increased, or venous sinus pressure is increased. CSF production falls as ICP rises. Compensation may occur through transventricular absorption of CSF and also by absorption along nerve root sleeves. Temporal and frontal horns dilate first, often asymmetrically. This may result in elevation of the corpus callosum, stretching or perforation of the septum pellucidum, thinning of the cerebral mantle, or enlargement of the third ventricle downward into the pituitary fossa (which may cause pituitary dysfunction).
The mechanism of NPH has not been elucidated completely. Current theories include increased resistance to flow of CSF within the ventricular system or subarachnoid villi; intermittently elevated CSF pressure, usually at night; and ventricular enlargement caused by an initial rise in CSF pressure; the enlargement is maintained despite normal pressure because of the Laplace law. Although pressure is normal, the enlarged ventricular area reflects increased force on the ventricular wall.
Incidence of congenital hydrocephalus is 3 per 1,000 live births, while the incidence of acquired hydrocephalus is not known exactly.
Incidence of acquired hydrocephalus is unknown. About 100,000 shunts are implanted each year in the developed countries, but little information is available for other countries.
In untreated hydrocephalus, death may occur by tonsillar herniation secondary to raised ICP with compression of the brain stem and subsequent respiratory arrest.
Shunt dependence occurs in 75% of all cases of treated hydrocephalus and in 50% of children with communicating hydrocephalus.
Patients are hospitalized for scheduled shunt revisions or for treatment of shunt complications or shunt failure.
Poor development of cognitive function in infants and children, or loss of cognitive function in adults, can complicate untreated hydrocephalus. It may persist after treatment.
Visual loss can complicate untreated hydrocephalus and may persist after treatment.
Generally, incidence is equal in males and females. The exception is Bickers-Adams syndrome, an X-linked hydrocephalus transmitted by females and manifested in males. NPH has a slight male preponderance.
Incidence of human hydrocephalus presents a bimodal age curve. One peak occurs in infancy and is related to the various forms of congenital malformations. Another peak occurs in adulthood, mostly resulting from NPH. Adult hydrocephalus represents approximately 40% of total cases of hydrocephalus.
Clinical features of hydrocephalus are influenced by the following:
Location of obstruction
Rapidity of onset
Symptoms in infants
Symptoms in children
Slowing of mental capacity
Headaches (initially in the morning) that are more significant than in infants because of skull rigidity
Neck pain suggesting tonsillar herniation
Vomiting, more significant in the morning
Blurred vision – Consequence of papilledema and later of optic atrophy
Double vision – Related to unilateral or bilateral sixth nerve palsy
Stunted growth and sexual maturation from third ventricle dilatation: This can lead to obesity and to precocious or delayed onset of puberty.
Difficulty in walking secondary to spasticity: This affects the lower limbs preferentially because the periventricular pyramidal tract is stretched by the hydrocephalus.
Symptoms in adults
Cognitive deterioration: It can be confused with other types of dementia in the elderly.
Headaches: These are more prominent in the morning because CSF is resorbed less efficiently in the recumbent position. This can be relieved by sitting up. As the condition progresses, headaches become severe and continuous.
Neck pain: If present, neck pain may indicate protrusion of cerebellar tonsils into the foramen magnum.
Nausea that is not exacerbated by head movements
Vomiting: Sometimes explosive, vomiting is more significant in the morning.
Blurred vision (and episodes of “graying out”): These may suggest serious optic nerve compromise, which should be treated as an emergency.
Double vision from sixth nerve palsy
Difficulty in walking
Incontinence: This indicates significant destruction of frontal lobes and advanced disease.
Symptoms of NPH
Gait disturbance is usually the first symptom and may precede other symptoms by months or years.
Dementia presents as an impairment of recent memory or as a “slowing of thinking.” Spontaneity and initiative are decreased. The degree can vary from patient to patient.
Urinary incontinence presents as a lack of or diminished awareness of the need to urinate. Some patients may have urgency.
Other symptoms that can occur include aggressive behavior, Parkinsonlike symptoms, and seizures.
Head enlargement: Head circumference is in the 98th percentile for the age or greater.
Dysjunction of sutures: This can be seen or palpated.
Dilated scalp veins: The scalp is thin and shiny with easily visible veins.
Tense fontanelle: The anterior fontanelle in infants who are held erect and are not crying may be excessively tense.
Setting-sun sign: In infants it is characteristic of increased ICP. Both ocular globes are deviated downward, the upper lids are retracted, and the white sclerae may be visible above the iris.
Increased limb tone: Spasticity preferentially affects the lower limbs. The cause is stretching of the periventricular pyramidal tract fibers by hydrocephalus.
Papilledema: if the raised ICP is not treated, this can lead to optic atrophy and vision loss.
Failure of upward gaze: This is due to pressure on the tectal plate through the suprapineal recess.
Macewen sign: A “cracked pot” sound is noted on percussion of the head.
Unsteady gait: This is related to spasticity in the lower extremities.
Large head: Sutures are closed, but chronic increased ICP will lead to progressive abnormal head growth.
Unilateral or bilateral sixth nerve palsy is secondary to increased ICP.
Papilledema: If raised ICP is not treated, it will lead to optic atrophy.
Failure of upward gaze and of accommodation indicates pressure on the tectal plate.
Unsteady gait is related to truncal and limb ataxia. Spasticity in legs also causes gait difficulty.
Large head: The head may have been large since childhood.
Unilateral or bilateral sixth nerve palsy is secondary to increased ICP.
Muscle strength is usually normal. No sensory loss is noted.
Reflexes may be increased, and Babinski response may be found in 1 or both feet.
Difficulty in walking varies from mild imbalance to inability to walk or to stand. Gait is characterized by short steps, inability to raise legs, and almost continuous activity in antigravity muscles. The patient cannot perform tandem walking and sways during Romberg test with eyes open or closed.
Sucking and grasping reflexes appear in late stages.
Congenital causes in infants and children
Stenoses of the aqueduct of Sylvius due to malformation: This is responsible for 10% of all cases of hydrocephalus in newborns.
Dandy-Walker malformation: This affects 2-4% of newborns with hydrocephalus.
Arnold-Chiari malformation type 1 and type 2
Agenesis of the foramen of Monro
Bickers-Adams syndrome: This is an X-linked hydrocephalus accounting for 7% of cases in males. It is characterized by stenosis of the aqueduct of Sylvius, severe mental retardation, and in 50% by an adduction-flexion deformity of the thumb.
Acquired causes in infants and children
Mass lesions account for 20% of all cases of hydrocephalus in children. These are usually tumors (eg, medulloblastoma, astrocytoma), but cysts, abscesses, or hematoma also can be the cause.
Intraventricular hemorrhage can be related to prematurity, head injury, or rupture of a vascular malformation.
Infections: Meningitis (especially bacterial) and, in some geographic areas, cysticercosis can cause hydrocephalus.
Increased venous sinus pressure: This can be related to achondroplasia, some craniostenoses, or venous thrombosis.
Iatrogenic: Hypervitaminosis A, by increasing secretion of CSF or by increasing permeability of the blood-brain barrier, can lead to hydrocephalus.
Causes of hydrocephalus in adults
Subarachnoid hemorrhage (SAH) causes one third of these cases by blocking the arachnoid villi. However, communication between ventricles and subarachnoid space is preserved. This hydrocephalus is obstructive and communicating.
Idiopathic hydrocephalus represents one third of cases of adult hydrocephalus.
Head injury, through the same mechanism as SAH, can result in hydrocephalus.
Tumors can cause blockage anywhere along the CSF pathways. The most frequent tumors associated with hydrocephalus are ependymoma, subependymal giant cell astrocytoma, choroid plexus papilloma, craniopharyngioma, pituitary adenoma, hypothalamic or optic nerve glioma, hamartoma, and metastatic tumors.
Prior posterior fossa surgery may cause hydrocephalus by blocking normal pathways of CSF flow.
Congenital aqueductal stenosis causes hydrocephalus but may not be symptomatic until adulthood.
Meningitis, especially bacterial, may cause hydrocephalus in adults.
All causes of hydrocephalus described in infants and children are present in adults who have had congenital or childhood-acquired hydrocephalus.
Causes of NPH
Posterior fossa surgery
Idiopathic, probably related to a deficiency of arachnoid granulations