Hydrocephalus

From Wikipedia, the free encyclopedia

Hydrocephalus
Other names	Water on the brain
Hydrocephalus as seen on a CT scan of the brain. The black areas in the middle of the brain (the lateral ventricles) are abnormally large and filled with fluid.
Pronunciation	/ˌhaɪdroʊˈsɛfələs/
Specialty	Neurosurgery
Symptoms	Babies: rapid head growth, vomiting, sleepiness, seizures Older people: Headaches, double vision, poor balance, urinary incontinence, personality changes, mental impairment
Causes	Neural tube defects, meningitis, brain tumors, traumatic brain injury, brain bleed during birth, intraventricular hemorrhage
Diagnostic method	Based on symptoms and medical imaging
Treatment	Surgery
Prognosis	Variable, often normal life
Frequency	Varies throughout the world, from 1 per 256 live births to 1 per 9,000, depending on access to prenatal health care, prenatal tests, and abortion

Hydrocephalus is a condition in which an accumulation of cerebrospinal fluid (CSF) occurs within the brain. This typically causes increased pressure inside the skull. Older people may have headaches, double vision, poor balance, urinary incontinence, personality changes, or mental impairment. In babies, it may be seen as a rapid increase in head size. Other symptoms may include vomiting, sleepiness, seizures, and downward pointing of the eyes.

Hydrocephalus can occur due to birth defects or be acquired later in life. Associated birth defects include neural tube defects and those that result in aqueductal stenosis. Other causes include meningitis, brain tumors, traumatic brain injury, intraventricular hemorrhage, and subarachnoid hemorrhage. The four types of hydrocephalus are communicating, noncommunicating, ex vacuo, and normal pressure. Diagnosis is typically made by physical examination and medical imaging.

Hydrocephalus is typically treated by the surgical placement of a shunt system. A procedure called a third ventriculostomy is an option in some people. Complications from shunts may include overdrainage, underdrainage, mechanical failure, infection, or obstruction. This may require replacement. Outcomes are variable, but many people with shunts live normal lives. Without treatment, death or permanent disability may occur.

About one to two per 1,000 newborns have hydrocephalus. Rates in the developing world may be higher. Normal pressure hydrocephalus is estimated to affect about 5 per 100,000 people, with rates increasing with age. Description of hydrocephalus by Hippocrates dates back more than 2,000 years. The word hydrocephalus is from the Greek ὕδωρ, hydōr, meaning 'water' and κεφαλή, kephalē, meaning 'head'.

Signs and symptoms

Illustration showing different effects of hydrocephalus on the brain and cranium

The clinical presentation of hydrocephalus varies with chronicity. Acute dilatation of the ventricular system is more likely to manifest with the nonspecific signs and symptoms of increased intracranial pressure (ICP). By contrast, chronic dilatation (especially in the elderly population) may have a more insidious onset presenting, for instance, with Hakim's triad (Adams' triad).

Symptoms of increased ICP may include headaches, vomiting, nausea, papilledema, sleepiness, or coma. With increased levels of CSF, there have been cases of hearing loss due to CSF creating pressure on the auditory pathways or disrupting the communication of inner ear fluid. Elevated ICP of different etiologies have been linked to sensorineural hearing loss (SNHL). Transient SNHL has been reported after the loss of CSF with shunt surgeries. Hearing loss is a rare but well-known sequela of procedures resulting in CSF loss. Elevated ICP may result in uncal or tonsillar herniation, with resulting life-threatening brain stem compression.

Hakim's triad of gait instability, urinary incontinence, and dementia is a relatively typical manifestation of the distinct entity normal-pressure hydrocephalus. Focal neurological deficits may also occur, such as abducens nerve palsy and vertical gaze palsy (Parinaud syndrome due to compression of the quadrigeminal plate, where the neural centers coordinating the conjugated vertical eye movement are located). The symptoms depend on the cause of the blockage, the person's age, and how much brain tissue has been damaged by the swelling.

In infants with hydrocephalus, CSF builds up in the central nervous system (CNS), causing the fontanelle (soft spot) to bulge and the head to be larger than expected. Early symptoms may also include:

• Eyes that appear to gaze downward
• Irritability
• Seizures
• Separated sutures
• Sleepiness
• Vomiting

Symptoms that may occur in older children can include:

• Brief, shrill, high-pitched cry
• Changes in personality, memory, or the ability to reason or think
• Changes in facial appearance and eye spacing (craniofacial disproportion)
• Crossed eyes or uncontrolled eye movements
• Difficulty feeding
• Excessive sleepiness
• Headaches
• Irritability, poor temper control
• Loss of bladder control (urinary incontinence)
• Loss of coordination and trouble walking
• Muscle spasticity (spasm)
• Slow growth (child 0–5 years)
• Delayed milestones
• Failure to thrive
• Slow or restricted movement
• Vomiting

Because hydrocephalus can injure the brain, thought and behavior may be adversely affected. Learning disabilities, including short-term memory loss, are common among those with hydrocephalus, who tend to score better on verbal IQ than on performance IQ, which is thought to reflect the distribution of nerve damage to the brain. Hydrocephalus that is present from birth can cause long-term complications with speech and language. Children can have issues such as nonverbal learning disorder, difficulty understanding complex and abstract concepts, difficulty retrieving stored information, and spatial/perceptual disorders. Children with hydrocephalus are often known in having the difficulty in understanding the concepts within conversation and tend to use words they know or have heard. However, the severity of hydrocephalus can differ considerably between individuals, and some are of average or above-average intelligence. Someone with hydrocephalus may have coordination and visual problems, or clumsiness. They may reach puberty earlier than the average child (this is called precocious puberty). About one in four develops epilepsy.

Cause

Congenital

A one-year-old girl with hydrocephalus showing "sunset eyes", before shunt surgery

 

Hydrocephalus in 2 French women, 1888/89 and 1920. Second patient also had congenital syphilis.

Congenital hydrocephalus is present in the infant prior to birth, meaning the fetus developed hydrocephalus in utero during fetal development. The most common cause of congenital hydrocephalus is aqueductal stenosis, which occurs when the narrow passage between the third and fourth ventricles in the brain is blocked or too narrow to allow sufficient cerebral spinal fluid to drain. Fluid accumulates in the upper ventricles, causing hydrocephalus.

Other causes of congenital hydrocephalus include neural-tube defects, arachnoid cysts, Dandy–Walker syndrome, and Arnold–Chiari malformation. The cranial bones fuse by the end of the third year of life. For head enlargement to occur, hydrocephalus must occur before then. The causes are usually genetic, but can also be acquired and usually occur within the first few months of life, which include intraventricular matrix hemorrhages in premature infants, infections, type II Arnold-Chiari malformation, aqueduct atresia and stenosis, and Dandy-Walker malformation. Hydrocephalus has also been seen in cases of congenital syphilis.

In newborns and toddlers with hydrocephalus, the head circumference is enlarged rapidly and soon surpasses the 97th percentile. Since the skull bones have not yet firmly joined, bulging, firm anterior and posterior fontanelles may be present even when the person is in an upright position.

The infant exhibits fretfulness, poor feeding, and frequent vomiting. As the hydrocephalus progresses, torpor sets in, and infants show lack of interest in their surroundings. Later on, their upper eyelids become retracted and their eyes are turned downwards ("sunset eyes") (due to hydrocephalic pressure on the mesencephalic tegmentum and paralysis of upward gaze). Movements become weak and the arms may become tremulous. Papilledema is absent, but vision may be reduced. The head becomes so enlarged that they eventually may be bedridden.

About 80–90% of fetuses or newborn infants with spina bifida—often associated with meningocele or myelomeningocele—develop hydrocephalus.

Acquired

This condition is acquired as a consequence of CNS infections, meningitis, brain tumors, head trauma, toxoplasmosis, or intracranial hemorrhage (subarachnoid or intraparenchymal), and is usually painful.

Type

The cause of hydrocephalus is not known with certainty and is probably multifactorial. It may be caused by impaired CSF flow, reabsorption, or excessive CSF production.

• Obstruction to CSF flow hinders its free passage through the ventricular system and subarachnoid space (e.g., stenosis of the cerebral aqueduct or obstruction of the interventricular foramina secondary to tumors, hemorrhages, infections or congenital malformations) and can cause increases in ICP.
• Hydrocephalus can also be caused by overproduction of CSF (relative obstruction) (e.g., choroid plexus papilloma, villous hypertrophy).
• Bilateral ureteric obstruction is a rare, but reported, cause of hydrocephalus.

Hydrocephalus can be classified into communicating and noncommunicating (obstructive). Both forms can be either congenital or acquired.

Communicating

Communicating hydrocephalus, also known as nonobstructive hydrocephalus, is caused by impaired CSF reabsorption in the absence of any obstruction of CSF flow between the ventricles and subarachnoid space. This may be due to functional impairment of the arachnoidal granulations (also called arachnoid granulations or Pacchioni's granulations), which are located along the superior sagittal sinus, and is the site of CSF reabsorption back into the venous system. Various neurologic conditions may result in communicating hydrocephalus, including subarachnoid/intraventricular hemorrhage, meningitis, and congenital absence of arachnoid villi. Scarring and fibrosis of the subarachnoid space following infectious, inflammatory, or hemorrhagic events can also prevent reabsorption of CSF, causing diffuse ventricular dilatation.

Noncommunicating

Noncommunicating hydrocephalus, or obstructive hydrocephalus, is caused by an obstruction to the flow of CSF.

• Foramen of Monro obstruction may lead to dilation of one, or if large enough (e.g., in colloid cyst), both lateral ventricles.
• The aqueduct of Sylvius, normally narrow, may be obstructed by a number of genetic or acquired lesions (e.g., atresia, ependymitis, hemorrhage, or tumor) and lead to dilation of both lateral ventricles, as well as the third ventricle.
• Fourth ventricle obstruction leads to dilatation of the aqueduct, as well as the lateral and third ventricles (e.g., Chiari malformation).
• The foramina of Luschka and foramen of Magendie may be obstructed due to congenital malformation (e.g., Dandy–Walker malformation).

Other

Hydrocephalus ex vacuo from vascular dementia as seen on MRI

• Normal pressure hydrocephalus (NPH) is a particular form of chronic communicating hydrocephalus, characterized by enlarged cerebral ventricles, with only intermittently elevated cerebrospinal fluid pressure. Characteristic triad of symptoms are; dementia, apraxic gait and urinary incontinence. The diagnosis of NPH can be established only with the help of continuous intraventricular pressure recordings (over 24 hours or even longer), since more often than not instant measurements yield normal pressure values. Dynamic compliance studies may be also helpful. Altered compliance (elasticity) of the ventricular walls, as well as increased viscosity of the cerebrospinal fluid, may play a role in the pathogenesis.
• Hydrocephalus ex vacuo also refers to an enlargement of cerebral ventricles and subarachnoid spaces, and is usually due to brain atrophy (as it occurs in dementias), post-traumatic brain injuries, and even in some psychiatric disorders, such as schizophrenia. As opposed to hydrocephalus, this is a compensatory enlargement of the CSF-spaces in response to brain parenchyma loss; it is not the result of increased CSF pressure.

Mechanism

Spontaneous intracerebral and intraventricular hemorrhage with hydrocephalus shown on CT scan

 

3D cast of lateral ventricles in hydrocephalus

Hydrocephalus is usually due to blockage of CSF outflow in the ventricles or in the subarachnoid space over the brain. In a person without hydrocephalus, CSF continuously circulates through the brain, its ventricles and the spinal cord and is continuously drained away into the circulatory system. Alternatively, the condition may result from an overproduction of the CSF, from a congenital malformation blocking normal drainage of the fluid, or from complications of head injuries or infections.

Compression of the brain by the accumulating fluid eventually may cause neurological symptoms such as convulsions, intellectual disability, and epileptic seizures. These signs occur sooner in adults, whose skulls are no longer able to expand to accommodate the increasing fluid volume within. Fetuses, infants, and young children with hydrocephalus typically have an abnormally large head, excluding the face, because the pressure of the fluid causes the individual skull bones—which have yet to fuse—to bulge outward at their juncture points. Another medical sign, in infants, is a characteristic fixed downward gaze with whites of the eyes showing above the iris, as though the infant were trying to examine its own lower eyelids.

The elevated ICP may cause compression of the brain, leading to brain damage and other complications. A complication often overlooked is the possibility of hearing loss due to ICP. The mechanism of ICP on hearing loss is presumed that the transmission of CSF pressure to and from the Perilymphatic space through a patent cochlear aqueduct. The cochlear aqueduct connects the Perilymphatic space of the inner ear with the subarachnoid space of the posterior cranial fossa. A loss of CSF pressure can induce Perilymphatic loss or endolymphatic hydrops resembling the clinical presentation of Ménière's disease associated hearing loss in the low frequencies.

CSF can accumulate within the ventricles, this condition is called internal hydrocephalus and may result in increased CSF pressure. The production of CSF continues, even when the passages that normally allow it to exit the brain are blocked. Consequently, fluid builds inside the brain, causing pressure that dilates the ventricles and compresses the nervous tissue. Compression of the nervous tissue usually results in irreversible brain damage. If the skull bones are not completely ossified when the hydrocephalus occurs, the pressure may also severely enlarge the head. The cerebral aqueduct may be blocked at the time of birth or may become blocked later in life because of a tumor growing in the brainstem.

Treatments

Procedures

Baby recovering from shunt surgery

Hydrocephalus treatment is surgical, creating a way for the excess fluid to drain away. In the short term, an external ventricular drain (EVD), also known as an extraventricular drain or ventriculostomy, provides relief. In the long term, some people will need any of various types of cerebral shunt. It involves the placement of a ventricular catheter (a tube made of silastic) into the cerebral ventricles to bypass the flow obstruction/malfunctioning arachnoidal granulations and drain the excess fluid into other body cavities, from where it can be resorbed. Most shunts drain the fluid into the peritoneal cavity (ventriculoperitoneal shunt), but alternative sites include the right atrium (ventriculoatrial shunt), pleural cavity (ventriculopleural shunt), and gallbladder. A shunt system can also be placed in the lumbar space of the spine and have the CSF redirected to the peritoneal cavity (lumbar-peritoneal shunt). An alternative treatment for obstructive hydrocephalus in selected people is the endoscopic third ventriculostomy (ETV), whereby a surgically created opening in the floor of the third ventricle allows the CSF to flow directly to the basal cisterns, thereby shortcutting any obstruction, as in aqueductal stenosis. This may or may not be appropriate based on individual anatomy. For infants, ETV is sometimes combined with choroid plexus cauterization, which reduces the amount of cerebrospinal fluid produced by the brain. The technique, known as ETV/CPC, was pioneered in Uganda by neurosurgeon Benjamin Warf and is now in use in several U.S. hospitals. Hydrocephalus can be successfully treated by placing a drainage tube (shunt) between the brain ventricles and abdominal cavity. Some risk exists of infection being introduced into the brain through these shunts, however, and the shunts must be replaced as the person grows.

External hydrocephalus

External hydrocephalus is a condition generally seen in infants which involves enlarged fluid spaces or subarachnoid spaces around the outside of the brain. This condition is generally benign, and resolves spontaneously by two years of age and therefore usually does not require insertion of a shunt. Imaging studies and a good medical history can help to differentiate external hydrocephalus from subdural hemorrhages or symptomatic chronic extra-axial fluid collections which are accompanied by vomiting, headaches, and seizures.

Shunt complications

Examples of possible complications include shunt malfunction, shunt failure, and shunt infection, along with infection of the shunt tract following surgery (the most common reason for shunt failure is infection of the shunt tract). Although a shunt generally works well, it may stop working if it disconnects, becomes blocked (clogged) or infected, or it is outgrown. If this happens, the CSF begins to accumulate again and a number of physical symptoms develop (headaches, nausea, vomiting, photophobia/light sensitivity), some extremely serious, such as seizures. The shunt failure rate is also relatively high (of the 40,000 surgeries performed annually to treat hydrocephalus, only 30% are a person's first surgery) and people not uncommonly have multiple shunt revisions within their lifetimes.

Another complication can occur when CSF drains more rapidly than it is produced by the choroid plexus, causing symptoms of listlessness, severe headaches, irritability, light sensitivity, auditory hyperesthesia (sound sensitivity), hearing loss, nausea, vomiting, dizziness, vertigo, migraines, seizures, a change in personality, weakness in the arms or legs, strabismus, and double vision to appear when the person is vertical. If the person lies down, the symptoms usually vanish quickly. A CT scan may or may not show any change in ventricle size, particularly if the person has a history of slit-like ventricles. Difficulty in diagnosing over-drainage can make treatment of this complication particularly frustrating for people and their families. Resistance to traditional analgesic pharmacological therapy may also be a sign of shunt overdrainage or failure.

Following placement of a ventriculoperitoneal shunt there have been cases of a decrease in post-surgery hearing. It is presumed that the cochlea aqueduct is responsible for the decrease in hearing thresholds. The cochlea aqueduct has been considered as a probable channel where CSF pressure can be transmitted. Therefore, the reduced CSF pressure could cause a decrease in Perilymphatic pressure and cause secondary endolymphatic hydrops. In addition to the increased hearing loss, there have also been findings of resolved hearing loss after ventriculoperitoneal shunt placement, where there is a release of CSF pressure on the auditory pathways.

The diagnosis of CSF buildup is complex and requires specialist expertise. Diagnosis of the particular complication usually depends on when the symptoms appear, that is, whether symptoms occur when the person is upright or in a prone position, with the head at roughly the same level as the feet.

Standardized protocols for inserting cerebral shunts have been shown to reduce shunt infections. There is tentative evidence that preventative antibiotics may decrease the risk of shunt infections.

Epidemiology

The hydrocephalus disease burden are concentrated in the developing world while North America and Canada has the least number of cases. A systematic review in 2019 estimated that there are 180,000 childhood hydrocephalus cases from African continent alone per year, followed by 90,000 cases from Southeast Asia and Western Pacific. Latin America also has high prevalence of hydrocephalus. However, data on hydrocephalus disease burden in adults are lacking.

History

Skull of a hydrocephalic child (1800s)

 

Adult male with hydrocephalus, 1901

In the pre-historic area, there were various paintings or artifacts depicting children or adults with macrocephaly (large head) or clinical findings of hydrocephalus. However, due to lack of writing, it was unknown how the people thought of the disorder at that time and the ways to treat the disease.

References to hydrocephalic skulls can be found in ancient Egyptian medical literature from 2,500 BC to 500 AD. Hydrocephalus was described more clearly by the ancient Greek physician Hippocrates in the fourth century BC, while a more accurate description was later given by the Roman physician Galen in the second century AD.

The first clinical description of an operative procedure for hydrocephalus appears in the Al-Tasrif (1,000 AD) by the Arab surgeon Abulcasis, who clearly described the evacuation of superficial intracranial fluid in hydrocephalic children. He described it in his chapter on neurosurgical disease, describing infantile hydrocephalus as being caused by mechanical compression. He wrote:

The skull of a newborn baby is often full of liquid, either because the matron has compressed it excessively or for other, unknown reasons. The volume of the skull then increases daily, so that the bones of the skull fail to close. In this case, we must open the middle of the skull in three places, make the liquid flow out, then close the wound and tighten the skull with a bandage.

Historical specimen of an infant with severe hydrocephalus, probably untreated

In 1881, a few years after the landmark study of Retzius and Key, Carl Wernicke pioneered sterile ventricular puncture and external drainage of CSF for the treatment of hydrocephalus. It remained an intractable condition until the 20th century, when cerebral shunt and other neurosurgical treatment modalities were developed.

It is a lesser-known medical condition; relatively little research is conducted to improve treatment, and still no cure has been found. In developing countries, the condition often goes untreated at birth. Before birth, the condition is difficult to diagnose, and access to medical treatment is limited. However, when head swelling is prominent, children are taken at great expense for treatment. By then, brain tissue is undeveloped and neurosurgery is rare and difficult. Children more commonly live with undeveloped brain tissue and consequential intellectual disabilities and restrictions.

Society and culture

Name

The word hydrocephalus is from the Greek ὕδωρ, hydōr meaning 'water' and κεφαλή, kephalē meaning 'head'. Other names for hydrocephalus include "water on the brain", a historical name, and "water baby syndrome".

Awareness campaign

Hydrocephalus awareness ribbon

September was designated National Hydrocephalus Awareness Month in July 2009 by the U.S. Congress in H.Res. 373. The resolution campaign is due in part to the advocacy work of the Pediatric Hydrocephalus Foundation. Prior to July 2009, no awareness month for this condition had been designated. Many hydrocephalus organizations, such as the One Small Voice Foundation, promote awareness and fundraising activities.

Exceptional case

One case of hydrocephalus was a man whose brain shrank to a thin sheet of tissue, due to a buildup of cerebrospinal fluid in his skull. As a child, the man had a shunt, but it was removed when he was 14. In July 2007, at age 44, he went to a hospital due to mild weakness in his left leg. When doctors learned of the man's medical history, they performed a CT and MRI scan, and were astonished to see "massive enlargement" of the lateral ventricles in the skull. Dr. Lionel Feuillet of Hôpital de la Timone in Marseille said, "The images were most unusual... the brain was virtually absent." Intelligence tests showed the person had an IQ of 75, considered "Borderline intellectual functioning", just above what would be officially classified as intectually disabled.

The person was a married father of two children, and worked as a civil servant, leading an at least superficially normal life, despite having enlarged ventricles with a decreased volume of brain tissue. "What I find amazing to this day is how the brain can deal with something which you think should not be compatible with life", commented Dr. Max Muenke, a pediatric brain-defect specialist at the National Human Genome Research Institute. "If something happens very slowly over quite some time, maybe over decades, the different parts of the brain take up functions that would normally be done by the part that is pushed to the side."

Notable cases

• Ice hockey player Colby Cave had acute obstructive hydrocephalus due to a colloid cyst.
• Author Sherman Alexie, born with the condition, wrote about it in his semi-autobiographical junior fiction novel The Absolutely True Diary of a Part-Time Indian.
• Prince William, Duke of Gloucester (1689–1700), probably contracted meningitis at birth, which resulted in this condition.
• Emperor Ferdinand I of Austria (1793–1875) became emperor in 1835 despite various health issues including hydrocephalus and epilepsy.
• In the American folklore of the states of Ohio, Michigan, and Connecticut, an urban legend exists about the melon heads, the inbred descendants of families of people born with hydrocephaly.
• Masato Kudo, a professional soccer player, died of hydrocephalus on October 21, 2022.

Intellectual giftedness

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Intellectual_giftedness 

Intellectual giftedness is an intellectual ability significantly higher than average. It is a characteristic of children, variously defined, that motivates differences in school programming. It is thought to persist as a trait into adult life, with various consequences studied in longitudinal studies of giftedness over the last century. There is no generally agreed definition of giftedness for either children or adults, but most school placement decisions and most longitudinal studies over the course of individual lives have followed people with IQs in the top 2.5 percent of the population—that is, IQs above 130. Definitions of giftedness also vary across cultures.

The various definitions of intellectual giftedness include either general high ability or specific abilities. For example, by some definitions, an intellectually gifted person may have a striking talent for mathematics without equally strong language skills. In particular, the relationship between artistic ability or musical ability and the high academic ability usually associated with high IQ scores is still being explored, with some authors referring to all of those forms of high ability as "giftedness", while other authors distinguish "giftedness" from "talent". There is still much controversy and much research on the topic of how adult performance unfolds from trait differences in childhood, and what educational and other supports best help the development of adult giftedness.

Identification

Overview

The identification of giftedness first emerged after the development of IQ tests for school placement. It has since become an important issue for schools, as the instruction of gifted students often presents special challenges. During the twentieth century, gifted children were often classified via IQ tests; other identification procedures have been proposed but are only used in a minority of cases in most public schools in the English-speaking world. Developing useful identification procedures for students who could benefit from a more challenging school curriculum is an ongoing problem in school administration.

Because of the key role that gifted education programs in schools play in the identification of gifted individuals, both children and adults, it is worthwhile to examine how schools define the term "gifted".

Definitions

Since Lewis Terman in 1916, psychometricians and psychologists have sometimes equated giftedness with high IQ. Later researchers (e.g., Raymond Cattell, J. P. Guilford, and Louis Leon Thurstone) have argued that intellect cannot be expressed in such a unitary manner, and have suggested more multifaceted approaches to intelligence.

Research conducted in the 1980s and 1990s has provided data that supports notions of multiple components to intelligence. This is particularly evident in the reexamination of "giftedness" by Sternberg and Davidson in their collection of articles Conceptions of Giftedness (1986; second edition 2005). The many different conceptions of giftedness presented, although distinct, are interrelated in several ways. Most of the investigators define giftedness in terms of multiple qualities, not all of which are intellectual. IQ scores are often viewed as inadequate measures of giftedness. Motivation, high self-concept, and creativity are key qualities in many of these broadened conceptions of giftedness.

Joseph Renzulli's (1978) "three ring" definition of giftedness is one frequently mentioned conceptualization of giftedness. Renzulli's definition, which defines gifted behaviors rather than gifted individuals, is composed of three components as follows: Gifted behavior consists of behaviors that reflect an interaction among three basic clusters of human traits—above average ability, high levels of task commitment, and high levels of creativity. Individuals capable of developing gifted behavior are those possessing or capable of developing this composite set of traits and applying them to any potentially valuable area of human performance. Persons who manifest or are capable of developing an interaction among the three clusters require a wide variety of educational opportunities and services that are not ordinarily provided through regular instructional programs.

In Identifying Gifted Children: A Practical Guide, Susan K. Johnsen explains that gifted children all exhibit the potential for high performance in the areas included in the United States' federal definition of gifted and talented students:

There is a federal government statutory definition of gifted and talented students in the United States.

The term "gifted and talented" when used in respect to students, children, or youth means students, children, or youth who give evidence of high-performance capability in areas such as intellectual, creative, artistic, or leadership capacity, or in specific academic fields, and who require services or activities not ordinarily provided by the school in order to fully develop such capabilities." (P.L. 103–382, Title XIV, p. 388)

This definition has been adopted partially or completely by the majority of the individual states in the United States (which have the main responsibility for education policy as compared to the federal government). Most states have a definition similar to that used in the State of Texas:

"gifted and talented student" means a child or youth who performs at or shows the potential for performing at a remarkably high level of accomplishment when compared to others of the same age, experience, or environment, and who

• exhibits high-performance capability in an intellectual, creative, or artistic area;
• possesses an unusual capacity for leadership; or
• excels in a specific academic field." (74th legislature of the State of Texas, Chapter 29, Subchapter D, Section 29.121)

The major characteristics of these definitions are (a) the diversity of areas in which performance may be exhibited (e.g., intellectual, creativity, artistic, leadership, academically), (b) the comparison with other groups (e.g., those in general education classrooms or of the same age, experience, or environment), and (c) the use of terms that imply a need for development of the gift (e.g., capability and potential).

Since the late 90s, the development of the brain of people with high IQ scores has been shown to be different to that of people with average IQ scores. A longitudinal study over 6 years has shown that high-IQ children have a thinner cerebral cortex when young, which then grows quickly and becomes significantly thicker than the other children's by the time they became teenagers.

Identification methods

IQ scores can vary for the same person, so a person does not always belong to the same IQ score range each time the person is tested. (IQ score table data and pupil pseudonyms adapted from description of KABC-II norming study cited in Kaufman 2009.)

Pupil	KABC-II	WISC-III	WJ-III
Asher	90	95	111
Brianna	125	110	105
Colin	100	93	101
Danica	116	127	118
Elpha	93	105	93
Fritz	106	105	105
Georgi	95	100	90
Hector	112	113	103
Imelda	104	96	97
Jose	101	99	86
Keoku	81	78	75
Leo	116	124	102

In psychology, identification of giftedness is usually based on IQ scores. The threshold of IQ = 130 is defined by statistical rarity. By convention, the 5% of scores who fall more than two standard deviations from the mean (or more accurately 1.96) are considered atypical. In the case of intelligence, these 5% are partitioned to both sides of the range of scores, and include the 2.5% who score more than two standard deviations below the mean and the 2.5% who score more than two standard deviations above the mean. Because the average of IQ is 100 and its standard deviation is 15, this rule places the threshold for intellectual disability at IQ = 70, and the symmetrical threshold for giftedness at IQ = 130 (rounded). This arbitrary threshold is used by most psychologists in most countries.

While IQ testing has the advantage of providing an objective basis for the diagnosis of giftedness, psychologists are expected to interpret IQ scores in the context of all available information: standardized intelligence tests ignore actual achievement and can fail to detect giftedness. For example, a specific learning disorder such as dyslexia or dyspraxia can easily decrease scores on intelligence tests and hide true intellectual ability.

In educational settings, many schools in the US use a variety of assessments of students' capability and potential when identifying gifted children. These may include portfolios of student work, classroom observations, achievement tests, and IQ test scores. Most educational professionals accept that no single criterion can be used in isolation to accurately identify a gifted child.

One of the criteria used in identification may be an IQ test score. Until the late 1960s, when "giftedness" was defined solely based on an IQ score, a school district simply set an arbitrary score (usually in the 130 range) and a student either did or did not "make the cut". This method is still used by many school districts because it is simple and objective. Although a high IQ score is not the sole indicator of giftedness, usually if a student has a very high IQ, that is a significant indicator of high academic potential. Because of this consideration, if a student scores highly on an IQ test, but performs at an average or below-average level academically, school officials may think that this issue warrants further investigation as an example of underachievement. However, scholars of educational testing point out that a test-taker's scores on any two tests may vary, so a lower score on an achievement test than on an IQ test neither necessarily indicates that the test-taker is underachieving nor necessarily that the school curriculum is under-challenging.

IQ classification varies from one publisher to another. IQ tests have poor reliability for determining test-takers' rank order at higher IQ levels, and are perhaps only effective at determining whether a student is gifted rather than distinguishing among levels of giftedness. The Wechsler test manuals have standard score ceilings of 160. However, higher ceilings, including scores into the exceptionally and profoundly gifted range, exist for the WISC-IV and WISC-V, which were specifically normed on large samples of gifted children. Today, the Wechsler child and adult IQ tests are by far the most commonly used IQ tests in hospitals, schools, and private psychological practice. Older versions of the Stanford-Binet test, now obsolete, and the Cattell IQ test purport to yield IQ scores of 180 or higher, but those scores are not comparable to scores on currently normed tests. The Stanford-Binet Third Revision (Form L-M) yields consistently higher numerical scores for the same test-taker than scores obtained on current tests. This has prompted some authors on identification of gifted children to promote the Stanford-Binet form L-M, which has long been obsolete, as the only test with a sufficient ceiling to identify the exceptionally and profoundly gifted, despite the Stanford-Binet L-M never having been normed on a representative national sample. Because the instrument is outdated, current results derived from the Stanford-Binet L-M generate inflated and inaccurate scores. The IQ assessment of younger children remains debated.

While many people believe giftedness is a strictly quantitative difference, measurable by IQ tests, some authors on the "experience of being" have described giftedness as a fundamentally different way of perceiving the world, which in turn affects every experience had by the gifted individual. This view is doubted by some scholars who have closely studied gifted children longitudinally.

Across cultures

Characteristics and attributes associated with giftedness varies across cultures. While intelligence is extremely important in Western and some other cultures, such an emphasis is not consistent throughout the world. For example, in Japan, there is more of a value placed on an individual's motivation and diligence. When Japanese students are given a task, they attribute success to factors like effort, whereas American students tend to attribute success to ability. Similarly, when Japanese students fail, they refer the failure to lack of effort. On the other hand, American students believe failure is due to a lack of ability. There are conceptions in Rural Kenya that identify four types of intelligence: initiative (paro), knowledge and skills (rieko), respect (luoro), and comprehension of how to handle real-life problems (winjo). Chan cites the Chinese belief that aspects of giftedness are innate, but that people can become gifted through industriousness, perseverance, and learning. Not all who are intellectually gifted display every noticeable characteristic.

There are many reasons gifted students who have various backgrounds are not as successful at Western intelligence/achievement tests:

• Not used to answering questions just for the purpose of showing knowledge – they must use their knowledge to respond to authentic problems.
• May perform poorly on paper-and-pencil tasks in an artificial lab setting.
• May perform poorly on a culturally biased test, especially if not their own.
• Have test anxiety or suffer from stereotype threat.

Many traits that demonstrate intellectual giftedness are identified across a multitude of cultures, such as:

• Displaying advanced reasoning and creative thinking, generating ideas beyond the norm
• Resourceful and adaptable
• Strongly motivated to understand the world
• Well developed vocabulary in native language
• Learns concepts quickly, and builds/develops these concepts
• Strong sense of justice and morality
• Displays leadership skills in various ways, such as persuasion, taking initiative, and leading by example
• Comprehending and using humor beyond their age

Developmental theory

Gifted children may develop asynchronously: their minds are often ahead of their physical growth, and specific cognitive and emotional functions are often developed differently (or to differing extents) at different stages of development. One frequently cited example of asynchronicity in early cognitive development is Albert Einstein, who was delayed in speech, but whose later fluency and accomplishments belied this initial delay. Psychologist and cognitive scientist Steven Pinker theorized that, rather than viewing Einstein's (and other famously gifted late-talking individuals) adult accomplishments as existing distinct from, or in spite of, his early language deficits, and rather than viewing Einstein's lingual delay itself as a "disorder", it may be that Einstein's genius and his delay in speaking were developmentally intrinsic to one another.

It has been said that gifted children may advance more quickly through stages established by post-Freudian developmentalists such as Jean Piaget. Gifted individuals also experience the world differently, resulting in certain social and emotional issues.

Francoy Gagne's (2000) Differentiated Model of Giftedness and Talent (DMGT) is a developmental theory that distinguishes giftedness from talent, offering explanation on how outstanding natural abilities (gifts) develop into specific expert skills (talents). According to DMGT theory, "one cannot become talented without first being gifted, or almost so". There are six components that can interact in countless and unique ways that foster the process of moving from having natural abilities (giftedness) to systematically developed skills.

These components consist of the gift (G) itself, chance (C), environmental catalyst (EC), intrapersonal catalyst (IC), learning/practice (LP) and the outcome of talent (T). It is important to know that (C), (IC), and (EC) can facilitate but can also hinder the learning and training of becoming talented. The learning/practice is the moderator. It is through the interactions, both environmental and intrapersonal that influence the process of learning and practice along with/without chance that natural abilities are transformed into talents.

Multiple intelligences theory

Main article: Theory of multiple intelligences

Multiple intelligences has been associated with giftedness or overachievement of some developmental areas (Colangelo, 2003). Multiple intelligences has been described as an attitude towards learning, instead of techniques or strategies (Cason, 2001).

Howard Gardner proposed in Frames of Mind (Gardner 1983/1994) that intellectual giftedness may be present in areas other than the typical intellectual realm. The concept of multiple intelligences (MI) makes the field aware of additional potential strengths and proposes a variety of curricular methods. Gardner argued that there are eight intelligences, or different areas in which people assimilate or learn about the world around them: interpersonal, intrapersonal, bodily-kinesthetic, linguistic, logical-mathematical, musical, naturalistic, and spatial-visual.

The most common criticism of Gardner's MI theory is "the belief by scholars that each of the seven multiple intelligences is in fact a cognitive style rather than a stand-alone construct". Others consider the theory not to be sufficiently empirical. This perspective has also been criticized on the grounds that it is ad hoc: that Gardner is not expanding the definition of the word "intelligence", but rather denies the existence of intelligence as traditionally understood, and instead uses the word "intelligence" where other people have traditionally used words like "ability" and "aptitude".

Identification of gifted students with MI is a challenge since there is no simple test to give to determine giftedness of MI. Assessing by observation is potentially most accurate, but potentially highly subjective. MI theory can be applied to not only gifted students, but it can be a lens through which all students can be assessed. This more global perspective may lead to more child-centered instruction and meet the needs of a greater number of children (Colangelo, 2003).

Characteristics

Generally, gifted or advanced students learn more quickly, deeply, and broadly than their peers. They may talk early, learn to read early, and progress at the same level as normal children who are significantly older. Gifted students also tend to demonstrate high reasoning ability, creativity, curiosity, a large vocabulary, and an excellent memory. They can often master concepts with few repetitions. They may also be perfectionistic, and frequently question authority. Some have trouble relating to or communicating with their peers because of disparities in vocabulary size (especially in the early years), personality, interests, and motivation. As children, they may prefer the company of older children or adults. Teachers may notice that gifted students tend to hover around them more than the other students. This is because gifted students sometimes think that they cannot relate to the students their own age, so they try to communicate with the teacher.

Giftedness is frequently not evenly distributed throughout all intellectual spheres. One gifted student may excel in solving logic problems yet be a poor speller. Another may be able to read and write at a far above-average level yet have trouble with mathematics.

It is possible that there are different types of giftedness with their own unique features, just as there are different types of developmental delay.

Giftedness may become noticeable in individuals at different points of development. While early development (i.e. speaking or reading at a very young age) usually comes with giftedness, it is not a determinant factor of giftedness.

Savantism

Savants are individuals who perform exceptionally in a single field of learning. More often, the terms savant and savantism describe people with a competence level in a single field of learning well beyond what is considered normal, even among the gifted community. Such individuals are alternatively termed idiot savants ─ a term that has been mentioned as early as the eighteenth century. Autistic savantism refers to the exceptional abilities occasionally exhibited by people with autism or other pervasive developmental disorders. These abilities often come with below-age-level functioning in most, if not all areas of skilled performance. The term was introduced in a 1978 article in Psychology Today describing this condition. It is also proposed that there are savants with normal or superior IQ such as those with Asperger syndrome, who demonstrate special abilities involving numbers, mathematics, mechanical, and spatial skills.

Gifted minority students in the United States

The majority of students enrolled in gifted programs are White; Black and Hispanic students constitute a smaller proportion than their enrollment in school. For example, statistics from 1993 indicate that in the U.S., Black students represented 16.2% of public school students, but only constituted 8.4% of students enrolled in gifted education programs. Similarly, while Hispanic students represented 9% of public school students, these students only represented 4.7% of those identified as gifted. However, Asian students make up only 3.6% of the student body, yet constitute 14% in the gifted programs. Poor students are also underrepresented in gifted programs, even more than Black and Hispanic students are.

Lack of equity and access in programs for the gifted has been acknowledged since the early twentieth century. In the 1920s, research by Lillian Steele Proctor pointed to systemic racism as a contributor to the relative invisibility of gifted African American youth. In their 2004 study, "Addressing the Achievement Gap Between Minority and Nonminority Children by Increasing Access to Gifted Programs" Olszewski-Kubilius et al. write that minority students are "less likely to be nominated by teachers as potential candidates for gifted programs and, if nominated, are less likely to be selected for the program, particularly when such traditional measures as I.Q. and achievement tests are used for identification."

This underrepresentation of such students in gifted programs is attributed to a multiplicity of factors including cultural bias of testing procedures, selective referrals and educator bias, and reliance on deficit-based paradigms. To address the inequities in assessment procedures, researchers suggest the use of multiple tests and alternative methods of testing, such as performance-based assessment measures, oral-expressiveness measures as well as non-verbal ability assessments (such as Naglieri Nonverbal Abilities Tests (NNAT) or Raven's Matrix Analogies Tests).

According to 2013-2014 data collected by the Office of Civil Rights of the Department of Education, White students have more opportunities and exposure to attending schools that offer gifted and talented education programs (GATE) than racial and ethnic minority students, specifically Black and Latino students. Data collected by the Office of Civil Rights department of the Department of Education also reveal that racial/ethnic minority students are underrepresented in gifted and talented education programs. Forty-nine percent of all students enrolled in schools that offer GATE programs are White. Whereas 42% of all students enrolled in schools that offer GATE programs are Latino and Black. Thus revealing that white people have more opportunities to be a part of a school that offers GATE programs. The issue is within these GATE programs 29% of the students are Latino and Black and 57% are White (U.S. Department of Education, 2016).

Weinstein's (2002) suggests that some teachers recommend racial minority students – with the exception of Asian students – to special education and remedial classes more often than gifted and talented classes due to teacher expectancy biases placed on racial minority students. Teachers' expectations of their students' academic performance influence how students perceive themselves. If a teacher expects more success academically from specific students, those students are prone to displaying behavior and work ethic that will set them apart from others in a positive light. Whereas if a teacher only expects the bare minimum from his or her students, those students will merely do what is expected of them (Weinstein, 2002).

Racial minority students who are perceived as being disadvantaged from their peers in regards to socioeconomic status tend to have less supportive relations with their teachers (Fitzpatrick, 2015). Due to this lack of support, teachers do not expect these disadvantaged students to go above and beyond, therefore they are often overlooked when it's time for gifted and talented education program nominations. Research suggests that teacher expectancy bias can also be diminish by matching the racial demographics of students to that of teachers. Gershenson and colleagues (2016) found that non-Black teachers held low expectations of their black students specifically in relation to black male students and math. Whereas, Black teachers held high expectations to black male students in regards to math. This finding suggests that racial diversity in our educators is a positive step toward diminishing teacher expectancy bias.

Weinstein and colleagues (1991) aimed to change the low expectations attached to racial minority students of an urban high school that placed many Black and Latino students in remedial programs rather than college preparatory or honor classes. The study aimed to prepare these racial minority students for college-level academic work while attending high school. With positive teacher attitudes toward students and greater teacher self-efficacy, the students who were once on track to being recommended for remedial classes were performing at advanced academic levels after 2 years of intervention. They were also more heavily involved in leadership roles at their high school. This study supports the claim that teacher expectancy contributes to how a student sees him or herself in regards to achievements (Weinstein et al., 1991).

Gifted students of color experience success when multicultural content is incorporated in the curriculum and furthermore when the curriculum itself is designed to be culturally and linguistically compatible. A culturally diverse curriculum and instruction encourages gifted minority students to experience a sense of belonging and validation as scholars. Furthermore, the educator's role in this process is significant as Lee et al. argue that "[t]eacher awareness and understanding of students' racial and cultural differences and their ability to incorporate multicultural perspectives into curricular content and instructional techniques may counter gifted minority students' discomfort in being one of the few minority students in gifted programs."

Twice-exceptional

The term twice-exceptional was coined by James J. Gallagher to denote students who are both gifted and have disabilities. In other words, twice-exceptional students are those who have two special needs. For instance, they might have gifted learning needs and a learning disability. Or, they may be a gifted learner and have a developmental disability, such as autism spectrum disorder.

People have known about twice-exceptional students for thirty years; however, identification and program strategies remain ambiguous. These students represent a unique challenge for the educational system. Teachers and educators will need to make special accommodations for their learning deficits (such as remediation), yet adapt the curriculum to meet their advanced learning needs (for instance, through acceleration or enrichment). Twice-exceptional students are considered to be at risk because they are hidden within the general population of their educational environment, and often viewed as either underachievers or average learners.

Early identification and intervention is critical; however, giftedness in the twice-exceptional population is often identified later than in the average population as it is masked by the disability. The disabilities may include auditory processing weaknesses, sensory-motor integration issues, visual perceptual difficulties, spatial disorientation, dyslexia, and attention deficits. Recognition of learning difficulties among the gifted is made extremely difficult by virtue of their ability to compensate. Among the signs that the student may be twice-exceptional are apparent inconsistencies between abilities and results, deficits in short-term memory and attention, and negative behaviors such as being sarcastic, negative, or aggressive.

A child prodigy who demonstrates qualities to be twice-exceptional may encounter additional difficulties. With insight at a young age, it is possible for them to be constantly aware of the risk of failure. This can be detrimental to their emotional state and academic achievement. If a child comprehends a subject well, but due to a developmental disorder receives poor grades in a subject, the child may have difficulty understanding why there is little success in that subject.

Social and emotional issues

Isolation

Social isolation is a common trait in gifted individuals, especially those with no social network of gifted peers. In order to gain popularity, gifted children will often try to hide their abilities to win social approval. Strategies include underachievement (discussed below) and the use of less sophisticated vocabulary when among same-age peers than when among family members or other trusted individuals.

Some believe that the isolation experienced by gifted individuals is not caused by giftedness itself, but by society's response to giftedness and to the rarity of peers. Plucker and Levy have noted that, "in this culture, there appears to be a great pressure for people to be 'normal' with a considerable stigma associated with giftedness or talent." To counteract this problem, gifted education professionals recommend creating a peer group based on common interests and abilities. The earlier this occurs, the more effective it is likely to be in preventing isolation. Since the mid-1940s, several high-IQ societies of varying levels of selectivity have been established to help gifted individuals find intellectual peers, the oldest ones being Mensa and Intertel, established in 1946 and 1966 respectively.

Research suggests that mathematically gifted adolescents might have deficiencies in social valuation & mentalization, while gifted adolescents in general may struggle with social adaptive learning.

Perfectionism

Perfectionism, while considered to have many positive aspects, can be another issue for gifted individuals. It is encouraged by the fact that gifted individuals tend to be easily successful in much of what they do.

Healthy perfectionism refers to having high standards, a desire to achieve, conscientiousness, or high levels of responsibility. It is likely to be a virtue rather than a problem, even if gifted children may have difficulty with healthy perfectionism because they set standards that would be appropriate to their mental age (the level at which they think), but they cannot always meet them because they are bound to a younger body, or the social environment is restrictive. In such cases, outsiders may call some behavior perfectionism, while for the gifted this may be their standard. It has been said that perfectionism "becomes desirable when it stimulates the healthy pursuit of excellence."

Some believe that perfectionism can be unhealthy. Unhealthy perfectionism stems from equating one's worth as a human being to one's achievements, and the simultaneous belief that any work less than perfect is unacceptable and will lead to criticism. Because perfection in the majority of human activities is neither desirable, nor possible, this cognitive distortion creates self-doubt, performance anxiety, and ultimately procrastination.

Unhealthy perfectionism can be triggered or further exacerbated by parents, siblings, or classmates with good or ill intentions. Parents are usually proud and will extensively praise the gifted child. On the other hand, siblings, comrades, and school bullies may generally become jealous or envious of the intellectual ease of the gifted child and tease him or her about any minor imperfection in his or her work, strength, clothes, appearance, or behavior. Either approach—positive reinforcement from parents or negative reactions from siblings and comrades for minor flaws—may push gifted children into equating their worth amongst their peers to their own abilities; thus, any imperfection could be viewed as a serious defect in themselves. This unhealthy perfectionism can be further exaggerated when the child counters bullying with the same tactics (i.e., insulting the less exceptional abilities of others), thus creating further disdain in himself for low or even average performance.

There are many theories that try to explain the correlation between perfectionism and giftedness. Perfectionism can become a problem as it frustrates and inhibits achievements.

D. E. Hamachek identified six specific, overlapping types of behavior associated with perfectionism. They are:

• Depression
• A nagging "I should" feeling
• Shame and guilt feelings
• Face-saving behavior
• Shyness and procrastination
• Self-deprecation

Underachievement

Underachievement is a significant issue for gifted learners. There is often a stark gap between the abilities of the gifted individual and their actual accomplishments. Many gifted students will perform extremely well on standardized or reasoning tests, only to fail a class exam. It is estimated that half of gifted children do not perform in school at a level that is up to their abilities. Studies of high school dropouts in the United States estimate that between 18% and 25% of the students who fail to graduate are gifted. This disparity can result from various factors, such as loss of interest in classes that are too easy or negative social consequences of being perceived as smart. Underachievement can also result from emotional or psychological factors, including depression, anxiety, perfectionism, low self esteem, or self-sabotage.

An often-overlooked contributor to underachievement is undiagnosed learning differences. A gifted individual is less likely to be diagnosed with a learning disorder than a non-gifted classmate, as the gifted child can more readily compensate for their paucities. This masking effect is dealt with by understanding that a difference of one standard deviation between scores constitutes a learning disability even if all of the scores are above average. Assessments may also fail to identify some gifted students entirely because their underachieving behaviours keep them from being recognized as exceptional.

Some gifted children may not be aware that they are gifted. One apparently effective way to attempt to reverse underachievement in gifted children includes educating teachers to provide enrichment projects based on students' strengths and interests without attracting negative attention from peers. Other methods include matching the underachiever with an achieving role model, correcting skill deficiencies and ensuring that proper assessments are in place to identify all learning issues with underachieving students.

Depression

It has been thought in the past that there is a correlation between giftedness and depression. This is not an established research finding. As Reis and Renzulli mention,

With the exception of creatively gifted adolescents who are talented in writing or the visual arts, studies do not confirm that gifted individuals manifest significantly higher or lower rates or severity of depression than those for the general population. Gifted children's advanced cognitive abilities, social isolation, sensitivity, and uneven development may cause them to face some challenging social and emotional issues, but their problem-solving abilities, advanced social skills, moral reasoning, out-of-school interests, and satisfaction in achievement may help them to be more resilient.

There is also no research that points to suicide attempt rates being higher in gifted adolescents than other adolescents.