In utero exposure to cocaine and other street drugs can lead to hydranencephaly.

As a recessive genetic condition, both parents must carry the asymptomatic gene and pass it along to their child, a chance of 25 percent. Despite determination of cause, hydranencephaly afflicts both males and females in equal numbers.

Because the shunt systems are too expensive for most people in developing countries, such people often die without getting a shunt. Worse, the rate of revision in shunt systems adds to the cost of shunting many times. Looking at this point, a study compares shunt systems and highlights the role of low-cost shunt systems in most of the developing countries. It compares the Chhabra shunt system to shunt systems from developed countries.

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

- Obstruction to CSF flow hinders the free passage of cerebrospinal fluid 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 central nervous system pressure.

- Hydrocephalus can also be caused by overproduction of cerebrospinal fluid (relative obstruction) (e.g., Choroid plexus papilloma, villous hypertrophy).

- Bilateral ureteric obstruction is a rare, but reported, cause of hydrocephalus.

Based on its underlying mechanisms, hydrocephalus can be classified into communicating and non-communicating (obstructive). Both forms can be either congenital or acquired.

In some cases, the defect is linked to mutations of the EMX2, SIX3, and Collagen, type IV, alpha 1 genes. Because having a sibling with schizencephaly has been statistically shown to increase risk of the disorder, it is possible that there is a heritable genetic component to the disease.

There is no known definitive single mechanism that causes colpocephaly. However, researchers believe there are many possible causes of colpocephaly. It is a common symptom of other neurological disorders in newborns, can be caused as a result of shunt treatment of hydrocephalus, developmental disorders in premature infants, due to intrauterine disturbances during pregnancy, genetic disorders, underdevelopment or lack of white matter in the cerebrum, and exposure of the mother and the developing fetus to medications, infections, radiation, or toxic substances. Also, it is usually more common in premature infants than in full-term infants, especially in babies born with hypoxia or lung immaturity.

Some of the central nervous system disorders which are associated with colpocephaly are as follows:

- polymicrogyria

- Periventricular leukomalacia (PVL)

- intraventricular hemorrhage

- Hydrocephalus

- schizencephaly

- microgyria

- microcephaly

- Pierre-Robin syndrome

- Neurofibromatosis

Often colpocephaly occurs as a result of hydrocephalus. Hydrocephalus is the accumulation of cerebrospinal fluid (CSF) in the ventricles or in the subarachnoid space over the brain. The increased pressure due to this condition dilates occipital horns causing colpocephaly.

The most generally accepted theory is that of neuronal migration disorders occurring during the second to fifth months of fetal life. Neuronal migration disorders are caused by abnormal migration, proliferation, and organization of neurons during early brain development. During the seventh week of gestation, neurons start proliferating in the germinal matrix which is located in the subependymal layer of the walls of the lateral ventricles. During the eighth week of gestation, the neurons then start migrating from the germinal zone to cortex along specialized radial glial fibers. Next, neurons organize themselves into layers and form synaptic contacts with other neurons present in the cortex. Under normal conditions, the neurons forming a germinal layer around ventricles migrate to the surface of the brain and form the cerebral cortex and basal ganglia. If this process is abnormal or disturbed it could result in the enlargement of the occipital horns of the lateral ventricles. Common prenatal disturbances that have been shown to disturb the neuronal migration process include the following:

- continuation of oral contraceptives

- exposure to alcohol

- intrauterine malnutrition

- intrauterine infections such as toxoplasmosis

- maternal drug ingestion during early pregnancy such as corticosteroids, salbutamol, and theophylline

Researchers also believe that these factors can cause destruction of neural elements that have previously been normally formed.

It is suggested that the underdevelopment or lack of white matter in the developing fetus could be a cause of colpocephaly. The partial or complete absence of white matter, also known as agenesis of the corpus callosum results in anatomic malformations that can lead to colpocephaly. This starts to occur around the middle of the second month to the fifth month of pregnancy. The lateral ventricles are formed as large cavities of the telencephalic vesicle. The size of the ventricles are decreased in normal development after the formation of the Foramen of Magendie, which decompresses the ventricular cavities. Myelination of the ventricular walls and association fibers of the corpus callosum and the calcarine fissure helps shape the occipital horns. In cases where this developmental process is interrupted, occipital horns are disproportionately enlarged.

Colpocephaly has been associated with chromosomal abnormalities such as trisomy 8 mosaic and trisomy 9 mosaic. A few reports of genetically transmitted colpocephaly are also found in literature. Some of these are of two siblings, monozygotic twins, and non-identical twins. The authors suggest a genetic origin with an autosomal or X-linked recessive inheritance rather than resulting from early prenatal disturbances.

The most widely accepted pathophysiological mechanism by which Chiari type I malformations occur is by a reduction or lack of development of the posterior fossa as a result of congenital or acquired disorders. Congenital causes include hydrocephalus, craniosynostosis (especially of the lambdoid suture), hyperostosis (such as craniometaphyseal dysplasia, osteopetrosis, erythroid hyperplasia), X-linked vitamin D-resistant rickets, and neurofibromatosis type I. Acquired disorders include space occupying lesions due to one of several potential causes ranging from brain tumors to hematomas.

Head trauma may cause cerebellar tonsillar ectopia, possibly because of dural strain. Additionally, ectopia may be present but asymptomatic until whiplash causes it to become symptomatic. Posterior fossa hypoplasia causes reduced cerebral and spinal compliance.

On average, IIH occurs in about one per 100,000 people, and can occur in children and adults. The median age at diagnosis is 30. IIH occurs predominantly in women, especially in the ages 20 to 45, who are four to eight times more likely than men to be affected. Overweight and obesity strongly predispose a person to IIH: women who are more than ten percent over their ideal body weight are thirteen times more likely to develop IIH, and this figure goes up to nineteen times in women who are more than twenty percent over their ideal body weight. In men this relationship also exists, but the increase is only five-fold in those over 20 percent above their ideal body weight.

Despite several reports of IIH in families, there is no known genetic cause for IIH. People from all ethnicities may develop IIH. In children, there is no difference in incidence between males and females.

From national hospital admission databases it appears that the need for neurosurgical intervention for IIH has increased markedly over the period between 1988 and 2002. This has been attributed at least in part to the rising prevalence of obesity, although some of this increase may be explained by the increased popularity of shunting over optic nerve sheath fenestration.

In utero exposure to cocaine and other street drugs can lead to schizencephaly.

It is not known what percentage of people with IIH will remit spontaneously, and what percentage will develop chronic disease.

IIH does not normally affect life expectancy. The major complications from IIH arise from untreated or treatment-resistant papilledema. In various case series, the long-term risk of ones vision being significantly affected by IIH is reported to lie anywhere between 10 and 25%.

The prevalence of congenital Chiari I malformation, defined as tonsilar herniations of 3 to 5 mm or greater, was previously believed to be in the range of one per 1000 births, but is likely much higher. Women are three times more likely than men to have a congenital Chiari malformation. Type II malformations are more prevalent in people of Celtic descent. A study using upright MRI found cerebellar tonsillar ectopia in 23% of adults with headache from motor-vehicle-accident head trauma. Upright MRI was more than twice as sensitive as standard MRI, likely because gravity affects cerebellar position.

Cases of congenital Chiari malformation may be explained by evolutionary and genetic factors. Typically, an infant's brain weighs around 400g at birth and triples to 1100-1400g by age 11. At the same time the cranium triples in volume from 500 cm to 1500 cm to accommodate the growing brain. During human evolution, the skull underwent numerous changes to accommodate the growing brain. The evolutionary changes included increased size and shape of the skull, decreased basal angle and basicranial length. These modifications resulted in significant reduction of the size of the posterior fossa in modern humans. In normal adults, the posterior fossa comprises 27% of the total intracranial space, while in adults with Chiari Type I, it is only 21%. If a modern brain is paired with a less modern skull, the posterior fossa may be too small, so that the only place where the cerebellum can expand is the foramen magnum, leading to development of Chiari Type I. H. neanderthalensis had platycephalic (flattened) skull. Some cases of Chiari are associated with platybasia (flattening of the skull base).

A genetic disorder called “Brickers-Adams-Edwards syndrome” or “X-linked hydrocephalus” has been discovered that leads to aqueductal stenosis. This disease is transmitted from mother to son. This disorder is caused by a point mutation in the gene for neural cell adhesion. Most males born with this have severe hydrocephalus, adducted thumbs, spastic motions, and intellectual problems. Females with this defect may have adducted thumbs or subnormal intelligence.

Bacterial meningitis can also result in gliotic blockage of the aqueduct. In utero infection or infection during infancy could both result in glial cell build up to make an obstruction.

There is neither a single cause of spina bifida nor any known way to prevent it entirely. However, dietary supplementation with folic acid has been shown to be helpful in reducing the incidence of spina bifida. Sources of folic acid include whole grains, fortified breakfast cereals, dried beans, leaf vegetables and fruits.

Folate fortification of enriched grain products has been mandatory in the United States since 1998. The U.S. Food and Drug Administration, Public Health Agency of Canada and UK recommended amount of folic acid for women of childbearing age and women planning to become pregnant is at least 0.4 mg/day of folic acid from at least three months before conception, and continued for the first 12 weeks of pregnancy.

Women who have already had a baby with spina bifida or other type of neural tube defect, or are taking anticonvulsant medication, should take a higher dose of 4–5 mg/day.

Certain mutations in the gene "VANGL1" have been linked with spina bifida in some families with a history of the condition.

Colpocephaly is usually non-fatal. There has been relatively little research conducted to improve treatments for colpocephaly, and there is no known definitive treatment of colpocephaly yet. Specific treatment depends on associated symptoms and the degree of dysfunction. Anticonvulsant medications can be given to prevent seizure complications, and physical therapy is used to prevent contractures (shrinkage or shortening of muscles) in patients that have limited mobility. Patients can also undergo surgeries for stiff joints to improve motor function. The prognosis for individuals with colpocephaly depends on the severity of the associated conditions and the degree of abnormal brain development.

A rare case of colpocephaly is described in literature which is associated with macrocephaly instead of microcephaly. Increased intracranial pressure was also found in the condition. Similar symptoms (absence of corpus callosum and increased head circumference) were noted as in the case of colpocephaly that is associated with microcephaly. A bi-ventricular peritoneal shunt was performed, which greatly improved the symptoms of the condition. Ventriculo-peritoneal shunts are used to drain the fluid into the peritoneal cavity.

Spina bifida is sometimes caused by the failure of the neural tube to close during the first month of embryonic development (often before the mother knows she is pregnant). Some forms are known to occur with primary conditions that cause raised central nervous system pressure, raising the possibility of a dual pathogenesis.

In normal circumstances, the closure of the neural tube occurs around the 23rd (rostral closure) and 27th (caudal closure) day after fertilization. However, if something interferes and the tube fails to close properly, a neural tube defect will occur. Medications such as some anticonvulsants, diabetes, obesity, and having a relative with spina bifida can all affect the probability of neural tube malformation.

Extensive evidence from mouse strains with spina bifida indicates that there is sometimes a genetic basis for the condition. Human spina bifida, like other human diseases, such as cancer, hypertension and atherosclerosis (coronary artery disease), likely results from the interaction of multiple genes and environmental factors.

Research has shown the lack of folic acid (folate) is a contributing factor in the pathogenesis of neural tube defects, including spina bifida. Supplementation of the mother's diet with folate can reduce the incidence of neural tube defects by about 70%, and can also decrease the severity of these defects when they occur. It is unknown how or why folic acid has this effect.

Spina bifida does not follow direct patterns of heredity as do muscular dystrophy or haemophilia. Studies show a woman having had one child with a neural tube defect such as spina bifida has about a 3% risk of having another affected child. This risk can be reduced with folic acid supplementation before pregnancy. For the general population, low-dose folic acid supplements are advised (0.4 mg/day).

In cases of aqueductal stenosis caused by tumor compression, a brain tumor in the region of the midbrain forms. More specific anatomically, a tumor forms in the pineal region which is dorsal to the midbrain and is level with the aqueduct of Sylvius. As the tumor grows and expands, it compresses the aqueduct to eventually obstruct it.

Recent population-based studies have estimated the prevalence of NPH to be about 0.5% in those over 65 years old, with an incidence of about 5.5 patients per 100,000 of people per year. This is in accordance with comparable findings stating that although normal pressure hydrocephalus can occur in both men and women of any age, it is found more often in the elderly population, with a peak onset generally in the sixth to seventh decades.

Low-pressure hydrocephalus (LPH) is a condition whereby ventricles are enlarged and the individual experiences severe dementia, inability to walk, and incontinence - despite very low intracranial pressure (ICP). Low pressure hydrocephalus appears to be a more acute form of normal pressure hydrocephalus. If not diagnosed in a timely fashion, the individual runs the risk of remaining in the low pressure hydrocephalic state or LPHS. Shunt revisions, even when they are set to drain at a low ICP, are not always effective. The pressure in the brain does not get high enough to allow the cerebrospinal fluid to drain in a shunt system, therefore the shunt is open, but malfunctioning in LPH. In cases of LPH, chronic infarcts can also develop along the corona radiata in response to the tension in the brain as the ventricles increase in size. Certain causes of LPH include trauma, tumor, bleeding, inflammation of the lining of the brain, whole brain radiation, as well as other brain pathology that affects the compliance of the brain parenchyma. One treatment for the LPHS is an external ventricular drain (EVD) set at negative pressures. According to Pang & Altschuler et al., a controlled, steady, negative pressure siphoning with EVD, carefully monitored with partial computer tomography scans is a safe and effective way of treating LPH. In their experience, this approach helps restore the brain mantle. They caution against dropping or raising the pressure of the EVD too quickly as it increases risk and also destabilizes the ventricles. Getting the ventricles smaller, is the initial step, stabilising them is the second step before placing a shunt – which is the final step in therapy. Any variation from this formula can lead to an ineffective, yet patent shunt system, despite a low-pressure setting. Care should be taken with EVD therapy, as mismanagement of the EVD can lead to long-term permanent complications and brain injury.

Genetic counseling is often recommended to provide more information about fetal CPCs, to answer questions and concerns, and to outline available options such as amniocentesis or a blood test from the mother. There is a possible association between ultrasound-detected fetal CPCs and Trisomy 18. It is not correlated to the presence of Trisomy 21 (Down syndrome).

Generally the risks are very low if there are no other risk factors. If no additional abnormalities are detected by a thorough "level II" ultrasound, the likelihood the fetus has trisomy 18 is very low.

A meta-analysis of 8 studies between 1990 and 2000 with choroid plexus cysts that were identified in second-trimester (an incidence of 1.2%). The incidence of the cysts in women younger than 35 was 1% (n=1017). The study found no cases of trisomy 18 in fetuses with cysts whose mother was younger than 35. The study concluded that "there is no evidence that detection of isolated choroid plexus cyst in women who are <35 years of age increases the risk of trisomy 18".

Other factors which may have a bearing on the baby's chances of developing chromosome problems include:

- mother's age at the expected date of delivery

- the results of serum screening; XAFP triple testing or quad screening

- evidence of other "fetal findings" seen at the time of the ultrasound that may suggest a chromosome problem

There are two types of normal pressure hydrocephalus: idiopathic and secondary. The secondary type of NPH can be due to a subarachnoid hemorrhage, head trauma, tumor, infection in the central nervous system, or a complication of cranial surgery.

The precise causes of syringomyelia are still unknown although blockage to the flow of cerebrospinal fluid has been known to be an important factor since the 1970s. Scientists in the UK and America continue to explore the mechanisms that lead to the formation of syrinxes in the spinal cord. It has been demonstrated a block to the free flow of cerebrospinal fluid is a contributory factor in the pathogenesis of the disease. Duke University in America and Warwick University are conducting research to explore genetic features of syringomyelia.

Surgical techniques are also being refined by the neurosurgical research community. Successful procedures expand the area around the cerebellum and spinal cord, thus improving the flow of cerebrospinal fluid thereby reducing the syrinx.

It is also important to understand the role of birth defects in the development of hindbrain malformations that can lead to syringomyelia as syringomyelia is a feature of intrauterine life and is also associated with spina bifida. Learning when these defects occur during the development of the fetus can help us understand this and similar disorders, and may lead to preventive treatment that can stop the formation of some birth abnormalities. Dietary supplements of folic acid prior to pregnancy have been found to reduce the number of cases of spina bifida and are also implicated in prevention of cleft palate and some cardiac defects.

Diagnostic technology is another area for continued research. MRI has enabled scientists to see conditions in the spine, including syringomyelia before symptoms appear. A new technology, known as dynamic MRI, allows investigators to view spinal fluid flow within the syrinx. CT scans allow physicians to see abnormalities in the brain, and other diagnostic tests have also improved greatly with the availability of new, non-toxic, contrast dyes.

Recent research has found that Dandy–Walker syndrome often occurs in patients with PHACES syndrome.

Vein of Galen malformations are devastating complications. Studies have shown that 77% of untreated cases result in mortality. Even after surgical treatment, the mortality rate remains as high as 39.4%. Most cases occur during infancy when the mortality rates are at their highest. Vein of Galen malformations are a relatively unknown affliction, attributed to the rareness of the malformations. Therefore, when a child is diagnosed with a faulty Great Cerebral Vein of Galen, most parents know little to nothing about what they are dealing with. To counteract this, support sites have been created which offer information, advice, and a community of support to the afflicted (, ).

Arachnoid cysts are seen in up to 1.1% of the population with a gender distribution of 2:1 male:female Only 20% of these have symptoms, usually from secondary hydrocephalus.

A study that looked at 2,536 healthy young males found a prevalence of 1.7% (95% CI 1.2 to 2.3%). Only a small percentage of the detected abnormalities require urgent medical attention.

Basilar invagination can be present at birth. If the condition develops after birth, it is usually the result of injury or diseases. If due to injury, about half the time it is caused by vehicle or bicycle accidents; 25% of the time by falls and 10% of the time by recreational activities such as diving accidents.

It also occurs in patients with bone diseases, such as osteomalacia, rheumatoid arthritis, Paget's disease, Ehlers-Danlos syndrome, Marfan syndrome, and osteogenesis imperfecta.