The cause of polymicrogyria is unclear. It is currently classified as resulting from abnormalities during late neuronal migration or early cortical organization of fetal development. Evidence for both genetic and non-genetic causes exists. Polymicrogyria appears to occur around the time of neuronal migration or early cortical development. Non-genetic causes include defects in placental oxygenation and in association with congenital infections, particularly cytomegalovirus.

An association with the gene WDR62 has been identified.

Because pachygyria is a structural defect no treatments are currently available other than symptomatic treatments, especially for associated seizures. Another common treatment is a gastrostomy (insertion of a feeding tube) to reduce possible poor nutrition and repeated aspiration pneumonia.

The term 'pachygyria' does not directly relate to a specific malformation but rather is used to generally describe physical characteristics of the brain in association with several neuronal migration disorders; most commonly disorders relating to varied degrees of lissencephaly. Lissencephaly is present in 1 of 85,470 births and the life span of those affected is short as only a few survive past the age of 20.

Pachygyria is a condition identified by a type of cortical genetic malformation. Clinicians will subjectively determine the malformation based on the degree of malposition and the extent of thickened abnormal grey differentiation present.

Approximately one out of every 50 (2%) children in the general population are said to have megalencephaly. Additionally, it is said that megalencephaly affects 3–4 times more males than females.

Those individuals that are classified with macrocephaly, or general head overgrowth, are said to have megalencephaly at a rate of 10–30% of the time.

Parents of a proband

- The parents of an affected individual are obligate heterozygotes and therefore carry one mutant allele.

- Heterozygotes (carriers) are asymptomatic.

Sibs of a proband

- At conception, each sibling of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.

- Once an at-risk sibling is known to be unaffected, the risk of his/her being a carrier is 2/3.

- Heterozygotes (carriers) are asymptomatic.

Offspring of a proband

- Offspring of a proband are obligate heterozygotes and will therefore carry one mutant allele.

- In populations with a high rate of consanguinity, the offspring of a person with GPR56-related BFPP and a reproductive partner who is a carrier of GPR56-related BFPP have a 50% chance of inheriting two GPR56 disease-causing alleles and having BFPP and a 50% chance of being carriers.

Other family members of a proband.

- Each sibling of the proband's parents is at a 50% risk of being a carrier

Polymicrogyria (PMG) is a condition that affects the development of the human brain by multiple small gyri (microgyri) creating excessive folding of the brain leading to an abnormally thick cortex. This abnormality can affect either one region of the brain or multiple regions.

The time of onset has yet to be identified; however, it has been found to occur before birth in either the earlier or later stages of brain development. Early stages include impaired proliferation and migration of neuroblasts, while later stages show disordered post-migration development.

The symptoms experienced differ depending on what part of the brain is affected. There is no specific treatment to get rid of this condition, but there are medications that can control the symptoms such as seizures, delayed development or weakened muscles as some of the noted effects.

The prognosis of megalencephaly depends heavily on the underlying cause and associated neurological disorders. Because the majority of megalencephaly cases are linked with autism, the prognosis is equivalent to the corresponding condition.

Since, hemimegalencephaly is associated with severe seizures, hemiparesis and mental retardation, the result is a poor prognosis. In most cases, those diagnosed with this type of megalencephaly usually do not survive through adulthood.

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.

Bilateral frontoparietal polymicrogyria (BFPP) is a genetic disorder with autosomal recessive inheritance that causes a cortical malformation. Our brain has folds in the cortex to increase surface area called gyri and patients with polymicrogyri have an increase number of folds and smaller folds than usual. Polymicrogyria is defined as a cerebral malformation of cortical development in which the normal gyral pattern of the surface of the brain is replaced by an excessive number of small, fused gyri separated by shallow sulci and abnormal cortical lamination. From ongoing research, mutation in GPR56, a member of the adhesion G protein-coupled receptor (GPCR) family, results in BFPP. These mutations are located in different regions of the protein without any evidence of a relationship between the position of the mutation and phenotypic severity. It is also found that GPR56 plays a role in cortical pattering.

In the developing brain, neural stem cells must migrate from the areas where they are born to the areas where they will settle into their proper neural circuits. Neuronal migration, which occurs as early as the second month of gestation, is controlled by a complex assortment of chemical guides and signals. When these signals are absent or incorrect, neurons do not end up where they belong. This can result in structurally abnormal or missing areas of the brain in the cerebral hemispheres, cerebellum, brainstem, or hippocampus.

Several genetic abnormalities in children with NMDs have been identified. Defects in genes that are involved in neuronal migration have been associated with NMDs, but the role they play in the development of these disorders is not yet well understood.

A study in Sweden investigated the impact of environmental factors on NMDs. The study indicated that there might be an impact of low or subnormal maternal BMI before and during pregnancy, maternal infection, such as rubella, and maternal smoking on fetal brain development, including neuronal migration. The roles of maternal BMI and congenital infections should be tested in future analytical studies.

NMDs occur in the instance that 1) neuroblasts do not migrate from all of the ventricles or migrate only part of the way, 2) only some of the neuroblasts reach the cortical layer, 3) neuroblasts overshoot the appropriate cortical layer and protrude into the subarachnoid space, or 4) the late stage organization of the neuronal layer in the cortex is disrupted. Abnormal migration ultimately results in abnormal gyral formation.

Neuronal migration disorder (NMD) refers to a heterogenous group of disorders that, it is supposed, share the same etiopathological mechanism: a variable degree of disruption in the migration of neuroblasts during neurogenesis. The neuronal migration disorders are cerebral dysgenesis, brain malformations caused by primary alterations during neurogenesis; on the other hand, brain malformations are highly diverse and refer to any insult to the brain during its formation and maturation due to intrinsic or extrinsic causes that ultimately will alter the normal brain anatomy. However, there is some controversy in the terminology because virtually any malformation will involve neuroblast migration, either primarily or secondarily.

Congenital bilateral perisylvian syndrome (CBPS) is a rare neurological disease characterized by paralysis of certain facial muscles and epileptic seizures.

Causes of lissencephaly can include viral infections of the uterus or the fetus during the first trimester, or insufficient blood supply to the fetal brain early in pregnancy. There are also a number of genetic causes of lissencephaly, including mutation of the reelin gene (on chromosome 7), as well as other genes on the X chromosome and on chromosome 17. Genetic counseling is usually offered if there is a risk of lissencephaly, coupled with genetic testing.

The prognosis for children with lissencephaly varies depending on the malformation. Many individuals remain in a 3–5 month developmental level. Some children with lissencephaly will be able to roll over, sit, reach for objects, and smile socially. Aspiration and respiratory disease are the most common causes of illness or death. In the past, life expectancy was said to be around two years of age. However, with advances in seizure control, and treatments for respiratory illness, most children live well beyond that age. With other advances in therapy, and the broader availability of services and equipment, some children with lissencephaly are able to walk with varying degrees of assistance and to perform other functions once thought too advanced.

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.

Microlissencephaly is listed in Orphanet database as a rare disease. There is no much information available about the epidemiology of microlissencepahly in literature. A PhD thesis has estimated the prevalence of microlissencepahly in South–Eastern Hungary between July 1992 and June 2006 to be a case every 91,000 live births (0.11:10,000).

Though the underlying cause of CBPS is unknown, it is thought to arise from improper migration of neuroblasts (neuronal stem cells) to the cerebral cortex in the embryonic brain. This causes the layers of the cerebral cortex to not form properly, and too many small folds (gyri) to form on the surface of the brain. This condition is called bilateral perisylvian polymicrogyria. The sulci, deep grooves on the brain, may also not form correctly. Cranial nerves are affected and cause muscle paralysis and spasms in the face and throat.

Microlissencephaly (MLIS) is a rare congenital brain disorder that combines severe microcephaly (small head) with lissencephaly (smooth brain surface due to absent sulci and gyri). Microlissencephaly is a heterogeneous disorder i.e. it has many different causes and a variable clinical course. Microlissencephaly is a malformation of cortical development (MCD) that occurs due to failure of neuronal migration between the third and fifth month of gestation as well as stem cell population abnormalities. Numerous genes have been found to be associated with microlissencephaly, however, the pathophysiology is still not completely understood.

The combination of lissencephaly with severe congenital microcephaly is designated as microlissencephaly only when the cortex is abnormally thick. If such combination exists with a normal cortical thickness (2.5 to 3 mm), it is known as "microcephaly with simplified gyral pattern" (MSGP). Both MLIS and MSGP have a much more severe clinical course than microcephaly alone. They are inherited in autosomal recessive manner. Prior to 2000, the term “microlissencephaly” was used to designate both MLIS and MSGP.

Strokes are one of the most common causes of Foix-Chavany-Marie Syndrome. The type of strokes associated with this syndrome include embolic and thrombotic strokes. Strokes affecting the middle cerebral artery and the branches that pass through or near the operculum are characteristic of FCMS.

Symptoms of infections specifically HIV and Herpes simplex encephalitis can cause FCMS. Numerous lesions can develop with HIV infections, which likely result in the development of FCMS.

Prognosis varies widely depending on severity of symptoms, degree of intellectual impairment, and associated complications. Because the syndrome is rare and so newly identified, there are no long term studies.

The prognosis varies widely from case to case, depending on the severity of the symptoms. However, almost all people reported with Aicardi syndrome to date have experienced developmental delay of a significant degree, typically resulting in mild to moderate to profound intellectual disability. The age range of the individuals reported with Aicardi syndrome is from birth to the mid 40s.

There is no cure for this syndrome.

Worldwide prevalence of Aicardi Syndrome is estimated at several thousand, with approximately 900 cases reported in the United States.

There is no cure for this condition. Treatment is supportive and varies depending on how symptoms present and their severity. Some degree of developmental delay is expected in almost all cases of M-CM, so evaluation for early intervention or special education programs is appropriate. Rare cases have been reported with no discernible delay in academic or school abilities.

Physical therapy and orthopedic bracing can help young children with gross motor development. Occupational therapy or speech therapy may also assist with developmental delays. Attention from an orthopedic surgeon may be required for leg length discrepancy due to hemihyperplasia.

Children with hemihyperplasia are thought to have an elevated risk for certain types of cancers. Recently published management guidelines recommend regular abdominal ultrasounds up to age eight to detect Wilms' tumor. AFP testing to detect liver cancer is not recommended as there have been no reported cases of hepatoblastoma in M-CM patients.

Congenital abnormalities in the brain and progressive brain overgrowth can result in a variety of neurological problems that may require intervention. These include hydrocephalus, cerebellar tonsillar herniation (Chiari I), seizures and syringomyelia. These complications are not usually congenital, they develop over time often presenting complications in late infancy or early childhood, though they can become problems even later. Baseline brain and spinal cord MRI imaging with repeat scans at regular intervals is often prescribed to monitor the changes that result from progressive brain overgrowth.

Assessment of cardiac health with echocardiogram and EKG may be prescribed and arrhythmias or abnormalities may require surgical treatment.

Infectious diseases are transmitted in several ways. Some of these infections may affect the brain or spinal cord directly. Generally, an infection is a disease that is caused by the invasion of a microorganism or virus.