Classification systems for malformations of the cerebellum are varied and are constantly being revised as greater understanding of the underlying genetics and embryology of the disorders is uncovered. A classification proposed by Patel S in 2002 divides cerebellar malformations in two broad groups; those with cerebellar hypoplasia and; those with cerebellar dysplasia.

- I. Cerebellar hypoplasia

- A. Focal hypoplasia

- 1. Isolated vermis

- 2. One hemisphere hypoplasia

- B. Generalized hypoplasia

- 1. With enlarged fourth ventricle (“cyst,”), Dandy-Walker continuum

- 2. Normal fourth ventricle (no “cyst”)

- a. With normal pons

- b. With small pons i. Normal foliation

- a) Pontocerebellar hypoplasias of Barth, types I and II

- b) Cerebellar hypoplasias, not otherwise specified

There are various symptoms of colpocephaly and patients can experience effects ranging from mild to severe. Some patients do not show most of the symptoms related to colpocephaly, such as psychomotor abnormalilities and agenesis of the corpus callosum. In some cases, signs appear later on in life and a significant number of children suffer only from minor disabilities.

The following list includes common symptoms of colpocephaly.

- partial or complete agenesis of the corpus callosum

- intellectual disability

- motor abnormalities

- visual defects such as, crossing of the eyes, missing visual fields, and optic nerve hypoplasia

- spasticity

- seizures

- cerebral palsy

Intracranial abnormalities include:

- Microcephaly

- Agenesis of the corpus callosum

- Meningomyelocele

- Lissencephaly

- Periventricular leukomalacia (PVL)

- Enlargement of the cisterna magna

- Cerebellar hypoplasia

The key features of this syndrome are an enlargement of the fourth ventricle; complete absence of the cerebellar vermis, the posterior midline area of cerebellar cortex responsible for coordination of the axial musculature; and cyst formation near the internal base of the skull. An increase in the size of the fluid spaces surrounding the brain as well as an increase in pressure may also be present. The syndrome can appear dramatically or develop unnoticed.

Symptoms, which often occur in early infancy, include slower motor development and progressive enlargement of the skull. In older children, symptoms of increased intracranial pressure such as irritability, vomiting, and convulsions and signs of cerebellar dysfunction such as unsteadiness and lack of muscle coordination or jerky movements of the eyes may occur. Other symptoms include increased head circumference, bulging at the back of the skull, problems with the nerves that control the eyes, face and neck, and abnormal breathing patterns.

Dandy–Walker syndrome is frequently associated with disorders of other areas of the central nervous system including absence of the corpus callosum, the bundle of axons connecting the two cerebral hemispheres, and malformations of the heart, face, limbs, fingers and toes.

The Dandy–Walker complex is a genetically sporadic disorder that occurs one in every 30,000 live births. Prenatal diagnosis and prognosis of outcomes associated with Dandy–Walker can be difficult. Prenatal diagnosis is possible with ultrasound. Because the syndrome is associated with an increased risk for fetal karyotype abnormalities, amniocentesis can be offered after prenatal diagnosis. There is a relative contraindication of taking Warfarin during pregnancy, as it is associated with an increased risk of Dandy–Walker syndrome if taken during the first trimester.

Non-progressive early onset ataxia and poor motor learning are the commonest presentation.

The DWS malformation is the most severe presentation of the syndrome. The posterior fossa is enlarged and the tentorium is in high position. There is complete agenesis of the cerebellar vermis. There is also cystic dilation of the fourth ventricle, which fills the posterior fossa. This often involves hydrocephalus and complications due to associated genetic conditions, such as Spina Bifida.

Callosal disorders can be diagnosed through brain imaging studies or during autopsy. They may be diagnosed through an MRI, CT scan, Sonography, prenatal ultrasound, or prenatal MRI.

Some syndromes that frequently include ACC are Aicardi syndrome, Andermann syndrome, Shapiro syndrome, acrocallosal syndrome, septo-optic dysplasia (optic nerve hypoplasia), Mowat–Wilson syndrome, John Sayden syndrome, Menkes syndrome, and L1CAM Syndrome. Some conditions that are sometimes associated with ACC include maternal nutritional deficiencies or infections, metabolic disorders, fetal alcohol syndrome, craniofacial abnormalities, and other oral and maxillofacial pathologies.

Colpocephaly is characterized by disproportionately large occipital horns of the lateral ventricles (also frontal and temporal ventricles in some cases). MRI and CT scans of patients demonstrate abnormally thick gray matter with thin poorly myelinated white matter. This happens as a result of partial or complete absence of the corpus callosum. Corpus callosum is the band of white matter connecting the two cerebral hemispheres. The corpus callosum plays an extremely important role in interhemispheric communication, thus lack of or absence of these neural fibers results in a number of disabilities.

The lemon sign on CT scans of patients refers to the shape of the fetal skull when the frontal bones lose their normal convex contour and appear flattened or inwardly scalloped. This gives the skull a shape similar to that of a lemon. The sign is seen on transverse sonograms of the fetal cranium obtained at the level of the ventricles.

A special case is found in literature where lissencephaly, colpocephaly, and septal agenesis are all present together. The CT scans of the patient shows the ventricular system having a unique appearance of a crown of a king. This is referred to as the 'CROWN SIGN'.

Cerebellar agenesis is a rare condition in which a brain develops without the cerebellum. The cerebellum controls smooth movement, and when it does not develop, the rest of the brain must compensate, which it cannot do completely. The condition is not fatal on its own, but people born without a cerebellum experience severe developmental delays, language deficits, and neurological abnormalities. As children with cerebellar agenesis get older, their movements usually improve. It can co-exist with other severe malformations of the central nervous system, like anencephaly, holoprosencephaly, and microencephaly.

The condition was first reported in 1831. 10 cases had been reported as of 1998. Agenesis of one half or another part of the cerebellum is more common than complete agenesis.

Cerebellar agenesis can be caused by mutations in the PTF1A gene.

The classical triad of symptoms that defines 3C syndrome includes certain heart defects, hypoplasia (underdevelopment) of the cerebellum, and cranial dysmorphisms, which can take various forms. The heart defects and cranial dysmorphisms are heterogeneous in individuals who are all classed as having Ritscher-Schinzel syndrome.

Heart defects commonly seen with Ritscher-Schinzel syndrome are associated with the endocardial cushion and are the most important factor in determining a diagnosis. The mitral valve and tricuspid valve of the heart can be malformed, the atrioventricular canal can be complete instead of developing into the interatrial septum and interventricular septum, and conotruncal heart defects, which include tetralogy of Fallot, double outlet right ventricle, transposition of the great vessels, and hypoplastic left heart syndrome. Aortic stenosis and pulmonary stenosis have also been associated with 3C syndrome.

The cranial dysmorphisms associated with 3C syndrome are heterogeneous and include a degree of macrocephaly, a large anterior fontanel, a particularly prominent occiput and forehead, ocular hypertelorism (wide-set eyes), slanted palpebral fissures, cleft palate, a depressed nasal bridge, cleft palate with associated bifid uvula, low-set ears, micrognathia (an abnormally small jaw), brachycephaly (flattened head), and ocular coloboma. Low-set ears are the most common cranial dysmorphism seen in 3C syndrome, and ocular coloboma is the least common of the non-concurrent symptoms (cleft lip co-occurring with cleft palate is the least common).

Cranial dysplasias associated with 3C syndrome are also reflected in the brain. Besides the cerebellar hypoplasia, cysts are commonly found in the posterior cranial fossa, the ventricles and the cisterna magna are dilated/enlarged, and Dandy-Walker malformation is present. These are reflected in the developmental delays typical of the disease. 75% of children with 3C syndrome have Dandy-Walker malformation and hydrocephalus.

Signs and symptoms in other body systems are also associated with 3C syndrome. In the skeletal system, ribs may be absent, and hemivertebrae, syndactyly (fusion of fingers together), and clinodactyly (curvature of the fifth finger) may be present. In the GI and genitourinary systems, anal atresia, hypospadia (misplaced urethra), and hydronephrosis may exist. Adrenal hypoplasia and growth hormone deficiency are associated endocrine consequences of Ritscher-Schinzel syndrome. Some immunodeficiency has also been reported in connection with 3C syndrome.

Many children with the disorder die as infants due to severe congenital heart disease. The proband of Ritscher and Schinzel's original study was still alive at the age of 21.

A fetus with 3C syndrome may have an umbilical cord with one umbilical artery instead of two.

Symptoms vary according to the abnormality, but often feature poor muscle tone and motor function, seizures, developmental delays, mental retardation, failure to grow and thrive, difficulties with feeding, swelling in the extremities, and a smaller than normal head. Most infants with an NMD appear normal, but some disorders have characteristic facial or skull features that can be recognized by a neurologist.

More than 25 syndromes resulting from abnormal neuronal migration have been described. Among them are syndromes with several different patterns of inheritance; genetic counseling thus differs greatly between syndromes.

- Lissencephaly

- Microlissencephaly

- Schizencephaly

- Porencephaly

- Pachygyria

- Polymicrogyria

- Agyria

- Macrogyria

- Microgyria

- Micropolygyria

- Neuronal heterotopias

- Agenesis of the corpus callosum

- Agenesis of the cranial nerves

- Band heterotopias

Focal cortical dysplasia. Miller-Dieker syndrome, , Fukuyama congenital muscular dystrophy and Walker Warburg syndrome are genetic disorders associated with lissencephaly.

3C syndrome, also known as CCC dysplasia, Craniocerebellocardiac dysplasia or Ritscher–Schinzel syndrome, is a rare condition, whose symptoms include heart defects, cerebellar hypoplasia, and cranial dysmorphism. It was first described in the medical literature in 1987 by Ritscher and Schinzel, for whom the disorder is sometimes named.

Neu-Laxova syndrome presents with severe malformations leading to prenatal or neonatal death. Typically, NLS involves characteristic facial features, decreased fetal movements and skin abnormalities.

Fetuses or newborns with Neu–Laxova syndrome have typical facial characteristics which include proptosis (bulging eyes) with eyelid malformations, nose malformations, round and gaping mouth, micrognathia (small jaw) and low set or malformed ears. Additional facial malformations may be present, such as cleft lip or cleft palate. Limb malformations are common and involve the fingers (syndactyly), hands or feet. Additionally, edema and flexion deformities are often present. Other features of NLS are severe intrauterine growth restriction, skin abnormalities (ichthyosis and hyperkeratosis) and decreased movement.

Malformations in the central nervous system are frequent and may include microcephaly, lissencephaly or microgyria, hypoplasia of the cerebellum and agenesis of the corpus callosum. Other malformations may also be present, such as neural tube defects.

Ethmocephaly is a type of cephalic disorder caused by holoprosencephaly. Ethmocephaly is the least common facial anomaly. It consists of a proboscis separating narrow-set eyes with an absent nose and microphthalmia (abnormal smallness of one or both eyes). Cebocephaly, another facial anomaly, is characterized by a small, flattened nose with a single nostril situated below incomplete or underdeveloped closely set eyes.

The least severe in the spectrum of facial anomalies is the median cleft lip, also called premaxillary agenesis.

Although the causes of most cases of holoprosencephaly remain unknown, some may be due to dominant or chromosome causes. Such chromosomal anomalies as trisomy 13 and trisomy 18 have been found in association with holoprosencephaly, or other neural tube defects. Genetic counseling and genetic testing, such as amniocentesis, is usually offered during a pregnancy if holoprosencephaly is detected. The recurrence risk depends on the underlying cause. If no cause is identified and the fetal chromosomes are normal, the chance to have another pregnancy affected with holoprosencephaly is about 6%.

There is no treatment for holoprosencephaly and the prognosis for individuals with the disorder is poor. Most of those who survive show no significant developmental gains. For children who survive, treatment is symptomatic. It is possible that improved management of diabetic pregnancies may help prevent holoprosencephaly, however there is no means of primary prevention.

Aniridia ataxia renal agenesis psychomotor retardation is a rare genetic disorder characterized by missing irises of the eye, ataxia, psychomotor retardation and abnormal kidneys. It is detected via genetic test.

This condition exists in a variety of forms, ranging from partial absence of the tail bone regions of the spine to absence of the lower vertebrae, pelvis and parts of the thoracic and/or lumbar areas of the spine. In some cases where only a small part of the spine is absent, there may be no outward sign of the condition. In cases where more substantial areas of the spine are absent, there may be fused, webbed, or smaller lower extremities and paralysis. Bowel and bladder control is usually affected.

Eye agenesis is a medical condition in which people are born with no eyes.

Symptoms begin in infancy and include:

- hypotonia

- areflexia

- amyotrophy

- variable degrees of dysgenesis of the corpus callosum

- mild to severe intellectual and developmental delay

- psychiatric problems including paranoid delusions, depression, hallucinations and autistic-like behavior

Neu–Laxova syndrome (also known as Neu syndrome or Neu-Povysilová syndrome, abbreviated as NLS) is a rare autosomal recessive disorder characterized by severe intrauterine growth restriction and multiple congenital malformations. Neu–Laxova syndrome is a very severe disorder, leading to stillbirth or neonatal death. It was first described by Dr. Richard Neu in 1971 and Dr. Renata Laxova in 1972 as a lethal disorder in siblings with multiple malformations. Neu–Laxova syndrome is an extremely rare disorder with less than 100 cases reported in medical literature.

Caudal regression syndrome or sacral agenesis (or hypoplasia of the sacrum) is a congenital disorder in which there is abnormal fetal development of the lower spine—the caudal partition of the spine.

It occurs at a rate of approximately one per 25,000 live births.

13q deletion syndrome is a rare genetic disease caused by the deletion of some or all of the large arm of human chromosome 13. It causes intellectual disability and congenital malformations that affect a variety of organ systems.

In medicine, agenesis () refers to the failure of an organ to develop during embryonic growth and development due to the absence of primordial tissue. Many forms of agenesis are referred to by individual names, depending on the organ affected:

- Agenesis of the corpus callosum - failure of the Corpus callosum to develop

- Renal agenesis - failure of one or both of the kidneys to develop

- Phocomelia - failure of the arms or legs to develop

- Penile agenesis - failure of penis to develop

- Müllerian agenesis - failure of the uterus and part of the vagina to develop

- Agenesis of the gallbladder - failure of the Gallbladder to develop. A person may not realize they have this condition unless they undergo surgery or medical imaging, since the gallbladder is neither externally visible nor essential.

Hydrolethalus can be readily diagnosed during pregnancy through the use of ultrasound, which will often reveal hydrocephaly and an abnormal structure of the brain.

Different areas of deletion are associated with different symptoms. Deletions from the centromere to 13q32 or any deletions including the 13q32 band are associated with slow growth, intellectual disability, and congenital malformations. Deletions from 13q33 to the end of the chromosome are associated with intellectual disability. Intellectual disabilities range from very mild to very severe, and can co-occur with behavioral disorders and/or autism spectrum disorders.

At birth, the main symptoms include low weight (due to intrauterine growth restriction), hypotonia, and feeding difficulties. Infants may also have cleft palate.

13q deletion syndrome gives a characteristic appearance to affected individuals, potentially including microphthalmia (small eyes), hypertelorism (wide-set eyes), thin forehead, high palate, underdeveloped midface, small mouth, small nose, broad, flat nasal bridge, short neck, low hairline, irregular or wrongly positioned teeth, low-set ears, micrognathia (small jaw), tooth enamel defects, short stature, microcephaly (small head), a prominent, long philtrum, and earlobes turned inwards.

Congenital heart disease is associated with 13q deletion syndrome. Common defects include atrial septal defect, tetralogy of Fallot, ventricular septal defect, patent ductus arteriosus, pulmonary stenosis, and coarctation of the aorta. Defects of the endocrine system, digestive system, and genitourinary system are also common. These include underdevelopment or agenesis of the pancreas, adrenal glands, thymus, gallbladder, and thyroid; Hirschsprung's disease; gastric reflux, imperforate anus, retention testis, ectopic kidney, renal agenesis, and hydronephrosis.

A variety of brain abnormalities are also associated with 13q deletion. They can include epilepsy, craniosynostosis (premature closing of the skull bones), spastic diplegia, cerebral hypotrophy, underdevelopment or agenesis of the corpus callosum, cerebellar hypoplasia, deafness, and, rarely, hydrocephalus, Dandy–Walker syndrome, and spina bifida. The eyes can be severely damaged and affected individuals may be blind. They may also have coloboma of the iris or choroid, strabismus, nystagmus, glaucoma, or cataracts.

Other skeletal malformations are found with 13q deletion syndrome, including syndactyly, clubfoot, clinodactyly, and malformations of the vertebrae and/or thumbs.

Deletions that include the 13q32 band, which contains the brain development gene ZIC2, are associated with holoprosencephaly; they are also associated with hand and foot malformations. Deletions that include the 13q14 band, which contains the tumor suppressor gene Rb, are associated with a higher risk of developing retinoblastoma, which is more common in XY children. Deletion of the 13q33.3 band is associated with hypospadias. Other genes in the potentially affected region include NUFIP1, HTR2A, PDCH8, and PCDH17.