Children affected by pilocytic astrocytoma can present with different symptoms that might include failure to thrive (lack of appropriate weight gain/ weight loss), headache, nausea, vomiting, irritability, torticollis (tilt neck or wry neck) difficulty to coordinate movements and visual complaints (including nystagmus). The complaints may vary depending on the location and size of the neoplasm. The most common symptoms are associated with increased intracranial pressure due to the size of the neoplasm.

Lhermitte–Duclos disease (LDD) (), also called dysplastic gangliocytoma of the cerebellum, is a rare, slowly growing tumor of the cerebellum, a gangliocytoma sometimes considered to be a hamartoma, characterized by diffuse hypertrophy of the granular layer of the cerebellum. It is often associated with Cowden syndrome. It was described by Jacques Jean Lhermitte and P. Duclos in 1920.

Pilocytic astrocytoma or juvenile pilocytic astrocytoma or cystic cerebellar astrocytoma (and its variant juvenile pilomyxoid astrocytoma) is a brain tumor that occurs more often in children and young adults (in the first 20 years of life). They usually arise in the cerebellum, near the brainstem, in the hypothalamic region, or the optic chiasm, but they may occur in any area where astrocytes are present, including the cerebral hemispheres and the spinal cord. These tumors are usually slow growing and benign. The neoplasms are associated with the formation of a single (or multiple) cyst(s), and can become very large.

Pilocytic astrocytomas are often cystic, and, if solid, tend to be well-circumscribed. It is characteristically easily seen on Computed tomography (CT scans) and Magnetic Resonance Imaging (MRI).

Juvenile pilocytic astrocytoma is associated with neurofibromatosis type 1 (NF1), and optic gliomas are among the most frequently encountered tumors in patients with this disorder. The majority of pilocytic astrocytomas have a unique KIAA1549-BRAF fusion gene.

Main clinical signs and symptoms include:

- headache

- movement disorders

- tremor

- visual disturbances

- abnormal EEG

- Diplopia

Patients with Lhermitte–Duclos disease and Cowden's syndrome may also have multiple growths on skin. The tumor, though benign, may cause neurological injury including abnormal movements.

MICROSCOPY(lhermitte-duclos disease)

1>Enlarged circumscribed cerebellar folia

2>internal granular layer is focally indistinct and is occupied by large ganglion cells

3>myelinated tracks in outer molecular layer

4>underlying white matter is atrophic and gliotic

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

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

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.

Diagnosis is usually based on clinical observation. Various sets of criteria have been suggested to identify the disorder in an individual patient, all of which include macrocephaly and a number of the following: somatic overgrowth, cutis marmorata, midline facial birthmark, polydactyly/syndactyly, asymmetry (hemihyperplasia or hemihypertrophy), hypotonia at birth, developmental delay, connective tissue defect and frontal bossing. Currently no consensus exists about which diagnostic criteria are definitive and so evaluation by a medical geneticist or other clinician with familiarity with the syndrome is usually needed to provide diagnostic certainty. It is not clear if there are some features which are mandatory to make the diagnosis, but macrocephaly appears essentially universal though may not be congenital. The distinctive vascular abnormalities of the skin often fade over time, making the diagnosis challenging in older children with this condition.

The brain can be affected in several ways in this syndrome. Some children are born with structural brain anomalies such as cortical dysplasia or polymicrogyria. While developmental delay is nearly universal in this syndrome it is variable in severity, with the majority having mild to moderate delays and a minority having severe cognitive impairment. Some patients are affected with a seizure disorder. White matter abnormalities on magnetic resonance imaging (MRI), suggesting a delay in white matter myelination, is commonly seen in early childhood. Some patients may have asymmetry of the brain, with one side being noticeably larger than the other.

One interesting phenomenon that seems very common in this syndrome is the tendency for disproportionate brain growth in the first few years of life, with crossing of percentiles on the head circumference growth charts. A consequence of this disproportionate brain growth appears to be a significantly increased risk of cerebellar tonsillar herniation (descent of the cerebellar tonsils through the foramen magnum of the skull, resembling a Chiari I malformation neuroradiologically) and ventriculomegaly/hydrocephalus. Such cerebellar tonsil herniation may occur in up to 70% of children with M-CM.

The medical literature suggests that there is a risk of cardiac arrhythmias in early childhood. The cause for this is unknown. In addition, a variety of different congenital cardiac malformations have been reported in a small number of patients with this disorder.

Like other syndromes associated with disproportionate growth, there appears to be a slightly increased risk of certain types of childhood malignancies in M-CM (such as Wilms' tumor). However, the precise incidence of these malignancies is unclear.

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.

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 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.

Neuroimaging like MRI is important. However, there was considerable intrafamilial variability regarding neuroimaging, with some individuals showing normal MRI findings. Early individual prognosis of such autosomal recessive cerebellar ataxias is not possible from early developmental milestones, neurological signs, or neuroimaging.

Non-progressive congenital ataxia (NPCA) is a non-progressive form of cerebellar ataxia which can occur with or without cerebellar hypoplasia.

The blockage of cerebrospinal fluid (CSF) flow may also cause a syrinx to form, eventually leading to syringomyelia. Central cord symptoms such as hand weakness, dissociated sensory loss, and, in severe cases, paralysis may occur.

A lateral pontine syndrome is a lesion which is similar to the lateral medullary syndrome, but because it occurs in the pons, it also involves the cranial nerve nuclei of the pons.

Chiari malformations (CMs) are structural defects in the cerebellum. They consist of a downward displacement of the cerebellar tonsils through the foramen magnum (the opening at the base of the skull), sometimes causing non-communicating hydrocephalus as a result of obstruction of cerebrospinal fluid (CSF) outflow. The cerebrospinal fluid outflow is caused by phase difference in outflow and influx of blood in the vasculature of the brain. The malformation is named for Austrian pathologist Hans Chiari. A type II CM is also known as an Arnold–Chiari malformation in honor of Chiari and German pathologist Julius Arnold.

CMs can cause headaches, difficulty swallowing (sometimes accompanied by gagging), choking and vomiting, dizziness, nausea, neck pain, unsteady gait (problems with balance), poor hand coordination (fine motor skills), numbness and tingling of the hands and feet, and speech problems (such as hoarseness).

Less often, people with Chiari malformation may experience ringing or buzzing in the ears (tinnitus), weakness, slow heart rhythm, or fast heart rhythm, curvature of the spine (scoliosis) related to spinal cord impairment, abnormal breathing, such as central sleep apnea, characterized by periods of breathing cessation during sleep, and, in severe cases, paralysis.

Usually symptoms of cerebellar hypoplasia can be seen immediately at birth in cats, but sometimes can take two months or so to become apparent in dogs. Cerebellar hypoplasia causes jerky movements, tremors and generally uncoordinated motion. The animal often falls down and has trouble walking. Tremors increase when the animal is excited and subside when at ease.

Onset of symptoms usually occur in early adulthood and is characterized by intention tremor, progressive ataxia, convulsions, and myoclonic epileptic jerks.

Tremors usually affect one extremity, primarily the upper limb, and eventually involve the entire voluntary motor system. Overall, the lower extremity is usually disturbed less often than the upper extremity.

Additional features of the syndrome include: an unsteady gait, seizures, muscular hypotonia, reduced muscular coordination, asthenia, adiadochokinesia and errors with estimating range, direction, and force of voluntary movements. Mental deterioration can occur, however it is rare.

The condition usually consists of:

Sensation to the face is preserved, due to the sparing of the trigeminal nucleus.

The syndrome is said to be "alternating" because the lesion causes symptoms both contralaterally and ipsilaterally. Sensation of pain and temperature is preserved, because the spinothalamic tract is located more laterally in the brainstem and is also not supplied by the anterior spinal artery (instead supplied by the posterior inferior cerebellar arteries and the vertebral arteries).

Damage to the following areas produces symptoms (from medial to lateral):

The combination of muscular hypotonia and fixed dilated pupils in infancy is suspicious of Gillespie syndrome. Early onset partial aniridia, cerebellar ataxia, and mental retardation are hallmark of syndrome. The iris abnormality is specific and seems pathognomonic of Gillespie syndrome. The aniridia consisting of a superior coloboma and inferior iris hypoplasia, foveomacular dysplasia.

Atypical Gillespie syndrome associated with bilateral ptosis, exotropia, correctopia, iris hypoplasia, anterior capsular lens opacities, foveal hypoplasia, retinal vascular tortuosity, and retinal hypopigmentation.

Neurological signs ar nystagmus, mild craniofacial asymmetry, axial hypotonia, developmental delay, and mild mental retardation. Mariën P did not support the prevailing view of a global mental retardation as a cardinal feature of Gillespie syndrome but primarily reflect cerebellar induced neurobehavioral dysfunctions following disruption of the cerebrocerebellar anatomical circuitry that closely resembles the "cerebellar cognitive and affective syndrome" (CeCAS).

Congenital pulmonary stenosis and helix dysplasia can be associated.

Pontocerebellar hypoplasia is classified as follows:

Pontine and cerebellar hypoplasia is also observed in certain phenotypes of X-linked mental retardation – so called MICPCH.

FHM signs overlap significantly with those of migraine with aura. In short, FHM is typified by migraine with aura associated with hemiparesis and, in FHM1, cerebellar degeneration. This cerebellar degeneration can result in episodic or progressive ataxia. FHM can also present with the same signs as benign familial infantile convulsions (BFIC) and alternating hemiplegia of childhood. Other symptoms are altered consciousness (in fact, some cases seem related to head trauma), gaze-evoked nystagmus and coma. Aura symptoms, such as numbness and blurring of vision, typically persist for 30–60 minutes, but can last for weeks and months. An attack resembles a stroke, but unlike a stroke, it resolves in time. These signs typically first manifest themselves in the first or second decade of life.

Deep brain stimulation may provide relief from some symptoms of Benedikt syndrome, particularly the tremors associated with the disorder.

Autosomal recessive cerebellar ataxia type 1 (ARCA1) is a condition characterized by progressive problems with movement. Signs and symptoms of the disorder first appear in early to mid-adulthood. People with this condition initially experience impaired speech (dysarthria), problems with coordination and balance (ataxia), or both. They may also have difficulty with movements that involve judging distance or scale (dysmetria). Other features of ARCA1 include abnormal eye movements (nystagmus) and problems following the movements of objects with their eyes. The movement problems are slowly progressive, often resulting in the need for a cane, walker, or wheelchair.