Small tumors (e.g., < 2.0 cm) usually are incidental findings at autopsy without having caused symptoms. Larger tumors may cause symptoms, depending on the size and location.

- Focal seizures may be caused by meningiomas that overlie the cerebrum.

- Progressive spastic weakness in legs and incontinence may be caused by tumors that overlie the parasagittal frontoparietal region.

- Tumors of the Sylvian aqueduct may cause myriad motor, sensory, aphasic, and seizure symptoms, depending on the location.

- Increased intracranial pressure eventually occurs, but is less frequent than in gliomas.

- Diplopia (Double vision) or uneven pupil size may be symptoms if related pressure causes a third and/or sixth nerve palsy.

Meningioma, also known as meningeal tumor, is typically a slow-growing tumor that forms from the meninges, the membranous layers surrounding the brain and spinal cord. Symptoms depend on the location and occur as a result of the tumor pressing on nearby tissue. Many cases never produce symptoms. Occasionally seizures, dementia, trouble talking, vision problems, one sided weakness, or loss of bladder control may occur.

Risk factors include exposure to ionizing radiation such as during radiation therapy, a family history of the condition, and neurofibromatosis type 2. As of 2014 they do not appear to be related to cell phone use. They appear to be able to form from a number of different types of cells including arachnoid cells. Diagnosis is typically by medical imaging.

If there are no symptoms, periodic observation may be all that is required. Most cases that result in symptoms can be cured by surgery. Following complete removal less than 20% recur. If surgery is not possible or all the tumor cannot be removed radiosurgery may be helpful. Chemotherapy has not been found to be useful. A small percentage grow rapidly and are associated with worse outcomes.

About one per thousand people in the United States are currently affected. Onset is usually in adults. In this group they represent about 30% of brain tumors. Women are affected about twice as often as men. Meningiomas were reported as early as 1614 by Felix Plater.

The cerebellopontine angle is the anatomic space between the cerebellum and the pons filled with cerebrospinal fluid. This is a common site for the growth of acoustic neuromas or schwannomas. A distinct neurologic syndrome of deficits occurs due to the anatomic proximity of the cerebellopontine angle to specific cranial nerves. Indications include unilateral hearing loss (85%), speech impediments, disequilibrium, tremors or other loss of motor control.

Tumors within the nerve canaliculi initially present with unilateral sensorineural hearing loss, unilateral tinnitus, or disequilibrium (vertigo is rare, on account of the slow growth of neuromas). Speech discrimination out of proportion to hearing loss, difficulty talking on the telephone are frequent accompaniments. Tumors extending into the CPA will likely present with disequilibrium or ataxia depending on the amount of extension on the brainstem. With brainstem extension, midfacial and corneal hypesthesia, hydrocephalus, and other cranial neuropathies become more prevalent.

For example, involvement of CN V from a cerebellopontine mass lesion often results in loss of the ipsilateral (same side of the body) corneal reflex (involuntary blink).

Patients with larger tumours can develop Bruns nystagmus ('dancing eyes') due to compression of the flocculi.

Symptoms are assessed on a case by case basis. Some cysts in the CNS can be asymptomatic (producing or showing no symptoms), depending on their location in the brain or spinal cord. If the cysts develop in critical areas of the central nervous system, they can present one or more of the following symptoms:

- Pressure in the spinal cord or brain

- Rupture of nerves around the cyst

- Weakness in specific parts of the body controlled by the cyst-infected brain region

- Inflammation

- Hydrocephalus

- Brainstem hemorrhage

- Seizures

- Visual disturbances and hearing Loss

- Headache

- Difficulty with balance or walking

In general, symptoms vary depending on the type of cyst and its location within the CNS.

Malignant meningioma is a rare, fast-growing tumor that forms in one of the inner layers of the meninges (thin layers of tissue that cover and protect the brain and spinal cord). Malignant meningioma often spreads to other areas of the body.

The World Health Organization classification system defines both grade II and grade III meningiomas as malignant. Historically, histological subtypes have also been used in classification including:

- clear cell (WHO grade II),

- chordoid (WHO grade II),

- rhabdoid (WHO grade III), and

- papillary (WHO grade III)

Benign or low grade meningiomas (WHO grade I) include meningothelial, fibrous, transitional, psammomatous, angiomatous, microcystic, secretory, lymphoplasmacyte-rich, and metaplastic.

There are many subtypes of lipomas:

- Adenolipomas are lipomas associated with eccrine sweat glands.

- Angiolipoleiomyomas are acquired, solitary, asymptomatic nodules, characterized histologically by well-circumscribed subcutaneous tumors composed of smooth muscle cells, blood vessels, connective tissue, and fat.

- Angiolipomas are painful subcutaneous nodules having all other features of a typical lipoma.

- Cerebellar pontine angle and internal auditory canal lipomas

- Chondroid lipomas are deep-seated, firm, yellow tumors that characteristically occur on the legs of women.

- Corpus callosum lipoma is a rare congenital brain condition that may or may not present with symptoms. This occurs in the corpus callosum, also known as the calossal commissure, which is a wide, flat bundle of neural fibers beneath the cortex in the human brain.

- Hibernomas are lipomas of brown fat.

- Intradermal spindle cell lipomas are distinct in that they most commonly affect women and have a wide distribution, occurring with relatively equal frequency on the head and neck, trunk, and upper and lower extremities.

- Neural fibrolipomas are overgrowths of fibro-fatty tissue along a nerve trunk, which often leads to nerve compression.

- Pleomorphic lipomas, like spindle-cell lipomas, occur for the most part on the backs and necks of elderly men and are characterized by floret giant cells with overlapping nuclei.

- Spindle-cell lipomas are asymptomatic, slow-growing subcutaneous tumors that have a predilection for the posterior back, neck, and shoulders of older men.

- Superficial subcutaneous lipomas, the most common type of lipoma, lie just below the surface of the skin. Most occur on the trunk, thigh, and forearm, although they may be found anywhere in the body where fat is located.

Hemangiopericytoma located in the cerebral cavity is an aggressive tumor of the Mesenchyme with oval nuclei with scant cytoplasm. "There is dense intercellular reticulin staining. Tumor cells can be fibroblastic, myxoid, or pericytic. These tumors, in contrast to meningiomas, do not stain with epithelial membrane antigen. They have a grade 2 or 3 biological behavior, and need to be distinguished from benign meningiomas because of their high rate of recurrence (68.2%) and metastases (Maier et al. 1992; Kleihues et al. 1993 )."

This category of cysts takes over areas of necrotic tissue in the brain from injuries, diseases, or abnormalities, which occur due to the central nervous system's nonregenerative nature. These cysts can affect all germ layers of the CNS, but are most common in the arachnoid mater, and the ventricular space, which may block CSF pathways. These cysts can be static (stationary) or progressive. Some examples of cysts originating from the CNS tissue include:

- Arachnoid cysts (Leptomeningeal cysts)

- Ependymal cysts

- Cystic cerebellar astrocytomas

- Colloid cysts

A diffuse intrinsic pontine glioma (DIPG) is a tumour located in the pons (middle) of the brain stem. The brain stem is the bottommost portion of the brain, connecting the cerebrum with the spinal cord. The majority of brain stem tumours occur in the pons and are diffusely infiltrating (they grow amidst the nerves), and therefore cannot be surgically removed. Glioma is a general name for any tumour that arises from the supportive tissue called glia, which help keep the neurons in place and functioning well. The brain stem contains all of the afferent (incoming) neurons within the spinal cord, as well as important structures involved in eye movements and in face and throat muscle control and sensation.

DIPG has a 5-year survival rate of <1%. The median overall survival of children diagnosed with DIPG is approximately 9 months. The 1- and 2-year survival rates are approximately 30% and less than 10%, respectively. These statistics make DIPG one of the most devastating pediatric cancers. Although 75–85% of patients show some improvement in their symptoms after radiation therapy, DIPGs almost always begin to grow again (called recurrence, relapse, or progression). Clinical trials have reported that the median time between radiation therapy and progression is 5–8.8 months. Patients whose tumors begin to grow again may be eligible for experimental treatment through clinical trials to try to slow or stop the growth of the tumor. However, clinical trials have not shown any significant benefit from experimental DIPG therapies so far.

DIPGs that progress usually grow quickly and affect important parts of the brain. The median time from tumor progression to death is usually very short, between 1 and 4.5 months. During this time, doctors focus on palliative care: controlling symptoms and making the patient as comfortable as possible.

A hemangiopericytoma (HPC) is a type of soft tissue sarcoma that originates in the pericytes in the walls of capillaries. When inside the nervous system, although not strictly a meningioma tumor, it is a meningeal tumor with a special aggressive behavior. It was first characterized in 1942.

A lipoma is a benign tumor made of fat tissue. They are generally soft to the touch, movable, and painless. They usually occur just under the skin but occasionally may be deeper. Most are less than 5 cm in size. Common locations include upper back, shoulders, and abdomen. A few people have a number of lipomas.

The cause is generally unclear. Risk factors include family history, obesity, and not enough exercise. Diagnosis is typically based on a physical exam. Occasionally medical imaging or tissue biopsy is used to confirm the diagnosis.

Treatment is typically by observation or surgical removal. Rarely the condition may recur following removal, however, this can generally be managed with repeat surgery. They are not generally associated with a future risk of cancer.

About 2% of people are affected. Lipomas typically occur in adults between 40 to 60 years of age. Males are more often affected than females. They are the most common non-cancerous soft tissue tumor. The first use of the term "lipoma" to describe these tumors was in 1709.

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.

Neurofibromatosis type II (also known as MISME syndrome - multiple inherited schwannomas, meningiomas, and ependymomas) is a genetic condition which may be inherited or may arise spontaneously. The main manifestation of the condition is the development of symmetric, benign brain tumors in the region of the cranial nerve VIII, which is the "auditory-vestibular nerve" that transmits sensory information from the inner ear to the brain. Many people with this condition also experience visual problems. NF II is caused by mutations of the "Merlin" gene, which seems to influence the form and movement of cells. The principal treatments consist of neurosurgical removal of the tumors and surgical treatment of the eye lesions. Historically the underlying disorder has not had any therapy due to the cell function caused by the genetic mutation. However, new drug research and some clinical trials have shown some promise in having beneficial effects. Collaborative research to find better treatments is ongoing, such as the work of the Synodos NF-2 Consortium of scientists.

The clinical spectrum of the condition is broad. In other words, people with NF II may develop a wide range of distinct problems.

1. Acoustic nerve: 90% of the patients show bilateral acoustic schwannomas on magnetic resonance imaging (MRI).

2. Other cranial nerves and meninges: About 50% of patients develop tumours in other cranial nerves or meningiomas.

3. Spinal cord: About 50% of the patients develop spinal lesions. Only 40% of the spinal lesions are symptomatic. The spinal tumours in NF II are separated in two groups. Intramedullary lesions are located within the spinal tissue and usually belong to the so-called spinal astrocytomas or ependymomas. The extramedullary lesions are located within the small space between the surface of the spinal cord and the bony wall of the spinal canal. These tumours belong to the schwannomas and meningiomas.

4. Skin: If children show neurofibromas, a diagnostic procedure should be performed to decide which form of neurofibromatosis causes the alterations.

5. Eyes: Studies on patients with NF II show that more than 90% of the affected persons suffer eye lesions. The most common alteration in NF II is the juvenile subcapsular cataract (opacity of the lens) in young people.

"Presenting symptoms" (initial concern that brings a patient to a doctor) of a lesion of the nervus vestibulocochlearis due to a tumour in the region of the cerebello-pontine angle are the following: hearing loss (98%), tinnitus (70%), dysequilibrium (67%), headache (32%), facial numbness and weakness (29% and 10% respectively).

"Clinical signs" (alterations that are not regarded by the patient and that can be detected by the doctor in a clinical examination) of the lesion in discussion are: abnormal corneal reflex (33%), nystagmus (26%), facial hypesthesia (26%).

Evaluation (study of the patient with technical methods) shows the enlargement of the porus acousticus internus in the CT scan, enhancing tumours in the region of the cerebello-pontine angle in gadolinium-enhanced MRI scans, hearing loss in audiometric studies and perhaps pathological findings in electronystagmography. Some times there are elevated levels of protein in liquor study.

In NF II, acoustic neuromas usually affect young people, whereas in sporadic forms of acoustic neuromas, the appearance of the tumour is limited to the elderly.

There are two forms of the NF II:

- The "Wishart-Phenotype" is characterized by multiple cerebral and spinal lesions in patients younger than 20 years and with rapid progression of the tumours.

- Patients that develop single central tumours with slow progression after age of 20 are thought to have the "Feiling-Gardner-Phenotype".

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

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.

Syringomyelia is a chronic progressive degenerative disorder characterized by a fluid-filled cyst located in the spinal cord. Its symptoms include pain, weakness, numbness, and stiffness in the back, shoulders, arms or legs. Other symptoms include headaches, the inability to feel changes in the temperature, sweating, sexual dysfunction, and loss of bowel and bladder control. It is usually seen in the cervical region but can extend into the medulla oblongata and pons or it can reach downward into the thoracic or lumbar segments. Syringomyelia is often associated with Chiari malformation type I and is commonly seen between the C-4 and C-6 levels. The exact development of syringomyelia is unknown but many theories suggest that the herniated tonsils in Chiari malformation type I form a "plug" which does not allow an outlet of CSF from the brain to the spinal canal. Syringomyelia is present in 25% of patients with Chiari malformation.

Brain herniation is a potentially deadly side effect of very high pressure within the skull that occurs when a part of the brain is squeezed across structures within the skull. The brain can shift across such structures as the falx cerebri, the tentorium cerebelli, and even through the foramen magnum (the hole in the base of the skull through which the spinal cord connects with the brain). Herniation can be caused by a number of factors that cause a mass effect and increase intracranial pressure (ICP): these include traumatic brain injury, intracranial hemorrhage, or brain tumor.

Herniation can also occur in the absence of high ICP when mass lesions such as hematomas occur at the borders of brain compartments. In such cases local pressure is increased at the place where the herniation occurs, but this pressure is not transmitted to the rest of the brain, and therefore does not register as an increase in ICP.

Because herniation puts extreme pressure on parts of the brain and thereby cuts off the blood supply to various parts of the brain, it is often fatal. Therefore, extreme measures are taken in hospital settings to prevent the condition by reducing intracranial pressure, or decompressing (draining) a hematoma which is putting local pressure on a part of the brain.

Brain herniation frequently presents with abnormal posturing a characteristic positioning of the limbs indicative of severe brain damage. These patients have a lowered level of consciousness, with Glasgow Coma Scores of three to five. One or both pupils may be dilated and fail to constrict in response to light. Vomiting can also occur due to compression of the vomiting center in the medulla oblongata.

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.

Cerebellar stroke syndrome is a condition in which the circulation to the cerebellum is impaired due to a lesion of the superior cerebellar artery, anterior inferior cerebellar artery or the posterior inferior cerebellar artery.

Cardinal signs include vertigo, headache, vomiting, and ataxia.

Cerebellar strokes account for only 2-3% of the 600 000 strokes that occur each year in the United States. They are far less common than strokes which occur in the cerebral hemispheres. In recent years mortality rates have decreased due to advancements in health care which include earlier diagnosis through MRI and CT scanning. Advancements have also been made which allow earlier management for common complications of cerebellar stroke such as brainstem compression and hydrocephalus.

Research is still needed in the area of cerebellar stroke management; however, it has been proposed that several factors may lead to poor outcomes in individuals who suffer from cerebellar stroke. These factors include:

1. Declining levels of consciousness

2. New signs of brainstem involvement

3. Progressing Hydrocephalus

4. Stroke to the midline of the cerebellum (a.k.a. the vermis)

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.

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