The risk of meningioma can be reduced by maintaining a normal body weight, and by avoiding unnecessary dental x-rays.

Several different types of magnetic resonance imaging (MRI) may be employed in diagnosis: MRI without contrast, Gd contrast enhanced T1-weighted MRI (GdT1W) or T2-weighted enhanced MRI (T2W or T2*W). Non-contrast enhanced MRI is considerably less expensive than any of the contrast enhanced MRI scans. The gold standard in diagnosis is GdT1W MRI.

The reliability of non-contrast enhanced MRI is highly dependent on the sequence of scans, and the experience of the operator.

The auditory brainstem response (ABR) test gives information about the inner ear (cochlea) and nerve pathways for hearing via ongoing electrical activity in the brain measured by electrodes placed on the scalp. Five different waves (I to V) are measured for each ear. Each waveform represents specific anatomical points along the auditory neural pathway. Delays of one side relative to the other suggest a lesion in cranial nerve VIII between the ear and brainstem or in the brainstem itself. The most reliable indicator for acoustic neuromas from the ABR is the interaural latency differences in wave V: the latency in the impaired ear is prolonged. Different studies have indicated the sensitivity of ABR for detection of acoustic neuromas 1cm or larger to be between 90 and 95%. Sensitivity for neuromas smaller than 1cm are 63-77%. A newer technology, stacked ABR, may have sensitivity as high as 95% with specificity 88% for smaller tumors. ABR is considerably more cost effective, but MRI provides more information.

Stapedius reflex (SR) and caloric vestibular response (CVR) are non-invasive otologic tests for auditory neural function. These are not primary diagnostics for CPA neuromas, and are usually used in conjunction

with ABR.

Observation with close imaging follow-up may be used in select cases if a meningioma is small and asymptomatic. In a retrospective study on 43 patients, 63% of patients were found to have no growth on follow-up, and the 37% found to have growth at an average of 4 mm / year. In this study, younger patients were found to have tumors that were more likely to have grown on repeat imaging; thus are poorer candidates for observation. In another study, clinical outcomes were compared for 213 patients undergoing surgery vs. 351 patients under watchful observation. Only 6% of the conservatively treated patients developed symptoms later, while among the surgically treated patients, 5.6% developed persistent morbid condition, and 9.4% developed surgery-related morbid condition.

Observation is not recommended in tumors already causing symptoms. Furthermore, close follow-up with imaging is required with an observation strategy to rule out an enlarging tumor.

Diagnosis is principally by MRI. Frequently, arachnoid cysts are incidental findings on MRI scans performed for other clinical reasons. In practice, diagnosis of symptomatic arachnoid cysts requires symptoms to be present, and many with the disorder never develop symptoms.

Additional clinical assessment tools that can be useful in evaluating a patient with arachnoid cysts include the mini-mental state examination (MMSE), a brief questionnaire-based test used to assess cognition.

The primary diagnosis is made with a computed tomography scan (CT scan). On a scan, hemangioblastoma shows as a well-defined, low attenuation region in the posterior fossa with an enhancing nodule on the wall. Sometimes multiple lesions are present.

The majority of patients can be expected to be cured of their disease and become long-term survivors of central neurocytoma. As with any other type of tumor, there is a chance for recurrence. The chance of recurrence is approximately 20%. Some factors that predict tumor recurrence and death due to progressive states of disease are high proliferative indices, early disease recurrence, and disseminated disease with or without the spread of disease through the cerebral spinal fluid. Long-term follow up examinations are essential for the evaluation of the outcomes that each treatment brings about. It is also essential to identify possible recurrence of CN. It is recommended that a cranial MRI is performed between every 6–12 months.

Most arachnoid cysts are asymptomatic, and do not require treatment. Where complications are present, leaving arachnoid cysts untreated, may cause permanent severe neurological damage due to the progressive expansion of the cyst(s) or hemorrhage (bleeding). However, with treatment most individuals with symptomatic arachnoid cysts do well.

More specific prognoses are listed below:

- Patients with impaired preoperative cognition had postoperative improvement after surgical decompression of the cyst.

- Surgery can resolve psychiatric manifestations in selected cases.

The outcome for hemangioblastoma is very good, if surgical extraction of the tumor can be achieved; excision is possible in most cases and permanent neurologic deficit is uncommon and can be avoided altogether if the tumor is diagnosed and treated early. Persons with VHL syndrome have a bleaker prognosis than those who have sporadic tumors since those with VHL syndrome usually have more than one lesion.

Bilateral vestibular schwannomas are diagnostic of NF2.

NF II can be diagnosed with 65% accuracy prenatally with chorionic villus sampling or amniocentesis.

Diagnosis is made through a combination of patient history, neurological examination, and medical imaging. Magnetic resonance imaging (MRI) is considered the best imaging modality for Chiari malformation since it visualizes neural tissue such as the cerebellar tonsils and spinal cord as well as bone and other soft tissues. CT and CT myelography are other options and were used prior to the advent of MRI, but they characterize syringomyelia and other neural abnormalities less well.

By convention the cerebellar tonsil position is measured relative to the basion-opisthion line, using sagittal T1 MRI images or sagittal CT images. The selected cutoff distance for abnormal tonsil position is somewhat arbitrary since not everyone will be symptomatic at a certain amount of tonsil displacement, and the probability of symptoms and syrinx increases with greater displacement, however greater than 5 mm is the most frequently cited cutoff number, though some consider 3–5 mm to be "borderline," and symptoms and syrinx may occur above that. One study showed little difference in cerebellar tonsil position between standard recumbent MRI and upright MRI for patients without a history of whiplash injury. Neuroradiological investigation is used to first rule out any intracranial condition that could be responsible for tonsillar herniation. Neuroradiological diagnostics evaluate the severity of crowding of the neural structures within the posterior cranial fossa and their impact on the foramen magnum. Chiari 1.5 is a term used when both brainstem and tonsillar herniation through the foramen magnum are present.

The diagnosis of a Chiari II malformation can be made prenatally through ultrasound.

Ferner et al. give three sets of diagnostic criteria for NF2:

1. Bilateral vestibular schwannoma (VS) or family history of NF2 plus Unilateral VS or any two of: meningioma, glioma, neurofibroma, schwannoma, posterior subcapsular lenticular opacities

2. Unilateral VS plus any two of meningioma, glioma, neurofibroma, schwannoma, posterior subcapsular lenticular opacities

3. Two or more meningioma plus unilateral VS or any two of glioma, schwannoma and cataract.

Another set of diagnostic criteria is the following:

- Detection of bilateral acoustic neuroma by imaging-procedures

- First degree relative with NF II and the occurrence of neurofibroma, meningiomas, glioma, or Schwannoma

- First degree relative with NF II and the occurrence of juvenile posterior subcapsular cataract.

The criteria have varied over time.

In the late 19th century, Austrian pathologist Hans Chiari described seemingly related anomalies of the hindbrain, the so-called Chiari malformations I, II and III. Later, other investigators added a fourth (Chiari IV) malformation. The scale of severity is rated I – IV, with IV being the most severe. Types III and IV are very rare.

Other conditions sometimes associated with Chiari malformation include hydrocephalus, syringomyelia, spinal curvature, tethered spinal cord syndrome, and connective tissue disorders such as Ehlers-Danlos syndrome and Marfan syndrome.

Chiari malformation is the most frequently used term for this set of conditions. The use of the term Arnold–Chiari malformation has fallen somewhat out of favor over time, although it is used to refer to the type II malformation. Current sources use "Chiari malformation" to describe four specific types of the condition, reserving the term "Arnold-Chiari" for type II only. Some sources still use "Arnold-Chiari" for all four types.

Chiari malformation or Arnold–Chiari malformation should not be confused with Budd-Chiari syndrome, a hepatic condition also named for Hans Chiari.

In Pseudo-Chiari Malformation, Leaking of CSF may cause displacement of the cerebellar tonsils and similar symptoms sufficient to be mistaken for a Chiari I malformation.

Surgical excision of the central neurocytoma is the primary consensus among practicing physicians. The surgeons perform a craniotomy to remove the tumor. The ability to remove the tumor and to what extent it is removed is dependent upon the location of the tumor and surgeon experience and preference. The extent of the disease plays a large part in determining how effective the surgery will be. The main goal of a complete surgical resection, of the tumor, can also be hindered by the adherence of the tumor to adjoining structures or hemorrhages. If there is a recurrence of the central neurocytoma, surgery is again the most notable treatment.

The Gold Standard for diagnosis of vestibular schwannoma is without doubt enhanced magnetic resonance imaging (MRI) yet several examinations may arise suspicion of vestibular schwannomas.

Routine auditory tests may reveal a loss of hearing and speech discrimination (the patient may hear sounds in that ear, but cannot comprehend what is being said). Pure tone audiometry should be performed to effectively evaluate hearing in both ears. In some clinics the clinical criteria for follow up testing for AN is a 15 dB differential in thresholds between ears for three consecutive frequencies.

An auditory brainstem response test (a.k.a. ABR) is a much more cost effective screening alternative to MRI for those at low risk of AN. This test provides information on the passage of an electrical impulse along the circuit from the inner ear to the brainstem pathways. An acoustic neuroma can interfere with the passage of this electrical impulse through the hearing nerve at the site of tumor growth in the internal auditory canal, even when hearing is still essentially normal. This implies the possible diagnosis of an acoustic neuroma when the test result is abnormal. An abnormal auditory brainstem response test should be followed by an MRI. The sensitivity of this test is proportional to the tumor size - the smaller the tumor, the more likely is a false negative result; small tumors within the auditory canal will often be missed. However, since these tumors would usually be watched rather than treated, the clinical significance of overlooking them may be negligible.

Advances in scanning and testing have made possible the identification of small acoustic neuromas (those still confined to the internal auditory canal). MRI using as an enhancing contrast material is the preferred diagnostic test for identifying acoustic neuromas. The image formed clearly defines an acoustic neuroma if it is present and this technique can identify tumors measuring down to 5 millimeters in diameter (the scan spacing).

When an MRI is not available or cannot be performed, a computerized tomography scan (CT scan) with contrast is suggested for patients in whom an acoustic neuroma is suspected. The combination of CT scan and audiogram approach the reliability of MRI in making the diagnosis of acoustic neuroma.

Visual fields associated with chiasmal syndrome usually leads to an MRI. Contrast can delineate arterial aneurysms and will enhance most intrinsic chiasmal lesions. If a mass is confirmed on MRI, an endocrine panel can help determine if a pituitary adenoma is involved.

In patients with functional adenomas diagnosed by other means, visual field tests are a good screen to test for chiasmal involvement. Visual fields tests will delinate chiasmal syndromes because the missing fields will not cross the midline. Junctional scotomas classically show ipsilateral optic disc neuropathy with contralateral superotemporal defects. Bitemporal hemianopia with or without central scotoma is present if the lesions have affected the body of the chiasm. A posterior chiasm lesion should only produce defects on the temporal sides of the central visual field.

Treatment involves removal of the etiologic mass and decompressive craniectomy. Brain herniation can cause severe disability or death. In fact, when herniation is visible on a CT scan, the prognosis for a meaningful recovery of neurological function is poor. The patient may become paralyzed on the same side as the lesion causing the pressure, or damage to parts of the brain caused by herniation may cause paralysis on the side opposite the lesion. Damage to the midbrain, which contains the reticular activating network which regulates consciousness, will result in coma. Damage to the cardio-respiratory centers in the medulla oblongata will cause respiratory arrest and (secondarily) cardiac arrest. Current investigation is underway regarding the use of neuroprotective agents during the prolonged post-traumatic period of brain hypersensitivity associated with the syndrome.

The standard work-up for AT/RT includes:

- Magnetic resonance imaging (MRI) of the brain and spine

- Lumbar puncture to look for M1 disease

- Computed tomography (CT) of chest and abdomen to check for a tumor

- Bone marrow aspiration to check for bone tumors. Sometimes the physician will perform a stem cell transplant

- Bone marrow biopsy

- Bone scan

The initial diagnosis of a tumor is made with a radiographic study (MRI or CT-). If CT was performed first, an MRI is usually performed as the images are often more detailed and may reveal previously undetected metastatic tumors in other locations of the brain. In addition, an MRI of the spine is usually performed. The AT/RT tumor often spreads to the spine. AT/RT is difficult to diagnose only from radiographic study; usually, a pathologist must perform a cytological or genetic analysis.

Examination of the cerebrospinal fluid is important (CSF), as one-third of patients will have intracranial dissemination with involvement of the CSF. Large tumor cells, eccentricity of the nuclei, and prominent nucleoli are consistent findings. Usually only a minority of AT/RT biopsies have rhabdoid cells, making diagnosis more difficult. Increasingly it is recommended that a genetic analysis be performed on the brain tumor, especially to find if a deletion in the INI1/hSNF5 gene is involved (appears to account for over 80% of the cases). The correct diagnosis of the tumor is critical to any protocol. Studies have shown that 8% to over 50% of AT/RT tumors are diagnosed incorrectly.

The clinical and pathology differential are different. From a pathology perspective, an endolymphatic sac tumor needs to be separated from metastatic renal cell carcinoma, metastatic thyroid papillary carcinoma, middle ear adenoma, paraganglioma, choroid plexus papilloma, middle ear adenocarcinoma, and ceruminous adenoma.

Wide excision is the treatment of choice, although attempting to preserve hearing. Based on the anatomic site, it is difficult to completely remove, and so while there is a good prognosis, recurrences or persistence may be seen. There is no metastatic potential. Patients who succumb to the disease, usually do so because of other tumors within the von Hippel-Lindau complex rather than from this tumor.

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.

Cytogenetics is the study of a tumor’s genetic make-up. Fluorescent "in situ" hybridization may be able to help locate a mutation or abnormality that may be allowing tumor growth. This technique has been shown to be useful in identifying some tumors and distinguishing two histologically similar tumors from each other (such as AT/RTs and PNETs). In particular, medulloblastmas/PNETs may possibly be differentiated cytogenetically from AT/RTs, as chromosomal deletions of 17p are relatively common with medulloblastoma and abnormalities of 22q11.2 are not seen. However, chromosomal 22 deletions are very comomon in AT/RTs.

In importance of the "hSNF5/INI1" gene located on chromosomal band 22q11.2 is highlighted, as the mutation’s presence is sufficient to change the diagnosis from a medulloblastoma or PNET to the more aggressive AT/RT classification. However, this mutation is not present in 100% of cases. Therefore, if the mutation is not present in an otherwise classic AT/RT immunohistochemical and morphologic pattern then the diagnosis remains an AT/RT.

Pituitary incidentalomas are pituitary tumors that are characterized as an incidental finding. They are often discovered by computed tomography (CT) or magnetic resonance imaging (MRI), performed in the evaluation of unrelated medical conditions such as suspected head trauma, in cancer staging or in the evaluation of nonspecific symptoms such as dizziness and headache. It is not uncommon for them to be discovered at autopsy. In a meta-analysis, adenomas were found in an average of 16.7% in postmortem studies, with most being microadenomas (<10mm); macrodenomas accounted for only 0.16% to 0.2% of the decedents. While non-secreting, noninvasive pituitary microadenomas are generally considered to be literally as well as clinically benign, there are to date scant studies of low quality to support this assertion.

It has been recommended in the current Clinical Practice Guidelines (2011) by the Endocrine Society - a professional, international medical organization in the field of endocrinology and metabolism - that all patients with pituitary incidentalomas undergo a complete medical history and physical examination, laboratory evaluations to screen for hormone hypersecretion and for hypopituitarism. If the lesion is in close proximity to the optic nerves or optic chiasm, a visual field examination should be performed. For those with incidentalomas which do not require surgical removal, follow up clinical assessments and neuroimaging should be performed as well follow-up visual field examinations for incidentalomas that abut or compress the optic nerve and chiasm and follow-up endocrine testing for macroincidentalomas.

If the medical history and the actual exam of the hemangioma look typical for PHACE Syndrome, more tests are ordered to confirm the diagnosis. These tests may include:

- Ultrasound

- Magnetic resonance imaging (MRI)

- Magnetic resonance angiography of the brain (MRA)

- Echocardiogram

- Eye exam by an eye doctor

- Other tests may be needed for diagnosis and treatment

The cumulative relative survival rate for all age groups and histology follow-up was 60%, 52%, and 47% at 5 years, 10 years, and 20 years, respectively. Patients diagnosed with a medulloblastoma or PNET are 50 times more likely to die than a matched member of the general population.

The most recent population-based (SEER) 5-year relative survival rates are 69% overall, but 72% in children (1–9 years) and 67% in adults (20+ years). The 20-year survival rate is 51% in children. Children and adults have different survival profiles, with adults faring worse than children only after the fourth year after diagnosis (after controlling for increased background mortality). Before the fourth year, survival probabilities are nearly identical. Longterm sequelae of standard treatment include hypothalamic-pituitary and thyroid dysfunction and intellectual impairment. The hormonal and intellectual deficits created by these therapies causes significant impairment of the survivors.