Mega cisterna magna needs to be distinguished from other causes of an enlarged retrocerebellar CSF space: arachnoid cyst: can be difficult to distinguish from a mega cisterna magna. epidermoid cyst: often shows a heterogeneous/dirty signal on FLAIR and restricted diffusion. cerebellar atrophy / cerebellar hypoplasia.

From April 1979 to June 1980; a total of 2089 patients were examined by CT; of these, 9 cases (0.43%) of mega cisterna magna were identified. The symptoms and signs of those 9 patients were headache, vertigo, nausea, right hemiparesis, convulsive seizure, hyperventilation syndrome, and tremor.

Causes of an enlarged cisterna magna include cerebellar hypoplasia, communicating hydrocephalus, and normal variation. Cerebellar hypoplasia is a frequent finding in the trisomies and therefore a careful search should be made for associated cardiac anomalies, growth retardation, and polyhydramnios.

The cisterna magna is located between the cerebellum and the dorsal surface of the medulla oblongata. Cerebrospinal fluid produced in the fourth ventricle drains into the cisterna magna via the lateral apertures and median aperture.

The majority of patients are asymptomatic; however, variable neurodevelopmental outcomes, including delayed speech and language development, motor development delay, visiospatial perception difficulties, and attention problems, has been observed in some patients.

Mega cisterna magna refers to a normal variant characterized by a truly focal enlargement of the CSF-filled subarachnoid space in the inferior and posterior portions of the posterior cranial fossa. It is an incidental finding on neuroimaging, and no imaging follow up is necessary.

Arachnoid cysts usually are located in the skull, brain, and rarely, in the spinal cord. The arachnoid cysts can grow to a large size if they continue to retain cerebrospinal fluid. In more extreme cases the cysts’ size may cause the head to change shape or may displace the surrounding lobes of the brain.

Mega cisterna magna occurs in approximately 1% of all brains imaged postnatally and has been associated with cerebrovascular infarction, inflammation, and infection, particularly cytomegalovirus, as well as with chromosomal abnormalities, especially trisomy 18.

Sometimes the septa are bowed laterally by the presence of intraventricular hemorrhage extending posterior to the vallecula (Figure 9). Blood in the cisterna magna has previously been shown to have a high positive predictive value for development of posthemorrhagic hydrocephalus.

A CM of more than 10 mm without associated anomalies suggests the diagnosis of isolated mega cisterna magna (MCM). Isolated MCM is defined as a distance between the vermis of the cerebellum and the inner border of the occipital bone of more than 10 mm on an axial plane through the CSP and the vermis.

Although differential of retrocerebellar arachnoid cysts and mega cisterna magna is of little clinical concern, as both lesions are mostly asymptomatic and require no follow-up, they are both frequently encountered lesions in clinical practice, as almost always incidental findings, that has different causative mechanisms and embryonic origins.

Cerebrospinal fluid is present in subarachnoid space. So it does not show any symptoms. As it is asymptomatic, so it cannot be diagnosed. If it is secondary to any pathological condition, then symptoms may appear. Headache is considered the common symptom related to mega cisterna magna.

The incidence of arachnoid cysts is unknown, though they are considered to be rarely present. Overall, arachnoid cysts represent less than 1% of all brain masses. The main differential diagnosis for a posterior fossa arachnoid cyst is between two other types of brain malformations called mega cisterna magna and Dandy–Walker malformation.

Mega cisterna magna is the enlargement of subarachnoid space containing cerebrospinal fluid. It is a non pathological enlargement of retrocerebellar cerebrospinal fluid space. It may occur due to infection or inflammation in cerebrospinal fluid. Abnormality in chromosome can lead to retrocerebellar CSF space.