What is Mega Cisterna Magna?
The cisterna magna is a space filled with a liquid called cerebrospinal fluid (CSF), which is positioned behind a part of the brain called the medulla and below another part called the cerebellum. Mega cisterna magna describes a specific malformation in this area, which involves an enlarged cisterna magna, absence of a condition called hydrocephalus (a buildup of too much CSF in the brain), and a normal cerebellar vermis (the part of the brain that separates the left and right side of the cerebellum).
The term mega cisterna magna was first brought up in the 1960s by someone named Gonsette. They initially described its size with certain measurements in various directions based on a procedure called ventriculography (an X-ray test of the ventricles in the brain). More recently, discussions around size have moved towards considering a cisterna magna greater than 10 mm on certain types of images of the brain to be called a mega cisterna magna.
What Causes Mega Cisterna Magna?
Blake’s pouch is like a small pouch that protrudes from the fourth ventricle, which is a structure in the brain. This is an area located at the back side of the brain. During development in the womb, Blake’s pouch is initially closed off from the surrounding space filled with cerebrospinal fluid (fluid that circulates in the brain and spinal cord). But it eventually becomes permeable, or able to allow fluid to pass through, and forms the opening known as the foramen of Magendie.
We’re not quite sure when this pouch becomes permeable. The mega cisterna magna is thought to develop as Blake’s pouch becomes permeable, allowing this brain fluid to flow downwards around the spinal cord and upwards through the foramen of Magendie.
By the end of the 7th week of pregnancy, a space known as the cisterna magna is fully formed within certain brain tissues. The cisterna magna is located in a small hollow space between the central section of the cerebellar tonsils (small parts of the brain located at the base) and the lower surface of the vermis, another part of the brain.
The cisterna magna extends towards the front up to the foramen of Magendie and down up to the first level of the cervical spine (the neck region). It’s limited at the back by a membrane and downwards from the back lower surface of the cerebellum (part of the brain located at the back) up to the top of the cervical spinal cord. The back of the cisterna magna is separated by the falx cerebelli, a structure located in the back part of the brain.
Risk Factors and Frequency for Mega Cisterna Magna
Mega cisterna magna is a condition that’s often identified incidentally – meaning it’s found when doing brain scans for other reasons. As a result, we don’t have exact numbers for how common it is, because it often doesn’t cause symptoms.
- In a study involving 19,301 brain scans, which were done for headaches or minor head injuries, 49 cases of mega cisterna magna were found.
- This suggests that about 2.5 out of every 1000 people may have this condition.
- It appears to affect males and females equally.
Signs and Symptoms of Mega Cisterna Magna
When assessing an adult patient, it’s important to discuss their childhood development and to explore any possible issues related to the nervous system, mental health, or cognitive function. During a newborn physical examination, it is necessary to look for any signs of nervous system abnormalities or other body malformations. This could include various symptoms like headaches, feeling sick or vomiting, tingling sensations, weakness, or difficulty balancing.
The specific areas explored during a neurological examination can vary with the patient’s age. Checks could be made for attention, motor skills, sensations, coordination, reflex responses, and automatic responses coordinated by the brainstem. Particularly in older patients, a mental status examination could be part of this check-up.
Testing for Mega Cisterna Magna
During prenatal care, it’s essential to check for any abnormal changes in the baby’s central nervous system and other parts of the body. One condition that doctors look out for is ‘Mega cisterna magna’. Initially, doctors would use a technique called ventriculography to investigate this, but it is not used often these days.
Nowadays, the preferred method is to use an ultrasound scan while the baby is still in the womb or just after birth before the baby’s fontanelle (or ‘soft spot’ on the head) closes up.
Once the fontanelle has closed, the best way to examine ‘Mega cisterna magna’ is through a computed tomography (CT) scan or magnetic resonance imaging (MRI) scan of the brain, with or without contrast. This helps doctors distinguish this condition from other similar-looking conditions. On these scans, ‘Mega cisterna magna’ will appear as a larger than usual space filled with cerebrospinal fluid (CSF) situated behind the cerebellum. It is typically larger than 10 mm, as seen on midline images, and the structure of the cerebellum, as well as the size of the brain’s ventricles, appear normal.
Before confirming a diagnosis of ‘Mega cisterna magna’, it is important to rule out other brain conditions, like an enlarged brain ventricle (ventriculomegaly) and an underdeveloped cerebellum (cerebellar hypoplasia). The scans should also show no signs of enhancement, which is an increase in visibility due to contrast. If there are any concerns, doctors may also recommend a neuropsychiatric evaluation, which will help understand if there are any brain-function related issues.
Treatment Options for Mega Cisterna Magna
If doctors happen to find a large cisterna magna (a fluid-filled space in the brain) during an examination or operation, it usually doesn’t require specific treatment. However, if the patient is experiencing symptoms such as headaches, seizures, or mental health issues that might be related to this condition, they might be prescribed medication to manage these symptoms.
Surgery is rarely an option for mega cisterna magna, and is typically only considered if the patient has hydrocephalus, which involves an accumulation of too much cerebrospinal fluid (CSF) in the brain. However, if a patient has hydrocephalus, it usually means that they don’t have mega cisterna magna. In rare cases, a surgery that involves removing a portion of the skull (suboccipital craniectomy) could be performed. Two early cases of patients with mega cisterna magna underwent this procedure but didn’t experience symptom relief.
There’s no officially recommended schedule for monitoring people with mega cisterna magna, as it’s still not clear when or if complications may arise. However, patients might be followed into adolescence and early adulthood because issues related to the condition, if any, may not show up during childhood. For adults who find out by chance that they have mega cisterna magna, there are no specific guidelines for follow-up.
If an adult has an MRI scan and incidentally discovers a large cisterna magna but has no symptoms, continuing to monitor the condition may not be necessary. However, if new symptoms develop, it might be a good idea to have repeat imaging done to see if there have been any changes.
What else can Mega Cisterna Magna be?
A posterior fossa arachnoid cyst is a fluid-filled area in the skull, that, like a mega cisterna magna, can be hard to differentiate. But, while arachnoid cysts match the cerebrospinal fluid (CSF) signal on CT and MRI scans like a mega cisterna magna, they can exert pressure on the brain (a mass effect). This pressure can obstruct the natural flow of fluid in the brain, leading to a condition known as hydrocephalus. They might also cause the back of the skull to become indented or scalloped.
A persistent Blake’s pouch cyst develops when there is a failure in the formation of the Blake’s pouch, a structure that appears during early embryonic development. It looks similar to a mega cisterna magna on imaging scans and is typically associated with hydrocephalus. But it is not linked to the underdevelopment of the cerebellum (cerebellar hypoplasia) or other brain abnormalities.
Dandy-Walker variant is usually an isolated condition but can be seen alongside many other conditions, including several syndromes and chromosomal abnormalities. It differs from the mega cisterna magna by having underdeveloped or, in rare cases, completely absent cerebellar vermis (part of the cerebellum). But it is not typically associated with hydrocephalus unless there’s an additional abnormality.
Epidermoid cysts are slow-growing, congenital tumors that develop from leftover skin elements. These cysts can look similar to mega cisterna magna on imaging scans as they both match CSF signal density. However, epidermoid cysts will show up as very bright on certain MRI sequences (diffusion-weighted imaging), while mega cisterna magna won’t.
Pilocytic astrocytomas, which make up about 15% of all central nervous system tumors, can also look similar to mega cisterna magna. But contrary here, you can typically find an associated enhancing nodule. They can potentially cause a mass effect too, leading to obstructive hydrocephalus. It’s not typically associated with cerebellar vermis hypoplasia unless there is a significant mass effect or another associated abnormality. It may or may not restrict diffusion on diffusion-weighted imaging and can be associated with a genetic disorder known as neurofibromatosis type 1.
What to expect with Mega Cisterna Magna
In general, adults with a condition called isolated mega cisterna magna – an enlargement of a space in the back of the brain – perform within normal limits on cognitive tests. Nonetheless, there are some indications that this group of patients may underperform in specific areas, such as memory, problem-solving functions, and verbal fluidity, when compared to people without this condition.
Research on the outcomes of patients with mega cisterna magna is not fully conclusive and the studies are not plentiful. An older study, which reviewed CT scan images from 1,260 individuals and identified 14 with isolated mega cisterna magna, found that more than half (57%) reported having long-term neurological problems.
However, there’s a cautious note that needs to be flagged here: CT scans aren’t very good at visualizing the rear part of the brain. So, there’s a possibility that some of these patients had other undetected brain conditions, which may have led to their neurological problems.
In newer research, ultrasound images of 15 unborn babies showed they had isolated mega cisterna magna. In all cases, the babies appeared to have developed typically, with no signs of neurological disorders. In a follow-up period of up to 69 months (almost six years), eight of these patients showed no neurologic disorders or developmental delays.
However, even these findings come with a caveat: assessing cognitive and behavioral disorders in young children isn’t always entirely accurate. Some of these issues may only become noticeable as the child grows older.
Possible Complications When Diagnosed with Mega Cisterna Magna
A recent analysis, which studied 144 unborn babies diagnosed with a condition called mega cisterna magna, revealed that about 12.6% had additional abnormalities within the central nervous system and 16.6% had abnormalities outside the central nervous system. This was the case when no discernable chromosome abnormalities were identified.
It’s also believed that the cerebellum, a part of the brain essential for motor control, is connected to many parts of the bigger brain through a specialized pathway. Therefore, the cerebellum may play a critical role in the functioning and coordination of the brain’s activities.
Several psychiatric conditions have been connected with mega cisterna magna, which include mania, bipolar disorder, schizophrenia, and a severe mental disorder known as catatonia.
However, because mega cisterna magna is so rare and there are very few reports about it, it’s hard to say whether there’s truly a link between this condition and mental disorders, or if these are mere coincidences.
Common Observations:
- 12.6% had additional abnormalities within CNS
- 16.6% had abnormalities outside CNS
- Some patients showed psychiatric conditions like mania, bipolar disorder, schizophrenia, and catatonia
- Cerebellum may play a significant role in coordinating brain’s activities
Preventing Mega Cisterna Magna
The exact number of people who have a condition known as mega cisterna magna is not certain because it’s quite rare and is found in less than 1% of the population according to studies. The symptoms of this condition are mixed and the more recent studies suggest that people with mega cisterna magna are less likely to have neurological problems, which are problems related to the brain and nerves.
Those who are affected by mega cisterna magna may display certain changes in the way their brain functions. They may have challenges with their memory, high-order functions like problem-solving, language skills like verbal fluency, and can also experience mental health disorders.
As of now, there does not exist a specific treatment or surgery for those with mega cisterna magna that have been proven to definitely help. So, typical treatments or surgeries aren’t necessarily beneficial for individuals with this condition.
