Introduction 

The cerebellum (meaning little brain in Latin) is an essential part of the brain and plays a key role in coordinating movement, controlling balance, and managing voluntary muscles (these are the muscles you consciously control, like the muscles in your arm that move when you reach towards a cup).¹ Cerebellar agenesis (CA) is a rare congenital (present at birth) disorder characterised by either a partial or complete absence of the cerebellum, resulting in varying changes to an individual's movement and cognition.² 

These changes to your brain are detected in the early stages of your life, either prenatally (before birth) or postnatally (after birth).³ In these situations, either an ultrasound, a computed tomography (CT), or better yet, a magnetic resonance imaging (MRI) is used. These scans will show the absence of cerebellar tissue, and alongside other characteristics, the diagnosis of CA is made.⁴ 

Another medical investigation is an electroencephalography (EEG). EEGs measure brain function both at rest and during sensory and cognitive tasks, and help give us some insight into how well our neurons and cerebral cortex are working.⁵ 

This article will go through what the diagnosis of CA means and what EEGs show to determine such a diagnosis. As well as answering the all-important question of how life with CA can look.

What is the cerebellum?

The cerebellum is the largest part of the hindbrain (the lower part of the brain).¹ The cerebrum (which is what our brain is mostly made up of) is separated from the cerebellum by a thin sheet of fibrous tissue called the tentorium cerebelli. The cerebellum is further divided into anterior and posterior lobes. The cerebellum contains many neurones (these are small nerve cells that send messages and signals all over your body and allow us to do simple tasks like breathe, eat, and even reach for that cup). The cerebellum receives information from voluntary muscles, the cerebral cortex (the outer part of your cerebrum), and also information about our balance. It can then plan movements in a fluid and smooth manner.¹ 

Imagine you’re reaching towards a cup of coffee. Your brain tells voluntary muscles in your arm to move towards that cup and your cerebellum makes sure that movement is controlled so that it doesn't tip over and spill everywhere. 

Understanding cerebellar agenesis

Before we try to understand the purpose of an EEG and what it records to support the diagnosis of CA, we must first come to terms with what CA means and the mechanism behind how it works. 

What is it?

CA is an extremely uncommon condition where people have either small or completely absent cerebellar tissue.^2,6 As we discussed, your cerebellum ensures a smooth and fluid coordination between movements. In the case of CA (where there is a large loss of cerebellar tissue as well as neurons), it can cause a variety of symptoms ranging from motor or mobility issues to language and comprehension difficulties.⁶

Causes 

The cerebellum forms early in life, as early as twelve weeks of gestation. found that genetic mutations in both copies of WNT1 (a signalling molecule), as well as disruption to the cerebellar development by loss of Ptf1a (a transcription factor that regulates certain gene expression), can lead to partial or total CA.^7,8

Symptoms 

Research found that the severity of both motor and cognitive impairment with CA was related to its location and onset.⁶ Those with the most severe and least specific symptoms developed CA early in life, while those who developed CA at a later age showed mild impairment.⁶ The cerebellum is involved with the coordination of motor and cognitive performances.¹ In a case report of two adults living with CA, symptoms included mental retardation, dysmetria (an inaccuracy with movements, for example, over- or underreaching when moving towards a cup), ataxia (balance issues that are seen as being unsteady on their feet), as well as dysarthria (speech difficulty).⁹

The basics of electrophysiology 

Electrophysiology studies the electrical signals of the brain and nervous system. This is mostly done with EEGs and evoked potentials (EP). These record the brain’s electrical activity in response to a given stimulus, like light or sound.¹⁰ 

Electroencephalogram (EEGs)

EEGs monitor the electrical activity of your brain that’s generated from specific neurones (these are called cortical pyramidal neurones and are responsible for processing information received from other neurones).¹⁰ The waves and patterns measured on an EEG are the total sum of the electrical potential of the neurones (this is basically the electrical energy generated by these neurones and is picked up by the EEG). The electrical energy generated can either move in a ‘positive’ or ‘negative’ direction, which controls how tall these waves look.¹⁰

Evoked Potentials (EP)

An EP is an average of the brain signals detected by an EEG precisely at the moment it receives a stimulus, whether that's sound, light or touch.¹¹ 

There are different types of EP:

Sensory EP (SEP)

These are action potentials (APs) generated from the spine or the brain that are due to a specific sensory pathway, like light or touch.¹¹

Visual EP (VEP)

APs caused as a result of visual stimulation using a reversing checkerboard pattern.¹¹

Brainstem auditory EP (BAEP)

APs generated as a result of a ‘clicking’ sound and an audible stimulus.¹¹

Somatosensory EP (SSEP)

APs generated due to peripheral nerve stimulation (these are the nerves that originate from the brain or spinal cord and carry messages to the rest of the body).¹¹

So what can these investigations show?

A recent study reported on the results of a functional MRI (fMRI) during a finger tapping test on someone with partial CA.¹² They found sufficient and equal blood flow to where the cerebellum should be. However, they disclosed that whilst partial CA should only show signs of mild cerebellar dysfunction, their electrophysiological testing showed severe problems in motor and cognitive areas.¹³ 

Another study found delays in eyeblink, moderate deficits in IQ, and problems with visual memory and attention.¹³ Similarly to the study mentioned previously, an fMRI was used to view brain activity during a tapping task. Based on the results, it is clear to see issues with cognition, such as speech and memory, as well as visuospatial and language tasks. Whilst the researchers found clear issues with the individual's cognition, their cortical areas (regions within the cerebral cortex) didn't differ widely compared to someone without CA. Whilst the impairments seen in this person's cognitive function are a consequence of the absent cerebellum, the second study highlighted that delayed development of motor skills may harm how well you can perform cognitive tasks.¹³ 

Think of it like this: the muscles in your tongue influence how well you speak. If you can’t control those muscles properly, your speech will be affected and may even be difficult to understand. 

Management of CA 

While there is currently no cure for CA, there is a wide range of supportive care available. This supportive care is designed to help make the management of the condition easier. A multidisciplinary approach is often the first line of help. A multidisciplinary team includes a wide range of professionals to provide tailored support for a wide range of symptoms, which can include neurologists, speech and physical therapists, pharmacists and much more. Apart from this, through genetic testing and early prenatal diagnosis, families can be better prepared, and healthcare specialists can begin structuring individualised care plans as soon as possible. 

Frequently Asked Questions (FAQs)

Can someone live a normal life without a cerebellum?

In rare cases, it is possible, individuals without it can survive and adapt surprisingly well. Whilst your cerebellum does have a very vital role, a report of two individuals with CA and moderate symptoms of gait (unsteady walk), mental retardation, and dysarthria, showed how their bodies were still able to carry out different functions - showing how to body can compensate.¹⁴ However, for the majority of people with CA, there will be challenges which they will have to face throughout their lives. 

How is Cerebellar Agenesis Diagnosed?

An MRI is widely used for the diagnosis of CA.⁴ It shows an absence of cerebellar tissue and underdeveloped areas of the brain.⁹ In the absence of the cerebellum, the back of the skull, where the cerebellum should be, is filled with cerebrospinal fluid and appears as a black space on these scans.

Can CA be inherited?

In some cases, yes. Some cases of CA are a result of genetic mutations of the WNT1 and Ptf1a genes.^7,8 Genetic screening is recommended, particularly if there is a known family history.

What are the treatment options?

There is currently no treatment for CA. There are however supportive options available and enable individuals with this condition and their families to take a more supportive and symptomatic approach. A multidisciplinary team consisting of many varied healthcare specialists are often the first line of help and will aim to manage any symptoms as well as improve the quality of life. 

Summary

CA is a rare congenital disorder that results in the complete or partial absence of the cerebellum.² The cerebellum is a section of the brain responsible for cognitive skills (like language and memory) as well as coordination of muscle movement.¹ CA typically causes symptoms of mental retardation, ataxic movements and many others.⁹ It is detected primarily via an MRI, and the diagnosis is supported with EP studies.^4,11 Currently, there is no cure, and supportive care is offered to help manage the symptoms and improve the quality of life.