The lower, middle, and upper cerebellar peduncles connect the cerebellum (a kind of small brain located in the lower and rear part of the brain) to the brainstem. These peduncles are tracts of white matter, or bundles made up of axons, the extensions of neurons. They are used to carry information between the cerebellum and other parts of the brain. 

There are three types of cerebellar peduncles: the inferior, middle, and superior cerebellar peduncles, which connect the cerebellum with the brainstem. They are in the form of tracts, or bundles of fibers grouping together axons, that is to say the part of the neuron which ensures the transmission of nerve information to other neurons. 

Located at the level of the brain, the cerebellar peduncles are located more precisely between the cerebellum, which occupies the lower and posterior part of the cranial cavity, and the brainstem, an elongated structure located between the brain and the spinal cord, which contains tracts sensory and motor.

Elongated in shape, these cerebellar peduncles look a bit like small feet, as their name indicates, “peduncles”. The widest are the middle cerebellar peduncles.

The cerebellar peduncles are therefore made up of bundles of axons, that is to say the fibrous extensions of neurons, which transmit information to other neurons in the form of nerve impulses.

Cerebellar peduncles connect the cerebellum to the brainstem. They belong to the white matter of the brain, that is to say the part of the neurons made up of the axons (the gray matter being represented by the body of the neuron, which also contains the nucleus). Thus, they are composed by fibrous extensions of neurons: they serve to convey information between the cerebellum and other parts of the brain.

Function of peduncles: conveying information in the form of nerve impulses

• The upper cerebellar peduncles contain axons that extend from the cerebellum to the red nucleus of the midbrain and some nuclei of the thalamus. They are therefore used to transmit information, in the form of nerve impulses, between the cerebellum and the thalamus or the midbrain (also made up of tracts of axons, as well as nuclei of neurons).
• The middle cerebellar peduncles are made up of axons that convey voluntary motor information. They convey these messages in the form of nerve impulses from the nuclei of the bridge (those which receive information from the motor areas of the cerebral cortex), to the cerebellum.
• The lower cerebellar peduncles consist of: 

  1. axons which convey information from proprioceptors of the trunk and limbs to the cerebellum; 

  2. axons, in particular those of the vestibular apparatus of the inner ear, which bring to the cerebellum information from the proprioceptors of the head;

  3. axons which are used to regulate the activity of cerebellar neurons;

  4. other axons, which originate from the cerebellum.

Cerebellum: a function of coordination and balance

The function of the cerebellum, to which the cerebellar peduncles connect the other parts of the brain, is to coordinate precise movements and to regulate posture and balance. The cerebellum would also be involved in cognitive functions and language.

Cerebellar syndrome

A cerebellar syndrome is the set of symptoms and signs resulting from damage to the cerebellum itself, or the cerebellar pathways, made up of the upper, middle and lower cerebellar peduncles.

Its symptoms are as follows:

• walking and balance disturbances, sometimes with falls;
• awkwardness in rapid movements;
• dysarthria (joint disorder, or damage to organs that play a role in speech such as the tongue or soft palate).

Its clinical signs are manifested by:

• a disturbance of balance and walking, also called cerebellar ataxia;
• a disorder in the performance of rapid voluntary movement;
• hypotonia;
• speech and writing disorders;
• nystagmus (involuntary, jerky oscillating motion of the eyeball).

Damage to the upper cerebellar peduncle

Alterations of the upper cerebellar peduncle are found, in particular, in patients suffering from progressive supranuclear palsy: a neurodegenerative disease which causes lesions of the central nervous system in the patient.

Damage to the middle cerebellar peduncle

Anomalies of the middle cerebellar peduncle can be found:

• in multi-systemized neurodegenerative atrophy (or MSA) of the cerebellar type, which is a neurodegenerative disorder including in particular Parkinson’s disease, and other related syndromes;
• in Wallerian degeneration of the peduncles (i.e. a process of nerve degeneration linked to a separation of the nerve from the area which ensures normal functioning);
• in ataxia syndrome (incoordination of movements);
• following abuse of toluene.

Damage following head trauma, for example to the lower cerebellar peduncle

Anomalies of the inferior cerebellar peduncle can be found in patients who have undergone a head trauma, which may for example present an injury to the lower cerebellar peduncles (a head trauma could also, potentially, cause lesions at the level of the two other types of brain). peduncles).

Tumors

Although very rare, tumors, called oligodendrogliomas, can affect the cerebellar peduncles: in fact, they represent less than 1% of oligodendrogliomas (which are tumors, begnines or malignant, affecting glia cells, oligodendrocytes, or cells whose main function is the formation of the myelin sheath which surrounds the nerve fibers, and therefore in particular the axons).

These are the main diseases and abnormalities relating to cerebellar peduncles, this list not necessarily being exhaustive.

Consult a neurologist

In the case of cerebellar syndromes, or neurodegenerative pathologies, in particular, in which there may be an anomaly of the cerebellar peduncles, the specialist to consult will be a neurologist, who will decide the course of treatment.

Sometimes, especially in some cases of progressive supranuclear palsy, medicines used to treat Parkinson’s disease will help bring temporary relief. Physiotherapists and occupational therapists will be able to suggest exercises, in particular helping to preserve the flexibility of the joints, and will be able to recommend safe strategies and measures to reduce the risk of falls.

Support by a rehabilitation doctor

Rehabilitation is a possible scenario in the management of pathologies resulting from abnormalities of the cerebellar peduncles. It will be coordinated by a rehabilitation doctor in a specialized rehabilitation center. It will aim to help the patient to recover the functions of balance, for example, by focusing the work of balance with paramedical professionals, physiotherapists and occupational therapists, in order to secure walking and prevent falls. The rehabilitation doctor will collaborate with a neurologist.

Consult an oncologist

An oncologist may be consulted in the event of a tumor or cancer affecting the cerebellar peduncles. This oncologist will also have to collaborate with a neurologist.

MRI and CT scan of the brain

• It is by performing a medical imaging examination, or an MRI of the brain, that it is possible to identify abnormalities or lesions of these peduncles.
• A brain scan can also identify alterations in these cerebellar peduncles.

Advanced structural imaging techniques

More recent imaging methods exist to observe cerebellar peduncles, including:

• the VBM Objectives technique (Voxel Based Morphometry) is a method allowing a voxel-to-voxel comparison of the local concentration of brain tissues (gray or white matter) within a group or between several groups (the voxel corresponds to the volume of a digitized image represented in 3D, that is to say a kind of pixel in 3D);
• the DTI (Diffusion Tensor Imaging) and DWI (Diffusion Weighted Imaging) techniques, a magnetic resonance imaging technique.
• Magnetic resonance volumetry;
• shape analysis;
• Magnetic resonance morphometry.