What Are MS Brain Lesions?
When you were told that you had multiple sclerosis (MS), you were probably told that you had lesions on your brain. You perhaps thought, “What? What the heck is a lesion?”
It can be a bit confusing because there are various types of brain lesions.
For example, you can have an abscess on your brain that is caused by infection – and this type of lesion is life-threatening.
An arteriovenous malformation (AVM) is when the arteries and veins of the brain basically twist together; the vessels are much more fragile and can leak blood into the brain. In addition, these vessels may not pump blood as efficiently, causing seizures.
Then there are cerebrovascular infarctions – strokes – when clusters of cells die. Next, brain tumors, both malignant and benign, are also considered lesions. Lastly, cerebral palsy is even considered a brain lesion – this type of lesion occurs in utero, does not progress over time, and can affect movement as well as communication skills.
So, finding a lesion on the brain that is diagnostic for MS can be a bit confusing. Let’s explain it a little bit, shall we?
What Can Cause Lesions on the Brain?
MS is a disease that affects the central nervous system (CNS); specifically, it is an autoimmune disease that attacks the myelin (the protective sheath the covers the nerve fibers). Because it attacks the myelin, it ends up destroying the nerve's ability to communicate, eventually causing the nerves to deteriorate and/or become permanently damaged.
Continued damage to the myelin basically causes scarring of the brain – and this scarring causes lesions to form on the brains surface. These lesions are what is seen on imaging, such as MRIs.
What Parts of the Brain are Affected by MS Lesions?
According to Rethink MS Relapses, brain lesions that are a result of MS are “hallmarks” of MS. They are “areas of damage that occur to tissue as a result of some sort of trauma. In this case, the lesions occur as a result of trauma induced by multiple sclerosis, which causes the immune system to mistakenly attack an area of the body.”
MS lesions can occur anywhere on the brain. However, they are most likely to occur on the optic nerve, the spinal cord, and the cerebellum.
It is also important to note that symptoms are highly specific to each person – although patient A and patient B may have lesions in the same areas, each may have different symptoms. Lesions are unpredictable and “there is no one-to-one comparison for how lesions in different areas of the brain correspond to specific symptoms.”
The Structure of Nerves
The nervous system is comprised of two parts. The brain and spinal cord make up the central nervous system. Nerves that go to and from the rest of the body comprise the peripheral nervous system.
The nervous system contains two types of cells. They are called neurons and neuroglia. Both have a role in the formation of lesions.
A neuron is composed of three main parts; the axon, dendrites, and cell body. It is believed that damaged neurons cannot regenerate. If they are damaged, the injury is permanent.
Axons are the portions of nerves that are directly damaged by lesions. The axon portion of a neuron may be microscopic or over a yard long; it depends on the specific nerve. Neurons carry messages between nerves or organs.
Neuroglial cells provide nourishment and protection to neurons. These cells are sometimes referred to as glial cells. They support the neurons and indirectly aid the transmission of messages.
Specialized kinds of neuroglia protect the nerves of the peripheral nervous system. The fatty myelin sheath contains the neuroglia, which can regenerate. They may be repaired; however, the tissue regeneration process may be slow, impeded by scar formation in the peripheral nervous system.
When MS occurs, the myelin sheath is weak and scarred by lesions, and its protective effects do not function adequately. Damage to neurons result and symptoms of MS appear.
There are areas along the axons of nerves called 'nodes of Ranvier' that speed up the transmission of messages along the nerve. These are the areas where lesions develop.