Brain tumors are abnormal growths of cells within the brain or surrounding structures, which can be non-cancerous or cancerous. Seizures are temporary episodes of uncontrolled, abnormal electrical activity in the brain that affect physical and mental function. Brain tumors are a recognized cause of seizures, and understanding this relationship involves exploring how tumors interact with brain tissue.
Understanding Brain Seizures
The brain functions through a complex network of nerve cells, called neurons, which communicate via electrical signals. These signals control thoughts, feelings, movements, and sensations, operating in a balanced and synchronized manner. A seizure occurs when there is a sudden, excessive burst of uncontrolled electrical activity among these neurons, disrupting normal brain messaging. This surge can manifest in various ways, from subtle changes in awareness or sensation to involuntary muscle movements or loss of consciousness. Seizures can begin in one specific area of the brain (focal onset) or involve wider areas across both sides (generalized onset).
How Tumors Directly Disrupt Brain Activity
Brain tumors can directly interfere with normal brain function, leading to seizure activity. The tumor’s presence can irritate or excite surrounding neurons, making them hyperexcitable and prone to abnormal firing.
As a tumor grows, it can compress adjacent brain tissue, disrupting neuronal pathways and electrical signaling. This mass effect increases pressure within the skull, impairing normal brain function and contributing to seizures. The pressure can distort brain structures, altering how electrical impulses travel.
Tumor invasion into healthy brain tissue can also lead to structural changes and the formation of scar tissue, known as gliosis. This scarring can perpetuate an imbalance in the brain’s electrical activity, creating an environment conducive to seizures.
Indirect Mechanisms of Seizure Generation
Brain tumors also induce broader physiological changes that can trigger seizures. Tumors can cause local inflammation and swelling (edema) in the surrounding brain tissue. This edema alters neuronal excitability and increases pressure within the skull, which can precipitate seizures.
Changes in blood flow and oxygenation also play a role. Tumors often disrupt the normal blood supply, creating areas of reduced oxygen (hypoxia). This oxygen deprivation contributes to abnormal neuronal firing and seizures.
Brain tumors can also create neurochemical imbalances by altering neurotransmitter concentrations. Some tumors release excessive glutamate, an excitatory neurotransmitter, which can overstimulate neurons. Tumors may also affect the balance of inhibitory neurotransmitters, such as GABA, promoting an environment where seizures are more likely.
Tumor Characteristics and Seizure Risk
Specific tumor characteristics influence the likelihood and nature of seizures. Certain tumor types are more commonly associated with seizures due to their growth patterns or inherent properties. Low-grade gliomas, gangliogliomas, and dysembryoplastic neuroepithelial tumors (DNETs) are examples of slow-growing tumors frequently linked to seizures, sometimes irritating surrounding brain tissue. Up to 70% of patients with gliomas, a common type of primary brain tumor, may experience seizures.
The tumor’s location within the brain significantly impacts seizure risk. Tumors situated in the cerebral cortex, particularly within the frontal and temporal lobes, are more prone to causing seizures.
The growth rate of a tumor can also influence seizure onset. Slow-growing tumors, such as low-grade gliomas, are more frequently associated with seizures compared to rapidly growing, high-grade tumors. This slower growth may allow for prolonged irritation and adaptation of brain tissue, creating a more epileptogenic environment over time.