Overview

Temporal lobe epilepsy (TLE) is the most common type of focal epilepsy, where seizures start in one part of the brain, typically deep in the temporal lobe. Many patients with TLE do not respond well to medications, and the condition can significantly affect memory, mood, and daily life.¹ Because of this, obtaining a clear understanding of where the seizures begin is essential, especially when considering surgery.²

Magnetic Resonance Imaging (MRI), particularly high-resolution scans, plays a key role in this process. It is considered the gold standard imaging modality to visualise TLE due to its high-resolution anatomical details. MRI techniques help enhance the diagnostic accuracy, helping improve localisation of epileptogenic zones.³ This article explores how MRI can reveal specific brain changes in TLE and how those findings can help guide diagnosis and treatment decisions.⁴ Other identifiable abnormalities include temporal neocortical atrophy, cortical malformations, tumours and changes in white matter.

Hippocampal sclerosis in TLE 

Hippocampal Sclerosis (HS) is the most common brain change seen in people with TLE. It means that part of the hippocampus, a brain structure critical for memory, has been damaged over time.⁷ This damage involves both the loss of nerve cells and scarring of brain tissue.⁸ Over time, this results in functional disruption, causing deficits in memory and seizures.

On MRI scans, the hippocampus in someone with HS may look smaller than usual, which doctors refer to as ‘atrophy’. This shrinkage is usually easiest to see on a T1-weighted images that are taken at just the right angle to show the hippocampus clearly.¹⁰ Other types of MRI, like the T2, might show the damaged area as brighter than normal, an effect caused by scarring in the tissue. With high-resolution imaging, doctors can also see that the normal structure inside the hippocampus has become blurred or lost altogether.¹¹

Hippocampal Sclerosis is a common cause of a type of epilepsy that starts in the temporal lobe of the brain. People with this condition often have seizures where they seem awake but are not fully aware of what’s happening around them. These seizures may begin with odd feelings like a sudden wave of fear or a fluttery sensation in the stomach. During the seizure, they might repeat simple actions, like lip-smacking or fiddling with their hands, without realising that they are doing it.¹² These types of seizures often begin in childhood or the teenage years, and if they continue over time, they can affect things like memory, learning, and emotional development. Brain scans like MRI, PET, or SPECT are often used together to get a better idea of what’s going on. While an MRI shows the structure of the brain, PET and SPECT scans help doctors see how certain areas are working during and between seizures.¹³

Clinical relevance and treatment implications

When seizures don’t respond to medication, doctors often turn to an MRI to see whether surgery might be an option. MRI can help pinpoint exactly where in the brain the seizures are starting, especially if there's clear evidence of damage like HS. If the problem is localised, surgery such as removing the affected part of the temporal lobe may help reduce or even stop seizures. MRI findings also help doctors weigh the risks and benefits of surgery and plan the best approach.

Although Hippocampal Sclerosis is one of the most common things seen in brain scans of people with TLE, it is not the only possible cause. Other changes in brain structure can also play a role, such as areas where brain development did not go as expected (called cortical dysplasia), certain types of brain tumours, or problems with blood vessels in the brain.^15,16 These differences can often be spotted on MRI, and each one may require a different kind of treatment, including surgery. Thanks to improvements in how brain images are analysed—and by combining this with other test results—doctors can better understand what’s going on, make more accurate predictions, and choose the most effective treatment. MRIs are also important for tracking the condition over time.

MRI findings in TLE

Apart from Hippocampal Sclerosis, Temporal Lobe Epilepsy is associated with various structural abnormalities, as mentioned.

 Extrahippocampal changes

Sometimes, the damage from TLE spreads beyond the hippocampus to other areas of the brain’s temporal lobe. This can appear as thinning of the brain’s outer layer (called the cortex), especially in parts responsible for language, memory, or hearing. These changes can also affect how well the brain’s white matter pathways are working, those are the connections that allow different brain areas to communicate.¹⁷

Enlargement of the temporal horn in the lateral ventricle

As the hippocampus shrinks from long-term damage, nearby fluid-filled spaces in the brain, like the temporal horn of the lateral ventricle, may appear larger. This change is often one of the earliest signs of hippocampal sclerosis on MRI.¹⁸

Developmental abnormalities 

Focal cortical dysplasia is a condition where a patch of brain tissue doesn’t form the right way before birth. These abnormal areas can act as seizure triggers and may look different on MRI depending on how severe the changes are. Heterotopia means that some brain cells didn’t migrate to the correct spot during development. Instead, they ended up in the wrong place, often near the brain’s fluid spaces, where they can cause seizures.²⁰

Low-grade tumours and focal seizures 

Certain brain tumours, especially slow-growing ones like gangliogliomas or dysembryoplastic neuroepithelial tumours (DNETs), are sometimes found in people with TLE. These tumours often begin during childhood or adolescence and might not cause other symptoms besides seizures. On MRI, they may appear as cyst-like or partially solid masses, often with unusual but not dangerous features.²²

White matter abnormalities

TLE can also affect the brain’s white matter—the parts responsible for sending signals between brain regions. Special MRI scans like diffusion tensor imaging (DTI) can detect damage in these communication pathways, which may contribute to memory or thinking problems seen in some patients with epilepsy.²³ 

Advanced MRI techniques for TLE evaluation

MRI is one of the most reliable tools doctors use to spot changes in the brain linked to TLE. But other advanced scans can also help. These can pick up even more subtle changes, like shrinkage in the hippocampus, shifts in brain activity, or damage to the brain’s wiring. These detailed images can help doctors make a more accurate diagnosis and plan the best treatment. 

Volumetric analysis in MRI for precise atrophy measurement 

Using computer programs, doctors can measure the exact size of different parts of the brain. This helps them spot areas like the hippocampus that may have shrunk because of long-standing seizure activity.

Functional MRI 

Functional MRI (fMRI) shows which parts of the brain are active when a person is thinking, speaking, or even resting. In epilepsy, fMRI is often used to figure out which side of the brain controls language or memory, so these critical areas can be avoided during surgery.²⁶

MR Spectroscopy for metabolic abnormalities 

MR spectroscopy is like a chemical test for the brain. It shows whether certain brain chemicals, like N-acetylaspartate, are lower than they should be, often a sign that the brain cells in that area are damaged or under stress.²⁷

Summary

MRI plays a vital role in understanding and treating temporal lobe epilepsy. It helps doctors see not just what’s wrong, but also what might be done to help. As imaging technology continues to advance, these tools will only become more powerful, helping guide more accurate diagnoses, safer surgeries, and better outcomes for people living with epilepsy.