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doi: 10.1097/01.NT.0000368756.91077.64
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Temporal Lobe Epilepsy MRI Abnormalities Common in Healthy Individuals

SAMSON, KURT

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ARTICLE IN BRIEF

In the first prospective study comparing MRI results between temporal lobe epilepsy (TLE) patients and those without any neurological illness or family history of seizure disorders, researchers found many common abnormalities, but only one shared almost exclusively by TLE patients.

MRI can help confirm temporal lobe epilepsy, however many healthy people also show abnormalities that are believed to be associated with the disorder, according to researchers at Graecia University in Catanzaro, Italy. The findings were reported ahead of the Feb. 16 print issue of Neurology.

In the first prospective study comparing MRI results between temporal lobe epilepsy (TLE) patients and those without any neurological illness or family history of seizure disorders, researchers found many common abnormalities, but only one shared almost exclusively by TLE patients.

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STUDY METHODS, RESULTS

Led by Antonio Gambardella, MD, associate professor of neurology, the team found similar rates of abnormal MRI hippocampal signal intensities in both groups, but hippocampal atrophy was seen almost exclusively in those with TLE.

A total of 99 TLE patients and 51 healthy subjects participated in the study. The findings were based on analysis of MRIs and fluid-attenuated inversion recovery (FLAIR), a technique routinely used to enhance MRI sensitivity in searching for brain lesions; by removing CSF content from brain segments being scanned, FLAIR can pick up more subtle changes in the brain.

Figure. MRI HYPERINT...
Figure. MRI HYPERINT...
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Images of cortical atrophy and signal intensities in the amygdala, hippocampus, cingulate gyrus, subcallosal area, and the insula, temporal parietal and occipital lobes were reviewed, and the results were then graded relative to cortical signal intensity in the frontal lobes.

Two neuroradiologists who were blinded to all clinical information reviewed the images independently, and their analyses were then evaluated both individually and collectively.

In an MRI, different targeted magnetic pulses invoke signal intensities, which are used to evaluate brain tissue. Elevated signal intensities, or hyperintensities, are associated with a number of different neurological conditions and diseases, including epilepsy. Signal intensities on the MRI image are determined by four basic parameters: proton density, T1 relaxation time, T2 relaxation time, and flow. By using different pulse sequences and by changing the imaging parameters to evaluate these variables, researchers can identify abnormalities associated with different neurological disease states.

The neuroradiologists' findings were consistent and repeatable, both individually and when taken together. In TLE patients, 47.5 percent showed either unilateral or bilateral major T2/FLAIR hyperintensities, and 19.2 percent showed hippocampal atrophy at the T1/IR sequences. However, among the healthy volunteers, 29.4 percent also showed unilateral or bilateral hyperintensities at rates similar to those in the patient group (p=0.08).

Unilateral hippocampal atrophy was observed in only one healthy subject, while hyperintensity plus structural hippocampal atrophy were only seen in the TLE group.

“The combination of these two variables represents the strongest and most reliable indicator of epilepsy,” the researchers concluded. To date, very few studies have investigated incidental findings of temporal lobe abnormalities in individuals without other signs of epilepsy, and an extremely low frequency of high signal intensities of mesial temporal structures on FLAIR images has been reported, the researchers noted. Such abnormalities are usually bilateral, and are typically seen in other cortical areas outside the temporal lobes without any signs of neuronal loss in other sequences, the authors noted.

However, no prior studies have compared MRI findings in healthy patients and those with confirmed TLE, only individuals with subtle neurological disturbances, such as headache, hearing loss, or vertigo. Moreover, none of the earlier studies have emphasized the occurrence of hippocampal atrophy on T1 IR images, according to the authors.

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WHAT'S NORMAL?

The signal hyperintensities seen in healthy controls could be due to intrinsic histological features of the hippocampus, they said, noting that in one recent histopathological study, microscopic abnormalities in the hippocampus, similar to those observed in patients who underwent temporal lobe resection for epileptic seizures, were also seen in autopsied brains from individuals without any history of neurological illnesses.

Abnormalities among the healthy volunteers in the current study led to further clinical evaluation to exclude any undetected seizure disorder, and all of them were examined by an epileptologist. However, the investigators reported no evidence of any undetected family or patient history of epilepsy, excluding possible undiagnosed epilepsy.

The authors emphasized that further studies are needed to clarify the relationship between MRI and their histological findings. With neuroimaging in clinical practice, they noted, MRI signs of hyperintensities should always be carefully assessed and interpreted in the proper clinical context.

Figure. DR. ANTONIO ...
Figure. DR. ANTONIO ...
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Patient symptoms “remain the bedrock on which we should base the diagnosis,” according to the authors. “This is particularly compelling in view of the high rate of incorrect diagnosis of epilepsy in individuals whose seizures have their basis in a psychogenic, cardiac, or metabolic disturbance,” they noted.

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THE CLINICAL CONTEXT

Selim R. Benbadis, MD, professor and director of the Comprehensive Epilepsy Program and Clinical Neurophysiology Laboratory at the University of South Florida and Tampa General Hospital, agreed that clinicians need to rely more on clinical diagnosis and less on imaging and other expensive tests in patients with suspected TLE.

“This is a very important paper because it shows just how many patients without temporal lobe epilepsy can have brain abnormalities on MRI suggesting otherwise,” he told Neurology Today in a telephone interview.

“Far too much emphasis is being placed on expensive tests, especially imaging, when they are only useful when looking for a specific abnormality that can confirm a disease. MRI can be dangerously inaccurate because it can become too sensitive for irrelevant findings. It can be very useful in finding causes for certain symptoms, but not in making a diagnosis of epilepsy,” he said.

According to Dr. Benbadis, an analogy can be drawn with using MRI to diagnose multiple sclerosis (MS) or back pain. “With MS, MRI findings mean little without the clinical context. Instead, a diagnosis must be based on clinical symptoms and examination. With back pain, you can find all kinds of bulges and abnormalities on MRI in patients without any pain whatsoever. When tests become too sensitive, you lose specificity.”

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REFERENCE

• Labate A, Gambardella A, Aguglia U, et al. Temporal lobe abnormalities on brain MRI in healthy volunteers: a prospective case-control study. Neurology 2010; 74;553–557.

©2010 American Academy of Neurology

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