MRI for epilepsy
Magnetic resonance imaging (MRI) is essential in the diagnosis and treatment of patients with seizure attacks. Replacing computed tomography (CT) in many brain imaging situations, MRI is the preferred imaging modality for epilepsy.
In this article, we look at how these basic brain examination methods are used in clinical practice.
The latest methods of examining the brain
Advances in radionuclide techniques such as single-photon emission CT / positron emission tomography and electromagnetic and magnetoencephalographic imaging are providing new insights into the pathophysiology of epilepsy. In addition, methods such as magnetic resonance spectroscopy of the brain are beginning to be actively used in treatment.
Although structural magnetic resonance imaging is now routinely used in the assessment and management of epilepsy, functional MRI ( fMRI ) has recently begun to provide a non-invasive and widely available method for assessing local brain functionality. FMRI studies of language and memory can show specific areas of activation in the cortical layers, are useful during preoperative assessment, and provide further understanding of the processes in the brain of patients with epilepsy. The use of fMRI to localize pathological phenomena can also contribute to the localization of the seizure focus and a better understanding of the pathophysiology of epilepsy. Combining fMRI with electroencephalogram (EEG) and other advanced brain imaging techniques can not only improve seizure control, but also provide valuable information for better understanding the pathophysiology of epilepsy and its consequences.
In this article, we look at how these basic brain examination methods are used in clinical practice.
How accurate is imaging in epilepsy
Solitary seizures like epileptic seizures can occur in 10% of the population, while true epilepsy is a chronic disease characterized by recurrent seizures that can occur in 2% of the population.
Current neuroimaging techniques are useful in diagnosing the underlying abnormalities of epilepsy. The information obtained from the use of imaging techniques can also aid in the correct classification of certain types of epileptic disorders and can delineate the genetics underlying some syndromes.
Neuroimaging is even more important for those patients who have, from a medical point of view, seizures of unknown origin. Advances in technologies for the localization of focal epileptogenic substrates, especially high-resolution structural images obtained after magnetic resonance imaging, have significantly improved the success of surgical treatment. This review compares the available imaging techniques and the practical application of brain imaging in the treatment of patients with epilepsy.
CT scan
Computed tomography uses ionizing radiation and can generate excellent contrast images of hard tissue as well as moderately good soft tissue images. CT has a number of advantages, including lower cost, faster scanning speed, affordability and ease of use, which provide relatively reliable image processing for most patients. Latest generation CT scans can generate images of the brain in seconds.
This method remains the leading method for examining patients with seizure attacks under certain conditions. And in newborns and infants, CT is secondary or has added value, but it serves as an important backup of ultrasound data. Computed tomography can accurately detect hemorrhages, heart attacks, gross malformations, lesions of the ventricular system, and lesions with underlying calcification. In older children and adults, this method is preferred perioperatively because it can quickly detect recent hemorrhage, hydrocephalus, and severe structural changes.
It should be recognized that the sensitivity of CT in people with epilepsy is slightly higher (up to 30%) than in the healthy population. The technique has generally poor sensitivity due to low resolution in the temporal fossa, and has no benefit in detecting temporary mesial sclerosis, the most common pathology of the brain in the temporal lobes.
Comparison of MRI and CT
The International League Against Epilepsy (ILAE) has ruled that computed tomography can be used for diagnostic imaging in epileptics if magnetic resonance imaging is not possible. It has been proven that CT may not detect abnormalities in 50% of patients with epileptogenic injuries, for example, small tumors and vascular defects. The ILAE also recommends that people with unexplained seizures have mandatory MRI scans. MRI is now considered the standard in the United States for treating these patients.
However, CT is still critical in emergency situations, especially in acute situations and postoperatively. In an acute seizure scenario, CT can accurately detect underlying pathologies such as trauma, hemorrhage, ischemic stroke, hydrocephalus, tumors, arteriovenous deformities, etc. In patients with any of the above pathologies, treatment will focus on neurosurgical intervention or supportive care.
For most primary patients, computed tomography is mandatory. In many patients with chronic epilepsy, with intermittent seizures, the initial examination showed a normal CT scan. Also, computed tomography is useful to exclude hemorrhages, subdural , epidural neoplasms, or hematomas.
Benefits of MRI as a diagnostic tool
MRI is the preferred imaging procedure for examining people with seizures. The advantages of magnetic resonance imaging over computed tomography are numerous and do not require further refinement. As with the EEG, MRI often does not end with a single exam. Several sessions of addressing different requests may be necessary to obtain all relevant information about the pathology of a particular person.
The sensitivity of MRI in detecting abnormalities related to the underlying pathologies of epileptic disease largely depends on the experience of the doctor. Temporal vascular sclerosis, small tumors, and trauma are more common in adults. And malformations are the most common basis of pathology in newborns and young children suffering from convulsive syndrome.
MRI and epilepsy management
Not all patients need neuroimaging . Such tests are unnecessary for well-defined idiopathic generalized epilepsy. However, there are reports of patients with overt generalized seizures or benign partial seizures, in which structural abnormalities are still visible on MRI. Children with uncomplicated febrile seizures and normal neurologic findings do not require brain imaging analysis. However, in the USA, for example, for practical and forensic reasons, almost all patients with epilepsy have an MRI of the brain.
On the other hand, structural neuroimaging studies should be performed in all patients with symptomatic generalized or focal seizures . Since magnetic resonance imaging is much preferable to computed tomography in detecting structural damage, it is suggested that magnetic resonance imaging should be mandatory when evaluating patients with seizures, especially if they have impaired coordination functions. In addition, MRI is done if seizures persist with previously normal CT or if there are progressive neurologic changes. Repeat MRI is indicated at intervals of 2–5 years, even with previously normal results in patients with persistent seizures.
Deciphering the detected lesions on MRI and the consequences of treatment
The pathologies discovered after the study of magnetic resonance imaging in a patient with epilepsy do not mean that this particular lesion is the culprit of the disease. Some brain lesions are epileptogenic , while others are not. Distinguishing them is difficult and often impossible without other information such as electrophysiology and clinical data. However, it is always useful to analyze the type of lesion and its location to assess the likelihood of the lesion being epileptogenic . Mesial temporary lesions and cortical malformations are more likely to be epileptogenic , whereas white matter cysts are less likely to be epileptogenic .
Thus, the nature and localization of the lesion detected on MRI allows predicting the course of the disease, prescribing the most adequate treatment and is a decisive factor in the success of a neurosurgical operation, if necessary.