Epilepsy is a chronic neurological disorder characterized by recurrent unprovoked seizures. These seizures are transient signs and/or symptoms due to abnormal, excessive, or synchronous neuronal activity in the brain [9]. Patients with nonlesional epilepsy constitute the most challenging group undergoing presurgical evaluation [2].
Volumetric MRI allows detection of subtle abnormalities of the brain that are difficult or impossible to reveal on visual inspection [10].
Several recent software tools have been developed to automatically obtain volumetric measures using different strategies. volBrain is a new software pipeline for volumetric brain analysis. This pipeline provides automatically volumetric brain information at different scales in a very simple web-based interface not requiring any installation or advanced computational requirements [8].
In the current study, volumetric and segmentation reporting were done using an online MRI-brain volumetric system at www.volbrain.com (volBrain version 1.0 for whole brain segmentation and HIPS version 1.0 hippocampus segmentation) using the automated method. Once the automatic process is complete, a PDF report was created containing volumetric data.
In the current study and on comparison between abnormal volume (group A) and normal volume group patients (group B) and regarding seizure frequency, we found that patients in group A have highly frequent seizures than those in group B.
Regarding seizure type, our study demonstrated that generalized epilepsy was more common than focal epilepsy in group A (75% generalized epilepsy versus 25% focal epilepsy). On the other hand, in group B patients, generalized epilepsy was 30% versus 70% focal epilepsy. The aforementioned results come in concordance with the study done by Debourdeau et al. [11]; in their study, they reported that generalized epilepsy was more common than partial epilepsy.
In our study, an abnormal EEG was found both in abnormal volume and normal volume group patients. This finding strengthens the fact that EEG is used in the diagnosis of epilepsy and continues to play a central role in both diagnosis and management of patients with seizure disorders.
The higher percentage of abnormal EEG in our study may be attributed to the highly frequent seizures that were recorded in our study as Farid et al. [12] stated that there are many factors that influence the recording of interictal epileptiform discharge in epileptic patients; among these factors is the frequency of seizures.
We proved a big role of volumetry in the diagnosis of epileptic patients that if their conventional MRI gives no pathology, we can diagnose them by volumetric MRI. In our study, the sensitivity of the right hippocampus subiculum volume and right hippocampus CA4-DG was 100%. The sensitivity of white matter volume and grey matter volume and thalamus was 85% and 75% and 55% respectively.
In agreement with high sensitivity of volumetric MRI in detection of hippocampus volume in epileptic patients was the study of Giorgio and his colleagues [10] which found that volumetric MRI was useful in the presurgical evaluation of the epileptogenic site in TLE, showing asymmetry of the hippocampal volume ipsilateral to the seizure focus with a sensitivity up to 95%.
Another study in 2012 done by Farid et al. [12] found that quantitative MR imaging-derived hippocampal asymmetries discriminated patients with temporal lobe epilepsy from control subjects with high sensitivity (86.7–89.5%) and specificity (92.2–94.1%).
We compared between groups A and B patients regarding the volumetric measurements, and we found a significant reduction in the volume of most measured areas including white matter, hippocampus CA4-DG and hippocampus subiculum, and thalamus; we also found a significant increase in the volume of grey matter.
Lee and his colleagues [13] investigated the possible associations between cognitive dysfunctions and regional grey matter/white matter volumes in patients with newly diagnosed pediatric epilepsy; they found that the most prominent structural abnormalities observed in newly diagnosed pediatric epilepsy were decreased GM volumes in the bilateral frontal areas, especially the left inferior frontal and right middle frontal gyri.
Beheshti and his colleagues [14] reported significant grey matter and white matter volume reductions in temporal lobe epilepsy patients with hippocampal sclerosis; they also observed a slight grey matter amygdala swelling in the right temporal lobe epilepsy patients without hippocampal sclerosis.
Bernasconi and his colleagues [15] reported that the hippocampal head, body, and the entorhinal and perirhinal cortices in epileptic patients were significantly reduced.
Guimarãesn and his colleagues [16] revealed that volume reduction in the hippocampus has been demonstrated in pediatric localization-related epilepsy, including mesial temporal lobe epilepsy (TLE) and extratemporal lobe epilepsy.
Our results are in concordance with many volumetric studies that focused on hippocampal brain region and revealed hippocampal volume reduction in epileptic patients [17,18,19,20].
There are many volumetric studies focused on thalamic brain region and revealed thalamic volume reduction and dysfunction in epileptic patients [15,16,17,18,19,20,21,22,23].
It has been reported that the thalamus as a part of the limbic network has well-developed anatomic connection with mesial temporal lobe structures [21], so it has been suggested that the thalamus plays an important role in the amplification and distribution of limbic seizures and hence the volumetric abnormalities that can be detected in the thalamus could be concluded as a result of recurrent seizures [22].
Bonilha and his colleagues [24] reported that juvenile myoclonic epilepsy patients exhibited significant volume reductions in thalamus. In 2018, Yoong and his colleagues [25] revealed that cognitive impairment in early onset epilepsy is associated with reduced thalamic volume. In our study, the thalamus had no significant difference in abnormal volume group of patients with generalized seizures than in the other groups of the study.
The observed volumetric changes of the thalamus in our study and others were congruent with the reported data which points to an increase in blood oxygenation level-dependent signal in both thalami during interictal epileptiform activity in idiopathic generalized epilepsy [26, 27]. These volumetric changes which were confined to the thalamus were explained by Aghakhani et al. [26] as the thalamus mediates motor functions via connections from the ventral anterior and lateral nuclei to the motor cortex, basal ganglia, and cerebellum.
On comparison between abnormal volume group and normal volume group patients with partial seizures regarding volumetric measurements, we found a smaller hippocampal volume and its parts and white matter volume in abnormal volume group patients than that of normal volume group (Fig. 4). Our result was in keeping with an Australian follow-up study which focused on epileptic diagnosed cases and demonstrated a significant hippocampal volume loss over a period of time [28]. Szabo et al. [22] found that patients with chronic temporal lobe epilepsy tend to have hippocampal volume loss. On the other hand, Liu et al. [29] found no relevant difference in hippocampal volume or other brain pathology after a period of time from follow-up.
Holtkamp et al. [30] concluded in their follow-up study of patients with focal epilepsy that recurrent seizures do not cause hippocampal volume change. This difference may be argued to the different methodological approaches that had been employed.
In our study, the correlation between seizure frequency and volumetric measurements of patients with partial epilepsy revealed significant correlation between the seizure frequency and brain volume, grey matter volume, and hippocampus.
The results of Pulsipher and colleagues [31] found a significant correlation between seizure frequency and hippocampal volume in patients with temporal lobe epilepsy. We only detected a significant decrease in hippocampus volume on the epileptogenic side. This observation was consistent with prior findings [32].
