Magnetic Resonance Spectroscopy and Histopathological Findings in Temporal Lobe Epilepsy

Abstract

Summary:Purpose: In some patients with temporal lobe epilepsy, histopathological evaluation of resected brain tissue after surgical treatment may reveal several features indicative of discrete cortical malformations. We sought to determine whether these histopathological features were accompanied by hippocampal changes detectable preoperatively by proton magnetic resonance (MR) spectroscopy and to evaluate their relationship with postoperative outcome.Methods: In 25 consecutive temporal lobe epilepsy patients who were scheduled for surgical treatment, MR spectroscopy was performed, and resected brain tissue was analyzed histopathologically for the presence of discrete cortical malformations (e.g., microdysgenesis). Outcome was assessed in all patients with an average postoperative period of 26 months.Results: In 13 patients, we found subtle, histopathologically detectable signs of cortical malformation: 6 of them with concomitant hippocampal sclerosis (dual pathology) and 7 without. The latter subgroup had a worse surgical outcome and showed enhanced bilateral and/or contralateral pathological changes in the hippocampal formation when investigated by MR spectroscopy.Conclusions: These data suggest that by showing contralaterally or bilaterally abnormal spectra, MR spectroscopy might be able to indicate pathological changes in subtle developmental disorders that are possibly more widespread over the brain. This observation may improve noninvasive diagnosis in presurgical evaluation and the neurobiological understanding of cortical malformations in pharmacoresistant temporal lobe epilepsy. Key Words: MR spectroscopy-Cortical malformations-Pharmacoresistant temporal lobe epilepsy-Neuropathology-Surgical outcome Histopathological analysis of resected brain tissue after surgical treatment can reveal different etiologies (1-3) in epilepsies that were considered "cryptogenic" before surgery, such as hippocampal sclerosis (HS) or cortical malformations (CMs). The diagnosis "cortical malformation" is often based on a high variety of subtle microscopic features, including heterotopic neurons or nodular heterotopia of neurons in the white matter, laminar disorganization, marked clustering of neurons (throughout layers II to VI), marked clustering of oligodendroglia in the white matter, glioneural hamartia, giant neurons, and balloon cell change. To elucidate the value and significance of these histopathological changes, Kasper et al. (4) compared brain tissue of surgically treated temporal lobe epilepsy patients with autopsy brains and demonstrated a higher prevalence of oligoclusters, hamartias, neurons in the white matter, and perivascular neurons in specimens from temporal lobe epilepsy patients. These changes can only be detected by precise histopathological analysis and then may be found as a single phenomenon in the temporal lobe or in combination with HS (dual pathology [DP]).Proton MR spectroscopy is reported to reveal histological abnormalities (particularly HS [5][6][7][8] but also CMs [9][10][11]) by obtaining s...

Role of proton magnetic resonance spectroscopy in preoperative evaluation of patients with mesial temporal lobe epilepsy

“…Contralateral spectroscopic alterations in MTLE may have a variety of causes, such as bilateral hippocampal sclerosis, widespread malformations of cortical development, non-specific damage of the hippocampus due to prolonged seizure activity, or its specific secondary damage due to preferential activation of the neural connections between hippocampi on both sides [11,23,33]. Our surgical series did not include any patient with bitemporal seizure origin, but contralateral spectroscopic abnormalities were noted in 89% of cases.…”

“…Several reports have suggested that 1 H-MRS-detected metabolic data might be useful for prediction of surgical outcome in patients with MTLE [13,15,16,23,24,26,28,29,31]. Two favorable factors for both postoperative reduction of seizure frequency and freedom from disabling seizures are usually mentioned: (1) significant asymmetry of the metabolic alterations with their predominance on the side of surgery and concordance with MRI and EEG data; and (2) the absence of the spectroscopic abnormalities in the contralateral temporal lobe.…”

1H MR spectroscopy in histopathological subgroups of mesial temporal lobe epilepsy

“…Significantly more frequent bilateral 1 H MRS abnormalities in MTLE patients with histopathologically proven temporal pole MCD were reported [27], and the authors speculated about more widespread developmental changes in patients with cortical malformations that could be responsible for bilateral 1 H MRS changes as well as for worse surgical outcomes in this group of patients. In contrast, four of our six cases with bilateral 1 H MRS abnormalities had no MCD in their temporal poles.…”

“…Malformations of cortical development (MCD) have been repeatedly found in a significant proportion of MTLE cases, especially in children [22][23][24][25]. It has been suggested that different histopathological subgroups of MTLE may have different etiopathogeneses [23,26], but a relationship to 1 H MRS findings has been only rarely approached [27].…”

Neuroimaging biomarkers of epileptogenesis

“…The combination of PMRSI and MRI volumetry can accurately and non-invasively lateralize TLE in the majority of patients [17]. Stefan et al found that PMRS could detect subtle abnormalities that were not apparent on MRI [107]. Another study indicated that hippocampal structural damage may be depicted by PMRS [36].…”