Histologically confirmed hippocampal structural features revealed by 3T MR imaging: potential to increase diagnostic specificity of mesial temporal sclerosis

Practical microscopic neuroanatomy of the limbic system and basal forebrain identifiable on clinical 3T MRI

Microscopic neuroanatomy of limbic system and basal forebrain on MRI is complex and is a terra incognita for many radiologists, clinicians, and neuroscientists. Interestingly, most of the important structures/at least anatomical regions containing these structures demonstrable on cadaveric and surgical dissections can be identified on clinical MRI, with 3T being much better than 1.5T. This article teaches the practical MRI identification of these structures which will greatly help in evaluating complex ailments like temporal lobe epilepsy, Alzheimer dementia, and other neuropsychiatric disorders. This knowledge will also aid in accurate reporting of tumor spread along the white matter fasciculi in the temporal stem/basal forebrain region. Limbic system includes the mesial temporal structures and their connections, piriform cortex including "area tempestas," and the septal area comprising of subcallosal area and paraterminal gyrus. Basal forebrain includes structures like substantia innominata with basal nucleus of Meynert, diagonal gyrus/diagonal band of Broca, and nucleus accumbens lying in between the anterior perforated substance inferiorly and the anterior commissure superiorly.

Loss of hippocampal dentation in hippocampal sclerosis and its relationship to memory dysfunction

OBJECTIVE

Hippocampal dentation (HD) is a "tooth-like" morphological feature observed on the inferior aspect of the human hippocampus. It has been found that HD varies dramatically in healthy adults and is positively associated with verbal and visual memory. In this work, we evaluate the loss of HD and its association to memory dysfunction in patients with temporal lobe epilepsy who have hippocampal sclerosis (HS).

METHODS

58 unilateral HS patients with neuropsychological data were identified from a retrospective database. T1w MPRAGE images (~1mm resolution) were upsampled to 0.25mm and were processed using ASHS software to obtain ultra high resolution segmentations and 3D renderings. Dentes were counted on the epileptic and contralateral sides, and associations were tested between dentation on the epileptic versus contralateral sides and measures of verbal and visuospatial memory with respect to the dominant versus non-dominant hemisphere.

RESULTS

The median number of dentes in epileptic hippocampi was significantly lower than in contralateral hippocampi (p<0.0001). Among cases with HS in the dominant hemisphere, verbal memory was significantly correlated with contralateral non-dominant hemisphere dentation (r = 0.45, p = 0.02). Similarly, among cases of HS in the non-dominant hemisphere, visual memory was significantly correlated with contralateral dominant hemisphere dentation (r = 0.50, p = 0.03). All other analyses were not significant.

SIGNIFICANCE

This is the first study characterizing dentation in TLE patients with HS and its memory correlates. There is marked loss of dentation in sclerotic hippocampi compared to the unaffected contralateral hippocampi. Material-specific measures of memory performance are paradoxically correlated with dentation contralateral to the side with HS, suggesting that contralateral functional capacity explains some of the variation in memory across TLE patients. Hippocampal dentation is an important variable to consider in understanding memory loss in TLE.

Investigation of synapses in the cortical white matter in human temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is one of the most common focal pharmacotherapy-resistant epilepsy in adults. Previous studies have shown significantly higher numbers of neurons in the neocortical white matter in TLE patients than in controls. The aim of this work was to investigate whether white matter neurons are part of the neuronal circuitry. Therefore, we studied the distribution and density of synapses in surgically resected neocortical tissue of pharmacotherapy-resistant TLE patients. Neocortical white matter of temporal lobe from non-epileptic patients were used as controls. Synapses and neurons were visualized with immunohistochemistry using antibodies against synaptophysin and NeuN, respectively. The presence of synaptophysin in presynaptic terminals was verified by electron microscopy. Quantification of immunostaining was performed and the data of the patients' cognitive tests as well as clinical records were compared to the density of neurons and synapses. Synaptophysin density in the white matter of TLE patients was significantly higher than in controls. In TLE, a significant correlation was found between synaptophysin immunodensity and density of white matter neurons. Neuronal as well as synaptophysin density significantly correlated with scores of verbal memory of TLE patients. Neurosurgical outcome of TLE patients did not significantly correlate with histological data, although, higher neuronal and synaptophysin densities were observed in patients with favorable post-surgical outcome. Our results suggest that white matter neurons in TLE patients receive substantial synaptic input and indicate that white matter neurons may be integrated in epileptic neuronal networks responsible for the development or maintenance of seizures.

Toward individualized prediction of seizure recurrence: Hippocampal neuroimaging features in a cohort of patients from a first seizure clinic

PURPOSE

We performed an exploratory analysis of electroencephalography (EEG) and neuroimaging data from a cohort of 51 patients with first seizure (FS) and new-onset epilepsy (NOE) to identify variables, or combinations of variables, that might discriminate between clinical trajectories over a one-year period and yield potential biomarkers of epileptogenesis.

METHODS

Patients underwent EEG, hippocampal and whole brain structural magnetic resonance imaging (MRI), diffusion tensor imaging (DTI), and magnetic resonance spectroscopy (MRS) within six weeks of the index seizure, and repeat neuroimaging one year later. We classified patients with FS as having had a single seizure (FS-SS) or having converted to epilepsy (FS-CON) after one year and performed logistic regression to identify combinations of variables that might discriminate between FS-SS and FS-CON, and between FS-SS and the combined group FS-CON + NOE. We performed paired t-tests to assess changes in quantitative variables over time.

RESULTS

Several combinations of variables derived from hippocampal structural MRI, DTI, and MRS provided excellent discrimination between FS-SS and FS-CON in our sample, with areas under the receiver operating curve (AUROC) ranging from 0.924 to 1. They also provided excellent discrimination between FS-SS and the combined group FS-CON + NOE in our sample, with AUROC ranging from 0.902 to 1. After one year, hippocampal fractional anisotropy (FA) increased bilaterally, hippocampal radial diffusivity (RD) decreased on the side with the larger initial measurement, and whole brain axial diffusivity (AD) increased in patients with FS-SS; hippocampal volume decreased on the side with the larger initial measurement, hippocampal FA increased bilaterally, hippocampal RD decreased bilaterally and whole brain AD, FA and mean diffusivity increased in the combined group FS-CON + NOE (corrected threshold for significance, q = 0.017).

CONCLUSION

We propose a prospective, multicenter study to develop and test models for the prediction of seizure recurrence in patients after a first seizure, based on hippocampal neuroimaging. Further longitudinal neuroimaging studies in patients with a first seizure and new-onset epilepsy may provide clues to the microstructural changes occurring at the earliest stages of epilepsy and yield biomarkers of epileptogenesis.

Anatomical Variations, Mimics, and Pitfalls in Imaging of Patients with Epilepsy

Epilepsy is among one of the most common neurologic disorders. The role of magnetic resonance imaging (MRI) in the diagnosis and management of patients with epilepsy is well established, and most patients with epilepsy are likely to undergo at least one or more MRI examinations in the course of their disease. Recent advances in high-field MRI have enabled high resolution in vivo visualization of small and intricate anatomic structures that are of great importance in the assessment of seizure disorders. Familiarity with normal anatomic variations is essential in the accurate diagnosis and image interpretation, as these variations may be mistaken for epileptogenic foci, leading to unnecessary follow-up imaging, or worse, unnecessary treatment. After a brief overview of normal imaging anatomy of the mesial temporal lobe, this article will review a few important common and uncommon anatomic variations, mimics, and pitfalls that may be encountered in the imaging evaluation of patients with epilepsy.

Etiology-related Degree of Sprouting of Parvalbumin-immunoreactive Axons in the Human Dentate Gyrus in Temporal Lobe Epilepsy

In the present study, we examined parvalbumin-immunoreactive cells and axons in the dentate gyrus of surgically resected tissues of therapy-resistant temporal lobe epilepsy (TLE) patients with different etiologies. Based on MRI results, five groups of patients were formed: (1) hippocampal sclerosis (HS), (2) malformation of cortical development, (3) malformation of cortical development + HS, (4) tumor-induced TLE, (5) patients with negative MRI result. Four control samples were also included in the study. Parvalbumin-immunoreactive cells were observed mostly in subgranular location in the dentate hilus in controls, in tumor-induced TLE, in malformation of cortical development and in MR-negative cases. In patients with HS, significant decrease in the number of hilar parvalbumin-immunoreactive cells and large numbers of ectopic parvalbumin-containing neurons were detected in the dentate gyrus' molecular layer. The ratio of ectopic/normally-located cells was significantly higher in HS than in other TLE groups. In patients with HS, robust sprouting of parvalbumin-immunoreactive axons were frequently visible in the molecular layer. The extent of sprouting was significantly higher in TLE patients with HS than in other groups. Strong sprouting of parvalbumin-immunoreactive axons were frequently observed in patients who had childhood febrile seizure. Significant correlation was found between the level of sprouting of axons and the ratio of ectopic/normally-located parvalbumin-containing cells. Electron microscopy demonstrated that sprouted parvalbumin-immunoreactive axons terminate on proximal and distal dendritic shafts as well as on dendritic spines of granule cells. Our results indicate alteration of target profile of parvalbumin-immunoreactive neurons in HS that contributes to the known synaptic remodeling in TLE.

Detection of partial loss of hippocampal striation at 1.5 Tesla magnetic resonance imaging

OBJECTIVES

Partial loss of hippocampal striation (PLHS) is recently described in 3 T and 7 T MR imaging as a sensitive indicator of hippocampal sclerosis.

PRIMARY OBJECTIVE

We described the demographic characteristics of the population with seizure disorder having PLHS at 1.5 T MR imaging and tried to see the relation of PLHS to the classic signs of hippocampal sclerosis.

SECONDARY OBJECTIVE

PLHS was also looked for in a small control population that had no seizure history.

METHODS

This retrospective study had the approval of the institutional review board. In patients demonstrating PLHS on oblique coronal T2-weighted images, the following were recorded: age, sex, EEG findings, side of PLHS, hippocampal atrophy and high signal intensity of the hippocampus. In control population, the following were recorded: age, sex, presence/absence of PLHS and indication for imaging.

RESULTS

The 116 PLHS subjects (age range 2-73 years) included 62 males and 54 females. Sixty-six (56.9%) of our PLHS subjects were less than 18 years of age: 44 (37.9%) under the age of 12 years and 22 (19%) of 12-18 years of age. Classic signs of hippocampal sclerosis were found in only 7 (6%) of the 116 subjects showing PLHS. All patients with classic signs showed PLHS on the same side. Of the control population (25 subjects, age range 3-76 years, 17 males and 8 females), one showed PLHS-he was a treated case of CNS lymphoma with gliotic changes, though there was no history of seizure.

CONCLUSION

PLHS is demonstrated at 1.5 T in both adult and paediatric population in this article and is much more common than the classic signs of hippocampal sclerosis (increased signal intensity and volume loss).

Increased expression of vascular endothelial growth factor-C and vascular endothelial growth factor receptor-3 after pilocarpine-induced status epilepticus in mice

Vascular endothelial growth factor (VEGF)-C and its receptor, vascular endothelial growth factor receptor (VEGFR)-3, are responsible for lymphangiogenesis in both embryos and adults. In epilepsy, the expression of VEGF-C and VEGFR-3 was significantly upregulated in the human brains affected with temporal lobe epilepsy. Moreover, pharmacologic inhibition of VEGF receptors after acute seizures could suppress the generation of spontaneous recurrent seizures, suggesting a critical role of VEGF-related signaling in epilepsy. Therefore, in the present study, the spatiotemporal expression of VEGF-C and VEGFR-3 against pilocarpine-induced status epilepticus (SE) was investigated in C57BL/6N mice using immunohistochemistry. At 1 day after SE, hippocampal astrocytes and microglia were activated. Pyramidal neuronal death was observed at 4 days after SE. In the subpyramidal zone, VEGF-C expression gradually increased and peaked at 7 days after SE, while VEGFR-3 was significantly upregulated at 4 days after SE and began to decrease at 7 days after SE. Most VEGF-C/VEGFR-3-expressing cells were pyramidal neurons, but VEGF-C was also observed in some astrocytes in sham-manipulated animals. However, at 4 days and 7 days after SE, both VEGFR-3 and VEGF-C immunoreactivities were observed mainly in astrocytes and in some microglia of the stratum radiatum and lacunosum-moleculare of the hippocampus, respectively. These data indicate that VEGF-C and VEGFR-3 can be upregulated in hippocampal astrocytes and microglia after pilocarpine-induced SE, providing basic information about VEGF-C and VEGFR-3 expression patterns following acute seizures.

Improved Detection of Subtle Mesial Temporal Sclerosis: Validation of a Commercially Available Software for Automated Segmentation of Hippocampal Volume

BACKGROUND AND PURPOSE

Identification of mesial temporal sclerosis is critical in the evaluation of individuals with temporal lobe epilepsy. Our aim was to assess the performance of FDA-approved software measures of hippocampal volume to identify mesial temporal sclerosis in patients with medically refractory temporal lobe epilepsy compared with the initial clinical interpretation of a neuroradiologist.

MATERIALS AND METHODS

Preoperative MRIs of 75 consecutive patients who underwent a temporal resection for temporal lobe epilepsy from 2011 to 2016 were retrospectively reviewed, and 71 were analyzed using Neuroreader, a commercially available automated segmentation and volumetric analysis package. Volume measures, including hippocampal volume as a percentage of total intracranial volume and the Neuroreader Index, were calculated. Radiologic interpretations of the MR imaging and pathology from subsequent resections were classified as either mesial temporal sclerosis or other, including normal findings. These measures of hippocampal volume were evaluated by receiver operating characteristic curves on the basis of pathologic confirmation of mesial temporal sclerosis in the resected temporal lobe. Sensitivity and specificity were calculated for each method and compared by means of the McNemar test using the optimal threshold as determined by the Youden J point.

RESULTS

Optimized thresholds of hippocampal percentage of a structural volume relative to total intracranial volume (<0.19%) and the Neuroreader Index (≤-3.8) were selected to optimize sensitivity and specificity (89%/71% and 89%/78%, respectively) for the identification of mesial temporal sclerosis in temporal lobe epilepsy compared with the initial clinical interpretation of the neuroradiologist (50% and 87%). Automated measures of hippocampal volume predicted mesial temporal sclerosis more accurately than radiologic interpretation (McNemar test, P < .0001).

CONCLUSIONS

Commercially available automated segmentation and volume analysis of the hippocampus accurately identifies mesial temporal sclerosis and performs significantly better than the interpretation of the radiologist.

Predictive coding: A contemporary view on the burden of normality and forced normalization in individuals undergoing epilepsy surgery

Following epilepsy surgery, a good psychosocial outcome is not necessarily contingent on a good seizure outcome. Increasingly, it is believed that "successful" surgery is a combination of both an acceptable and expected seizure status as well as the individual's perception of improvements in quality of life (QOL). The factors that create this optimal outcome remain an ongoing area of research in the epilepsy community. That being said, there have been some major breakthroughs in observing and understanding poor outcomes seen in a subset of postoperative patients with epilepsy. Characteristics of burden of normality and forced normalization are two phenomena that have been evident in cases of poor postoperative outcomes. In this review, we provide a summary of research and concepts used to explain these poor QOL outcomes for a seemingly successful surgery and suggest a contemporary view in understanding the mechanism of forced normalization through understanding the brain as a predictive organ. Using such a predictive coding model together with recommendations of other studies, we suggest the crucial need for a preoperative intervention addressing patient predictions and expectations to optimize on the benefits achievable through epilepsy surgery.

Diffusion tensor MRI shows progressive changes in the hippocampus and dentate gyrus after status epilepticus in rat - histological validation with Fourier-based analysis

Imaging markers for monitoring disease progression, recovery, and treatment efficacy are a major unmet need for many neurological diseases, including epilepsy. Recent evidence suggests that diffusion tensor imaging (DTI) provides high microstructural contrast even outside major white matter tracts. We hypothesized that in vivo DTI could detect progressive microstructural changes in the dentate gyrus and the hippocampal CA3bc in the rat brain after status epilepticus (SE). To test this hypothesis, we induced SE with systemic kainic acid or pilocarpine in adult male Wistar rats and subsequently scanned them using in vivo DTI at five time-points: prior to SE, and 10, 20, 34, and 79 days post SE. In order to tie the DTI findings to changes in the tissue microstructure, myelin- and glial fibrillary acidic protein (GFAP)-stained sections from the same animals underwent Fourier analysis. We compared the Fourier analysis parameters, anisotropy index and angle of myelinated axons or astrocyte processes, to corresponding DTI parameters, fractional anisotropy (FA) and the orientation angle of the principal eigenvector. We found progressive detectable changes in DTI parameters in both the dentate gyrus (FA, axial diffusivity [D_||], linear anisotropy [CL] and spherical anisotropy [CS], p<0.001, linear mixed-effects model [LMEM]) and the CA3bc (FA, D_||, CS, and angle, p<0.001, LMEM; CL and planar anisotropy [CP], p<0.01, LMEM) post SE. The Fourier analysis revealed that both myelinated axons and astrocyte processes played a role in the water diffusion anisotropy changes detected by DTI in individual portions of the dentate gyrus (suprapyramidal blade, mid-portion, and infrapyramidal blade). In the whole dentate gyrus, myelinated axons markedly contributed to the water diffusion changes. In CA3bc as well as in CA3b and CA3c, both myelinated axons and astrocyte processes contributed to water diffusion anisotropy and orientation. Our study revealed that DTI is a promising method for noninvasive detection of microstructural alterations in the hippocampus proper. These alterations may be potential imaging markers for epileptogenesis.

Hippocampal internal architecture and postoperative seizure outcome in temporal lobe epilepsy due to hippocampal sclerosis

PURPOSE

Semi-quantitative analysis of hippocampal internal architecture (HIA) on MRI has been shown to be a reliable predictor of the side of seizure onset in patients with temporal lobe epilepsy (TLE). In the present study, we investigated the relationship between postoperative seizure outcome and preoperative semi-quantitative measures of HIA.

METHODS

We determined HIA on high in-plane resolution preoperative T2 short tau inversion recovery MR images in 79 patients with presumed unilateral mesial TLE (mTLE) due to hippocampal sclerosis (HS) who underwent amygdalohippocampectomy and postoperative follow up. HIA was investigated with respect to postoperative seizure freedom, neuronal density determined from resected hippocampal specimens, and conventionally acquired hippocampal volume.

RESULTS

HIA ratings were significantly related to some neuropathological features of the resected hippocampus (e.g. neuronal density of selective CA regions, Wyler grades), and bilaterally with preoperative hippocampal volume. However, there were no significant differences in HIA ratings of the to-be-resected or contralateral hippocampus between patients rendered seizure free (ILAE 1) compared to those continuing to experience seizures (ILAE 2-5).

CONCLUSIONS

This work indicates that semi-quantitative assessment of HIA on high-resolution MRI provides a surrogate marker of underlying histopathology, but cannot prospectively distinguish between patients who will continue to experience postoperative seizures and those who will be rendered seizure free. The predictive power of HIA for postoperative seizure outcome in non-lesional patients with TLE should be explored.

Detection of aberrant hippocampal mossy fiber connections: Ex vivo mesoscale diffusion MRI and microtractography with histological validation in a patient with uncontrolled temporal lobe epilepsy

Understanding the neurobiology and functional connectivity of hippocampal structures is essential for improving the treatment of mesial temporal lobe epilepsy. At the macroscale, in vivo MRI often reveals hippocampal atrophy and decreased fractional anisotropy, whereas at the microscopic scale, there frequently is evidence of neuronal loss and gliosis. Mossy fiber sprouting in the dentate gyrus (DG), with evidence of glutamatergic synapses in the stratum moleculare (SM) putatively originating from granule cell neurons, may also be observed. This aberrant connection between the DG and SM could produce a reverberant excitatory circuit. However, this hypothesis cannot easily be evaluated using macroscopic or microscopic techniques. We here demonstrate that the ex vivo mesoscopic MRI of surgically excised hippocampi can bridge the explanatory and analytical gap between the macro‐ and microscopic scale. Specifically, diffusion‐ and T₂‐weighted MRI can be integrated to visualize a cytoarchitecture that is akin to immunohistochemistry. An appropriate spatial resolution to discern individual cell layers can then be established. Processing of diffusion tensor images using tractography detects extra‐ and intrahippocampal connections, hence providing a unique systems view of the hippocampus and its connected regions. Here, this approach suggests that there is indeed an aberrant connection between the DG and SM, supporting the sprouting hypothesis of a reverberant excitatory network. Mesoscopic ex vivo MR imaging hence provides an exciting new avenue to study hippocampi from treatment‐resistant patients and allows exploration of existing hypotheses, as well as the development of new treatment strategies based on these novel insights. Hum Brain Mapp 37:780–795, 2016. © 2015 Wiley Periodicals, Inc.

Neuroimaging for patient selection for medial temporal lobe epilepsy surgery: Part 1 Structural neuroimaging

The objective of part one of this review is to present the structural neuroimaging techniques that are currently used to evaluate patients with temporal lobe epilepsy (TLE), and to discuss their potential to define patient eligibility for medial temporal lobe surgery. A PubMed query, using Medline and Embase, and subsequent review, was performed for all English language studies published after 1990, reporting neuroimaging methods for the evaluation of patients with TLE. The extracted data included demographic variables, population and study design, imaging methods, gold standard methods, imaging findings, surgical outcomes and conclusions. Overall, 56 papers were reviewed, including a total of 1517 patients. This review highlights the following structural neuroimaging techniques: MRI, diffusion-weighted imaging, tractography, electroencephalography and magnetoencephalography. The developments in neuroimaging during the last decades have led to remarkable improvements in surgical precision, postsurgical outcome, prognosis, and the rate of seizure control in patients with TLE. The use of multiple imaging methods provides improved outcomes, and further improvements will be possible with future studies of larger patient cohorts.

Partial epilepsy: A pictorial review of 3 TESLA magnetic resonance imaging features

Epilepsy is a disease with serious consequences for patients and society. In many cases seizures are sufficiently disabling to justify surgical evaluation. In this context, Magnetic Resonance Imaging (MRI) is one of the most valuable tools for the preoperative localization of epileptogenic foci. Because these lesions show a large variety of presentations (including subtle imaging characteristics), their analysis requires careful and systematic interpretation of MRI data. Several studies have shown that 3 Tesla (T) MRI provides a better image quality than 1.5 T MRI regarding the detection and characterization of structural lesions, indicating that high-field-strength imaging should be considered for patients with intractable epilepsy who might benefit from surgery. Likewise, advanced MRI postprocessing and quantitative analysis techniques such as thickness and volume measurements of cortical gray matter have emerged and in the near future, these techniques will routinely enable more precise evaluations of such patients. Finally, the familiarity with radiologic findings of the potential epileptogenic substrates in association with combined use of higher field strengths (3 T, 7 T, and greater) and new quantitative analytical post-processing techniques will lead to improvements regarding the clinical imaging of these patients. We present a pictorial review of the major pathologies related to partial epilepsy, highlighting the key findings of 3 T MRI.

Invariance in current dipole moment density across brain structures and species: physiological constraint for neuroimaging

Although anatomical constraints have been shown to be effective for MEG and EEG inverse solutions, there are still no effective physiological constraints. Strength of the current generator is normally described by the moment of an equivalent current dipole Q. This value is quite variable since it depends on size of active tissue. In contrast, the current dipole moment density q, defined as Q per surface area of active cortex, is independent of size of active tissue. Here we studied whether the value of q has a maximum in physiological conditions across brain structures and species. We determined the value due to the primary neuronal current (q primary) alone, correcting for distortions due to measurement conditions and secondary current sources at boundaries separating regions of differing electrical conductivities. The values were in the same range for turtle cerebellum (0.56-1.48 nAm/mm(2)), guinea pig hippocampus (0.30-1.34 nAm/mm(2)), and swine neocortex (0.18-1.63 nAm/mm(2)), rat neocortex (~2.2 nAm/mm(2)), monkey neocortex (~0.40 nAm/mm(2)) and human neocortex (0.16-0.77 nAm/mm(2)). Thus, there appears to be a maximum value across the brain structures and species (1-2 nAm/mm(2)). The empirical values closely matched the theoretical values obtained with our independently validated neural network model (1.6-2.8 nAm/mm(2) for initial spike and 0.7-3.1 nAm/mm(2) for burst), indicating that the apparent invariance is not coincidental. Our model study shows that a single maximum value may exist across a wide range of brain structures and species, varying in neuron density, due to fundamental electrical properties of neurons. The maximum value of q primary may serve as an effective physiological constraint for MEG/EEG inverse solutions.

3T MRI quantification of hippocampal volume and signal in mesial temporal lobe epilepsy improves detection of hippocampal sclerosis

BACKGROUND AND PURPOSE

In mesial temporal lobe epilepsy, MR imaging quantification of hippocampal volume and T2 signal can improve the sensitivity for detecting hippocampal sclerosis. However, the current contributions of these analyses for the diagnosis of hippocampal sclerosis in 3T MRI are not clear. Our aim was to compare visual analysis, volumetry, and signal quantification of the hippocampus for detecting hippocampal sclerosis in 3T MRI.

MATERIALS AND METHODS

Two hundred three patients with mesial temporal lobe epilepsy defined by clinical and electroencephalogram criteria had 3T MRI visually analyzed by imaging epilepsy experts. As a second step, we performed automatic quantification of hippocampal volumes with FreeSurfer and T2 relaxometry with an in-house software. MRI of 79 healthy controls was used for comparison.

RESULTS

Visual analysis classified 125 patients (62%) as having signs of hippocampal sclerosis and 78 (38%) as having normal MRI findings. Automatic volumetry detected atrophy in 119 (95%) patients with visually detected hippocampal sclerosis and in 10 (13%) with visually normal MR imaging findings. Relaxometry analysis detected hyperintense T2 signal in 103 (82%) patients with visually detected hippocampal sclerosis and in 15 (19%) with visually normal MR imaging findings. Considered together, volumetry plus relaxometry detected signs of hippocampal sclerosis in all except 1 (99%) patient with visually detected hippocampal sclerosis and in 22 (28%) with visually normal MR imaging findings.

CONCLUSIONS

In 3T MRI visually inspected by experts, quantification of hippocampal volume and signal can increase the detection of hippocampal sclerosis in 28% of patients with mesial temporal lobe epilepsy.

Medial temporal cortices in ex vivo magnetic resonance imaging

This review focuses on the ex vivo magnetic resonance imaging (MRI) modeling of medial temporal cortices and associated structures, the entorhinal verrucae and the perforant pathway. Typical in vivo MRI has limited resolution due to constraints on scan times and does not show laminae in the medial temporal lobe. Recent studies using ex vivo MRI have demonstrated lamina in the entorhinal, perirhinal, and hippocampal cortices. These studies have enabled probabilistic brain mapping that is based on the ex vivo MRI contrast, validated to histology, and subsequently mapped onto an in vivo spherically warped surface model. Probabilistic maps are applicable to other in vivo studies.

Evaluating hippocampal internal architecture on MRI: inter-rater reliability of a proposed scoring system

BACKGROUND

Asymmetry of hippocampal internal architecture (HIA) has been reported to be a frequent imaging finding in epilepsy patients with temporal lobe epilepsy (TLE) who exhibit other signs of hippocampal sclerosis. HIA asymmetry may also be an independent predictor of the side of seizure onset in patients with otherwise normal MRI scans. The study of HIA asymmetry and its relationship to the laterality of TLE would benefit from a reliable method of assessing the clarity of HIA in MRI scans. We propose a visual scoring system that rates HIA clarity from 1 (imperceptible) to 4 (excellent) and report the inter-rater reliability (IRR) of this system.

METHODS

In the initial preliminary phase of this study we examined IRR using a kappa statistic (κ) among a mixed group of expert and non-expert reviewers using only a brief description of the scoring system to score single images from a series of patients. In the second phase we explored the effect of training on the use of our HIA scoring system by assessing IRR among neuroimaging experts before and after a brief interactive training session. In this phase, multiple slices from each patient were scored. Separate κ values and intraclass correlation coefficients (ICC) were calculated from the scores given to each hippocampal image and from the asymmetry of scores between left and right for each slice. In the third phase the effect of training on non-expert reviewers was explored using a similar approach as with the expert reviewers.

RESULTS

In the preliminary phase of the study, HIA scoring of single images showed substantial agreement among expert reviewers (κHIA=0.65), fair agreement among non-expert reviewers (κHIA=0.27), and a fair to moderate degree of agreement among all the reviewers as a whole (κHIA=0.40). In the second phase, prior to training there was substantial agreement among expert reviewers in regard to the individual HIA scores (κHIA=0.62; ICCHIA=0.81) but only moderate agreement on the degree of asymmetry (κAsym=0.47; ICCAsym=0.71). Training improved agreement on the individual HIA scores (κHIA=0.58-0.72; ICCHIA=0.76-0.84) and on the degree of asymmetry (κAsym=0.61-0.67; ICCAsym=0.81-0.85). Among non-expert reviewers, scores improved from only a fair degree of agreement pre-training (κHIA=0.25, κAsym=0.25; ICCHIA=0.68, ICCAsym=0.66) to a moderate level of agreement after training (κHIA=0.54, κAsym=0.52; ICCHIA=0.78, ICCAsym=0.81).

CONCLUSIONS

The proposed HIA scoring system has a substantial degree of inter-rater reliability among experienced neuroimaging reviewers. Training improves the detection of asymmetries in HIA score in particular. Non-expert reviewers can employ the system with a moderate degree of reliability, and training has an even greater impact on the improvement of scoring reliability.

Predictive value of hippocampal internal architecture asymmetry in temporal lobe epilepsy

BACKGROUND

Asymmetry of hippocampal internal architecture (HIA) clarity has been suggested to be a sign of hippocampal sclerosis (HS) and is frequently associated with other MRI findings of HS. The goal of this work is to use a previously developed HIA visual scoring system (Ver Hoef et al., 2013) to quantify HIA asymmetry in a retrospective series of consecutive temporal lobe epilepsy (TLE) patients and evaluate its value in predicting laterality of seizure onset both in patients with other signs of HS (HS+) and those without (HS-).

METHODS

The HIA scoring system was used to rate hippocampal asymmetry and to assess the agreement between HIA and seizure lateralization. The median values of the average HIA scores for each hippocampus were compared for HS+ epileptogenic hippocampi, HS- epileptogenic hippocampi, and non-epileptogenic hippocampi with a Kruskal-Wallis one-way analysis of variance by ranks. Pair-wise differences between groups were evaluated with the two-tailed Mann-Whitney U test. A logistic regression model examined the utility of average HIA asymmetry score in predicting the true laterality of seizure onset as determined by video-EEG. Sensitivity and specificity are calculated using various asymmetry thresholds in each patient group.

RESULTS

Fifty-five patients were identified who met inclusion criteria. Thirteen patients (24%) were found to have hippocampal atrophy and/or signal abnormality indicative of HS (HS+) and 42 did not (HS-). Significant differences were observed in the distribution of individual and average HIA scores between each of the groups of hippocampi, with HS+ hippocampi having the lowest HIA scores and non-epileptogenic hippocampi having the highest. Logistic regression analysis showed that the average HIA asymmetry score was a strong predictor of the laterality of seizure onset (β=3.93508, p<0.001). HIA asymmetry remained significant even after adjustment for HS+/HS- status (β=3.8854, p<0.001). Among HS- patients, when the average HIA asymmetry score was equal to or exceeded a threshold value of 0.5, the specificity for correctly predicting the side of seizure onset was between 95% and 100% with a sensitivity of 40-45%. Among HS+ patients, a threshold of 0.3 yielded a sensitivity of 85% and specificity of 100%.

CONCLUSIONS

In this report we show for the first time that HIA asymmetry is a significant predictor of the laterality of seizure onset in TLE patients with otherwise normal MRI findings, and that the proposed HIA scoring system has high specificity and moderate sensitivity for lateralizing seizure onset in patients with TLE.

Variability of sclerosis along the longitudinal hippocampal axis in epilepsy: a post mortem study

Detailed neuropathological studies of the extent of hippocampal sclerosis (HS) in epilepsy along the longitudinal axis of the hippocampus are lacking. Neuroimaging studies of patients with temporal lobe epilepsy support that sclerosis is not always localised. The extent of HS is of relevance to surgical planning and poor outcomes may relate to residual HS in the posterior remnant. In 10 post mortems from patients with long histories of drug refractory epilepsy and 3 controls we systematically sampled the left and right hippocampus at seven coronal anatomical levels along the body to the tail. We quantified neuronal densities in CA1 and CA4 subfields at each level using Cresyl Violet (CV), calretinin (CR), calbindin (CB) and Neuropeptide Y (NPY) immunohistochemistry. In the dentate gyrus we graded the extent of granule cell dispersion, patterns of CB expression, and synaptic reorganisation with CR and NPY at each level. We identified four patterns of HS based on patterns of pyramidal and interneuronal loss and dentate gyrus reorganisation between sides and levels as follows: (1) symmetrical HS with anterior-posterior (AP) gradient, (2) symmetrical HS without AP gradient, (3) asymmetrical HS with AP gradient and (4) asymmetrical cases without AP gradient. We confirmed in this series that HS can extend into the tail. The patterns of sclerosis (classical versus atypical or none) were consistent between all levels in less than a third of cases. In conclusion, this series highlights the variability of HS along the longitudinal axis. Further studies are required to identify factors that lead to focal versus diffuse HS.

Correlation between calbindin expression in granule cells of the resected hippocampal dentate gyrus and verbal memory in temporal lobe epilepsy

Calbindin expression of granule cells of the dentate gyrus is decreased in temporal lobe epilepsy (TLE) regardless of its etiology. In this study, we examined the relation between reduction of calbindin immunoreactivity and the verbal and visuo-spatial memory function of patients with TLE of different etiologies. Significant linear correlation was shown between calbindin expression and short-term and long-term percent retention and retroactive interference in auditory verbal learning test (AVLT) of patients including those with hippocampal sclerosis. In addition, we found significant linear regression between calbindin expression and short-term and long-term percent retention of AVLT in patients whose epilepsy was caused by malformation of cortical development or tumor and when no hippocampal sclerosis and substantial neuronal loss were detected. Together with the role of calbindin in memory established in previous studies on calbindin knock-out mice, our results suggest that reduction of calbindin expression may contribute to memory impairments of patients with TLE, particularly, when neuronal loss is not significant.

3.0 T MRI of 2000 consecutive patients with localisation-related epilepsy

OBJECTIVES

Clinical guidelines suggest that all patients diagnosed with localised seizures should be investigated with MRI to identify any epileptogenic structural lesions, as these patients may benefit from surgical resection. There is growing impetus to use higher field strength scanners to image such patients, as some evidence suggests that they improve detection rates. We set out to review the detection rate of radiological abnormalities found by imaging patients with localised seizures using a high-resolution 3.0 T epilepsy protocol.

METHODS

Data were reviewed from 2000 consecutive adult patients with localisation-related epilepsy referred between January 2005 and February 2011, and imaged at 3.0 T using a standard epilepsy protocol.

RESULTS

An abnormality likely to be related to seizure activity was identified in 403/2000 (20.2%) patients, with mesial temporal sclerosis diagnosed in 211 patients. 313/2000 (15.6%) had lesions potentially amenable to surgery. Abnormalities thought unrelated to seizure activity were found in 324/2000 (16.1%), with 8.9% having evidence of ischaemic disease.

CONCLUSIONS

Since the introduction of the then National Institute for Clinical Excellence guidelines in 2004, the detection rate of significant pathology using a dedicated 3.0 T epilepsy protocol has not fallen, despite the increased numbers of patients being imaged. This is the largest study of epilepsy imaging at 3.0 T to date and highlights the detection rates of significant pathology in a clinical setting using a high-strength magnet. The prevalence of ischaemic disease in this population is significantly higher than first thought, and may not be incidental, as is often reported.

Determining surgical candidacy in temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is the most common form of adult epilepsy that is amenable to surgical treatment. In the carefully selected patient, excellent seizure outcome can be achieved with minimal or no side effects from surgery. This may result in improved psychosocial functioning, achieving higher education, and maintaining or gaining employment. The objective of this paper is to discuss the surgical selection process of a patient with TLE. We define what constitutes a patient that has medically refractory TLE, describe the typical history and physical examination, and distinguish between mesial TLE and neocortical TLE. We then review the role of routine (ambulatory/sleep-deprived electroencephalography (EEG), video EEG, magnetic resonance imaging (MRI), neuropsychological testing, and Wada testing) and ancillary preoperative testing (positron emission tomography, single-photon emission computed tomography (SPECT), subtraction ictal SPECT correlated to MRI (SISCOM), magnetoencephalography, magnetic resonance spectroscopy, and functional MRI) in selecting surgical candidates. We describe the surgical options for resective epilepsy surgery in TLE and its commonly associated risks while highlighting some of the controversies. Lastly, we present teaching cases to illustrate the presurgical workup of patients with medically refractory TLE.

Degree and pattern of calbindin immunoreactivity in granule cells of the dentate gyrus differ in mesial temporal sclerosis, cortical malformation- and tumor-related epilepsies

A loss of calbindin immunoreactivity in granule cells of the hippocampal dentate gyrus is a characteristic feature of temporal lobe epilepsy with hippocampal sclerosis. Whether decreased calbindin expression is unique to the hippocampal sclerosis associated with cryptogenic temporal lobe epilepsy, or also occurs in tumor- or malformation-related epilepsy, is unknown. We show that calbindin immunoreactivity in granule cells has been decreased in epilepsy regardless of its etiology. In cases of cortical malformations or hippocampal sclerosis, calbindin immunoreactivity was undetectable in most granule cells. In tumor-related resections, in patients who had a long history of epileptic seizures, calbindin was detected only in one-third of granule cells. Regardless of etiology, calbindin expression correlated with age of onset and with duration of the epilepsy. In contrast to tumor-induced epilepsy, where calbindin-immunoreactive granule cells were equally distributed in the granule cell layer, in hippocampal sclerosis and malformation-related epilepsy, two-thirds of calbindin-immunoreactive granule cells were located in the outer half and only one-third in the inner half of the layer. Developmentally, granule cells at the border of the molecular layer are ontogenetically the oldest, and those at the border of the hilus are the youngest. The reduction of calbindin immunoreactivity in ontogenetically younger granule cells highlights the deleterious effect of early occurring epilepsy and initial early precipitating injury, including febrile seizures that may substantially affect developing immature granule cells, but less the earlier born matured ones.