Incomplete inversion of the hippocampus--a common developmental anomaly

Medial positioning of the hippocampus and hippocampal fissure volume in developmental topographical disorientation

Developmental topographical disorientation (DTD) refers to the lifelong inability to orient by means of cognitive maps in familiar surroundings despite otherwise well-preserved general cognitive functions, and the absence of any acquired brain injury or neurological condition. While reduced functional connectivity between the hippocampus and other brain regions has been reported in DTD individuals, no structural differences in gray matter tissue for the whole brain neither for the hippocampus were detected. Considering that the human hippocampus is the main structure associated with cognitive map-based navigation, here, we investigated differences in morphological and morphometric hippocampal features between individuals affected by DTD (N = 20) and healthy controls (N = 238). Specifically, we focused on a developmental anomaly of the hippocampus that is characterized by the incomplete infolding of hippocampal subfields during fetal development, giving the hippocampus a more round or pyramidal shape, called incomplete hippocampal inversion (IHI). We rated IHI according to standard criteria and extracted hippocampal subfield volumes after FreeSurfer's automatic segmentation. We observed similar IHI prevalence in the group of individuals with DTD with respect to the control population. Neither differences in whole hippocampal nor major hippocampal subfield volumes have been observed between groups. However, when assessing the IHI independent criteria, we observed that the hippocampus in the DTD group is more medially positioned comparing to the control group. In addition, we observed bigger hippocampal fissure volume for the DTD comparing to the control group. Both of these findings were stronger for the right hippocampus comparing to the left. Our results provide new insights regarding the hippocampal morphology of individuals affected by DTD, highlighting the role of structural anomalies during early prenatal development in line with the developmental nature of the spatial disorientation deficit.

Clinicoradiological Profile of Incomplete Hippocampal Inversion Diagnosed on MR Neuroimaging

Background and Purpose

Incomplete hippocampal inversion (IHI) is a developmental failure of normal hippocampal inversion. Previous studies have described IHI in epilepsy and non-epilepsy subjects. IHI has also been reported with malformations of cortical development (MCDs) and corpus callosal agenesis that have association with neuropsychiatric disorders such as autism spectrum disorder (ASD). This study aims to describe the clinical profile of magnetic resonance imaging (MRI)-diagnosed IHI.

Materials and Methods

We studied patients with IHI who were identified after a retrospective review of the MRI archives of the past 3 years. The MRI findings of partial and total IHI were included. The clinical profiles associated with IHI were classified into epilepsy and non-epilepsy categories.

Results

A retrospective review of MRI done over 3 years revealed 54 cases of IHI (32 left-sided, 20 bilateral, and 2 isolated right-sided), and out of 74 IHI, 59 were of total type and 15 partial. Thirty-six subjects (61.1%) had epilepsy (9 with neurodevelopmental problems), 17 subjects (31.5%) had ASD, and 4 subjects (7.4%) had only neurodevelopmental disorders. MCDs were seen in 7 (12.9%): polymicrogyria (4), periventricular heterotopia (2), and pachygyria (1). Hippocampal volume loss was seen in 10, and contralateral mesial temporal sclerosis was seen in 2 patients.

Conclusion

Hippocampal inversion has been reported in MRI scans of patients with epilepsy, ASD, MCDs, and many other related disorders. Further studies are required to know its occurrence among patients who get MRI scans due to many other disorders such as headaches, psychiatric disorders, minor hear trauma, and perinatal insults. If possible, studies among normal populations also need to be done.

Hippocampal rotation is associated with ventricular atrial size

BACKGROUND

Fetal ventriculomegaly is a source of apprehension for expectant parents and may present prognostic uncertainty for physicians. Accurate prenatal counseling requires knowledge of its cause and associated findings as the differential diagnosis is broad. We have observed an association between ventriculomegaly and incomplete hippocampal inversion.

OBJECTIVE

To determine whether ventricular size is related to incomplete hippocampal inversion.

MATERIALS AND METHODS

We retrospectively evaluated pre- and postnatal brain MRIs in normal subjects (mean GA, 31 weeks; mean postnatal age, 27 days) and patients with isolated ventriculomegaly (mean GA, 31 weeks; mean postnatal age, 68 days) at a single academic medical center. Lateral ventricular diameter, multiple qualitative and quantitative markers of hippocampal inversion, and evidence of intraventricular hemorrhage were documented.

RESULTS

Incomplete hippocampal inversion and ventricular size were associated in both normal subjects (n=51) and patients with ventriculomegaly (n=32) (P<0.05). Severe ventriculomegaly was significantly associated with adverse clinical outcome in postnatal (P=0.02) but not prenatal (P=0.43) groups. In all additional cases of isolated ventriculomegaly, clinical outcome was normal over the time of assessment (mean 1±1.9 years; range 0.01 to 10 years).

CONCLUSION

Lateral ventricular atrial diameter and incomplete hippocampal inversion are associated. Less hippocampal inversion correlates with larger atria. For every 1-mm increase in fetal ventricular size, the odds of incomplete hippocampal inversion occurring increases by a factor of 1.6 in normal controls and 1.4 in patients with ventriculomegaly.

Clinical factors associated with microstructural connectome related brain dysmaturation in term neonates with congenital heart disease

Objective

Term congenital heart disease (CHD) neonates display abnormalities of brain structure and maturation, which are possibly related to underlying patient factors, abnormal physiology and perioperative insults. Our primary goal was to delineate associations between clinical factors and postnatal brain microstructure in term CHD neonates using diffusion tensor imaging (DTI) magnetic resonance (MR) acquisition combined with complementary data-driven connectome and seed-based tractography quantitative analyses. Our secondary goal was to delineate associations between mild dysplastic structural brain abnormalities and connectome and seed-base tractography quantitative analyses. These mild dysplastic structural abnormalities have been derived from prior human infant CHD MR studies and neonatal mouse models of CHD that were collectively used to calculate to calculate a brain dysplasia score (BDS) that included assessment of subcortical structures including the olfactory bulb, the cerebellum and the hippocampus.

Methods

Neonates undergoing cardiac surgery for CHD were prospectively recruited from two large centers. Both pre- and postoperative MR brain scans were obtained. DTI in 42 directions was segmented into 90 regions using a neonatal brain template and three weighted methods. Clinical data collection included 18 patient-specific and 9 preoperative variables associated with preoperative scan and 6 intraoperative (e.g., cardiopulmonary bypass and deep hypothermic circulatory arrest times) and 12 postoperative variables associated with postoperative scan. We compared patient specific and preoperative clinical factors to network topology and tractography alterations on a preoperative neonatal brain MRI, and intra and postoperative clinical factors to network topology alterations on postoperative neonatal brain MRI. A composite BDS was created to score abnormal findings involving the cerebellar hemispheres and vermis, supratentorial extra-axial fluid, olfactory bulbs and sulci, hippocampus, choroid plexus, corpus callosum, and brainstem. The neuroimaging outcomes of this study included (1) connectome metrics: cost (number of connections) and global/nodal efficiency (network integration); (2) seed based tractography methods of fractional anisotropy (FA), radial diffusivity, and axial diffusivity. Statistics consisted of multiple regression with false discovery rate correction (FDR) comparing the clinical risk factors and BDS (including subcortical components) as predictors/exposures and the global connectome metrics, nodal efficiency, and seed based- tractography (FA, radial diffusivity, and axial diffusivity) as neuroimaging outcome measures.

Results

A total of 133 term neonates with complex CHD were prospectively enrolled and 110 had analyzable DTI. Multiple patient-specific factors including d-transposition of the great arteries (d-TGA) physiology and severity of impairment of fetal cerebral substrate delivery (i.e., how much the CHD lesion alters typical fetal circulation such that the highest oxygen and nutrient rich blood from the placenta are not directed toward the fetal brain) were predictive of preoperative reduced cost (p < 0.0073) and reduced global/nodal efficiency (p < 0.03). Cardiopulmonary bypass time predicted postoperative reduced cost (p < 0.04) and multiple postoperative factors [extracorporeal membrane oxygenation (ECMO), seizures and cardiopulmonary resuscitation (CPR)] were predictive of postoperative reduced cost and reduced global/nodal efficiency (p < 0.05). Anthropometric measurements (weight, length, and head size) predicted tractography outcomes. Total BDS was not predictive of brain network topology. However, key subcortical components of the BDS score did predict key global and nodal network topology: abnormalities of the cerebellum predicted reduced cost (p < 0.0417) and of the hippocampus predicted reduced global efficiency (p < 0.0126). All three subcortical structures predicted unique alterations of nodal efficiency (p < 0.05), including hippocampal abnormalities predicting widespread reduced nodal efficiency in all lobes of the brain, cerebellar abnormalities predicting increased prefrontal nodal efficiency, and olfactory bulb abnormalities predicting posterior parietal-occipital nodal efficiency.

Conclusion

Patient-specific (d-TGA anatomy, preoperative impairment of fetal cerebral substrate delivery) and postoperative (e.g., seizures, need for ECMO, or CPR) clinical factors were most predictive of diffuse postnatal microstructural dysmaturation in term CHD neonates. Anthropometric measurements (weight, length, and head size) predicted tractography outcomes. In contrast, subcortical components (cerebellum, hippocampus, olfactory) of a structurally based BDS (derived from CHD mouse mutants), predicted more localized and regional postnatal microstructural differences. Collectively, these findings suggest that brain DTI connectome and seed-based tractography are complementary techniques which may facilitate deciphering the mechanistic relative contribution of clinical and genetic risk factors related to poor neurodevelopmental outcomes in CHD.

Medial Temporal Lobe Anatomy

The medial temporal lobe (MTL) is a complex anatomic region encompassing the hippocampal formation, parahippocampal region, and amygdaloid complex. To enable the reader to understand the well-studied regional anatomic relationships and cytoarchitecture that form the basis of functional connectivity, the authors have created a detailed yet approachable anatomic reference for clinicians and scientists, with special attention to MR imaging. They have focused primarily on the hippocampal formation, discussing its gross structural features, anatomic relationships, and subfield anatomy and further discuss hippocampal terminology and development, hippocampal connectivity, normal anatomic variants, clinically relevant disease processes, and automated hippocampal segmentation software.

Incomplete hippocampal inversion: diagnostic criteria and effect on epilepsy, seizure localization and therapeutic outcome in children

PURPOSE

Elaborate a simple Magnetic Resonance Imaging (MRI)-based score to define Incomplete Hippocampal Inversion (IHI) in children (Phase 1), and evaluate the relation of IHI with (A) epilepsy, (B) seizure localization and (C) therapeutic response in a paediatric population (Phase 2).

METHODS

In Phase 1, incompletely inverted hippocampi were matched to completely inverted hippocampi. Multiple qualitative and quantitative hippocampal and extra-hippocampal features were evaluated in coronal-oblique T1-weighted (T1W) and coronal T2-weighted (T2W) images. Multivariate analysis was performed to elaborate the MRI-based score to define IHI. In Phase 2, epilepsy patients were matched to controls, and the T1W and T2W scores were applied. Multivariate analysis was performed to assess the relation of IHI and epilepsy, seizure localization and therapeutic response.

RESULTS

The hippocampal diameter ratio and parahippocampal angle in the coronal-oblique T1-weighted images, and the hippocampal diameter ratio and collateral sulcus depth in the coronal T2-weighted images predicted IHI in Phase 1. Simple and practical imaging-based scores were developed and are available on the website: https://ihiscore.netlify.app/. The Area Under the Receiver Operating Characteristic Curve of the T1W and T2W scores were, respectively, 0.965 and 0.983. In Phase 2, IHI independently predicted epilepsy (OR = 3.144, 95% CI = 1.981-4.991, p < 0.001), temporal lobe epilepsy (OR = 4.237, 95% CI = 1.586-11.318, p = 0.004), and drug resistant epilepsy (OR = 7.000, 95% CI = 2.800-17.500, p < 0.001).

CONCLUSION

The association between IHI and temporal lobe epilepsy (and the lack of association with extra-temporal epilepsy) favours the possibility of a relation between IHI and the pathophysiology of seizures in epileptic patients. Furthermore, IHI is a potential prognostic marker for therapeutic response in epilepsy.

Structural and Functional Deviations of the Hippocampus in Schizophrenia and Schizophrenia Animal Models

Schizophrenia is a grave neuropsychiatric disease which frequently onsets between the end of adolescence and the beginning of adulthood. It is characterized by a variety of neuropsychiatric abnormalities which are categorized into positive, negative and cognitive symptoms. Most therapeutical strategies address the positive symptoms by antagonizing D2-dopamine-receptors (DR). However, negative and cognitive symptoms persist and highly impair the life quality of patients due to their disabling effects. Interestingly, hippocampal deviations are a hallmark of schizophrenia and can be observed in early as well as advanced phases of the disease progression. These alterations are commonly accompanied by a rise in neuronal activity. Therefore, hippocampal formation plays an important role in the manifestation of schizophrenia. Furthermore, studies with animal models revealed a link between environmental risk factors and morphological as well as electrophysiological abnormalities in the hippocampus. Here, we review recent findings on structural and functional hippocampal abnormalities in schizophrenic patients and in schizophrenia animal models, and we give an overview on current experimental approaches that especially target the hippocampus. A better understanding of hippocampal aberrations in schizophrenia might clarify their impact on the manifestation and on the outcome of this severe disease.

High Incidence of Hippocampal Abnormalities in Pediatric Patients with Congenital Cytomegalovirus Infection

BACKGROUND

Congenital cytomegalovirus (CMV) infection exhibits polymicrogyria, intracranial calcification, white matter lesions, and several types of intracranial lesions on magnetic resonance imaging (MRI), in addition to various developmental disorders and epilepsies. However, little is known on the presence of hippocampal abnormality in this affliction. The aim of this study is to clarify the incidence of hippocampal abnormality in congenital CMV infection.

METHODS

Seventeen children diagnosed as having congenital CMV infection along with 17 age-matched pediatric controls were retrospectively evaluated by brain MRI and clinical review. The measurement data were obtained from conventional coronal sections in this retrospective study. Hippocampal malrotation (HIMAL) was defined as a hippocampal diameter ratio (i.e., the ratio of the height and width of the hippocampus) of >0.92.

RESULTS

Hippocampal diameter ratios were significantly higher in the congenital CMV infection group (0.99 [range: 0.70-1.58] on the right side and 0.85 [range: 0.66-1.39] on the left side) than in controls (0.71 [range: 0.58-0.91] and 0.70 [range: 0.50-1.00], respectively). HIMAL was present in 17 of 34 hippocampi (50%) in the congenital CMV infection group and 1 of 34 hippocampi (2.9%) in controls. No correlations were detected between HIMAL and intelligence quotient/developmental quotient or the occurrences of autism spectrum disorder or epilepsy.

CONCLUSION

This study is the first to demonstrate the incidence of hippocampal abnormality to be significantly higher in congenital CMV infection patients than in age-matched controls. Further study is necessary to clarify the associations of HIMAL with other clinical and developmental features.

Hippocampal Malrotation Could Be Less Significant in Epilepsy Caused by Focal Cortical Dysplasia Type I and Type II

Objectives

Debates over the relationship between hippocampal malrotation (HIMAL) and epilepsy continue without consensus. This study explores the role of HIMAL in a cohort of epilepsy caused by focal cortical dysplasia (FCD).

Methods

In this study, 90 patients with epilepsy caused by FCD type I and type II and 48 healthy adults underwent a 3 Tesla MRI following a dedicated epilepsy protocol for the analysis of the prevalence and morphologic features of HIMAL. In addition, numerous clinical characteristics and hippocampal volumes were evaluated.

Results

The cohort included a total of 90 patients (32 were HIMAL, 58 were non-HIMAL). Among these patients, 32 (35.6%) had HIMAL (22 left, four right, and six bilateral), which did not differ from the 48 controls, where 16 (33.3%) had HIMAL (12 left, two right, and two bilateral). Neither the quantitative features of HIMAL (diameter ratio, dominant inferior temporal sulcus height ratio, medial distance ratio, dominant inferior temporal sulcus angle, and parahippocampal angle), nor the accompanying characteristics of HIMAL (vertical dominant inferior temporal sulcus, enlarged temporal horn, and a low position of ipsilateral fornix) showed differences between patients with FCD and controls. No statistical difference in the clinical characteristics between FCD patients with HIMAL and those without was found. Neither the side nor the existence of HIMAL was correlated with the lateralization and location of FCD. As to the hippocampal volume, there was no difference between FCD patients with HIMAL and those without.

Conclusion

Hippocampal malrotation is a common morphologic variant in healthy controls as well as in patients with epilepsy caused by FCD type I and type II. Hippocampal malrotation could be less significant in epilepsy caused by FCD type I and type II.

Involvement of Incomplete Hippocampal Inversion in Intractable Epilepsy: Evidence from Neuropsychological Studies

Background

The age of onset of seizure, seizure types, frequency of seizure, structural abnormalities in the brain, and antiepileptic medication (polytherapy) causes increased incidence of anxiety and depression in intractable epilepsy patients.

Aim

To compare the anxiety and depression levels in intractable epileptic patients with structural abnormalities [malformations of cortical development (MCD) and incomplete hippocampal inversion (IHI)] and without structural abnormalities.

Materials and Methods

Participants were selected from (239 males and 171 females) intractable epilepsy patients. They were grouped into four groups; Group 1: 51 nonepileptic age-matched controls, Group 2: 41 intractable epilepsy patients without any brain abnormality, Group 3: 17 intractable epilepsy patients with MCD, and Group 4: 30 intractable epilepsy patients with isolated IHI. Neuropsychiatric tools used were Multiphasic Personality Questionnaire and Weschlers Adult Intelligence Scale to assess anxiety, depression, and intelligence. Groups were classified using 1.5T conventional magnetic resonance imaging and hippocampal volumetric studies. Group comparison design was used.

Results

Demographic variables of intractable epilepsy, including seizure types, the frequency of seizure, the age of seizure onset, and antiepileptic drug therapies, did not show significant association between the groups using Chi-square P value. Analysis of variance showed significant anxiety and depression in epileptic patients than the control group (P < 0.01). Post hoc analysis using Tukey's B test showed significant difference in anxiety and depression scores between group value. In group 3 and 4, anxiety scores were significantly different but not depression scores.

Conclusion

The present study concludes high prevalence of anxiety and depression in intractable seizure. Anxiety is observed predominantly when there is IHI along with depression. We emphasize the need to identify IHI in intractable epilepsy and assess anxiety and depression to treat them effectively.

Identifying Clinical Clues in Children With Global Developmental Delay / Intellectual Disability With Abnormal Brain Magnetic Resonance Imaging (MRI)

Global developmental delay / intellectual disability are common pediatric conditions. Brain magnetic resonance imaging (MRI), although an important diagnostic tool in the evaluation of these patients, often requires general anesthesia. Recent literature suggests that unnecessary general anesthesia exposure should be avoided in early years because of possible long-term negative neurodevelopmental sequelae. This study sought to identify clinical clues associated with brain MRI abnormalities in children with global developmental delay / intellectual disability in an attempt to provide guidance to physicians on selecting patients who would benefit from an MRI. Retrospective chart review analysis was conducted for patients presenting to a pediatric neurology tertiary care center between 2014 and 2017 for a first clinic evaluation for global developmental delay / intellectual disability. Detailed clinical history and physical examination findings were analyzed and correlated with brain MRI findings. The majority (218/327, 67%) of children referred for evaluation of global developmental delay / intellectual disability underwent complete clinical and radiologic evaluations. Mean age was 37.9 months (±32.5 standard deviation) and 116 were males (53%). Motor deficits were predominant in most subjects (122/218, 56%). Abnormal MRI findings were observed in 153 children (70%), with the most prevalent abnormalities noted within the white matter (104/153, 68%), corpus callosum (77/153, 50%), and the hippocampus (50/153, 33%). Abnormal MRI findings were prevalent in children with predominant motor delay (84, 69%) and cognitive disability (3, 100%) as well as those with visual and hearing impairment (P < .05). The presence of facial dysmorphisms (57/71, P = .02); cranial nerve abnormalities (79/100; P = .007) and abnormal reflexes (16, P = .01) on examination also correlated significantly with increased MRI abnormalities.

Hippocampal Malrotation: A Genetic Developmental Anomaly Related to Epilepsy?

Hippocampal malrotation (HIMAL) is an increasingly recognized neuroimaging feature but the clinical correlation and significance in epilepsies remain under debate. It is characterized by rounded hippocampal shape, deep collateral, or occipitotemporal sulcus, and medial localization of the hippocampus. In this review, we describe the embryonic development of the hippocampus and HIMAL, the qualitative and quantitative diagnosis issues, and the pathological findings of HIMAL. HIMAL can be bilateral or unilateral and more on the left side. Furthermore, the relevance of HIMAL diagnosis in clinical practice, including its role in epileptogenesis and the impact on the pre-surgical decision are reviewed. Finally, the relationship between HIMAL and hippocampal sclerosis (HS) and the possible role of genetics in the etiology of HIMAL are discussed. The evidence so far suggested that HIMAL does not have a significant role in epileptogenesis or surgical decision. HIMAL could be a genetic developmental imaging feature that represents a more diffuse but subtle structural error during brain development. Many questions remain to be explored, such as possible cognitive alteration associated with HIMAL and whether HIMAL predisposes to the development of HS. Further studies using high-quality MRI, unified consensus qualitative and quantitative diagnostic criteria, and comprehensive cognitive assessment are recommended.

Incomplete hippocampal inversion in schizophrenia: prevalence, severity, and impact on hippocampal structure

Incomplete hippocampal inversion (IHI) is an anatomical variant of the human brain resulting from an arrest in brain development, especially prevalent in the left hemisphere. We hypothesized that IHI is more common in schizophrenia and contributes to the well-known hippocampal structural differences. We studied 199 schizophrenia patients and 161 healthy control participants with 3 T MRI to establish IHI prevalence and the relationship of IHI with hippocampal volume and asymmetry. IHI was more prevalent (left hemisphere: 15% of healthy control participants, 27% of schizophrenia patients; right hemisphere: 4% of healthy control participants, 10% of schizophrenia patients) and more severe in schizophrenia patients compared to healthy control participants. Severe IHI cases were associated with a higher rate of automated segmentation failure. IHI contributed to smaller hippocampal volume and increased R > L volume asymmetry in schizophrenia. The increased prevalence and severity of IHI supports the neurodevelopmental model of schizophrenia. The impact of this developmental variant deserves further exploration in studies of the hippocampus in schizophrenia.

Incomplete hippocampal inversion and epilepsy: A systematic review and meta-analysis

OBJECTIVE

Incomplete hippocampal inversion (IHI) is a relatively frequent radiological finding at visual inspection in both epilepsy and healthy controls, but its clinical significance is unclear. Here, we systematically retrieve and assess the association between epilepsy and IHI using a meta-analytic approach. Additionally, we estimate the prevalence of IHI in patients with malformation of cortical development (MCD).

METHODS

We systematically searched two databases (Embase and PubMed) to identify potentially eligible studies from their inception to December 2019. For inclusion, studies were population-based, case-control, observational studies reporting on epilepsy and IHI. The risk of developing epilepsy in IHI (estimated with odds ratio [ORs]) and the frequency of IHI among patients with MCD are provided.

RESULTS

We screened 3601 records and assessed eligibility of 2812 full-text articles. The final material included 13 studies involving 1630 subjects. Seven studies (1329 subjects: 952 epileptic and 377 nonepileptic) were included for the estimation of the risk of developing epilepsy in the presence of IHI. The estimated OR of active epilepsy in IHI was 1.699 (95% confidence interval = 0.880-3.281), with moderate heterogeneity across studies (I²  = 71%). Seven studies (591 patients) provided information about the frequency of IHI in MCD. Up to one third of patients with MCD (27.9%) presented coexistent IHI.

SIGNIFICANCE

The present findings confirm that IHI is commonly observed in patients with MCD especially in periventricular nodular heterotopia or polymicrogyria. However, the estimated OR indicates overall weak increased odds of epilepsy in people with IHI, suggesting that the presence of isolated IHI cannot be considered a strong independent predictor for epilepsy development. Clear-cut neuroradiological criteria for IHI and advanced postprocessing analyses on structural magnetic resonance imaging scans are recommended to highlight differences between epileptogenic and nonepileptogenic IHI.

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.

Looking for indicative magnetic resonance imaging signs of hippocampal developmental abnormalities in patients with mesial temporal lobe epilepsy and healthy controls

OBJECTIVE

To evaluate the frequency of qualitative features for hippocampal developmental abnormalities (HiDeA) definition on magnetic resonance imaging (MRI) in mesial temporal lobe epilepsy (MTLE) patients and healthy controls, highlighting which were more sensitive and specific to the epileptic syndrome.

METHODS

We enrolled 93 healthy controls and 187 MTLE patients. Among patients, 133 were MRI-negative and 54 had hippocampal sclerosis (HS). Two blinded, trained investigators defined HiDeA if three signs were present, including at least one of the following: (1) globular hippocampal shape (HCS), (2) verticalized collateral sulcus, and (3) medial positioning of hippocampus (HCP). After evaluating the prevalence of HiDeA in MTLE and controls, we assessed the frequency of each sign. Then, we classified differences in type or number of HiDeA diagnostic features, calculating their sensitivity and specificity. Fisher exact test was used to assess statistical significance.

RESULTS

HiDeA was detected in 36 of 187 MTLE cases (19.25%) and in eight of 93 (8.6%) controls. In particular, HiDeA was present in 25 of 133 (18.8%) patients with MRI-negative MTLE. Among all visual criteria here considered, HCS showed higher sensitivity both in the MRI-negative MTLE group (88%) and in the HS-MTLE group (91%). HCP, thickened subiculum, and reduction of the upper horizontal portion of the parahippocampal gyrus (HCTH) signs demonstrated a 100% specificity in both groups. In healthy controls, HCS was confirmed to have the highest sensitivity (100%), whereas HCP showed the highest specificity (98.8%). All these criteria were statistically associated with HiDeA. Electroencephalographic focus was concordant with the HiDeA side in 52.2% of MTLE patients. An association was not found among signs of HiDeA and treatment responsiveness.

SIGNIFICANCE

We identified characteristic signs of HiDeA, such as HCTH or HCP, differentiating HiDeA features between MTLE and healthy controls. The identification of sensitive and, more importantly, specific criteria of HiDeA could be helpful to make a more confident visual diagnosis.

Deviations in early hippocampus development contribute to visual hallucinations in schizophrenia

Auditory hallucinations (AHs) are certainly the most emblematic experiences in schizophrenia, but visual hallucinations (VHs) are also commonly observed in this developmental psychiatric disorder. Notably, several studies have suggested a possible relationship between the clinical variability in hallucinations' phenomenology and differences in brain development/maturation. In schizophrenia, impairments of the hippocampus, a medial temporal structure involved in mnesic and neuroplastic processes, have been repeatedly associated with hallucinations, particularly in the visual modality. However, the possible neurodevelopmental origin of hippocampal impairments in VHs has never been directly investigated. A classic marker of early atypical hippocampal development is incomplete hippocampal inversion (IHI). In this study, we compared IHI patterns in healthy volunteers, and two subgroups of carefully selected schizophrenia patients experiencing frequent hallucinations: (a) those with pure AHs and (b) those with audio-visual hallucinations (A+VH). We found that VHs were associated with a specific IHI pattern. Schizophrenia patients with A+VH exhibited flatter left hippocampi than patients with pure AHs or healthy controls. This result first confirms that the greater clinical impairment observed in A+VH patients may relate to an increased neurodevelopmental weight in this subpopulation. More importantly, these findings bring crucial hints to better specify the sensitivity period of A+VH-related IHI during early brain development.

Genome wide association study of incomplete hippocampal inversion in adolescents

Incomplete hippocampal inversion (IHI), also called hippocampal malrotation, is an atypical presentation of the hippocampus present in about 20% of healthy individuals. Here we conducted the first genome-wide association study (GWAS) in IHI to elucidate the genetic underpinnings that may contribute to the incomplete inversion during brain development. A total of 1381 subjects contributed to the discovery cohort obtained from the IMAGEN database. The incidence rate of IHI was 26.1%. Loci with P<1e-5 were followed up in a validation cohort comprising 161 subjects from the PING study. Summary statistics from the discovery cohort were used to compute IHI heritability as well as genetic correlations with other traits. A locus on 18q11.2 (rs9952569; OR = 1.999; Z = 5.502; P = 3.755e-8) showed a significant association with the presence of IHI. A functional annotation of the locus implicated genes AQP4 and KCTD1. However, neither this locus nor the other 16 suggestive loci reached a significant p-value in the validation cohort. The h² estimate was 0.54 (sd: 0.30) and was significant (Z = 1.8; P = 0.036). The top three genetic correlations of IHI were with traits representing either intelligence or education attainment and reached nominal P< = 0.013.

Abnormal hippocampal structure and function in juvenile myoclonic epilepsy and unaffected siblings

Juvenile myoclonic epilepsy is the most common genetic generalized epilepsy syndrome, characterized by a complex polygenetic aetiology. Structural and functional MRI studies demonstrated mesial or lateral frontal cortical derangements and impaired fronto-cortico-subcortical connectivity in patients and their unaffected siblings. The presence of hippocampal abnormalities and associated memory deficits is controversial, and functional MRI studies in juvenile myoclonic epilepsy have not tested hippocampal activation. In this observational study, we implemented multi-modal MRI and neuropsychological data to investigate hippocampal structure and function in 37 patients with juvenile myoclonic epilepsy, 16 unaffected siblings and 20 healthy controls, comparable for age, gender, handedness and hemispheric dominance as assessed with language laterality indices. Automated hippocampal volumetry was complemented by validated qualitative and quantitative morphological criteria to detect hippocampal malrotation, assumed to represent a neurodevelopmental marker. Neuropsychological measures of verbal and visuo-spatial learning and an event-related verbal and visual memory functional MRI paradigm addressed mesiotemporal function. We detected a reduction of mean left hippocampal volume in patients and their siblings compared with controls (P < 0.01). Unilateral or bilateral hippocampal malrotation was identified in 51% of patients and 50% of siblings, against 15% of controls (P < 0.05). For bilateral hippocampi, quantitative markers of verticalization had significantly larger values in patients and siblings compared with controls (P < 0.05). In the patient subgroup, there was no relationship between structural measures and age at disease onset or degree of seizure control. No overt impairment of verbal and visual memory was identified with neuropsychological tests. Functional mapping highlighted atypical patterns of hippocampal activation, pointing to abnormal recruitment during verbal encoding in patients and their siblings [P < 0.05, familywise error (FWE)-corrected]. Subgroup analyses indicated distinct profiles of hypoactivation along the hippocampal long axis in juvenile myoclonic epilepsy patients with and without malrotation; patients with malrotation also exhibited reduced frontal recruitment for verbal memory, and more pronounced left posterior hippocampal involvement for visual memory. Linear models across the entire study cohort indicated significant associations between morphological markers of hippocampal positioning and hippocampal activation for verbal items (all P < 0.05, FWE-corrected). We demonstrate abnormalities of hippocampal volume, shape and positioning in patients with juvenile myoclonic epilepsy and their siblings, which are associated with reorganization of function and imply an underlying neurodevelopmental mechanism with expression during the prenatal stage. Co-segregation of abnormal hippocampal morphology in patients and their siblings is suggestive of a genetic imaging phenotype, independent of disease activity, and can be construed as a novel endophenotype of juvenile myoclonic epilepsy.

Sudden unexpected death with rare compound heterozygous variants in PRICKLE1

Progressive myoclonus epilepsy-ataxia syndrome (EPM5) is an autosomal recessive form of progressive myoclonus epilepsy that has been associated with a homozygous missense mutation in PRICKLE1. We report a 23-year-old male who died shortly after refractory convulsion and respiratory failure. Autopsy showed unilateral hippocampal malformation without significant neuronal loss or gliosis. Genetic analysis that targeted both epilepsy and cardiac disease using next-generation sequencing revealed two variants of PRICKLE1. Additional investigation showed that the patient's father (p.Asp760del) and mother (p.Asp201Asn) each had a mutation in this gene. The present case shows that EPM5 can also be caused by compound heterozygous mutations.

Evaluation of hippocampal infolding angle and incomplete hippocampal inversion in pediatric patients with epilepsy and febrile seizures

PURPOSE

We aimed to investigate the frequency of incomplete hippocampal inversion (IHI) and the hippocampal infolding angle (HIA) in pediatric patients with no additional abnormal findings in the brain.

METHODS

Pediatric brain magnetic resonance imaging (MRI) examinations conducted between September 2012 and February 2015 were screened and 83 patients with epilepsy, 49 patients with febrile convulsion, and 74 control patients were included in this retrospective study. Presence of IHI was evaluated and HIA was measured on MRI.

RESULTS

IHI was found in 23 patients in the epilepsy group (27.7%), 15 patients in the febrile convulsion group (30.6%), and 14 patients in the control group (19.0%), with no significant difference between the groups (P = 0.27). Compared with the epilepsy and febrile convulsion groups, HIA was significantly larger in the control group in sections of the right cerebral pedincule, the left cerebral pedincule, and the right superior cerebellar pedincule. No correlation was found between the laterality of the epileptogenic focus in the epilepsy group and existence of IHI, nor between age and HIA values among the groups.

CONCLUSION

Although IHI is not an uncommon abnormality in the normal pediatric population, decreased HIA is more frequently found in patients with epilepsy or febrile convulsions.

"Unforgettable" - a pictorial essay on anatomy and pathology of the hippocampus

Abstract

The hippocampus is a small but complex anatomical structure that plays an important role in spatial and episodic memory. The hippocampus can be affected by a wide range of congenital variants and degenerative, inflammatory, vascular, tumoral and toxic-metabolic pathologies. Magnetic resonance imaging is the preferred imaging technique for evaluating the hippocampus. The main indications requiring tailored imaging sequences of the hippocampus are medically refractory epilepsy and dementia. The purpose of this pictorial review is threefold: (1) to review the normal anatomy of the hippocampus on MRI; (2) to discuss the optimal imaging strategy for the evaluation of the hippocampus; and (3) to present a pictorial overview of the most common anatomic variants and pathologic conditions affecting the hippocampus.

Teaching points

• Knowledge of normal hippocampal anatomy helps recognize anatomic variants and hippocampal pathology.

• Refractory epilepsy and dementia are the main indications requiring dedicated hippocampal imaging.

• Pathologic conditions centered in and around the hippocampus often have similar imaging features.

• Clinical information is often necessary to come to a correct diagnosis or an apt differential.

Brain Dysplasia Associated with Ciliary Dysfunction in Infants with Congenital Heart Disease

OBJECTIVE

To test for associations between abnormal respiratory ciliary motion (CM) and brain abnormalities in infants with congenital heart disease (CHD) STUDY DESIGN: We recruited 35 infants with CHD preoperatively and performed nasal tissue biopsy to assess respiratory CM by videomicroscopy. Cranial ultrasound scan and brain magnetic resonance imaging were obtained pre- and/or postoperatively and systematically reviewed for brain abnormalities. Segmentation was used to quantitate cerebrospinal fluid and regional brain volumes. Perinatal and perioperative clinical variables were collected.

RESULTS

A total of 10 (28.5%) patients with CHD had abnormal CM. Abnormal CM was not associated with brain injury but was correlated with increased extraaxial cerebrospinal fluid volume (P < .001), delayed brain maturation (P < .05), and a spectrum of subtle dysplasia including the hippocampus (P < .0078) and olfactory bulb (P < .034). Abnormal CM was associated with higher composite dysplasia score (P < .001), and both were correlated with elevated preoperative serum lactate (P < .001).

CONCLUSIONS

Abnormal respiratory CM in infants with CHD is associated with a spectrum of brain dysplasia. These findings suggest that ciliary defects may play a role in brain dysplasia in patients with CHD and have the potential to prognosticate neurodevelopmental risks.

Mesial temporal lobe morphology in intractable pediatric epilepsy: so-called hippocampal malrotation, associated findings, and relevance to presurgical assessment

OBJECTIVE Diagnostic criteria for hippocampal malrotation (HIMAL) on brain MRI typically include a rounded hippocampus, vertical collateral sulcus, and architectural blurring. Relationship to epileptogenesis remains speculative, and usefulness for surgical guidance is unknown. The study was performed to determine the prevalence of hippocampal rotational anomalies in a cohort of pediatric patients with intractable epilepsy undergoing evaluation for surgery and to determine the significance of this finding in the context of surgical planning. METHODS Forty-eight surgically treated children with intractable epilepsy were compared with matched healthy subjects; reviewers were blinded to surgical side. Each temporal lobe was evaluated for rounded hippocampus, blurring, vertical collateral sulcus, wide choroidal fissure, enlarged temporal horn, low fornix, hippocampal signal, and findings of hippocampal sclerosis. A mesial temporal lobe (MTL) score was calculated by summing the number of features, and the collateral sulcus angle (CSA) was measured in each temporal lobe. Surgical side, pathological diagnosis, and imaging findings elsewhere in the brain were tabulated. Presence of HIMAL, associated imaging features, and MTL score were compared between sides, between epilepsy and control groups, in relationship to side of surgery, and in relationship to postoperative outcome. RESULTS Only 3 epilepsy patients (6.2%) and no controls exhibited all 3 features of HIMAL (p = 0.12). Eight of 48 (16.7%) epilepsy versus 2 of 48 (4.6%) control subjects had both a rounded hippocampus and vertical collateral sulcus (suggesting HIMAL) (p = 0.045). In control and epilepsy subjects, most findings were more prevalent on the left, and the left CSA was more vertical (p < 0.0001). Epilepsy subjects had higher MTL scores (z = -2.95, p = 0.002) and more acute CSAs (p = 0.04) than controls. Only lateralizing raw MTL score had a significant association with surgical side (p = 0.03, OR 7.33); however, this was not significant when hippocampal sclerosis cases were excluded. HIMAL findings were more prevalent and MTL scores were higher in patients with resections involving the temporal lobes. On group analysis, HIMAL findings did not predict eventual surgical side and did not predict outcome, although the numbers are small. In 4 patients the abnormally rotated hippocampus was resected and showed hippocampal sclerosis and/or dysplastic changes on histopathology. All of these patients had a good outcome after surgery. CONCLUSIONS While increased in prevalence in children with intractable epilepsy, imaging findings of HIMAL did not have preoperative lateralizing utility in this group. Findings of HIMAL (including round hippocampus, architectural blurring, and vertical collateral sulcus) did not predict outcome after surgery, although the small number of patients with these findings limits evaluation. In the small number of patients in which the malrotated hippocampus was removed, outcome was good. Further research is needed to continue to define this association in children with intractable epilepsy, focusing on a temporal lobe cohort.

Hippocampal volume predicts antidepressant efficacy in depressed patients without incomplete hippocampal inversion

Background

Incomplete hippocampal inversion (IHI), also called malrotation, is a frequent atypical anatomical pattern of the hippocampus. Because of the crucial implication of the hippocampus in Major Depressive Disorder (MDD) and the neurodevelopmental hypothesis of MDD, we aimed to assess the prevalence of IHI in patients with MDD, the link of IHI with hippocampal volume (HV) and the impact of IHI on the predictive value of HV for response and remission after antidepressant treatment.

Methods

IHI (right and left, partial and total and IHI scores) and HV were assessed in 60 patients with a current Major Depressive Episode (MDE) in a context of MDD and 60 matched controls. Patients were prospectively assessed at baseline and after one, three and six months of antidepressant treatment for response and remission.

Results

The prevalence of IHI did not significantly differ between MDD patients (right = 23.3%; left = 38.3%) and controls (right = 16.7%; left = 33.3%). IHI was not significantly associated with MDD clinical characteristics. IHI alone did not predict response and remission after antidepressant treatment. However, an interaction between left HV and left IHI predicted six-month response (p = 0.04), HDRS score decrease (p = 0.02) and both three-month (p = 0.04) and six-month (p = 0.03) remission. A case-control design in 30 matched patients with or without left IHI confirmed that interaction. In patients without left IHI, left HV at baseline were smaller in six-month non-remitters as compared to remitters (2.2(± 0.43) cm³ vs 2.97(± 0.5) cm³ p = 0.02), and in six-month non-responders as compared to responders (2.18(± 0.42) cm³ vs 2.86(± 0.54) cm³, p = 0.03). In patients with left IHI, no association was found between left HV at baseline and antidepressant response and remission.

Conclusion

IHI is not more frequent in MDD patients than in controls, is not associated with HV, but is a confounder that decreases the predictive value of hippocampal volume to predict response or remission after antidepressant treatment. IHI should be systematically assessed in future research studies assessing hippocampal volume in MDD.

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Incomplete hippocampal inversion (IHI) is not significantly more frequent in MDD than in controls.

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IHI is not significantly associated with MDD clinical characteristics.

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Hippocampal volume predicts antidepressant efficacy in MDD patients without IHI.

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Hippocampal volume does not predict antidepressant efficacy in patients with IHI.

Incomplete Hippocampal Inversion: A Comprehensive MRI Study of Over 2000 Subjects

The incomplete-hippocampal-inversion (IHI), also known as malrotation, is an atypical anatomical pattern of the hippocampus, which has been reported in healthy subjects in different studies. However, extensive characterization of IHI in a large sample has not yet been performed. Furthermore, it is unclear whether IHI are restricted to the medial-temporal lobe or are associated with more extensive anatomical changes. Here, we studied the characteristics of IHI in a community-based sample of 2008 subjects of the IMAGEN database and their association with extra-hippocampal anatomical variations. The presence of IHI was assessed on T1-weighted anatomical magnetic resonance imaging (MRI) using visual criteria. We assessed the association of IHI with other anatomical changes throughout the brain using automatic morphometry of cortical sulci. We found that IHI were much more frequent in the left hippocampus (left: 17%, right: 6%, χ(2)-test, p < 10(-28)). Compared to subjects without IHI, subjects with IHI displayed morphological changes in several sulci located mainly in the limbic lobe. Our results demonstrate that IHI are a common left-sided phenomenon in normal subjects and that they are associated with morphological changes outside the medial temporal lobe.

Temporal lobe anatomy: eight imaging signs to facilitate interpretation of MRI

PURPOSE

The temporal lobe is anatomically and functionally complex. However, relatively few radiologic signs are described to facilitate recognition of temporal lobe sulci and gyri in clinical practice. We devised and tested 8 radiologic signs of temporal lobe anatomy.

METHODS

Images from volumetric magnetization-prepared rapid gradient-echo imaging were analyzed of 100 temporal lobes from 26 female and 24 male patients. Patient age ranged from 1 to 79 years (mean 19 years; standard deviation 16 years). Standardized axial, coronal, and sagittal planes were evaluated and cross-referenced. Eight signs to delineate the superior temporal gyrus, Heschl gyrus (HG), parahippocampal gyrus, rhinal sulcus, collateral sulcus proper, or the occipitotemporal sulcus, or a combination, were evaluated in the sagittal or axial plane. Two neuroradiologists independently evaluated each sign; the sign was considered present only with positive reader agreement.

RESULTS

All 8 signs were present in most patients. The most frequent signs were the posterior insular corner to identify HG in the axial plane (100 %), pointed STG to identify STG in the axial plane (98 %), and parahippocampal Y to identify the posterior parahippocampal gyrus in the sagittal plane (98 %). The frequencies were similar between the right and left cerebral hemispheres.

CONCLUSIONS

Temporal lobe gyri and sulci can be reliably identified in multiple planes using anatomic signs.

Glutaric aciduria type 1: neuroimaging features with clinical correlation

BACKGROUND

Glutaric aciduria type 1 is a rare neurometabolic disease with high morbidity.

OBJECTIVE

To describe the MR imaging abnormalities in glutaric aciduria type 1 and to identify any association between the clinical and imaging features.

MATERIALS AND METHODS

MRI scans of 29 children (mean age: 16.9 months) with confirmed diagnosis of glutaric aciduria type 1 were retrospectively reviewed. Gray matter and white matter scores were calculated based on a previously published pattern-recognition approach of assessing leukoencephalopathies. Hippocampal formation and opercular topography were assessed in relation to the known embryological basis. MRI scores were correlated with morbidity score.

RESULTS

The most consistent MRI abnormality was widened operculum with dilatation of the subarachnoid spaces surrounding underdeveloped frontotemporal lobes. Incomplete hippocampal inversion was also seen. The globus pallidus was the most frequently involved gray matter structure (86%). In addition to the central tegmental tract, white matter abnormalities preferentially involved the central and periventricular regions. The morbidity score correlated with the gray matter abnormality score (P = 0.004). Patients with dystonia had higher gray matter and morbidity scores.

CONCLUSION

Morbidity is significantly correlated with abnormality of gray matter, rather than white matter, whether secondary to acute encephalopathic crisis or insidious onset disease.

Hippocampal abnormalities in magnetic resonance imaging (MRI) of 15q duplication syndromes

Patients with 15q duplication syndromes, including isodicentric chromosome 15 and interstitial duplications, usually present with autism spectrum disorder, intellectual disability, and frequently epilepsy. Neuroimaging studies in these patients are typically reported as normal, but nonspecific findings such as thinning of the corpus callosum and increased pericerebral spaces have been reported. A review of brain magnetic resonance imaging (MRI) studies of 11 individuals seen at the Massachusetts General Hospital Dup15q Center was performed. Hippocampus morphology was specifically reviewed, as a recent neuropathologic study has found frequent hippocampal heterotopias and dysplasias in these disorders. Two subjects had unilateral hippocampal sclerosis and 6 had bilateral hippocampal malformations. Hypoplasia of the corpus callosum was present in 2 subjects.

Neuroimaging findings in 41 low-functioning children with autism spectrum disorder: a single-center experience

The data on the rate of brain imaging abnormalities in autistic spectrum disorders are still inconsistent. A recent study on patients with high-functioning autism found that approximately 90% of children had normal magnetic resonance imaging (MRI) scans whereas an unexpected high rate of MRI abnormalities was reported in 77 nonsyndromic autistic children with or without intellectual disability. The aim of this study was to evaluate the prevalence of neuroradiologic findings in low-functioning autistic children compared to controls matched for age. Minor brain abnormalities were found in 44% of patients and 22% of controls. Our main result is the high rate of mega cisterna magna in autistic patients. High rate of minor neuroradiologic abnormalities in low-functioning autistic patients could contribute to the research about the various endophenotypes and complete the clinical assessment of children with autistic spectrum disorder and intellectual disability.

Magnetic resonance imaging in adults with epilepsy: a pictorial essay

This pictorial essay highlights the role of the radiologist as a member of the adult epilepsy multidisciplinary team, and gives an overview of MRI-evident epileptogenic lesions.

Hippocampal malrotation is associated with chromosome 22q11.2 microdeletion

BACKGROUND

Patients with chromosome 22q11.2 deletion syndrome (22q11DS) are at a seven fold increased risk of developing seizures. However, only a fraction of these patients exhibit structural abnormalities such as polymicrogyria (PMG) and periventricular nodular heterotopia (PNH) that are known to cause seizures and to be associated with 22q11DS. In this study we used a dedicated seizure imaging protocol to look for additional structural abnormalities in these individuals that may explain the elevated risk of seizure disorder in this patient group.

METHODS

Nineteen consecutive adult subjects with 22q11DS underwent a 3 Tesla MRI with a dedicated high-resolution seizure protocol. Neurological exam was performed in all patients. Genome-wide analysis excluded the presence of other pathogenic microdeletions or duplications.

RESULTS

Structural abnormalities were found in 11 of 14 subjects with sufficient image quality. These included three patients with PNH, one of whom had associated PMG. In addition, there was a surprisingly high prevalence of unilateral hippocampal malrotation (HIMAL), observed in 9 of 14 cases (64%). EEG findings showed interictal epileptiform discharges with focal distribution in four patients and generalized discharges in one patient.

CONCLUSION

The results suggest that, in addition to other known structural abnormalities, 22q11DS is associated with HIMAL. It has been suggested that this developmental abnormality of the hippocampus may predispose or otherwise contribute to epileptogenesis. However in this study we observed HIMAL in a large proportion of patients, with and without epilepsy. Therefore, other as yet unknown factors may contribute to the high prevalence of epilepsy in this population.

Morphological variations of hippocampal formation in epilepsy: image, clinical and electrophysiological data

Morphological variations of hippocampal formation (MVHF) are observed in patients with epilepsy but also in asymptomatic individuals. The precise role of these findings in epilepsy is not yet fully understood. This study analyzes the hippocampal formation (HF) morphology of asymptomatic individuals (n = 30) and of patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis (MTLE-HS) (n = 68), patients with malformations of cortical development (MCD) (n = 34), or patients with pure morphological variations of hippocampal formation (pure MVHF) (n = 12). Main clinical and electrophysiological data of patients with MVHF were also analyzed. Morphological variations of hippocampal formation are more frequently observed in patients with MCD than in patients with MTLE-HS or in asymptomatic individuals. Patients with pure morphological variations of hippocampal formation showed higher incidence of extratemporal seizure onset. Refractoriness seems to be more associated with other abnormalities, like HS or MCD, than with the HF variation itself. Thus, although morphological HF abnormalities might play a role in epileptogenicity, they seem to contribute less to refractoriness.

Asymmetric development of the hippocampal region is common: a fetal MR imaging study

BACKGROUND AND PURPOSE

Hippocampal development is poorly understood. This study evaluated the normal development of the hippocampal region during the fetal period by using MR imaging.

MATERIALS AND METHODS

MR images of 63 fetuses without intracranial pathology were reviewed independently by 2 radiologists with no knowledge of the fetal GA. Three MR images were performed postmortem and 60 in vivo. The progress of hippocampal inversion was analyzed in coronal sections, and the left and right sides of the hippocampal region were compared in every case.

RESULTS

The fetuses in the postmortem examinations were at GWs 17-18 and in the in vivo examinations, at GWs 19-36. The hippocampal sulcus was open, bi- or unilaterally, in 39 fetuses. The oldest was at GW 32. The sulcus was closed at GW 21 at the earliest, unilaterally. In 26/63 fetuses (41%), the deepening or closure of the hippocampal sulcus or hippocampal inversion was asymmetric; in 23 fetuses, the right side developed faster. A shallow collateral sulcus was found earliest at GW 17. A deep collateral sulcus was visible earliest at GW 26 unilaterally, but in all fetuses from GW 31 onward, it was seen bilaterally. The orientation of the collateral sulcus was not related to the GA.

CONCLUSIONS

There are wide individual temporal variations in the development and the inversion process of the hippocampal sulcus as well as in the formation of the collateral sulcus. Asymmetric development is common, and in most of the asymmetric cases, the right hippocampus develops faster.

Hippocampal sclerosis in temporal lobe epilepsy: findings at 7 T¹

PURPOSE

To determine if ultrahigh-field-strength magnetic resonance (MR) imaging can be used to detect subregional hippocampal alterations.

MATERIALS AND METHODS

Subjects provided written consent to participate in this prospective institutional review board-approved HIPAA-compliant study. T1- and T2-weighted 7-T brain MR images were acquired in 11 healthy subjects and eight patients with temporal lobe epilepsy (TLE). In all subjects, images were qualitatively examined for evidence of hippocampal atrophy, signal change, and malrotation with the Bernasconi definition, and digitations of the hippocampal heads were counted (agreement was measured with the κ statistic). Data were analyzed quantitatively with manual subregional hippocampal body segmentation. Subregional data in individual subjects with TLE were compared with data in control subjects to detect deviation from the control range for volume measures on each side and with asymmetry indexes.

RESULTS

All eight patients with TLE had hippocampal abnormalities on the epileptogenic side. Subregional analysis revealed selective lateral Ammon horn atrophy in six patients and diffuse Ammon horn and dentate gyrus atrophy in one patient. Paucity of hippocampal digitations occurred on the epileptogenic side in all patients with TLE and also on the contralateral side in three patients (interrater κ value, 0.80). Hippocampal malrotation was observed in three patients with TLE and four control subjects.

CONCLUSION

Ultrahigh-field-strength MR imaging permitted detection of selectively greater Ammon horn atrophy in patients with TLE and hippocampal sclerosis. Paucity of digitations is a deformity of the hippocampal head that was detected independent of hippocampal atrophy in patients with mesial TLE.

Development of the hippocampal region demonstrated by fetal MRI. A preliminary report

Coronal slices of three fetal MRIs performed post mortem and 37 performed in utero, all without intracranial pathology, was assessed. Progress of the hippocampal inversion was analyzed, the left and right sides were compared and occurrence of the collateral sulcus was revealed. The fetuses in the post mortem examinations were at gestation weeks (GW) 17-18 and in the in utero examinations at GW 19-35. The symmetric development of the hippocampal sulcus was revealed in 26 subjects and asymmetric in 14. The non-ovoid hippocampal formation could be evaluated at GW 24 at earliest and an ovoid hippocampus at GW 29. The collateral sulcus could be recognized at GW 17 in post mortem and at GW 22 in in utero examinations. From GW 29 onwards it was seen in all fetuses and it was symmetric in all but one case. Evaluation of the hippocampi is difficult on fetal MRI, especially in in utero examinations. The hippocampal development is not fulfilled at GW 21 as presumed. There is a wide temporal variation in the development of the hippocampal region, and the developmental process does not progress simultaneously in the right and left side of the same individual.

Hippocampal development at gestation weeks 23 to 36. An ultrasound study on preterm neonates

INTRODUCTION

During fetal development, the hippocampal structures fold around the hippocampal sulcus into the temporal lobe. According to the literature, this inversion should be completed at gestation week (GW) 21. Thereafter, the hippocampal shape should resemble the adult shape. However, incomplete hippocampal inversion (IHI) is found in 19% of the common population. The aim of this study was to study fetal hippocampal development by examining neonates born preterm.

METHODS

We analyzed cranial ultrasound examinations, performed as a part of the routine assessment of all preterm infants, over a 3-year period and excluded the infants with brain pathology. The final material consisted of 158 children born <35 GW. A rounded form (the ratio between the horizontal and vertical diameters of the hippocampal body <or=1) in coronal slices was considered the sign of IHI.

RESULTS

The age at examination was 23-24 GW in 24 neonates, 25-28 GW in 70 neonates, and 29-36 GW in 64 neonates. IHI was found in 50%, 24%, and 14%, respectively. The difference between the neonates <25 GW and >or=25 GW was statistically highly significant (p < 0.001). The frequency of bilateral IHI was highest in the youngest age group. In the other groups, the left-sided IHI was the most common.

CONCLUSION

In about 50% of the neonates, hippocampal inversion is not completed up to GW 24; but from 25 GW onwards, the frequency and laterality of IHI is similar to that in the adult population.

Hippocampal malrotation in pediatric patients with epilepsy associated with complex prefrontal dysfunction

PURPOSE

The cognitive consequences of hippocampal malrotation (HIMAL) were investigated in a matched control study of children with epilepsy.

METHODS

Seven children with HIMAL were compared on a range of memory and attention tasks with 21 control children with epilepsy without temporal role pathology and 7 children with epilepsy and magnetic resonance imaging (MRI)-documented hippocampal sclerosis. In addition, in a statistical morphometric analysis, MRI studies from four children with HIMAL were compared to similar images of 20 age-matched typically developing control children.

RESULTS

Although the task battery was sensitive to the memory deficit of the children with hippocampal sclerosis, it did not reveal memory impairment in the patients with HIMAL. In contrast, the patients with HIMAL were impaired on the attentionally more demanding dual tasks, compared to both the control and the hippocampal sclerosis group. The structural MRI analysis revealed morphometric abnormalities in the tail of the affected hippocampus, the adjacent neocortex, and the ipsilateral medial thalamus. The basal forebrain was bilaterally affected. Abnormalities in remote cortex were found in the ipsilateral temporal lobe, the contralateral anterior cingulate gyrus, and bilateral in the dorsolateral and lateral-orbitofrontal prefrontal cortex.

DISCUSSION

Because the prefrontal cortical regions have been shown to be active during dual-task performance, the MRI results converge with the neuropsychological findings of impairment on these tasks. We conclude that HIMAL had no direct memory repercussions, but was secondary to subtle but widespread neurologic abnormalities that also affected morphology and functioning of the prefrontal cortex.

Incomplete hippocampal inversion-is there a relation to epilepsy?

Incomplete hippocampal inversion (IHI) has been described in patients with epilepsy or severe midline malformations but also in nonepileptic subjects without obvious developmental anomalies. We studied the frequency of IHI in different epilepsy syndromes to evaluate their relationship. Three hundred patients were drawn from the regional epilepsy register. Of these, 99 were excluded because of a disease or condition affecting the temporal lobes or incomplete data. Controls were 150 subjects without epilepsy or obvious intracranial developmental anomalies. The coronal MR images were analysed without knowledge of the clinical data. Among epilepsy patients, 30% had IHI (40 left-sided, 4 right-sided, 16 bilateral). Of controls, 18% had IHI (20 left-sided, 8 bilateral). The difference was statistically significant (P < 0.05). Of temporal lobe epilepsy (TLE) patients, 25% had IHI, which was not a significantly higher frequency than in controls (P = 0.34). There was no correlation between EEG and IHI laterality. A total of 44% of Rolandic epilepsy patients and 57% of cryptogenic generalised epilepsy patients had IHI. The IHI frequency was very high in some epileptic syndromes, but not significantly higher in TLE compared to controls. No causality between TLE and IHI could be found. IHI can be a sign of disturbed cerebral development affecting other parts of the brain, maybe leading to epilepsy.