Hippocampal abnormalities in an MR imaging series of patients with tuberous sclerosis

Incidence and Characteristics of Cerebellar Atrophy/Volume Loss in Children with Confirmed Diagnosis of Tuberous Sclerosis Complex

Objectives: The goal of our study was to determine the incidence of cerebellar atrophy, assess the imaging findings in the posterior fossa and determine the incidence of hippocampal sclerosis in a cohort of pediatric patients with confirmed tuberous sclerosis complex (TSC). Material and methods: MRI studies of 98 TSC pediatric patients (mean age 7.67 years) were evaluated for cerebellar atrophy, cerebral/cerebellar tubers, white matter lesions, subependymal nodules, subependymal giant cell astrocytomas, ventriculomegaly, and hippocampal sclerosis. Clinical charts were revisited for clinical symptoms suggesting cerebellar involvement, for seizures and treatment for seizures, behavioral disorders and autism. Results: Cerebral tubers were present in 97/98 cases. In total, 97/98 had subependymal nodules, 15/98 had SEGA, 8/98 had ventriculomegaly and 4/98 had hippocampal sclerosis. Cerebellar tubers were found in 8/98 patients (8.2%), whereas cerebellar atrophy was described in 38/98 cases (38.8%). In 37/38 patients, cerebellar volume loss was mild and diffuse, and only one case presented with left hemi-atrophy. Briefly, 32/38 presented with seizures and were treated with anti-seizure drugs. In total, 8/38 (21%) presented with behavioral disorders, 10/38 had autism and 2/38 presented with seizures and behavioral disorders and autism. Conclusions: Several studies have demonstrated cerebellar involvement in patients with TSC. Cerebellar tubers differ in shape compared with cerebral tubers and are associated with cerebellar volume loss. Cerebellar atrophy may be focal and diffuse and one of the primary cerebellar manifestations of TSC, especially if a TSC2 mutation is present. Cerebellar degeneration may, however, also be secondary/acquired due to cellular damage resulting from seizure activity, the effects of anti-seizure drugs and anoxic-ischemic injury from severe seizure activity/status epilepticus. Further, prospective studies are required to identify and establish the pathogenic mechanism of cerebellar atrophy in patients with TSC.

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.

Independent temporal lobe epilepsy in patients with tuberous sclerosis complex

Tuberous sclerosis complex (TSC) is a rare disease that involves multiple organs, including the brain; approximately 80%-90% of TSC patients exhibit TSC-associated epilepsy. Independent temporal lobe epilepsy (TLE), TSC-unrelated epilepsy, is particularly rare in patients with TSC. Here, we describe three patients with TSC with independent TLEs that were confirmed by stereo-electroencephalography (EEG), postoperative pathological findings, and seizure outcome at follow-up. The patients were retrospectively enrolled at two centers; their ictal epileptiform discharge onsets were determined using electrode contacts in the hippocampus during stereo-EEG. The three patients underwent anterior temporal lobectomies and remained seizure-free at 1-5 years after surgery. Postoperative pathological examinations confirmed hippocampal sclerosis in all three patients. Furthermore, postoperative intelligence quotient improvement was evident in one patient, while the quality of life was improved in two patients at 12 months after surgery.

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.

Sexual Dimorphism and Hemispheric Asymmetry of Hippocampal Volumetric Integrity in Normal Aging and Alzheimer Disease

BACKGROUND AND PURPOSE

Asymmetric atrophy of the hippocampus is an important clinical finding in normal aging and Alzheimer disease. In this study, we investigate the associations between the magnitude and asymmetry of hippocampal volumetric integrity and age, sex, and dementia severity.

MATERIALS AND METHODS

We have recently developed a rapid fully automatic algorithm to measure the hippocampal parenchymal fraction, an index of hippocampal volumetric integrity on structural MR imaging of the brain. We applied this algorithm to measure the hippocampal parenchymal fraction bilaterally on 775 MR imaging volumes scanned from 198 volunteers in a publicly available data base. All subjects were right-handed and older than 60 years of age. Subjects were categorized as cognitively healthy (n = 98), with mild cognitive impairment (n = 70), or with mild/moderate Alzheimer disease (n = 30). We used linear mixed-effects models to analyze the hippocampal parenchymal fraction and its asymmetry with respect to age, sex, dementia severity, and intracranial volume.

RESULTS

After controlling for age, sex, and intracranial volume, we found that the magnitude of the hippocampal parenchymal fraction decreased and its asymmetry increased significantly with dementia severity. Also, hippocampal parenchymal fraction asymmetry was significantly higher in men after controlling for all other variables, but there was no sex effect on hippocampal parenchymal fraction magnitude. The magnitude of the hippocampal parenchymal fraction decreased and its asymmetry increased significantly with age in subjects who were cognitively healthy, but associations with age were different in nature in the mild cognitive impairment and Alzheimer disease groups.

CONCLUSIONS

Hippocampal atrophy progresses asymmetrically with age in cognitively healthy subjects. Hippocampal parenchymal fraction asymmetry is significantly higher in men than women and in mild cognitive impairment/Alzheimer disease relative to cognitively healthy individuals.

Tuberous sclerosis complex coexistent with hippocampal sclerosis

Tuberous sclerosis and hippocampal sclerosis are both well-defined entities associated with medically intractable epilepsy. To our knowledge, there has been only one prior case of these two pathologies being co-existent. We report a 7-month-old boy who presented with intractable seizures at 2 months of age. MRI studies showed diffuse volume loss in the brain with bilateral, multiple cortical tubers and subcortical migration abnormalities. Subependymal nodules were noted without subependymal giant cell astrocytoma. Genetic testing revealed TSC2 and PRD gene deletions. Histopathology of the hippocampus showed CA1 sclerosis marked by loss of neurons in the CA1 region. Sections from the temporal, parietal and occipital lobes showed multiple cortical tubers characterized by cortical architectural disorganization, gliosis, calcifications and increased number of large balloon cells. Focal white matter balloon cells and spongiform changes were also present. The patient underwent resection of the right fronto-parietal lobe and a subsequent resection of the right temporal, parietal and occipital lobes. The patient is free of seizures on anti-epileptic medication 69 months after surgery. Although hippocampal sclerosis is well documented to be associated with coexistent focal cortical dysplasia, the specific co-existence of cortical tubers and hippocampal sclerosis appears to be rare.

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.

Significance of tuber size for complications of tuberous sclerosis complex

INTRODUCTION

Tuberous sclerosis complex (TSC) is one of the most frequent neurocutaneous disorders. Cortical tubers are the most common pathological changes in TSC and they are directly related to the disease's main clinical manifestations: seizures, mental retardation, and autistic behaviour.

OBJECTIVE

The aim of this study is to establish a correlation between tuber size and the severity of clinical features in TSC.

MATERIAL AND METHODS

We performed a retrospective study of the clinical and imaging findings from 45 TSC patients (22 females and 23 males) and compared the clinical features with the location, size, and number of the cortical tubers in each patient.

RESULTS

Four patients had voluminous tubers located in 1 or both cerebral hemispheres. All of these patients had intractable seizures and severe mental retardation; 3 of these cases also presented with autistic behaviour, despite tubers having been resected in all 4 patients. Thirteen patients had tubers of large-to-average size, and all patients in this group showed intractable seizures and mental retardation. Nine patients who had experienced infantile spasms during the first year of life presented autistic behaviour. Multiple tubers of small to average size were found in 28 patients. In general, this group had seizures that responded well to antiepileptic drugs and a low prevalence of autism. In 3 patients who all presented good seizure control and normal intelligence, single cortical/subcortical tubers were located in the frontal or occipital lobes. Of the total of 45 patients, 13 had cerebellar as well as cerebral tubers; these were generally present in cases with more severe clinical features.

CONCLUSIONS

Although large tubers are less common than small to medium-sized ones, they are much more likely to be accompanied by severe clinical symptoms (seizures, mental retardation and autistic behaviour), even when the smaller tubers are quite numerous.

Neurosurgical treatment of tuberous sclerosis complex lesions

BACKGROUND

Tuberous sclerosis complex (TSC) is an autosomal dominantly inherited syndrome. Renal disease is the main cause of death. Brain disorders are the origin of more frequent and severe problems, such as tumors, epilepsy, and mental retardation. Participation of neurosurgeons in the study and especially in the treatment of TSC patients is often required.

MATERIALS AND METHODS

Two types of pathological conditions mainly require neurosurgical interventions in TSC: subependymal giant cell astrocytomas (SGCA) and cortical tubers. SGCA are located in the cerebral region close to the foramina of Monroe, uni- or bilaterally, and originate in hamartomas that can grow slowly as well as rapidly, even suddenly, especially in cases with intratumoral cyst, causing increased intracranial pressure (ICP) with severe risk for visual loss and life. Neurosurgeons have to participate in the follow-up of the patients as soon as the risk of ICP exists to remove the tumor when the criteria of SGCA growth are present. The other intracranial lesions that require neurosurgical intervention by are the cortical tubers.

CONCLUSION

These dysplastic lesions are associated with TSC in almost the 100% of affected persons and are the cause of epilepsy in most patients. The seizures can be resistant to antiepileptic medication in many cases in which a tuber is identified as the origin of the focal seizures after functional studies, such as EEG, MR, PET, etc. In these cases, only surgical removal of the tuber and the perituberal epileptogenic foci can cure the epilepsy. Large tubers are more epileptogenic than smaller ones.

Genetic analysis of tuberous-sclerosis genes 1 and 2 in nonlesional focal epilepsy

Germline mutations of TSC1 (harmartin) and TSC2 (tuberin) are known to cause tuberous sclerosis (TSC), an autosomal dominant disorder with severe neurological and systemic manifestations. In addition, increasing data indicate aberrant patterns of allelic variants in patients with lesion-associated epilepsy, but absence of other stigmata of TSC. Animal models of TSC suggested that mutations in the TSC2 gene, even in absence of manifest neuropathological changes, induce aberrant neuronal activity. On this basis, we have carried out a mutational analysis of TSC1 and TSC2 in patients with pharmarcoresistant focal epilepsy without evidence of epileptogenic lesions on neuroradiological and histopathological examination (n=10). SSCP analysis revealed an allelic variant of TSC2 to be significantly increased (exon 41: 50.0% vs controls 14%, P=0.0132), which previously was reported to be increased in gangliogliomas and mineralized focal cortical dysplasia as well. Our data suggest allelic imbalances of TSC2 in nonlesional focal epileptic tissue.

Mechanisms of neurocognitive dysfunction and therapeutic considerations in tuberous sclerosis complex

PURPOSE OF REVIEW

Mendelian disorders that affect cognition provide a unique opportunity to study the mechanisms of neurodevelopmental disorders through the examination of genetic defects in animals and development of hypotheses that can be tested in human beings. Tuberous sclerosis complex (TSC) is a genetic disease that presents with epilepsy, autism, and intellectual disability. Here we review recent advances in our understanding of TSC pathogenesis and signaling pathways that may be modulated to treat the neurological symptoms.

RECENT FINDINGS

Accumulating evidence suggests that TSC patients have nontuber abnormalities that contribute to the development of the neurological phenotype- in particular, disorganization of axon tracts and deficient myelination. TSC mouse models have failed to replicate the human neuropathology entirely, but have shed light on the cellular abnormalities and the neurobehavioral phenotypes. Most importantly, cell culture and animal models have identified the mTORC1 pathway as a therapeutic target in this disease.

SUMMARY

Preclinical data strongly suggest that TSC is a disease of abnormal neuronal connectivity. The high incidence of neurodevelopmental deficits, early detection of the disease in very young ages, and availability of mTORC1 inhibitors make TSC a model for other Mendelian disorders of neurocognition and an avenue for the mechanism-based treatment trials of neurodevelopmental disorders.