Anterior striatum with dysmorphic neurons associated with the epileptogenesis of focal cortical dysplasia

Basal ganglia dysplasia and mTORopathy: A potential cause of postoperative seizures in focal cortical dysplasia

Pathogenic somatic MTOR variants in the cerebral cortex are a frequent cause of focal cortical dysplasia (FCD). We describe a child with drug and surgery-resistant focal epilepsy due to FCD type II who developed progressive enlargement and T2 signal hyperintensity in the ipsilateral caudate and lentiform nuclei. Histopathology of caudate nucleus biopsies showed dysmorphic neurons, similar to those in resected cortex. Genetic analysis of frontal and temporal cortex and caudate nucleus identified a pathogenic somatic MTOR variant [NM_004958.4:c.4375G > C (p.Ala1459Pro)] that was not present in blood-derived gDNA. The mean variant allele frequency ranged from 0.4% to 3.2% in cerebral cortex and up to 5.4% in the caudate nucleus. The basal ganglia abnormalities suggest more widespread, potentially hemispheric dysplasia in this patient, consistent with the pathogenic variant occurring in early cerebral development. This finding provides a potential explanation for persistent seizures in some patients with seemingly complete resection of FCD or disconnection of a dysplastic hemisphere.

Branch atheromatous disease has a stronger association with late-onset epileptic seizures than lacunar infarction in Japanese patients

Objective

To evaluate the relationship between late-onset epileptic seizures and non-cortical infarction (namely, lacunar infarction and branch atheromatous disease [BAD]) in Japanese patients.

Methods

We reviewed the medical records and brain magnetic resonance imaging findings of all patients with ischemic stroke admitted to the Departments of Neurology, Neurosurgery, and Stroke Unit at Kurashiki Central Hospital from 1 January 2011 to 31 December 2012. Patients with lacunar infarction and BAD were enrolled; those with cortical and brain stem ischemic lesions were excluded. We analyzed the clinical features of patients who developed late-onset epileptic seizures after cerebral infarction.

Results

Eighty-five patients with lacunar infarction and 99 patients with BAD were enrolled. Four patients with BAD subsequently developed epileptic seizures (2.2% of total patients, 4.0% of patients with BAD), whereas no patients with lacunar infarction developed epileptic seizures. All patients with epileptic seizures had infarction involving the basal ganglia or thalamus. Three of them had multiple cerebral microbleeds, and two had dementia.

Conclusions

Patients with BAD, but not with lacunar infarction, might have a higher risk of developing epileptic seizures than the general population. Non-cortical infarctions with involvement of the basal ganglia or thalamus may increase the risk of subsequent late-onset epileptic seizures.

Interactions between frontal and posterior oscillatory dynamics support adjustment of stimulus processing during reinforcement learning

Reinforcement learning (RL) in humans is subserved by a network of striatal and frontal brain areas. The electrophysiological signatures of feedback evaluation are increasingly well understood, but how those signatures relate to the use of feedback to guide subsequent behavioral adjustment remains unclear. One mechanism for post-feedback behavioral optimization is the modulation of sensory processing. We used source-reconstructed MEG to test whether feedback affects the interactions between sources of oscillatory activity in the learning network and task-relevant stimulus-processing areas. Participants performed a probabilistic RL task in which they learned associations between colored faces and response buttons using trial-and-error feedback. Delta-band (2-4 Hz) and theta-band (4-8 Hz) power in multiple frontal regions were sensitive to feedback valence. Low and high beta-band power (12-20 and 20-30 Hz) in occipital, parietal, and temporal regions differentiated between color and face information. Consistent with our hypothesis, single-trial power-power correlations between frontal and posterior-sensory areas were modulated by the interaction between feedback valence and the relevant stimulus characteristic (color versus identity). These results suggest that long-range oscillatory coupling supports post-feedback updating of stimulus processing.

Brain dysplasia evoked by gamma irradiation at different stages of prenatal development leads to different tonic and clonic seizure reactivity

Rats with brain dysplasia evoked by interruption of different stages of prenatal neurogenesis show characteristic variations in susceptibility to seizures depending on the neurochemical specificity of pharmacological agents used to evoke seizures. To verify a discrepancy between the data obtained using different pharmacological models, neurochemically neutral electroshocks were applied here. To produce brain dysplasia of different degrees, pregnant Wistar rats were exposed to a single 1.0Gy dose of gamma rays on gestation days 13, 15, 17 or 19. From the postnatal day 60, their male offspring (E13s, E15s, E17s and E19s, respectively) were subjected to 21 daily electrical stimulations to evoke seizures. Profiles of tonic and clonic reactivity to electrical stimulation significantly differed from those observed following pilocarpine or kainic acid administration. E17s showed minimal intensity of tonic but maximal of clonic responses. On the contrary, very high tonic and low clonic reactivity was observed in E13s and E15s. Periventricular nodular heterotopias (PNHs) were observed exclusively in E15s and E17s. Generally, the size of PNHs was correlated positively with susceptibility to tonic seizures but negatively with susceptibility to clonic seizures. Analogous correlations with the size of the neocortex were opposite. E13s and E19s had brains devoid PNHs but showed high tonic seizure susceptibility similar to that in E15s. It can therefore be concluded that PNHs modified the type of seizure reactivity from tonic to clonic, depending of their size, but the presence of PNHs was not necessary for the development of seizure susceptibility itself.

Surgical management of cortical dysplasia in infancy and early childhood

PURPOSE

To describe operative procedures, seizure control and complications of surgery for cortical dysplasia (CD) causing intractable epilepsy in infancy and early childhood.

METHODS

Fifty-six consecutive children (less than 6years old) underwent resective epilepsy surgery for CD from December 2000 to August 2011. Age at surgery ranged from 2 to 69months (mean 23months) and the follow-up was from 1 to 11years (mean 4years 4months).

RESULTS

Half of the children underwent surgery during infancy at an age less than 10months, and the majority (80%) of these infants needed extensive surgical procedures, such as hemispherotomy and multi-lobar disconnection. Seizure free (ILAE class 1) outcome was obtained in 66% of the cases (class 1a; 55%): 85% with focal resection (n=13), 50% with lobar resection (n=18), 71% with multilobar disconnection (n=7) and 67% with hemispherotomy (n=18). Peri-ventricular and insular structures were resected in 23% of focal and 61% of lobar resections. Repeated surgery was performed in 9 children and 5 (56%) became seizure free. Histological subtypes included hemimegalencephaly (16 patients), polymicrogyria (5 patients), and FCD type I (6 patients), type IIA (19 patients), type IIB (10 patients). Polymicrogyria had the worst seizure outcome compared to other pathologies. Surgical complications included 1 post-operative hydrocephalus, 1 chronic subdural hematoma, 2 intracranial cysts, and 1 case of meningitis. No mortality or severe morbidities occurred.

CONCLUSIONS

Early surgical intervention in children with CD and intractable seizures in infancy and early childhood can yield favorable seizure outcome without mortality or severe morbidities although younger children often need extensive surgical procedures.

Surgical pathologic features of cerebral cortical lesions taken from 600 patients with intractable epilepsy

OBJECTIVES

To determine the scope of histopathological variation in lesions responsible for epileptogenesis, I retrospectively reviewed the features of surgical specimens taken consecutively from 600 patients with intractable epilepsy.

METHODS

The patients were divided into three groups on the basis of age at seizure onset: 94 patients with infantile onset (before 1year of age), 307 patients with juvenile onset (between 1 and 12years of age), and 199 patients with adolescent/adult onset (at 13years of age or beyond). Histological and immunohistochemical evaluations of the surgical specimens were performed.

RESULTS

In the infant group, seizure duration was significantly shorter than in the other groups, and malformations caused by abnormalities of cortical development, including focal cortical dysplasia (FCD) type IIa/b, tuberous sclerosis, hemimegalencephaly, and polymicrogyria were predominant, whereas in the juvenile and adolescent/adult groups, other lesions such as hippocampal sclerosis (HS), tumors, FCD type I, and vascular lesions were frequently observed. For patients with HS, seizure duration in the juvenile group was significantly longer than in the adolescent/adult group. FCD type IIIa was noted in nearly half of patient with HS in both juvenile and adolescent/adult groups. The causative tumors included dysembryoplastic neuroepithelial tumors, gangliogliomas, astrocytomas, and other glioneuronal and glial tumors.

CONCLUSION

Various histopathological entities and types, showing clear predominance depending on the age at seizure onset, were observed in patients with epilepsy. These features appear to provide information on the pathomechanisms of the lesions and their clinical relevance in affected patients.

Novel pathological abnormalities of deep brain structures including dysplastic neurons in anterior striatum associated with focal cortical dysplasia in epilepsy

OBJECT

Some patients are not seizure free even after epileptogenic cortical resection. The authors recently described a case of frontal lobe epilepsy cured after the resection of periventricular white matter and striatum, in which dysplastic neurons were revealed. The authors attempted to confirm similar cases.

METHODS

They reviewed the records of 8 children with frontal lobe epilepsy who had daily (7) or monthly (1) seizures and underwent resections including deep brain structures.

RESULTS

Five patients underwent multiple resections. Neuroimaging of the deep structures showed the transmantle sign in 3 patients, ictal hyperperfusion in 6, reduced iomazenil uptake in 2, and spike dipole clustering in 6. All patients became seizure free postoperatively. Focal cortical dysplasia of various types was diagnosed in all patients. Dysmorphic neurons were found in the cortex and subcortical white matter of 5 patients. The striatum was verified in 3 patients in whom dysmorphic neurons were scattered. In the periventricular white matter, prominent astrocytosis was evident in all cases.

CONCLUSIONS

Pathological abnormalities such as dysmorphic neurons and astrocytosis in deep brain structures would play a key role in epileptogenesis.

Development and dysgenesis of the cerebral cortex: malformations of cortical development

The cerebral cortex develops in several stages from a pseudostratified epithelium at 5 weeks to an essentially complete cortex at 47 weeks. Cortical connectivity starts with thalamocortical connections in the 3rd trimester only and continues until well after birth. Vascularity adapts to proliferation and connectivity. Malformations of cortical development are classified into disorders of specification, proliferation/apoptosis, migration, and organization. However, all processes are intermingled, as for example a dysplastic cell may migrate incompletely and not connect appropriately. However, this classification is convenient for didactic purposes as long as the complex interactions between the different processes are kept in mind.