Subcortical nodular heterotopia: a functional MRI and somatosensory evoked potentials study

Intracranial Electroencephalography Reveals Selective Responses to Cognitive Stimuli in the Periventricular Heterotopias

Our recent work suggests that non-lesional epileptic brain tissue is capable of generating normal neurophysiological responses during cognitive tasks, which are then seized by ongoing pathologic epileptic activity. Here, we aim to extend the scope of our work to epileptic periventricular heterotopias (PVH) and examine whether the PVH tissue also exhibits normal neurophysiological responses and network-level integration with other non-lesional cortical regions. As part of routine clinical assessment, three adult patients with PVH underwent implantation of intracranial electrodes and participated in experimental cognitive tasks. We obtained simultaneous recordings from PVH and remote cortical sites during rest as well as controlled experimental conditions. In all three subjects (two females), cognitive experimental conditions evoked significant electrophysiological responses in discrete locations within the PVH tissue that were correlated with responses seen in non-epileptic cortical sites. Moreover, the responsive PVH sites exhibited correlated electrophysiological activity with responsive, non-lesional cortical sites during rest conditions. Taken together, our work clearly demonstrates that the PVH tissue may be functionally organized and it may be functionally integrated within cognitively engaged cortical networks despite its anatomic displacement during neurodevelopment.SIGNIFICANCE STATEMENT Periventricular heterotopias (PVH) are developmentally abnormal brain tissues that frequently cause epileptic seizures. In a rare opportunity to obtain direct electrophysiological recordings from PVH, we were able to show that, contrary to common assumptions, PVH functional activity is similar to healthy cortical sites during a well-established cognitive task and exhibits clear resting state connectivity with the responsive cortical regions.

Direct and Collateral Alterations of Functional Cortical Circuits in a Rat Model of Subcortical Band Heterotopia

Subcortical band heterotopia (SBH), also known as double-cortex syndrome, is a neuronal migration disorder characterized by an accumulation of neurons in a heterotopic band below the normotopic cortex. The majority of patients with SBH have mild to moderate intellectual disability and intractable epilepsy. However, it is still not clear how cortical networks are organized in SBH patients and how this abnormal organization contributes to improper brain function. In this study, cortical networks were investigated in the barrel cortex in an animal model of SBH induced by in utero knockdown of Dcx, main causative gene of this condition in human patients. When the SBH was localized below the Barrel Field (BF), layer (L) four projection to correctly positioned L2/3 pyramidal cells was weakened due to lower connectivity. Conversely, when the SBH was below an adjacent cortical region, the excitatory L4 to L2/3 projection was stronger due to increased L4 neuron excitability, synaptic strength and excitation/inhibition ratio of L4 to L2/3 connection. We propose that these developmental alterations contribute to the spectrum of clinical dysfunctions reported in patients with SBH.

Functional and resting-state characterizations of a periventricular heterotopic nodule associated with epileptogenic activity

The object of this study was to extensively characterize a region of periventricular nodular heterotopia (PVNH) in an epilepsy patient to reveal its possible neurocognitive functional role(s). The authors used 3-T MRI approaches to exhaustively characterize a single, right hemisphere heterotopion in a high-functioning adult male with medically responsive epilepsy, which had manifested during late adolescence. The heterotopion proved to be spectroscopically consistent with a cortical-like composition and was interconnected with nearby ipsilateral cortical fundi, as revealed by fiber tractography (diffusion-weighted imaging) and resting-state functional connectivity MRI (rsfMRI). Moreover, the region of PVNH demonstrated two novel characterizations for a heterotopion. First, functional MRI (fMRI), as distinct from rsfMRI, showed that the heterotopion was significantly modulated while the patient watched animated video scenes of biological motion (i.e., cartoons). Second, rsfMRI, which demonstrated correlated brain activity during a task-negative state, uniquely showed directionality within an interconnected network, receiving positive path effects from patent cortical and cerebellar foci while outputting only negative path effects to specific brain foci.These findings are addressed in the context of the impact on noninvasive presurgical brain mapping strategies for adult and pediatric patient workups, as well as the impact of this study on an understanding of the functional cortical architecture underlying cognition from a neurodiversity and evolutionary perspective.

Diffusion tensor imaging of heterotopia: changes of fractional anisotropy during radial migration of neurons

PURPOSE

Diffusion tensor imaging provides better understanding of pathophysiology of congenital anomalies, involving central nervous system. This study was aimed to specify the pathogenetic mechanism of heterotopia, proved by diffusion tensor imaging, and establish new findings of heterotopia on fractional anisotropy maps.

MATERIALS AND METHODS

Diffusion-weighted imaging data from 11 patients (M : F = 7 : 4, aged from 1 to 22 years, mean = 12.3 years) who visited the epilepsy clinic and received a routine seizure protocol MRI exam were retrospectively analyzed. Fractional anisotropy (FA) maps were generated from diffusion tensor imaging of 11 patients with heterotopia. Regions of interests (ROI) were placed in cerebral cortex, heterotopic gray matter and deep gray matter, including putamen. ANOVA analysis was performed for comparison of different gray matter tissues.

RESULTS

Heterotopic gray matter showed signal intensities similar to normal gray matter on T1 and T2 weighted MRI. The measured FA of heterotopic gray matter was higher than that of cortical gray matter (0.236 +/- 0.011 vs. 0.169 +/- 0.015, p < 0.01, one way ANOVA), and slightly lower than that of deep gray matter (0.236 +/- 0.011 vs. 0.259 +/- 0.016, p < 0.01).

CONCLUSION

Increased FA of heterotopic gray matter suggests arrested neuron during radial migration and provides better understanding of neurodevelopment.

Giant subcortical heterotopia involving the temporo-parieto-occipital region: a challenging cause of drug-resistant epilepsy

The clinical, radiological, neurophysiological and neuropsychological findings of three patients with giant subcortical heterotopia are reported. All patients experienced psychomotor and behaviour improvement after surgery. Two subjects are seizure-free after complete excision of the heterotopia; the third patient significantly improved following subtotal removal (Engel's class II). Patients affected by giant subcortical heterotopias can have a favourable prognosis after the surgical removal of the malformation, even following long-lasting epilepsy.

Electric stimulation of periventricular heterotopia: participation in higher cerebral functions

Gray matter heterotopia are a common cause of pharmacoresistant epilepsy. Recently, several case studies have addressed the question of whether heterotopia can contribute to physiological cerebral functions. We describe two cases that demonstrate a functional role for periventricular heterotopia in higher cognitive processes. During presurgical diagnostics, two patients underwent electric stimulation of both the periventricular heterotopia and the overlying cortex. This revealed a functional role of periventricular heterotopia in higher cerebral functions such as language and complex visual and acoustic processing. Furthermore, stimulation of the overlying cortex led to unusually intense positive phenomena, including complex acoustic and gustatory hallucinations and language production. These cases illustrate that periventricular heterotopic neurons can contribute to higher cerebral functions. Interestingly, the anterior-to-posterior representation of these functions is comparable to the normal anterior-to-posterior representation in a normal neocortex (similar to a periventricular "minicortex" in early developmental stages).