State of the Art Epilepsy Imaging: An Update

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

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

Reactive A1 Astrocyte-Targeted Nucleic Acid Nanoantiepileptic Drug Downregulating Adenosine Kinase to Rescue Endogenous Antiepileptic Pathway

Resistance to traditional antiepileptic drugs is a major challenge in chronic epilepsy treatment. MicroRNA-based gene therapy is a promising alternative but has demonstrated limited efficacy due to poor blood-brain barrier permeability, cellular uptake, and targeting efficiency. Adenosine is an endogenous antiseizure agent deficient in the epileptic brain due to elevated adenosine kinase (ADK) activity in reactive A1 astrocytes. We designed a nucleic acid nanoantiepileptic drug (tFNA-ADK^ASO@AS1) based on a tetrahedral framework nucleic acid (tFNA), carrying an antisense oligonucleotide targeting ADK (ADK^ASO) and A1 astrocyte-targeted peptide (AS1). This tFNA-ADK^ASO@AS1 construct effectively reduced brain ADK, increased brain adenosine, mitigated aberrant mossy fiber sprouting, and reduced the recurrent spontaneous epileptic spike frequency in a mouse model of chronic temporal lobe epilepsy. Further, the treatment did not induce any neurotoxicity or major organ damage. This work provides proof-of-concept for a novel antiepileptic drug delivery strategy and for endogenous adenosine as a promising target for gene-based modulation.

An electric-field-responsive paramagnetic contrast agent enhances the visualization of epileptic foci in mouse models of drug-resistant epilepsy

For patients with drug-resistant focal epilepsy, excision of the epileptogenic zone is the most effective treatment approach. However, the surgery is less effective in the 15-30% of patients whose lesions are not distinct when visualized by magnetic resonance imaging (MRI). Here, we show that an intravenously administered MRI contrast agent consisting of a paramagnetic polymer coating encapsulating a superparamagnetic cluster of ultrasmall superparamagnetic iron oxide crosses the blood-brain barrier and improves lesion visualization with high sensitivity and target-to-background ratio. In kainic-acid-induced mouse models of drug-resistant focal epilepsy, electric-field changes in the brain associated with seizures trigger breakdown of the contrast agent, restoring the T1-weighted magnetic resonance signal, which otherwise remains quenched due to the distance-dependent magnetic resonance tuning effect between the cluster and the coating. The electric-field-responsive contrast agent may increase the probability of detecting seizure foci in patients and facilitate the study of brain diseases associated with epilepsy.