Imaging in the Epilepsies Exhaustive Study Guide

Overview and Importance of Imaging in Epilepsy

  • Core Objectives of Imaging:     - Understand Aetiology: Determining the underlying cause or origin of the epileptic condition.     - Identify Lesion: Pinpointing structural abnormalities within the brain that may be triggering seizures.     - Surgical Consideration: Evaluating whether a patient is a candidate for surgical intervention and planning the procedure.

  • Key Literatures for Review:     - Localisation in focal epilepsy: Chowdhury et al., Practical Neurology 2021.     - Methodology for classification of epilepsy syndromes: Wirrell et al., Epilepsia 2022.     - Brain imaging in the assessment for epilepsy surgery: Duncan et al., Lancet Neurology 2016.

ILAE Seizure Type Classification (2017)

  • Focal Onset Seizures:     - Awareness Levels: Can be "Aware" or "Impaired Awareness."     - Motor Onset Subtypes: Includes automatisms, atonic, clonic, epileptic spasms, hyperkinetic, myoclonic, and tonic.     - Nonmotor Onset Subtypes: Includes autonomic, behavior arrest, cognitive, emotional, and sensory.     - Progression: Focal seizures can evolve into bilateral tonic-clonic seizures.

  • Generalized Onset Seizures:     - Motor Subtypes: Tonic-clonic, clonic, tonic, myoclonic, myoclonic-tonic-clonic, myoclonic-atonic, atonic, and epileptic spasms.     - Nonmotor (Absence) Subtypes: Typical, atypical, myoclonic, and eyelid myoclonia.

  • Unknown Onset Seizures:     - Motor: Tonic-clonic, epileptic spasms.     - Nonmotor: Behavior arrest.

  • Unclassified: Seizures that do not fit into the above categories due to inadequate information or unusual characteristics.

Anatomical Localisation and Seizure Semiology

  • Frontal Lobe:     - Pre-central Gyrus: Generates clonic seizures, sometimes tonic (involving the face, arm, or leg).     - SMA (Supplementary Motor Area) / Premotor: Asymmetric tonic seizures (SMA) or complex motor movements.     - DLPFC (Dorsolateral Prefrontal Cortex) / Orbitofrontal: Complex automatisms, dialeptic symptoms, and semipurposeful behavior.     - Frontal Eyefields: Characterized by head and eye version (turning).     - Mesial Prefrontal / Anterior Cingulate: Hyperkinetic seizures, ictal fear, and vocalization.     - Broca’s Area: Expressive language impairment or related symptoms.     - Frontal Operculum: Hypersalivation and clonic movements.

  • Temporal Lobe:     - Mesiotemporal: Behavioral arrest, automatisms, gustatory aura, or psychic aura.     - Amygdala: Autonomic signs such as tachycardia and apnoea.     - Temporal Neocortex (Heschl’s Gyrus): Auditory aura.

  • Parietal Lobe:     - Post-central Gyrus: Somatosensory symptoms including tingling and numbness.     - Precuneus: Altered visual perception.     - Superior Parietal Lobule: Altered body perception.

  • Occipital Lobe and Junctions:     - Primary Visual Cortex: Visual symptoms such as flashing colored or bright lights.     - Visual Association Areas: Complex visual hallucinations, kinetopsia (motion blindness), macropsia/micropsia (objects appearing larger/smaller), and autoscopy (seeing one's own body).     - Parieto-occipital Junction: Eye version and nystagmus.

  • Subcortical/Other:     - Hypothalamus: Gelastic (laughing) seizures.     - Insula (Anterior): Viscerosensory symptoms (e.g., abdominal aura, "laryngon" or throat tightness) and autonomic signs (nausea, hypersalivation, sweating).     - Insula (Posterior): Painful sensations, including burning or tingling.

Epilepsy Syndromes by Age of Onset

  • Developmental and Epileptic Encephalopathy (DEE) and Progressive Neurological Deterioration:     - Neonatal/Infancy: Early Infantile DEE, Infantile Epileptic Spasm Syndrome (IESS), Epilepsy in Infancy with Migrating Focal Seizures, and Dravet Syndrome.     - Childhood/Adolescent: Lennox-Gastaut Syndrome (LGS), Epilepsy with Myoclonic-Atonic Seizures, Rasmussen Syndrome, Gelastic Seizures with Hypothalamic Hamartoma, and Febrile Infection-Related Epilepsy Syndrome (FIRES).     - Miscellaneous: Hemiconvulsion-Hemiplegia-Epilepsy, Progressive Myoclonus Epilepsy, and DEE with Spike-Wave Activation in Sleep.

  • Focal Epilepsy Syndromes:     - Neonatal/Infantile: Self-limited Familial Neonatal and Infantile Epilepsy, Self-limited (Familial) Infantile Epilepsy.     - Childhood: Self-Limited Epilepsy with Centro-Temporal Spikes (SELECTS), Self-Limited Epilepsy with Autonomic Seizures (SeLEAS), Childhood Occipital Visual Epilepsy (COVE).     - Adolescent/Adult: Mesial Temporal Lobe Epilepsy (MTLE) with Hippocampal Sclerosis, Sleep-Related Hypermotor (Hyperkinetic) Epilepsy, Photosensitive Occipital Lobe Epilepsy (POLE), and Epilepsy with Auditory Features.

  • Generalized Epilepsy Syndromes:     - Childhood: Childhood Absence Epilepsy (CAE), Myoclonic Epilepsy in Infancy, Epilepsy with Eyelid Myoclonia, and Epilepsy with Myoclonic Absences.     - Adolescent/Adult: Juvenile Myoclonic Epilepsy (JME), Juvenile Absence Epilepsy (JAE), and Epilepsy with Generalized Tonic-Clonic Seizures Alone.

Imaging Modalities in Epilepsy

  • Computed Tomography (CT): Used for acute assessment or when MRI is unavailable.
  • Magnetic Resonance Imaging (MRI):     - Standard clinical imaging utilizes strength levels of 1.5T and 3T.     - Historical context includes Nikola Tesla's early magnetism studies and early 1980s MR images (e.g., of a bell pepper).
  • Positron Emission Tomography (PET): Specifically FDG-PET to identify areas of glucose hypometabolism (e.g., hypometabolism in the left temporal lobe indicating focal seizure origin).
  • Magnetoencephalography (MEG): Measures magnetic fields produced by neuronal activity.
  • Single-Photon Emission Computed Tomography (SPECT): Used to assess blood flow during or between seizures.

Clinical Case Examples

  • Tuberous Sclerosis (in DEE):     - MRI Findings (Axial T2 and FLAIR): Multiple bilateral subcortical hyperintensities consistent with cortical tubers.     - Subependymal Hamartomas: Multiple rounded lesions dispersed at the lateral ventricles.

  • Rasmussen Syndrome:     - Clinical Presentation: A 12-year-old female affecting the left hemisphere, 18 months post-seizure onset.     - EEG: Shows low-voltage spike wave discharge interictally.     - MRI (Axial FLAIR): Shows focal hyperintensity and atrophy in the left supplementary motor area (SMA).     - Seizure Type: Motor seizures resulting from SMA involvement.

  • Focal Cortical Dysplasia (FCD):     - Classification (ILAE 2022/2011): Includes types FCD 1A, 1B, 2B, 3A, 3C, and 3D.     - Visual Markers: Pathological layering and cellular abnormalities visible on high-resolution imaging and histopathology.

  • Focal Childhood Epilepsies:     - SeLEAS: Age range 1-14 years (usual 3-6); multifocal high voltage spikes; occipital spikes with fixation-off sensitivity.     - SELECTS: Age range 3-14 years (peak 7); centrotemporal spikes; remission usually by puberty.     - COVE: Age range 1-19 years (usual 8-9); occipital spikes.     - POLE: Range 1-50 years (mean 11).

Epilepsy Surgery and MDT Approach

  • Surgical Interventions:     - Focal Ablation: Targeted destruction of seizure-generating tissue.     - Focal Resective Surgery: Removal of the lesion or the specific area of the brain where seizures originate.     - Callosotomy: Severing the corpus callosum to prevent seizure spread between hemispheres.     - Vagal Nerve Stimulation (VNS): An implanted device used to modulate seizure activity via the vagus nerve.

  • The Neuroradiology MDT: Multidisciplinary Team meetings are essential because "many sets of eyes are better than one" for interpreting complex imaging in epilepsy.