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Surgical Management of Epilepsy

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SURGICAL MANAGEMENT OF EPILEPSY

Eric R. Trumble, MD

NEUROSURGEONS FOR KIDS

Definition of Epilepsy

Epilepsy implies a periodic recurrence of seizures with or without convulsions

Seizures result from an excessive synchronous discharge of cortical neurons and is characterized by changes in electrical activity

A convulsion implies violent, involuntary contraction(s) of the voluntary muscles

Diagnosis of Epilepsy

Clinical history is key

  • Experience at onset
  • Report of observers
  • Postictal experience

Electroencephalogram

  • Generalized syndrome: commonly abnormal
  • Partial seizures: rarely abnormal on first recording

Imaging study: MRI

Classification of Seizures: Generalized Seizures

  • Absence seizures
  • Tonic-clonic seizures
  • Myoclonic seizures
  • Tonic seizures
  • Clonic seizures
  • Atonic seizures

Classification of Seizures: Absence (Petit Mal)

  • Brief alterations of awareness
  • Activity arrest, starring, automatisms
  • Pick-up where they left-off
  • Average age 8-10years
  • Classic EEG Pattern of 3Hz/sec
  • Females slightly more than males
  • Hyperventilation provokes onset

Classification of Seizures: Tonic-Clonic

  • Any age onset and M=F
  • Stiff extension of body/extremities followed by violent, rhythmic, symmetric movements
  • Alteration of consciousness followed by confusion and sleepiness
  • Changes in respiration, bladder and bowel

Classification of Seizures: Myoclonic

  • Brief, random, lightning-like movements
  • May occur singly or in clusters
  • Seconds in duration, no post-ictal changes
  • Various age onset
  • Can be resistant to therapy

Classification of Seizures: Tonic

  • Symmetric, rhythmic movements of extremities as in Tonic/Clonic seizures
  • Often occur out of sleep

Classification of Seizures: Atonic

  • Abrupt loss of tone
  • Frequently associated with trauma
  • Positive alteration consciousness with variable post-ictal changes

Classification of Seizures

  • Partial seizures
  • Simple partial seizures
  • Complex partial seizures
  • Impaired consciousness at outset
  • Simple partial evolving to lost consciousness
  • Partial seizures evolving to general tonic-clonic seizures (GTCS)

Classification of Seizures: Simple Partial

  • Often called Benign Rolandic
  • Hallmark is preservation of consciousness
  • Classic pattern on EEG
  • M=F, average age onset 7-8
  • +/- therapy necessary
  • Often “outgrown”
  • May not be “so benign”

Classification of Seizures: Complex Partial

  • Change in consciousness
  • Most common epilepsy in children
  • Automatisms, deja vue, auras or alice in wonderland changes seen
  • Focal motor movements of any limb
  • Variable duration and severity
  • Any age onset

Monotherapy AED

Classic Versus Newer Anticonvulsants

Classic AEDs

  • Phenobarbital   
  • Phenytoin (Dilantin®)
  • Primidone (Mysoline®)
  • Carbamazepine (Tegretol®)
  • Valproate (Depakote®/Depacon®)
  • Ethosuximide (Zarontin®)

Newer AEDs

  • Felbamate (Felbatol®)
  • Gabapentin (Neurontin®)
  • Lamotrigine (Lamictal®)
  • Levetiracetam (Keppra®)
  • Oxcarbazepine (Trileptal®)
  • Tiagabine (Gabitril®)
  • Topiramate (Topamax®)
  • Vigabitrin (Sabril®)
  • Zonisamide (Zonegran®)

Mechanisms of Action: Antiepileptic Drugs

  • Sodium channel effects
  • Potassium channels and GABA release
  • GABAergic effects
    • Precursors, mimicry, and transporters
  • Glutamate regulation-neuroprotection
  • Calcium channels and transmitter release

Anticonvulsants: Mechanisms of Action

Choice and Use of Drugs

Pharmacoresistant Epilepsy

Previously Untreated Epilepsy Patients (n=470)1

 

Patient Typically Not Considered Surgical Epilepsy Candidate Unless:

  • They have failed at least 3 adequate anti-convulsant trials
    • Definition of failure varies
  • EEG confirming epilepsy
  • Recent MRI
  • Family/patient willing to consider surgery

Etiology:

  • Focal
    • Lesion
    • Anatomically Normal
    • Temporal
    • Extra-Temporal
  • Multi-Focal/Generalized

Epilepsy Associated with Cortical Malformation:

  • 20% of epilepsy patients
  • Mental retardation
  • Autism
  • Neuropsychiatric syndromes

Cell Migration Disorders:

Heterotopias - A failure of neuronal migration from the periventricular matrix to the cortex; asymptomatic or mental retardation or seizure

Agyria - No gyri (lissencephaly) or a few malformed gyri (pachygyria)

Polymicrogyria - Excessive number of gyri are formed with shallow sulci; sporadic (congenital ischemia/hypoxia, infection) or familial; asymptomatic, mental retardation or seizure

Focal cortical dysplasia

HEMIMEGALENCEPHALY

Cell Migration Disorders:

Heterotopias - A failure of neuronal migration from the periventricular matrix to the cortex; asymptomatic or mental retardation or seizure

Agyria - No gyri (lissencephaly) or a few malformed gyri (pachygyria)

Polymicrogyria - Excessive number of gyri are formed with shallow sulci; sporadic (congenital ischemia/hypoxia, infection) or familial; asymptomatic, mental retardation or seizure

Focal cortical dysplasia

Lissencephaly

Lissencephaly

Cell Migration Disorders:

Heterotopias - A failure of neuronal migration from the periventricular matrix to the cortex; asymptomatic or mental retardation or seizure

Agyria - No gyri (lissencephaly) or a few malformed gyri (pachygyria)

Polymicrogyria - Excessive number of gyri are formed with shallow sulci; sporadic (congenital ischemia/hypoxia, infection) or familial; asymptomatic, mental retardation or seizure

Focal cortical dysplasia
 

Polymicrogyria - Diffuse

Polymicrogyria - Localized

Polymicrogyria - Localized

Cell Migration Disorders:

Heterotopias - A failure of neuronal migration from the periventricular matrix to the cortex; asymptomatic or mental retardation or seizure

Agyria - No gyri (lissencephaly) or a few malformed gyri (pachygyria)

Polymicrogyria - Excessive number of gyri are formed with shallow sulci; sporadic (congenital ischemia/hypoxia, infection) or familial; asymptomatic, mental retardation or seizure

Focal cortical dysplasia

Tuberous Sclerosis -Tubers

Surgical Management of Epileptiform Lesions

TAKE THEM OUT!!!

Consider monitoring, either with surface EEG or with implanted grids. However, once lesion is confirmed to be source of epileptiform discharges, TAKE THEM OUT!!!

Corticectomy

Work-up includes: Stage I

  • Surface EEG-Video Monitoring
  • Head MRI with and without contrast
  • Neuropsychological testing

Stage II

  • Invasive EEG
    • Grids, strips, and depth electrodes
  • Functional Imaging
    • Wada, PET, SPECT, fMRI

Success

  • Temporal lobe epilepsy
    • 90% were seizure free
    • 98% had a >90% reduction in seizures1
  • Extra-temporal lobe epilepsy
    • 70% were seizure-free2
  1. Cukiert et al: Neurosurg Focus. 2002 Oct 15;13(4):ecp2
  2. Kazemi et al: Epilepsia. 1997 Jun;38(6):670-7.

Multi-focal Epilepsy

  • Temporal lobe epilepsy
    • 90% were seizure free
    • 98% had a >90% reduction in seizures1
  • Extra-temporal lobe epilepsy
    • 70% were seizure-free2
  1. Cukiert et al: Neurosurg Focus. 2002 Oct 15;13(4):ecp2
  2. Kazemi et al: Epilepsia. 1997 Jun;38(6):670-7.

VNS Therapy

  • Implantable pulse generator and lead
  • Mild electrical pulses applied to the left vagus nerve in the neck send signals to the brain
  • Automatic intermittent stimulation
  • Magnet use allows patient/caregiver
    • On-demand stimulation
    • On-demand side effect control
  • Simple in-office programming
  • Assured compliance

Vagus Nerve Stimulation Implantation

VNS Surgical Technique

  • Creation of left chest sub-cutaneous pocket
  • Cut-down to left vagus nerve
  • Attachment of lead to nerve
  • Tunneling on lead
  • Lead test
  • Programming
  • Closure

VNS System Implant: The Exposed Carotid Sheath

Final Electrode/Anchor Tether Placement

Use of the integrated anchor tether helps prevent force transfer to the electrodes.

Pulse Generator: Programmable Parameters