docSeizure Imaging: Surgery for Medically Intractable Epilepsy
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Seizure Imaging: Surgery for Medically Intractable Epilepsy
Seizure Imaging: Surgery for Medically Intractable Epilepsy Unni Udayasankar MD Assistant Professor Cleveland Clinic Children’s Hospital Objectives • Common indications and rationale for pediatric epilepsy surgery • Review the role of imaging in preoperative assessment • Understand the major types of epilepsy surgery performed • Radiopathological correlation in surgical causes of epilepsy Identifying Surgical Candidates • Medical intractability in Epilepsy: – Two appropriately chosen, well-tolerated first line antiepileptic drug regimens have failed due to lack of efficacy. – Where the minimum seizure free period is one year or 3 times the pretreatment inter-seizure interval, whichever is longer. • Surgical candidacy to be determined on a case by case basis using data from an extensive multimodality assessment. • Plasticity phenomenon: Early surgical intervention can maximize efficacy, recovery, and cognitive potential. *Kwan P, Arzimanoglou A, Berg ST, et al. Definition of drug resistant epilepsy. Consensus proposal by the ad hoc Task Force of the ILAE Commission on Theraputic Strategies. Epilepsia. 2010; 51:1069-77. Key Considerations for Surgery Is a structural lesion identified? (MRI) Is an epileptogenic zone identified? (EEG, functional imaging) Are the lesion and epileptogenic zone concordant? Location? Relationship to eloquent cortex? (MR landmarks, functional imaging) Focal or extensive? Single or multiple? Unilateral or bilateral? Presurgical Assessment Modalities EEG Subdural grid MRI PET/SPECT MEG DTI/Tractography fMRI Invasive electrodes fMRI Motor Rhyming Passive Listening Word generation Nuclear Medicine Studies • Interictal Positron Emission Tomography (PET) • Ictal Single Photon Emission Computed Tomography (SPECT) • Identify eloquent cortex to be spared • Identify or confirm ictal focus • Identify pathophysiology of partial and generalized seizures • ictal hypermetabollism will be seen not only in the source lesion, but in any cortex to which the seizure has spread Common Types of Epilepsy Surgery Goals of surgery: – To resect the epileptogenic zone, OR – To disconnect avenues of seizure spread Types of surgery – – – – – – – Lesionectomy Temporal Lobectomy Hemispherectomy Corpus Callosotomy Multiple Subpial Transections Radiosurgery Vagal nerve stimulators Lesionectomy Focal Cortical Dysplasia • Most common cause • Types – FCD Type I (non-Taylor) – FCD Type II (Taylor) • Two variants – Hemimegalencephaly – Tuberous sclerosis A and B FCD FCD Taylor Type IIB with balloon cells FCD: Lesionectomy FCD: Taylor Type II Multifocal lesionectomy Tuberous sclerosis MCD Lesionectomy: Tumors • Almost all originate from cerebral cortex • Mixture of glial and neural elements • Benign biological behavior • Low mitotic activity • Stable or slow growing • Associated with cortical dysplasia or dysplastic neuronal elements Ganglioglioma PXA PXA DNET Oligodendroglioma Pilomyxoid Astrocytoma (PMA) Angiocentric glioma Atypical Meningioma Lesionectomy: Cavernous malformation Lesionectomy: Scar Lesionectomy: Post herpetic encephalomalacia Temporal Lobectomy • Intractable temporal lobe lesion – Malformations of cortical development – Neoplasm – Mesial Temporal Sclerosis (MTS) – Vascular anomalies Temporal Lobectomy Selective Amygdalohippocampectomy “Standard” Anterior Temporal Lobectomy Temporal Lobectomy Temporal Lobectomy Selective Amygdalohippocampectomy In selective amygdalohippocampectomy, goal is to preserve remaining temporal lobe. Access to mesial structures is challenging; approaches include trans-Sylvian, lateral trans-cortical, subtemporal, and variations. Temporal Lobectomy: MCD Temporal Lobectomy: Ganglioglioma Temporal Lobectomy: Oligodendroglioma Cavernous Malformation Right temporal AVM Extended Lesionectomy/Lobectomy Aicardi syndrome Cystic Encephalomalacia Sturge Weber Syndrome Sturge Weber Syndrome Sturge-Weber Syndrome Grade II Oligoastrocytoma Polymicrogyria Schizencephaly Old non-accidental injury Hemispherectomy • Typical Indications: Secondary generalized seizures where focus is large or multifocal involving only one hemisphere. – – – – – • Rasmussens Encephalitis Ishemic or traumatic injury Sturge Weber Hemimegencephly Diffuse (unilateral) migration disorder Two main techniques share goal of rendering disordered hemisphere behaviorly non-functional. 1. Anatomic Hemispherectomy – Remove involved hemisphere, leaving only deep structures. 2. Functional Hemispherectomy – Disconnect white matter tracts with more limited resection. Anatomic Hemispherectomy • When anatomic hemispherectomy is considered, the epileptogenic hemisphere is usually severely dysfunctional – Hemiparesis – Language mediated by the contralateral hemisphere • Therefore extensive resection may be justified. • Frontal, parietal, occipital and temporal lobes are removed, leaving the basal ganglia, thalamus, and brainstem. Anatomic Hemispherectomy: Large MCD Hemimegalencephaly Hemimegalencephaly Anatomic Hemispherectomy: Chronic Post surgical changes Functional Hemispherectomy • A “window” of cortex may be removed to then make the appropriate white matter transections. • White matter tracts that are disconnected – – – – – Corpus Callosum Coronal radiata/internal capsule Fornix Anterior Commisure Outflow tracts of the amygdala Functional Hemispherectomy Rassmussen’s encephalitis Rassmussen’s Encephalitis Cystic encephalomalacia , functional hemispherectomy Functional Hemispherectomy . Corpus Callosotomy • Typical Indications: – Intractable seizures without resectable focus or when only incomplete resection is possible – Patients may have multiple epileptogenic zones – Drop attacks Corpus Callosotomy Multiple Subpial Transections • Typical Indications: Epileptogenic zone in dominant eloquent cortex • A “disconnection” type procedure to avoid resecting eloquent structures: Hypothalamic Hamartoma Epilepsy Surgeries Summary Surgical Objectives Technique Candidates Example lesions Lesionectomy Discrete resectable lesions (usually noneloquent cortex) •Neoplasm •Vascular •Focal MOCD •Encephalomalacia Temporal Lobectomy Lesions isolated to temporal lobe •Any of above involving temporal lobe, including MTS Extensive or multifocal unilateral epileptogenic foci •Sturge-Weber •Rasmussen’s Encephalitis •Hemimegancephaly Extensive or multifocal bilateral epileptogenic foci or no resectable focus •Extensive MOCD •Lesion of dominant eloquent cortex Resection: Remove the epileptogenic focus Anatomic Hemispherectomy Disconnection: Interrupt cortical connections to limit seizure spread Functional Hemispherectomy Corpus Callosotomy Multiple Subpial Epileptogenic foci in eloquent cortex Transections •Lesion of dominant eloquent cortex
