Epilepsy Surgery

What You'll Learn

Any patient who has failed two appropriately chosen, tolerated ASMs (mono- or combination) should be referred to a comprehensive epilepsy center for surgical evaluation (ILAE 2010 drug-resistant epilepsy definition; frequently tested board concept). Up to 30–40% of epilepsy patients meet criteria.
ATL is the most common and best-studied epilepsy surgery; 60–70% Engel I for mTLE with hippocampal sclerosis at 1 year
RCT evidence: Wiebe 2001 = 58% vs. 8% surgery vs. medical; ERSET = 73% vs. 0% — among the largest treatment effects in neurology
SAH achieves 55–65% Engel I with better cognitive preservation; LITT/SLAH achieves 55–60% (SLATE trial: 58%) with shortest recovery
Lesionectomy outcomes depend on pathology: low-grade tumors 75–90% > cavernomas 70–80% > FCD II 50–70% > HS 60–70% > MRI-negative 30–45%
Corpus callosotomy: palliative for drop attacks (tonic/atonic) in LGS; eliminates drops in 55%; anterior 2/3 first
Hemispherotomy: 73% seizure-free in children; indications = Rasmussen, hemimegalencephaly, perinatal stroke, Sturge-Weber
Long-term: 66% maintain seizure freedom at >5 years; 22–37% recurrence beyond 10 years; ~50% achieve ASM freedom after successful surgery

HighYield Pearls

DRE trigger: failure of 2 appropriately chosen, tolerated ASMs (ILAE 2010) → refer to comprehensive epilepsy center; affects 30–40% of epilepsy patients
ATL resection limits: dominant 3.5–4.5 cm, nondominant 5–6 cm from temporal pole; resects amygdala + hippocampus + parahippocampal gyrus
ATL complications: superior quadrantanopia (~18%, Meyer loop), verbal memory decline (~44% dominant ATL), naming decline (34% dominant)
Wiebe 2001 NEJM RCT: ATL 58% vs medical 8% seizure-free at 1 yr — NNT = 2, largest treatment effect in neurology
LITT for MTLE-HS: SLATE trial 58% Engel I; better neuropsych outcomes than ATL; outpatient/short stay; ideal for mesial sclerosis, hypothalamic hamartoma, deep cavernoma
Hemispherotomy > hemispherectomy: disconnection (not removal) → 73% seizure-free in children; indications = Rasmussen, hemimegalencephaly, perinatal MCA stroke, Sturge-Weber
Corpus callosotomy: palliative for drop attacks (tonic/atonic) in LGS/Dravet; eliminates drops in 55–80%; anterior 2/3 first to avoid disconnection syndrome
RNS (NeuroPace): bilateral mesial temporal foci, eloquent cortex, multifocal — closed-loop; median ≥70% seizure reduction at 9 yr; benefit accumulates over years
VNS: open-loop palliative; ~50% reduction in ~50% of patients (“50/50 rule”); hoarseness/cough/dyspnea on stimulation
SANTE / ANT-DBS: FDA-approved 2018 for focal DRE; bilateral anterior thalamic nucleus; centromedian targeted for generalized epilepsy
Histopathology hierarchy: low-grade tumor (75–90%) > cavernoma (70–80%) > HS (60–70%) > FCD IIb (50–70%) > MRI-negative (30–45%)
Pediatric: earlier surgery → better cognitive trajectory; young brain plasticity preserves motor function post-hemispherotomy

🔍 Quick ReferenceProcedure · Outcomes / histopathology · Complications

Procedure indications

MTLE with hippocampal sclerosis → ATL (mainstay) or SelAH or LITT
Drop attacks (tonic/atonic) in LGS / Dravet → corpus callosotomy (anterior 2/3)
Rasmussen encephalitis / hemimegalencephaly / Sturge-Weber / large perinatal MCA stroke → hemispherotomy
Hypothalamic hamartoma / deep cavernoma / periventricular nodular heterotopia → LITT (MR-guided laser ablation)
Seizure focus in eloquent cortex (motor/language) → multiple subpial transection (MST) or RNS
Bilateral mesial temporal / multifocal DRE → RNS (NeuroPace, closed-loop)
Palliative when resection not possible → VNS or ANT-DBS (SANTE)
Focal cortical dysplasia / tumor / encephalomalacia (extra-temporal) → extra-temporal cortical resection / lesionectomy

Outcomes / histopathology

MTLE-HS (Wieser type 1a–c) → best outcome — 60–70% Engel I after ATL
FCD type IIb (transmantle sign, balloon cells) → 50–70% Engel I if completely resected
Low-grade glioma / DNET / ganglioglioma → 75–90% Engel I (best lesional outcome)
Cavernoma → 70–80% Engel I after lesionectomy + hemosiderin rim
MRI-negative / non-lesional focal epilepsy → 30–45% Engel I (worst outcome)
SelAH vs ATL → 55–65% Engel I, better naming/verbal memory preservation
LITT (SLATE trial) → 58% Engel I for MTLE-HS, superior neuropsych profile
Pediatric hemispherotomy → 73% seizure-free; preserved motor function via contralateral plasticity

Complications

Superior quadrantanopia (“pie in the sky”) → ATL (Meyer loop in optic radiation, ~18%)
Verbal memory decline (~44%) / naming decline (34%) → dominant (left) ATL
Disconnection syndrome (alien hand, mutism) → complete corpus callosotomy (avoided by anterior 2/3 first)
Hoarseness, cough, dyspnea on stimulation → VNS (left vagus stimulation)
Hemiparesis / hemianopia (permanent major deficit ~4.7%) → any resective epilepsy surgery
De novo depression / anxiety (“burden of normality”) → post-ATL (10–20%)
Transient CN III/IV palsy from retraction → ATL / SelAH (~2%)
Hydrocephalus / aseptic meningitis → hemispherotomy

Drug-Resistant Epilepsy (DRE) Definition

ILAE 2010 definition (Kwan et al., Epilepsia 2010): DRE = failure of two appropriately chosen, tolerated, and used ASM schedules — whether as monotherapy or in combination — to achieve sustained seizure freedom
DRE is the gateway to surgical referral
Up to 30–40% of epilepsy patients have DRE

💎 Board Pearl

ILAE 2010 DRE = failure of 2 appropriately chosen, tolerated, and used ASMs (mono- or combination) to achieve sustained seizure freedom. DRE triggers surgical referral; 30–40% of epilepsy patients meet criteria.

Anterior Temporal Lobectomy (ATL)

Overview

Most common and best-studied epilepsy surgery worldwide
Standard procedure for mesial temporal lobe epilepsy (mTLE) with hippocampal sclerosis
Resects anterior temporal neocortex + mesial structures (amygdala, hippocampus, parahippocampal gyrus)

Resection Extent

Dominant hemisphere: 3.5–4.5 cm from temporal pole
Nondominant hemisphere: 5–6 cm from temporal pole
Intraoperative ECoG may guide additional resection beyond standard limits

Outcomes

Engel I at 1 year: 60–70% for mTLE with HS; 40–55% without HS
Wiebe 2001 (NEJM): RCT — surgery 58% vs. medical 8% seizure-free at 1 year
ERSET 2012 (JAMA): n=38 (terminated early for slow accrual); 11/15 (73%) surgical vs. 0/23 (0%) medical seizure-free during year 2
NNT = 2 (Wiebe; ARR = 0.58 − 0.08 = 0.50) — one of the largest treatment effects in clinical neurology

Complications

Complication	Incidence	Notes
Superior quadrantanopia	~18%	Disruption of Meyer loop (optic radiation)
Verbal memory decline	~44% clinically meaningful decline after dominant ATL (Sherman 2011)	Higher risk with strong preoperative memory, late onset, normal contralateral hippocampus
Naming decline	34% (dominant side)	Due to lateral temporal neocortex resection
De novo psychiatric symptoms	10–20%	Depression, anxiety; “burden of normality”
Cranial neuropathies	~2%	Transient CN III/IV from retraction
Major permanent deficits	4.7%	Hemiparesis, hemianopia
Mortality	<0.6%	All epilepsy surgeries

💎 Board Pearl

Dominant ATL resection limit = 3.5–4.5 cm; nondominant = 5–6 cm. Left ATL carries the highest risk of verbal memory (44%) and naming (34%) decline — boards test cognitive risk stratification by laterality.

Selective Amygdalohippocampectomy (SAH)

Key Points

Targets only mesial structures (amygdala, hippocampus, parahippocampal gyrus) while preserving lateral temporal neocortex
Engel I: 55–65% — may be slightly lower than standard ATL
Cognitive advantage: better naming and verbal memory preservation, especially with transsylvian approach

Surgical Approaches

Approach	Access Route	Key Risk
Transsylvian	Through sylvian fissure	MCA branch injury; technically demanding
Transcortical	Through middle/inferior temporal gyrus	Visual field defect (Meyer loop disruption)
Subtemporal	Under temporal lobe	Vein of Labbé injury; retraction injury

Less tissue removed than ATL — may have slightly lower seizure-free rates
Best for patients where cognitive preservation is a priority, especially dominant hemisphere

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