Temporal Lobe Epilepsy
Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy in adults, accounting for approximately 60–70% of all focal epilepsies referred to epilepsy centers. It is subdivided into mesial temporal lobe epilepsy (mTLE), which arises from the hippocampus, amygdala, and parahippocampal gyrus, and lateral (neocortical) temporal lobe epilepsy (lTLE), which originates from the temporal neocortex. TLE is the prototypical drug-resistant epilepsy: approximately one-third of patients fail to achieve seizure freedom with antiseizure medications alone, making it the most common indication for epilepsy surgery. Hippocampal sclerosis is the pathological hallmark of mTLE and is the single most common structural lesion identified in surgical epilepsy series.
Bottom Line
- Mesial TLE is the most common focal epilepsy syndrome in adults; hippocampal sclerosis (HS) is its defining pathological substrate, characterized by selective neuronal loss in CA1, CA3, CA4, and dentate hilus with relative sparing of CA2
- Semiology: The classic mTLE seizure begins with an epigastric rising sensation (aura), progresses to behavioral arrest with oroalimentary and manual automatisms, impaired awareness lasting 60–120 seconds, and prolonged postictal confusion; contralateral dystonic posturing and ipsilateral hand automatisms lateralize the seizure onset
- EEG: Interictal anterior temporal sharp waves (F7/F8, T3/T4) are the hallmark; ictal patterns show rhythmic 5–9 Hz theta activity over the ipsilateral temporal region
- MRI: Hippocampal atrophy with T2/FLAIR hyperintensity; loss of internal architecture on coronal thin-cut sequences; quantitative volumetry increases sensitivity
- Drug resistance: ~30% of mTLE patients are pharmacoresistant; anterior temporal lobectomy with amygdalohippocampectomy yields 60–80% seizure freedom (Engel Class I) in HS cases
- Lateral TLE is less common, presents with auditory auras or complex visual phenomena, and has a less predictable surgical outcome than mTLE with HS
Classification and Epidemiology
TLE is classified within the ILAE 2022 framework as a focal epilepsy syndrome with variable age of onset. The ILAE recognizes mesial temporal epilepsy with hippocampal sclerosis as a distinct syndrome and familial mesial temporal lobe epilepsy as a separate genetic entity. TLE typically presents between the second and fourth decades of life, although it can manifest at any age.
| Feature | Mesial TLE (mTLE) | Lateral (Neocortical) TLE (lTLE) |
|---|---|---|
| Frequency | ~80% of TLE | ~20% of TLE |
| Typical onset zone | Hippocampus, amygdala, entorhinal cortex | Superior or middle temporal gyrus, fusiform gyrus |
| Common etiology | Hippocampal sclerosis (65–70% of surgical specimens) | Tumors (ganglioglioma, DNET), cortical dysplasia, cavernous malformations |
| Typical aura | Epigastric rising, déjà vu, fear, olfactory | Auditory hallucinations (buzzing, ringing), auditory illusions, vertiginous, complex visual |
| Automatisms | Oroalimentary (lip smacking), manual (picking, fumbling) | Less prominent; may have early contralateral versive movements |
| Seizure duration | 60–120 seconds; prolonged postictal confusion | Often shorter; postictal confusion may be brief |
| EEG interictal | Anterior temporal sharp waves (F7/F8, T3/T4) | Mid-to-posterior temporal spikes (T5/T6); may be less localizing |
| MRI finding | Hippocampal atrophy & T2/FLAIR hyperintensity | Lesion-specific (tumor, dysplasia, cavernoma) or MRI-negative |
| Surgical outcome | 60–80% Engel I (seizure-free) with HS | 50–60% Engel I (lesional); lower if MRI-negative |
Hippocampal Sclerosis
Pathology
Hippocampal sclerosis (HS) is defined by selective neuronal loss and reactive astrogliosis in specific hippocampal subfields. The ILAE classification recognizes three histopathological subtypes:
| ILAE HS Type | Pattern of Neuronal Loss | Frequency | Clinical Associations |
|---|---|---|---|
| Type 1 (classical) | Severe loss in CA1, CA4 (hilus); moderate in CA3; relative sparing of CA2 | 60–80% | History of initial precipitating injury (febrile seizures, encephalitis); best surgical outcome |
| Type 2 (CA1-predominant) | Predominantly CA1 loss; other subfields relatively preserved | 5–10% | Less likely childhood precipitating event; less favorable surgical outcome |
| Type 3 (CA4-predominant) | Predominantly CA4 and dentate granule cell loss | 4–7% | Often associated with dual pathology; less favorable surgical prognosis |
Pathogenesis of HS
The pathogenesis of HS involves a complex interplay of initial precipitating injuries, neuronal excitotoxicity, and reorganization:
- Initial precipitating injury (IPI): A history of prolonged febrile seizures, CNS infection, or perinatal injury is present in 50–80% of mTLE-HS patients; the IPI is hypothesized to initiate a cascade of hippocampal damage
- Latent period: A seizure-free interval (typically 5–15 years) occurs between the IPI and the onset of habitual temporal lobe seizures
- Epileptogenesis: Progressive neuronal loss, mossy fiber sprouting (aberrant granule cell axon reorganization), and gliosis create abnormal excitatory circuits
- Granule cell dispersion: Widening of the dentate granule cell layer (≥10 cells thick) is a characteristic histological finding seen in ~40% of HS specimens
MRI Findings
MRI is the cornerstone of noninvasive HS diagnosis. An epilepsy-dedicated MRI protocol at ≥1.5T (ideally 3T) with coronal thin-cut sequences perpendicular to the long axis of the hippocampus is essential:
- T2/FLAIR hyperintensity: Increased signal in the hippocampus reflecting gliosis
- Hippocampal atrophy: Volume loss best appreciated on coronal T1-weighted images; quantitative volumetry increases sensitivity by 10–15% over visual inspection
- Loss of internal architecture: Loss of normal hippocampal digitations on high-resolution sequences
- Secondary signs: Ipsilateral temporal horn enlargement, temporal lobe volume loss, mammillary body atrophy, fornix atrophy
- Bilateral HS: Present in 10–20% of patients; associated with worse cognitive outcomes and reduced surgical seizure-freedom rates
MRI-Negative mTLE
- ~20–30% of patients with electroclinical mTLE have no visible hippocampal abnormality on standard MRI
- Consider quantitative hippocampal volumetry, T2 relaxometry, and 7T MRI to detect subtle abnormalities
- PET (ipsilateral temporal hypometabolism) and SPECT (ictal hyperperfusion) provide complementary localizing information
- MRI-negative mTLE has lower seizure-freedom rates after surgery (50–60% vs. 70–80% for MRI-positive HS)
- Consider invasive EEG monitoring with stereo-EEG before proceeding to resection
Clinical Semiology
Auras in mTLE
Auras (focal aware seizures) are reported by 80–90% of mTLE patients and carry significant localizing value:
| Aura Type | Description | Frequency in mTLE | Localizing Value |
|---|---|---|---|
| Epigastric rising | Sensation of nausea, butterflies, or a rising feeling from abdomen to chest/throat | 50–70% | Strongly suggests mesial temporal onset (insular involvement also possible) |
| Déjà vu / Jamais vu | Intense feeling of familiarity or unfamiliarity with the current experience | 20–40% | Mesial temporal, especially entorhinal cortex |
| Fear / Anxiety | Sudden, intense, unprovoked fear or dread without external stimulus | 15–30% | Amygdala involvement |
| Olfactory | Unpleasant, burning, or unidentifiable odor (cacosmia) | 5–10% | Uncus / piriform cortex; less common, highly specific |
| Gustatory | Metallic or unpleasant taste | 5–10% | Insular or opercular cortex; may suggest non-mesial onset |
| Autonomic | Palpitations, flushing, piloerection, pupillary dilation | 10–20% | Amygdala, insular cortex |
Ictal Semiology
The classic mTLE focal impaired awareness seizure follows a stereotyped evolution:
- Aura (seconds): Usually epigastric rising or experiential (déjà vu, fear)
- Behavioral arrest: Motionless stare with unresponsiveness; marks loss of awareness
- Automatisms (30–120 seconds): Oroalimentary (lip smacking, chewing, swallowing) and distal manual (picking, fumbling, fidgeting with objects); automatisms are ipsilateral to the seizure onset zone
- Contralateral dystonic posturing: Sustained tonic posturing of the arm contralateral to seizure onset; one of the most reliable lateralizing signs (90% lateralizing value)
- Secondary generalization: Focal to bilateral tonic-clonic seizure occurs in 30–50% of untreated mTLE patients
- Postictal phase (minutes to hours): Confusion, disorientation, automatisms, and amnesia; postictal aphasia (with dominant hemisphere onset) or postictal nose wiping (ipsilateral hand)
Key Lateralizing Signs in TLE
- Contralateral dystonic posturing: ~90% lateralizing to contralateral hemisphere
- Ipsilateral hand automatisms: Hand automatisms are ipsilateral to the epileptogenic zone
- Postictal nose wiping: Performed with the ipsilateral hand in ~90% of cases
- Ictal speech preservation: Suggests nondominant hemisphere onset
- Postictal aphasia: Strongly suggests dominant temporal lobe onset
- Head version: Forced, sustained turning of the head contralateral to the seizure onset (late version → contralateral; early, non-forced turning may be ipsilateral)
- Figure-4 sign: Asymmetric tonic limb posturing during secondary generalization; the extended arm is contralateral to the seizure onset
EEG Findings
Interictal EEG
Interictal epileptiform discharges (IEDs) in mTLE are characterized by anterior temporal sharp waves and spikes, best seen at F7/F8 and T3/T4 (or T7/T8 in the 10-10 system). Key features include:
- Morphology: Sharp waves with phase reversal at the anterior temporal electrodes; typically maximum negativity at F7/F8
- Activation by sleep: IED frequency increases 2–3-fold during NREM sleep; sleep-deprived EEG increases diagnostic yield from ~50% to 70–80%
- Lateralization: Unilateral IEDs concordant with imaging lateralize the seizure onset in >90% of cases
- Bilateral independent IEDs: Present in 30–40% of mTLE patients; when >80% are unilateral, lateralization remains reliable
- Temporal intermittent rhythmic delta activity (TIRDA): 1–3 Hz rhythmic delta over the temporal region; has similar lateralizing value to IEDs
Ictal EEG
The ictal onset of mTLE seizures typically shows:
- Rhythmic theta activity: 5–9 Hz rhythmic activity over the ipsilateral temporal region, often beginning at F7/F8 or T3/T4
- Evolution: Gradual increase in amplitude, decrease in frequency, and spread to adjacent electrodes over seconds to minutes
- Postictal regional slowing: Ipsilateral temporal polymorphic delta activity after seizure termination; lateralizes to the seizure onset zone
- Limitations: Scalp EEG may not detect seizures confined to the mesial temporal structures; 10–20% of mTLE seizures show no clear scalp EEG changes at onset
EEG Pitfalls in TLE
- Bilateral TLE occurs in 10–20% of patients with apparent unilateral mTLE; invasive monitoring may be needed to determine the predominant side
- Temporal IEDs can be seen in asymptomatic individuals (incidental EEG finding); clinical correlation is essential
- The "wicket spikes" normal variant can mimic temporal sharp waves; distinguish by the absence of after-going slow waves and their arciform morphology
- Generalized spike-and-wave discharges may coexist with temporal IEDs in some patients, suggesting a dual pathology or misdiagnosis
- Frontal lobe and insular seizures can propagate rapidly to temporal structures, producing a "pseudo-temporal" pattern on scalp EEG
Drug-Resistant TLE and Surgical Evaluation
Definition of Drug Resistance
Drug-resistant epilepsy is defined by the ILAE as failure to achieve sustained seizure freedom after adequate trials of two appropriately chosen and tolerated antiseizure medications (whether as monotherapy or in combination). In mTLE with HS, drug resistance is common: approximately 60–75% of patients with unilateral HS ultimately develop pharmacoresistant seizures.
Presurgical Evaluation
The presurgical evaluation is a multidisciplinary process designed to localize the epileptogenic zone and assess the risks and benefits of surgical intervention:
| Investigation | Role in TLE Evaluation | Key Findings |
|---|---|---|
| MRI (epilepsy protocol) | Primary imaging modality; detect and lateralize HS or other lesions | Hippocampal atrophy, T2/FLAIR hyperintensity, loss of internal architecture |
| Video-EEG monitoring | Capture habitual seizures; localize ictal onset; confirm semiologic concordance | Ipsilateral temporal onset, concordant with MRI lateralization |
| FDG-PET | Interictal hypometabolism lateralizes the epileptogenic temporal lobe | Ipsilateral temporal hypometabolism in 70–90% of mTLE-HS; may extend beyond hippocampus |
| Ictal SPECT | Hyperperfusion at seizure onset localizes the epileptogenic zone | Ipsilateral temporal hyperperfusion; requires injection within 30 seconds of seizure onset |
| Neuropsychological testing | Assess baseline cognitive function; predict postoperative memory decline | Verbal memory decline risk with dominant (usually left) temporal resection; material-specific memory lateralizes function |
| Wada test / fMRI | Lateralize language and memory function; assess risk of postoperative amnesia | fMRI increasingly replacing Wada for language lateralization; Wada may still be needed for memory assessment |
| Invasive EEG (stereo-EEG) | Required when noninvasive data are discordant or when MRI is negative | Depth electrodes in hippocampus and amygdala; can detect seizure onset not visible on scalp EEG |
Surgical Options
- Anterior temporal lobectomy (ATL) with amygdalohippocampectomy: Standard procedure for mTLE-HS; resects 3.5–4.5 cm of anterior temporal neocortex (nondominant) or 3–4 cm (dominant), plus amygdala and hippocampus; 60–80% seizure-free (Engel Class I) at 2 years
- Selective amygdalohippocampectomy (SAH): Spares temporal neocortex; comparable seizure outcomes to ATL in some series; potentially better neuropsychological outcome; technically challenging
- Laser interstitial thermal therapy (LITT): Minimally invasive MRI-guided laser ablation of the hippocampus and amygdala; seizure-free rates of 50–60% at 2 years; shorter hospitalization; lower cognitive decline risk
- Responsive neurostimulation (RNS): Closed-loop cortical stimulation; 50–70% seizure reduction at 2 years; option for bilateral TLE or when resection risk is unacceptable
- Vagus nerve stimulation (VNS): Palliative neuromodulation; ~50% of patients achieve ≥50% seizure reduction; does not typically produce seizure freedom
Evidence for Early Surgery Referral
- The ERSET trial (2012) demonstrated that early surgery (within 2 years of drug resistance) in mTLE was superior to continued medical therapy: 73% seizure-free at 2 years (surgery) vs. 0% (medical)
- Despite Level 1 evidence, the average time from epilepsy onset to surgery remains 20+ years at most centers
- The ILAE recommends referral to an epilepsy surgery center after failure of two appropriate ASMs
- Delay in surgery is associated with worse postoperative cognitive outcomes, reduced employment, and lower quality of life
- Predictors of favorable surgical outcome: unilateral HS on MRI, concordant ictal EEG, concordant semiology, absence of contralateral abnormalities
Familial Mesial Temporal Lobe Epilepsy
Familial mesial temporal lobe epilepsy (FMTLE) is a recognized ILAE syndrome characterized by:
- Autosomal dominant inheritance with variable penetrance
- Focal seizures with prominent déjà vu, psychic auras, and autonomic symptoms
- Typically benign course with good response to antiseizure medications
- Normal MRI in most cases (no hippocampal sclerosis)
- Interictal EEG may be normal or show subtle temporal discharges
- Genetic basis incompletely understood; no single gene identified; polygenic susceptibility suspected
Epilepsy With Auditory Features
Epilepsy with auditory features (formerly autosomal dominant lateral temporal epilepsy) is a familial focal epilepsy arising from the lateral temporal neocortex:
- Onset typically in adolescence or young adulthood
- Focal aware seizures with auditory symptoms (buzzing, humming, ringing) or receptive aphasia
- May progress to focal impaired awareness or focal to bilateral tonic-clonic seizures
- Associated with LGI1 gene mutations (30% of families) and rarely RELN variants
- Good response to carbamazepine/oxcarbazepine in most patients
- MRI is typically normal; EEG shows lateral temporal spikes
Cognitive and Psychiatric Comorbidities
Cognitive Impact of TLE
Temporal lobe epilepsy is associated with characteristic cognitive deficits that reflect the anatomical substrate of the disease:
- Memory impairment: The hallmark cognitive deficit of mTLE; verbal memory deficits lateralize to the dominant (usually left) hemisphere; visuospatial memory deficits lateralize to the nondominant (usually right) hemisphere; this material-specific pattern aids presurgical lateralization
- Language: Dominant TLE may cause anomia, word-finding difficulty, and verbal fluency impairment; these deficits may be subtle on bedside testing and require formal neuropsychological assessment
- Executive function: Subtle deficits in planning, inhibition, and cognitive flexibility have been described, likely reflecting the disruption of temporal-frontal network connectivity
- Accelerated cognitive decline: Ongoing drug-resistant seizures are associated with progressive memory decline; both hippocampal atrophy progression and the cumulative effects of seizures contribute; this observation supports early surgical intervention
Psychiatric Comorbidities
| Psychiatric Condition | Prevalence in TLE | Key Features |
|---|---|---|
| Depression | 30–50% | Most common psychiatric comorbidity; bidirectional relationship with epilepsy; may precede seizure onset; associated with reduced quality of life; screen with validated tools (NDDI-E, PHQ-9) |
| Anxiety | 20–40% | Generalized anxiety, social anxiety, and specific seizure-related anxiety; may coexist with depression; interictal anxiety is more common than ictal fear |
| Interictal dysphoric disorder | 15–20% | Blume-type disorder; episodic dysphoria with irritability, depressed mood, anxiety, anergia, insomnia, and pain; may not meet criteria for major depressive disorder |
| Psychosis | 2–7% | Postictal psychosis (typically after seizure clusters; lucid interval of 12–72 hours); interictal psychosis (chronic, schizophrenia-like; associated with long-standing TLE); alternative psychosis (forced normalization — psychotic symptoms emerging during seizure-free periods) |
| Personality changes | Variable | Geschwind syndrome (hypergraphia, hyperreligiosity, altered sexual behavior, circumstantiality, viscosity) — historically described but controversial; likely represents a spectrum rather than a distinct syndrome |
Psychiatric Considerations in Surgical TLE
- Depression and anxiety generally improve after successful surgery (seizure freedom), with studies showing 40–60% improvement rates
- De novo psychiatric symptoms (depression, anxiety, psychosis) develop in approximately 5–10% of patients after surgery, even when seizures are controlled
- Preoperative psychiatric comorbidity is NOT a contraindication to surgery but requires careful preoperative psychiatric optimization and close postoperative monitoring
- Postictal psychosis risk may initially increase in the early postoperative period if seizures occur; risk decreases with sustained seizure freedom
- Quality of life improvements after successful surgery are substantial and extend beyond seizure control to include mood, employment, driving, and social functioning
Prognosis
The long-term prognosis of TLE depends heavily on the underlying etiology and treatment approach:
- Medical therapy alone: Only 25–40% of mTLE-HS patients achieve long-term seizure freedom with ASMs; cognitive decline and psychiatric comorbidities (depression, anxiety) are common with ongoing seizures
- Postoperative outcomes: 60–80% Engel Class I at 2 years for unilateral HS; 70% maintain seizure freedom at 10 years; ASM withdrawal is possible in 25–50% of seizure-free patients after 2–5 years
- SUDEP risk: Drug-resistant TLE carries an elevated risk of sudden unexpected death in epilepsy; successful surgery reduces SUDEP risk substantially
- Cognitive outcomes: Verbal memory may decline after dominant temporal resection, but overall quality of life improves significantly; younger age at surgery is associated with better cognitive outcomes
- Psychiatric outcomes: Depression and anxiety improve in most patients after successful surgery; de novo psychiatric symptoms occur in ~5–10%
Red Flags in TLE Evaluation
- Rapidly progressive temporal lobe epilepsy with memory decline in an older adult: consider autoimmune encephalitis (LGI1, GAD65 antibodies) or paraneoplastic etiology
- TLE with bilateral independent seizure onset on EEG may indicate bilateral HS or extra-temporal propagation — invasive monitoring is critical before surgery
- Dual pathology (HS plus extrahippocampal lesion) occurs in 5–30% of surgical TLE cases and may require broader resection
- New-onset TLE with an enhancing temporal mass: rule out high-grade glioma; low-grade tumors (ganglioglioma, DNET) are common but do not typically enhance
- History of encephalitis (especially HSV) preceding TLE: consider the possibility of autoimmune epilepsy with ongoing antibody-mediated pathology
References
- Nascimento FA, Friedman D, Peters JM, et al. Focal epilepsies: update on diagnosis and classification. Epileptic Disord 2023;25(1):1–17.
- Riney K, Bogacz A, Somerville E, et al. International League Against Epilepsy classification and definition of epilepsy syndromes with onset at a variable age: position statement by the ILAE Task Force on Nosology and Definitions. Epilepsia 2022;63(6):1443–1474.
- Blümcke I, Thom M, Aronica E, et al. International consensus classification of hippocampal sclerosis in temporal lobe epilepsy: a Task Force report from the ILAE Commission on Diagnostic Methods. Epilepsia 2013;54(7):1315–1329.
- Engel J Jr, McDermott MP, Wiebe S, et al. Early surgical therapy for drug-resistant temporal lobe epilepsy: a randomized trial (ERSET). JAMA 2012;307(9):922–930.
- Wiebe S, Blume WT, Girvin JP, Eliasziw M. A randomized, controlled trial of surgery for temporal-lobe epilepsy. N Engl J Med 2001;345(5):311–318.
- Cendes F, Sakamoto AC, Spreafico R, Bingaman W, Becker AJ. Epilepsies associated with hippocampal sclerosis. Acta Neuropathol 2014;128(1):21–37.
- Jobst BC, Cascino GD. Resective epilepsy surgery for drug-resistant focal epilepsy: a review. JAMA 2015;313(3):285–293.
- Skidmore CT. Neuroimaging in epilepsy. Continuum (Minneap Minn) 2025;31(1, Epilepsy):61–80.
- Gooley S, Crompton DE, Berkovic SF. ILAE genetic literacy series: familial focal epilepsy syndromes. Epileptic Disord 2022;24(2):221–228.
- Kwan P, Arzimanoglou A, Berg AT, et al. Definition of drug resistant epilepsy: consensus proposal by the ad hoc Task Force of the ILAE Commission on Therapeutic Strategies. Epilepsia 2010;51(6):1069–1077.
- Scheffer IE, Berkovic S, Capovilla G, et al. ILAE classification of the epilepsies: position paper of the ILAE Commission for Classification and Terminology. Epilepsia 2017;58(4):512–521.
- Wieser HG, Blume WT, Fish D, et al. ILAE Commission Report. Proposal for a new classification of outcome with respect to epileptic seizures following epilepsy surgery. Epilepsia 2001;42(2):282–286.