AANS2000AANS2000Internet Outline of

Neurosurgery

E. R. Flotte MD, 2009

 

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www.outlineofneurosurgery.com

 

 

Epilepsy

 

 

Neurology: Seizures

 

General

·         Intractable: failed at least 3 meds. Occurs in 30%

·         Remission: seizure-free off medications for 5 or more years

·         Reviews: Neurosurgical Focus 9/08

·         Audio: Neurobiology of Epilepsy – During M

Antiepileptics

·         Non-enzyme inducing: Kepra (po only), Lamictal (po only), Depakote (causes bleeding?)

·         Tegretol: causes leucopenia, hepatitis

Status Epilepticus

·         30+ minutes seizure activity or multiple seizures without regaining consciousness

·         Step-wise: ABCs, Thiamine/Glucose IV, CT when stable

·         Ativan (4mg x 2 - 0.1mg/kg, IV or rectal) & Dilantin/Fosphenytoin load (20mg/kg then 5mg/kg/d).

·         Phenobarbitol (<100mg/min up to 20mg/kg) until seizures stop. Watch BP.

·         >30 mins: Intubate and pentobarbital (or Versed) infusion or  general anesthesia

Hippocampal Sclerosis

·         AKA Ammon’s Horn Sclerosis (AHS)

·         Correlated with Mesial Temporal Sclerosis (MTS) on MRI (↑ FLAIR/T2). Hypometabolism on PET

·         Correlated with febrile seizures

·         Seen with Timm stain – CA1 & CA3 loss

Hypothalamic hamartoma

·         Causes gelastic seizures initially, then complex-partial or generalized. Responds well to radiosurgery.

o    Gelastic seizures: laughing fits. Other causes: hypothalamic glioma, 3rd ventricle tumor, temporal lobe epilepsy, infantile spasms, etc.

Tumors

·         Seizure focus is usually in the surrounding brain, not in the tumor

·         Single or controlled seizures – do lesionectomy. Intractable seizures – lesionectomy plus intraoperative ECOG and resection of seizure focus

Cortical Dysplasia

·         With complete resection of epileptogenic focal cortical dysplasia, 87% have good seizure outcome

New Onset Seizures

·         Most recommend CT and/or MRI.  Some repeat in 3-6 months.

·         EEG performed, and if normal then sleep-deprived EEG

 

 

Preoperative Evaluation

·         CNS Course: Identifying Candidates for Epilepsy Surgery (Kanner AM)

Phase I:

Imaging

·         MRI (FLAIR)

If nonlesional then proceed with:

·         PET

o    Ictal PET shows hypermetabolism in focus. Interictal PET shows hypometabolism in focus in 70%.

o    Sensitvity in TLE 60-90%

o    Does not correlate with histopathological changes (eg atrophy)

·         SPECT

o    Subtraction Ictal-Interictal SPECT shows hypermetabolism in focus

·         Can coregister T1 MRI with PET, SPECT, grid xray for image guidance (JN3/04)

·         Possibly MR Spectroscopy, FMRI triggered spike detection

Scalp EEG/Video-EEG

·         Dense-array EEG. EEG Dipole Analysis

·         Provocative: hyperventilation

·         Magnetoencephalography

Neuropsychological Testing

·         Cognitive and functional deficits, memory reserve

 

Phase II:

Invasive monitoring

Subdural Grids & Strips:

·         Scalp EEG fails to localize focus in 30%. Used to confirm preoperative hypothesis.

·         Standard: 2 placed perpendicular to temporal lobe (consider 1 medial & parallel)

·         Electrocorticography may assist in grid placement

·         Low-amplitude high-frequency activity at onset correlates with good surgical outcome. Electrodes recording higher-frequency spikes are closer to focus

·         Stereoelectroencephalography: Stereotactic placement of depth electrodes

·         Sphenoid and foramen ovale electrodes used

Depth Electrodes

 

WADA test:

·         Injection of sodium amobarbital into ICA. Used to predict language & memory localization.

·         Speech: arrest not enough, must have naming errors.

·         Memory:  Uses:

o    1) Memory localization: less reliable than speech. (Note hippocampal blood supply mainly from PCA)

o    2) Focus localization: able to detect side of eplieptogenic focus in 40-80%, incorrect in <10%, indeterminate 20-50%. Memory improves when given on side of focus.

 

Surgery

Lesionectomy

·         MRI lesion with concordant EEG: 80-90% seizure-free at 12 months

o    Nonlesional postop seizure-free 30-50%

 

Temporal Lobectomy

·         Complications: Superior quadrantopsia most common (higher if resection >5.5cm posterior)

o    Anterior choroidal a. can loop into choroids plexus – avoid coagulating choroid plexus

o    CNS Course: Complications of Temporal Lobe Operations for Intractable Epilepsy (Byrne RW)

·         Anterior temporal lobectomy (corticoamygdalohippocampectomy):

o    70-94% Engle I-II.

o    Wiebe S NEJM 2001:  Only RCT  58% (complex) seizure-free, 8% off medicine. 10% adverse effects, 55% visual field deficits

o    Diplopia 19% (due to CN4 palsy, resolves).

o    Extent: 4-5cm in nondominant lobe, 3.5-4cm dominant lobe.

o    Open choroidal fissure between hippocampus and choroids plexus (vessels run between choroids plexus & thalamus). Be aware of basal temporal language area (N5/04)

o    “Temporal lobotomy”: See N6/04

·         Selective Amygdalohippocampectomy: Transsylvian approach described by Yasargil & Wieser (1982).

o    74% Engle class I-II in kids. Versus ATL: No difference in adults, worse control in peds.

o    Pterional craniotomy. Carotid cistern opened – visualize uncus. Sylvian fissure opened (anterior 1/3 of insula, 2cm of M2 – broad opening may cause vasospasm). Incision of limen insulae just medial to superior temporal gyrus. Enter temporal horn.

o    See Wurm G N6/00 (Neuronav-guided),

·         ATL vs SelAH: Tanriverdi T JN3/08

 

Multiple Subpial Transections

·         Used to make disconnections in eloquent cortex

·         Used alone: 15% seizure-free, 35% improved, 50% unchanged. Combined with resection: 40% seizure-free, 40% improved, 20% unchanged.

·         Used in Landau-Kleffner Syndrome in which epileptic aphasia develops in previously normal child

 

Corpus Callosotomy:

·         Indications: Secondary generalized, atonic (drop attacks), infantile hemiplegia, Rasmussens, Lennox-gastaut.

o    Contraindicated in crossed dominance (left-handedness with left-sided speech) – obtain WADA in all left-handed patients.

·         Most commonly anterior 2/3rds is sectioned, interhemispheric approach

·         Complications:

o    Anterior: ¯ spontaneous speech (SMA), nondominant leg paresis & grasping, urge incontinence (all usually temporary). Permanent speech deficit with mixed cerebral dominance (speech & motor on opposite sides).

o    Posterior: interhemispheric disconnection syndrome (¯ tactile sensation & vision on nondominant side, bradyphrenia, incontinence

o    Complete: as above + nondominant hand doesn’t perform commands (can perform antagonistic actions)

 

Hemispherectomy

·         Indications: Hemiplegia with intractable seizures: Rasmussen’s disease, cortical dysplasia, hemispheric infarct.

·         Anatomic: Complete resection of hemisphere. Complications: hydrocephalus, superficial siderosis.

·         Functional: Removal of central cortex and temporal lobe, basal ganglia left intact but disconnected from cortex, disconnection of contralateral hemisphere. 25% reoperation for recurrent seizures.

·         Other techniques: Hemispherotomy (JN:P2/04, JN11/04).

 

Vagal Nerve Stimulator:

·         Effective on left side only (reason unknown).

·         Efficacy: All seizure types equally reduced. 42% reduction in seizures @ 18mo, very few seizure free. Equivalent to adding another medicine. “50% improvement in 50% of patients”

o    Can be effective after failed craniotomy (N11/04)

o    Cochrane Database: VNS for partial seizures appears to be an effective and well tolerated treatment. Adverse effects of hoarseness, cough, pain, paresthesias, and dyspnea are associated with the treatment but appear to be reasonably well tolerated as dropouts were rare.

·         Complications: Coughing, voice changes, throat pain, drooling, laughing, torticollis, urinary retention. (No cardiac changes reported.)

 

Extratemporal Epilepsy Surgery

·         Occipital Epilepsy: about 5%. Visual auras/hallucinations common. Cortical malformations most common cause. Tandon N JN2/09

·         CNS Course: Surgery for Extra-Temporal Lobe Epilepsy (Boling W)

 

Intraoperative Electrocorticography

·         Done either with strips or the “Hellraiser

·         Under general anaesthesia avoid benzodiazepines and babituates. Under local use only narcotics (fentanyl) and droperidol.

 

Perioperative

·         Taper and discontinue AEDs 24hrs preop. Continue AEDs 1-2 years.

 

Radiosurgery

·         Dose limited by optic chiasm and brainstem.  Takes >9mos to work; auras or seizures may increase before decreasing.  May take up to 3yrs before considering retreatment.

·         One report using 20Gy (N6/04) showed 0/5 improvement with MTS and possibly worsened cognitive testing. Marseilles group (Regis) report 82% seizure-free and another 12% significantly improved using 25Gy. T2 signal peaks at 1yr.

·         Multicenter trial (led by UCSF) currently ongoing.

 

Deep brain stimulation: of anterior thalamic nucleus and other areas (centromedian nucleus, STN, hippocampus) being investigated

 

 

Text Copyright 2009

Revised 6/1/09


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Disclaimer: This outline is complied, not original.  Sources are being added retrospectively. 

It is intended for personal educational use by students and residents.  It is not intended to guide clinical decision making. Accuracy and timeliness cannot be guaranteed.