General
- Aims more at controlling tumour- related epilepsy than tumour growth.
Preop assessment
- See Seizure work up
- Neuroimaging
- To identify additional epileptogenic lesions (i.e. to properly delineate the epileptogenic vs. tumorous lesion).
- Depth electrode recordings or ECoG recordings
- May suggest taking the resection more dorsally if the epileptological benefit is felt to outweigh the potentially adverse neuropsychological sequelae.
Resection margins
- ‘Extended’ lesionectomies for extratemporal and temporolateral LEATs causing neocortical temporal lobe epilepsy (i.e. gross total tumour resections with removal of a 0.5– 1 cm rim of surrounding cortical tissues).
- Tumours involving the temporomesial structures should be resected together with any abnormal hippocampus/ parahippocampus and a rim of adjoining temporomesial tissues
- If the lesion lies within or borders eloquent cortex, restrict ourselves to simple lesionectomies.
- Requires a formal and invasive preoperative epileptological work- up or intraoperative electroencephalograph (EEG) recordings (ECoG))
- Tumour resections AND
- Resection surrounding rim of cortex (‘extended lesionectomy’)
- Additional corticectomy
- Removal of temporomesial structures
- Evidence
- Against extended epileptogenic zone excision
- Because simple lesionectomies is the often good epileptological outcome seen after such surgery.
- 80% of patients with temporal low grade tumours and epilepsy will become seizure- free following gross total tumour resections (Englot et al., 2012).
- The preservation of neurological function
- Even in experienced hands temporomesial resections carry a quite low but nevertheless measurable risk of hemiparesis, dysphasia, and significant visual field cuts.
- Neuropsychological outcomes following surgery for temporal lobe epilepsy may be better following more restricted resections when compared to temporal lobectomies (Schramm, 2008).
- Experience suggests that dominant hippocampal surgery may carry higher risks for neurocognitive deterioration (e.g. memory deficits).
- Resection of MR imaging and histopathologically negative hippocampal tissue carries a significant risk for memory impairment (especially if the dominant hemisphere is involved), while patients with a diseased hippocampus have deficits usually already before surgery and memory deterioration is less frequent (Helmstaedter et al., 2011).
- More extensive hippocampal resections did not result in better epileptological outcomes
- Schramm et al., 2011: RCT n=207 with mesial temporal lobe epilepsy (>95% due to mesial temporal lobe sclerosis)
- For extended epileptogenic zone excision
- More patients may become seizure- free if a hippocampectomy and/ or corticectomy in addition to a gross total resection is performed (86– 87% as compared to 79% according to a recent survey) (Englot et al., 2012).
- Of note, these figures likely underestimate the impact of extended resections on seizure outcomes, since cases with more difficult epilepsy will probably more often undergo more extensive surgeries.
- The appropriate surgical strategy will have to take into account the pathophysiology of the epilepsy.
- Patients with pharmacoresistant epilepsy and glioneuronal LEATs not uncommonly harbour additional epileptogenic pathologies such as:
- Cortical dysplasias
- Can be found in association with up to a quarter of gangliogliomas and are even more frequently together with DNTs (Thom et al., 2012).
- Additional hippocampal sclerosis may be seen in LEAT cases
- Tumours may not only cause seizures through pressure on and irritation of surrounding brain (the rationale behind the concept of a simple lesionectomy).
- Tumour-associated seizures may commonly originate in the border zone (sometimes termed ‘collision zone’) between the tumour and surrounding normal brain, as well as distant brain areas as evidenced, for example, by ECoG recordings (Zaghloul and Schramm, 2011).
Tailored temporal lobe resections
- Are directed by the results of the initial stage of depth or subdural grid electrode invasive monitoring.
- Because the cases typically involve discordant non-invasive findings, they are more likely to demonstrate complex pathologic findings, including
- Purely lateral temporal lesions such as cortical dysplasia, tumours, vascular malformations
- “Dual pathology” of mesial temporal sclerosis plus another lesion, or
- The absence of any definitive pathologic etiologic diagnosis.
Amygdalohippocampectomy or Selective amygdalohippocampectomy (SAH)
- More targeted mesial temporal resections that spared temporal neocortex
- Were envisioned as possible means of providing equivalent seizure control with fewer neuropsychological sequelae
Topectomy
- Resection of cortex sparing underlying white matter
- Indication
- Resection that are tailored by the findings of invasive monitoring to include the epileptogenic lesion and the epileptogenic zone while sparing functionally eloquent cortical regions.
- Outcome
- Resection of epileptogenic cortex while incompletely removing the epileptogenic lesion is associated with a lower incidence of seizure control.
- On the other hand, resection of the lesion alone, whether tumour or vascular malformation, is associated with a lower incidence of seizure control than resection of the lesion plus surrounding epileptogenic zone.
- This surrounding epileptogenic zone may at times prove to contain cortical dysplasia on pathologic evaluation.
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