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27.10.2009
הדפס  
Magnetoencephalography (MEG) is suggested as a localizing technique of epileptogenic areas in drug-resistant seizure patients due to intracraneal lesions

Amo Seizure

Seizure 2003; 12: 19–22
doi:10.1016/S1059–1311(02)00148-6

Magnetoencephalographic localization of peritumoral temporal epileptic focus previous surgical resection

CARLOS AMO †, CRISTÓBAL SALDAÑA ‡, MERCEDES GONZÁLEZ HIDALGO §, FERNANDO MAESTÚ †, ALBERTO FERNÁNDEZ †, JUAN ARRAZOLA ¶& TOMÁS ORTIZ †

†Centro de Magnetoencefalograf´ıa, Universidad Complutense de Madrid, Madrid, Spain; ‡Servicio de Neurocirug´ıa, Hospital Cl´ınico San Carlos, Madrid, Madrid, Spain; §Servicio de Neurofisiolog´ıa, Hospital Cl´ınico San Carlos, Madrid, Madrid, Spain; ¶Servicio de Radiolog´ıa, Hospital Cl´ınico San Carlos, Madrid, Madrid, Spain

Correspondence to: Dr Tomás Ortiz, Centro de Magnetoencefalograf´ıa, Facultad de Medicina, Pabellón 8, Universidad Complutense de Madrid, Avenida Complutense s/n 28040 Madrid, Spain. E-mail:
cmeg@eucmos.sim.ucm.es

Magnetoencephalography (MEG) is suggested as a localizing technique of epileptogenic areas in drug-resistant seizure patients due to intracraneal lesions. A male 42-year-old patient who begins at 26 with partial complex drug-resistant seizures is put forward. MRI shows a 9 mm diameter lesion located in left superior temporal gyrus which seems compatible with cavernoma. Both conventional and sleep deprivation EEGs have proved normal. Sleep EEG shows sharp waves in left temporal region. MEG helps to localize interictal spike and spike-wave activity, as well as wide slow wave (2–7 Hz) activity areas. Craniotomy under analgesia and aware sedation conditions is carried out. Intrasurgery cortical electric stimulation assisted by neuronavigator causes a limited partial complex seizure which the patient recognizes to be exactly like his. Thus, MEG localization of the epileptogenic area is confirmed. Surgical resection of both the lesion and the epileptogenic area is carried out. The patient remains free from seizures 9 months after surgery. A control MEG study reveals no epileptogenic nor slow wave activity. Conclusion: in this particular case, MEG has proven to be a useful presurgical evaluation technique to localize epileptogenic activity, validated by intrasurgical cortical stimulation.

© 2002 Published by Elsevier Science Ltd on behalf of BEA Trading Ltd.

Key words: cavernoma; refractory epilepsy; magnetoencephalography; neurosurgery.


INTRODUCTION
Magnetoencephalography (MEG) is a technique which allows the registration of epileptogenic dis¬charges without distortion and with a high spatial (millimetres) and temporal (milliseconds) resolution, lessening other studies’ invasive degree1.Itisvery useful in cases in which EEG comes out to be un¬specific. Combining MEG results with MRI, its spa¬tial localizing capacity of the clinical or subclinical episode would be increased2.
Patients affected by epileptic seizures secondary to tumoral pathology can be susceptible of both tumor and epileptogenic area resection, which can be de¬limited by intrasurgical corticography and confirmed by cortical electrical stimulation. Both these intrasur¬gical techniques could validate MEG as a presurgery epileptogenic area localizing diagnosis method.
We describe a single case of partial complex re¬fractory seizures secondary to a left temporal lobe cavernoma. Surgical resection of the lesion and of the adjacent epileptogenic area localized by MEG and confirmed intrasurgically by electrical cortical stimulation derives into seizure-free results.

CLINICAL CASE
One 42-year-old patient affected by drug-resistant partial complex seizures. Clinical onset at 26 with
1059–1311/02/120019 + 04 $35.00/0 © 2002 Published by Elsevier Science Ltd on behalf of BEA Trading Ltd.
overnight episodes consisting of involuntary move¬ments of all four extremities, along with guttural sound emission and head torsion to the left. A year since, he presents daily episodes of speech arrest with onset difficulty which are followed by dysnomia and paraphasic language; no environmental disconnection or automatisms. Twice he had generalized seizures. From then on, he undergoes treatment on topiramate and carbamazepin, without any significant clinical changes.
Present treatment on topiramate (400 mg/day) and lamotrigin (200 mg/day) results in daily language dysfunction episodes (speech arrest, dysnomia or paraphasia) as well as environmental disconnection episodes.
Neurological examination was normal. Conven¬tional and sleep deprivation EEGs were normal. Sleep EEG showed isolated infrequent paroxystic discharges (sharp waves-slow wave) in left temporal region. MRI shows a 9 mm diameter intraparenchymatous lesion in left temporal gyrus, with a T1 heterogeneous inten¬sity signal (high intensity nucleus and low intensity surrounding ring), most likely corresponding to a cavernoma.
A magnetoencephalografic recording was carried out using a 148 channel whole-head MEG Magnes 2500 WH (4-D NeuroImaging Technologies, Inc., San Diego, CA) inside a magnetic shielded room. Simultaneous electroencephalogram (EEG), elec¬trocardiogram (EKG) and electrooculogram (EOG) electrodes were installed and registered during the
C. Amo et al.

MEG studies. EKG and EOG helped to spot arti¬facts, and conventional scalp EEG electrodes (10–20 international system) assisted in identifying sleep patterns3. During the run the patient remained awake with eyes closed, and no activation methods were employed. A 30 minutes run was acquired using a (0.1–100 Hz) band-pass filter and a 678.17 Hz sam¬ple rate. MEG and EEG data were digitized and filtered (1–70 Hz band-pass filter) for analysis. The signal analysis comprised visually selected seg¬ments which contained epileptogenic or slow wave activity free from artifact obtained from the MEG traces.

Interictal epileptogenic activity was registered in left MEG channels A95, A96, A113 and A114 (Fig. 1).The corresponding dipoles were localized in left su¬perior temporal gyrus, above and behind the lesion (Fig. 2).Slow wave 3–7 Hz activity was located in temporal and parietal regions next to the lesion (not shown in Fig. 2).
Left temporal craniotomy was carried out being the patient under local anaesthesia and aware sedation. Lesion’s anatomical and MEG functional data were in¬troduced into the navigator program. During surgery, a 2 mA electrical cortical stimulation was carried out, with 0.1 milliseconds duration 50 Hz stimuli bursts, and a total duration of 4 seconds4. When MEG epilep¬togenic location areas were stimulated (Fig. 2a), a lim¬ited partial complex seizure episode occurred, which the patient recognized as identical to his own previous seizure episodes. 

 
Fig. 1: Interictal epileptogenic activity in left MEG channels.
MEG pre-surgical localization of epileptic focus 

 
Fig. 2: MSI showing intraparenchymatous lesions in the left superior temporal gyrus. White triangles stand for epileptogenic
activity dipoles.

Complete resection of the lesion was made as well as of the adjacent area which seemed compatible with previous gliosis/bleeding along with superior temporal gyrus cortex concordant with ictal discharge areas. MEG postsurgery recording (1 month after surgery) shows no sign of slow waves nor epilepto¬genic activity. Nine months after surgery, the patient is in complete symptomatic remission (no postsurgi¬cal functional neurological sequel), seizure free and undergoing treatment on topiramate (400 mg/day) and lamotrigin (200 mg/day).


DISCUSSION
With regard to the cavernomas’ surgery, resection of the peripheral gliotic tissue along with the lesionec¬tomy is an option that improves associated seizure
C. Amo et al.

remission5. Reduction of the number of postsurgery seizure episodes is lower in drug-resistant epilepsy patients6. Also, a longer evolution time and a higher rate of seizure episodes worsen surgical results7. Thus, the sooner the cavernoma resection takes place the better it would be to prevent epileptogenic activ¬ity spreading to other areas and their development as autonomous epileptogenic foci8. For example, PET brain metabolism studies regarding perilesional regions adjacent to the resection, revealed a lower metabolism activity before and after surgery. The non-resection of these perilesional regions is related with poorer surgical results9. Presurgical study evaluates electroclinical, neuroradiological and tumor localiza¬tion correlation. In cases in which this correlation is not clear, different surgery strategies may be regarded (lesionectomy vs. wide resection)10. This is the reason why a more precise diagnose regarding epileptogenic areas’ resection would be very useful just as, for ex¬ample, intrasurgical electrocorticography facilitates irritable perilesional areas’ resection, resulting in total seizure suppression in up to 78% of the cases11.

In our particular case, despite the 16-year-evolution seizure episodes and the antiepileptic drug treatment resistance of the patient, total remission of these has been achieved. Thus, MRI fusion with MEG locat¬ing results and cortical stimulation has shown that the epileptogenic area was localized in the left superior temporal gyrus.


CONCLUSION
In this case, MEG has proven to be a valuable presur¬gical functional epileptogenic activity locating evalu¬ation test, validated by intrasurgical electrical cortical stimulation.


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