J Korean Neurosurg Soc 36 : 93-101, 2004
KISEP
Clinical Article
Parietal Lobe Epilepsy : Surgical Treatment and Outcome Chi Heon Kim, M.D.,1 Chun - Kee Chung, M.D.,1 Sang Kun Lee, M.D.,2 Yoon Kyung Lee, M.D.,3 Je G. Chi, M.D.3 Departments of Neurosurgery,1 Neurology,2 Pathology,3 Seoul National University College of Medicine; Clinical Research Institute, Seoul National University Hospital; Neuroscience Research Institute, Medical Research Center, Seoul National University, Seoul, Korea Objective : Parietal lobe epilepsy(PLE) is neither common nor easily diagnosed because of its variable clinical features. To elucidate its characteristics and surgical outcome, the authors review their surgical experiences. Methods : Between September 1994 and August 2001, 38 patients with parietal lobe epilepsy received surgical treatment at our Hospital. All patients underwent resection, mainly involving the parietal lobe. In most patients, preoperative evaluation included interictal and ictal electroencephalography, magnetic resonance image, positron emission tomography, and interictal and ictal single photon emission computed tomography. The male to female ratio was 23:15. Age at surgery ranged from 4 to 38 years (median, 25). Results : Preoperatively over 60% were considered not to be PLE, even though PLE was the most common (15/38, 39.8 %). The most common seizure type was complex partial seizure (26/38, 68.4%) rather than simple partial seizure (3/38, 7.9%). Invasive study was performed in 37 of the 38 patients. Monitoring duration was from 4 to 18 days (median, 8 days). Awake operations under regional anesthesia were performed in 20 patients (52.6%). Follow-up periods ranged from 14 to 81 months (mean, 50.7). Seizure disappeared in 15 (Engel’s classification I, 39.5%), and rare seizure remained in 5 (Engel II, 13.2%). Thirteen patients showed a worthwhile improvement (Engel III, 34.2%) and 5 no worthwhile improvement (Engel IV, 13.2%). Pathologies were diverse, the most common being cortical dysplasia (94.3%). Conclusion : Since PLE is difficult to diagnose preoperatively, an invasive study covering the parietal lobe is mandatory, if PLE is suspected. Cortical dysplasia was the most common etiology, thus awake operation under regional anesthesia and intraoperative brain mapping is helpful during extensive resection in order to spare the eloquent cortex. Using this protocol, PLE can be controlled surgically with a satisfactory result and a reasonably low level of complications.
KEY WORD : Parietal lobe epilepsy.
Introduction
Materials and Methods
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urgery for intractable epilepsy provides many patients not only with freedom or substantial relief from seizures, but also functional improvement and an increased quality of life 23). Parietal seizures account for 6% of all seizures, but the frequency of parietal lobe epilepsy(PLE) may be underestimated because of difficulties in its diagnosis, especially in cases with no structural lesion3,9,11,23,27). To elucidate the characteristics and surgical outcome of intractable epilepsy, the authors reviewed their surgical experiences. Received：March 11, 2004 Accepted：May 17, 2004 Address for reprints：Chun-Kee Chung, M.D., Department of Neurosurgery, Seoul National University College of Medicine, 28 Yeongeon-dong, Jongno-gu, Seoul 110-744, Korea Tel : 02) 760-3701 , Fax : 02) 744-8459 E-mail :
[email protected]
etween September 1994 and August 2001, 38 patients with parietal lobe epilepsy received surgical treatment at Seoul National University Hospital. All patients underwent resection involving the parietal lobe. We defined parietal lobe epilepsy not as ‘seizure occurred only in the parietal lobe’ but ‘seizure occurred mainly in the parietal lobe’. Clinical data and the imaging findings of 38 patients were reviewed. Information about aura and semiology were obtained by reviewing patients’ charts and by self-descriptions obtained from patients. We also reviewed data upon clinical features, which were prospectively maintained. Age at surgery ranged from 4 to 38 years (median, 25), and age at onset of seizure ranged from 3 months to 25 years (median, 10 years). Postoperative follow-up duration ranged from 14 to 81 months (mean, 50.7), and the male to female ratio was 23:15. VOLUME 36
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Preoperative diagnostic studies included ictal/interictal scalp-electroencephalography(EEG) monitoring, magnetic resonance(MR) imaging, photon emission tomography(PET), and ictal/interictal single photon emission computed tomography(SPECT), functional MR imaging and the Wada test. Seizure was classified according to the ILAE classification5). Video ictal EEG monitoring was performed in all patients and this data was reviewed. Mean duration of monitoring was eight days (4 to 18 days). Pre- and postoperative MR images were reviewed. Preoperative images were available in 27 patients, and postoperative MR images in 23. If images were not available, the neuroradiologist’s reading results were reviewed instead. According to these data, abnormalities in the ipsilateral parietal lobe occurred in 11/38 (28.9 %). Positron emission tomograph (PET) and ictal/interictal single photon emission computed tomography (SPECT) was also performed. Aura, semiology, MRI findings, and the result of PET and ictal/interictal SPECT were all analyzed to localize the seizure onset zone. Invasive study (subdural grid, strip insertion, and monitoring) covering the suspicious region was performed to all patients except one, and if the result was not diagnostic then a second invasive study was performed (12 of 37, 32.4%). A third invasive study was performed in one patient. Invasive study was not performed in one patient because of a discrete cystic lesion clearly visible by MRI and PET, showing decreased metabolism in this area. Mean duration of monitoring was 8 days (4 to 18). After mapping the seizure onset zone, extraoperative functional mapping via stimulation of the grid and strip was performed. Awake operation under regional anesthesia of the scalp and intraoperative brain mapping by electrical cortical stimulation was also performed in 20 patients, if the desired resection site was close to the motor or sensory cortex, or in the left parietal lobe. Resection was limited to the seizure onset zone and irritative zone, and the functional cortex as confirmed by intra/extraoperative brain mapping was saved. After resection of the seizure onset zone, anti-epileptic medication was continued and tapered-out according to seizure outcome during the follow up. The mapping protocol
tude of 17.5mA (isolated biphasic stimulator S12; Grass instrument; Massachusetts; USA, 1995). The physicians watched for any evidence of spontaneous changes such as muscle twitching, and the patient was asked to report if any somatosensory, visual, psychic, auditory, or other changes occurred. To define the language area, we presented the figures of common objects for naming and sentences for reading; these were used previously in the Wada test. Awake craniotomy
After administering fentanyl 50~100mcg intravenously, a scalp nerve block was done to supraorbital, supratrochlear, auriculotemporal, and to the lesser and greater occipital nerves on the surgical side with 0.25% bupivacaine containing 1:200,000 epinephrine. The incision site was infiltrated with the same local anesthetics. Oxygen was given by nasal cannula. During operation fentanyl was infused. Propofol was not infused until mapping was successfully performed. Invasive blood pressure, end-tidal CO2 and the respiratory rate were monitored throughout the operation and arterial blood gas analysis was performed intermittently. Intraoperative stimulation
Before the operation, information was offered regarding the reasons for an awake craniotomy and what would be done during that portion of period. The operating table was well padded. Both arms were positioned to be readily visualized by testing physicians. A support holding surgical drapes was prepared for the patient to see the test material or the physicians. Stimulation was delivered via grid electrodes or a stimulating probe. The electrical stimulation and testing methods were the same as those used for the extraoperative stimulation. Statistical analysis Outcome was subdivided as over and as less than a 90% seizure reduction. Factors that had influence on outcome were analyzed for using Pearson Chi-square and Fischer’s exact test. The Mann-Whitney test was used for analysis the influence of age at operation and the age at onset.
Results
Extraoperative stimulation
We utilized 0.3-msec pulses of alternating polarity with pulses of each polarity separated by 20 msec with 50-pulseper-second trains of 5 to 7 seconds duration. The starting amplitude was 1.5mA. We increased intensity in steps of 1mA, until functional changes were observed, or maximum ampli94 J Korean Neurosurg Soc 36
Preoperative work-up Seven patients had a history of head trauma, three patients had encephalitis, and two patients had meningitis. One patient had a history of birth trauma. Febrile convulsion was seen in 10 patients. A history of pre-term birth or febrile disease of an
CH Kim, et al.
unknown cause was obtained in one patient each. In 18 patients (47.4%), there was no remarkable preceding event. Thirty patients (78.9%) patients showed aura. Sensorimotor auras were seen in only 12 (31.6 %) patients. Among these, 2 showed bilaterally and one showed ipsilateral to the seizure onset zone. Thus, true somatosensory aura was seen in only 9 patients (23.7%). Motor aura was seen in only one patient (sense of weakness). A tingling sensation was the most common sensory aura followed by pain, a thermal sense, and numbness. Visual aura was seen in 5 patients : visual darkness in 2, flashing in 2, and diplopia in one. Oroalimentary aura (OAA) was seen in 4 and auditory hallucination in 2. A sense of fear, anxiety, a light headache, and a strange feeling were also noted. Some patients showed more than one aura. The most common seizure type was complex partial seizure (CPS : 26/38, 68.4%) rather than simple partial seizure (SPS : 3/38, 7.9%), and this was followed by generalized tonic clonic seizure (GTC : 5/38, 13.2%). More than one seizure type was showed by 4 patients (CPS and GTC, CPS and SPS, SPS and GTC). Secondary generalization was seen in 32 patients (84.2%). The most common presentation was tonic and/or clonic movement (32/38, 84.2%) contralateral to the seizure onset zone in 14, followed by bilateral in 17, and ipsilateral in one. Interestingly, automatism of oral, oroalimentary or of an extremity was seen in 18 patients, and behavioral arrest or a motionless staring in 12, suggesting the temporal lobe as a symptomatogenic zone. Other symptoms were head and/or eye version in 12, eye blinking in 4, laughing in one, a silly smile in one, head hobbing in one and fencing posture in one. Many patients showed more than two presentations; these findings implied a variable propagation pathway of the epileptic discharge. Data on interictal scalp (EEG) was available in all patients except one. Lateralization was possible in 25 patients, localization in 3, false lateralization in 3, normal in 3, and both hemispheres were lateralized in 3. Video-EEG results were available in all patients. Lateralization was possible in 31 patients, localization in 4, and neither lateralization nor localization in 3. Magnetic resonance imaging(MRI) revealed an abnormality in twenty-six 26 patients (68.4%). However, abnormalities involving the parietal lobe only were observed in 14 patients. Of these, 3 patients showed bilateral parietal cerebromalacia. Only 11 cases showed an ipsilateral parietal lesion. Other abnormalities were; hippocampal atrophy (HA) in 4, cortical atrophy in 3, hippocampal atrophy and cortical atrophy in 2, cortical atrophy and biventricular signal change in one, cortical dysplasia and cortical atrophy in one, and a tumorous lesion in
one. Of these 11 cases, 4 patients had a dual lesion and in 3 patients, hippocampal atrophy was accompanied (cortical atrophy+biventricular signal change, 1; bilateral cortical atrophy+HA, 1; cortical atrophy+HA, 2). One patient showed bilateral hippocampal atrophy. In positron emission tomography(PET) localization of the seizure onset zone was possible in 11 patients (28.9%) and lateralization in 15 patients (39.5%). False lateralization was seen in one patient and bilateral hypometabolism also in one. Ictal SPECT was performed in 28 patients. Localization was possible in 7 (25%), lateralization in 15 (53.6%), false lateralization in 2, bilateral hyperfusion in 3, and normal in one. Interictal SPECT was performed in 21 patients. Lateralization was possible in 7 (52.4%), localization in 8 (38.1%), no lateralization/localization was possible in one and another was falsely lateralized. With these data, preoperative diagnosis was variable. Initially, parietal lobe epilepsy (PLE) was diagnosed in 13 (39.8%). Of these, multilobar involvement was suspected in 2 (FLE+PLE, TLE+PLE). In nearly 60% of patients, other diagnoses (lateral TLE, 9; FLE, 6; OLE, 5; etc.) were made preoperatively. Surgical approach and complication Surgical resection was performed in all patients, and included the parietal lobe. The majority of patients underwent invasive study (subdural grid and strip insertion, and and ictal EEG monitoring) (37 of 38, 97.4%), because in most patients, the exact location of the epileptogenic zone was unsure by EEG, MRI, PET, and ictal/interictal SPECT. Moreover, the seizure onset zone is close to the eloquent sensory motor and language areas, so it is mandatory to verify functional brain mapping via electrical stimulation to the inserted grid and strip to prevent or minimize morbidity and neurological deficit. One patient showed a discrete cystic lesion on the right superior parietal lobe, and PET localized this lesion, so invasive study was not performed. Invasive study was performed twice in 12 and three times in one. After extraoperative mapping of the seizure onset zone and functional brain mapping, an awake operation under general anesthesia was performed in 20 patients (52.6%). Motor and sensory, language, and right/left orientation were monitored intraoperatively. Resection included the whole extent of the visible lesion, if present, or the whole ictal onset zone and irritative zone, bounded by sulci or the functional cortex. Underlying white matter was resected if feasible. During and after resection, intraoperative mapping was performed intermittently to ensure that the functional cortex was preserved. The operation was performed twice in one patient due to recurred seizure (refer to the illustrative case VOLUME 36
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Table 1. The site of resection (n=38) The site of surgery Right P T-P F-P-T F-P P-O F + P* T + P* ATL + P* ATL + P-T* Left P P-O P-O-T F-P ATL + P-O* F + P + corpus callosotomy*
number 6 3 2 1 1 2 2 1 1 10 3 2 2 1 1
* dual pathologies P : parietal lobectomy, lobulectomy, or gyrectomy. O : resection including some portion of occipital lobe. T : resection including some portion of temporal lobe. F : resection including some portion of frontal lobe. ATL : anterior temporal lobectomy. AH : amygdalohippocampectomy
below). Right parietal resection was performed in 19 patients and left in 19. Sixteen patients received parietal resection only, and the remaining received resection of other lobes also. Accompanying resection sites were temporal (12), followed by frontal (8) and occipital (7). A double lesion was occurred in 8 patients (Table. 1). Complications occurred postoperatively in 20 patients (52.6%). The most common complication was visual field defect (10 of 38, 26.3%). If visual field defect was considered an unavoidable side effect rather than a complication, complications were found in 15 (39.5%). Sensory motor complications occurred in 7 patients and 3 patients showed a permanent motor complication. Left hand weakness (motor grade III/V) after right fronto-parieto-temporal resection was noted in one and permanent right hemiparesis (motor grade III/V) after left temporo-parietal resection in one. Unfortunately, although extraoperative functional mapping was performed, intraoperative functional mapping was not possible in these two children, because of poor cooperation. However, permanent slight right leg weakness (motor grade IV/V) occurred after left parietal resection by an awake operation in one child; she was able to walk independently, but complained of difficulty in running. Transient dysarthria developed in two patients after left fronto-parietal and left parietal resection, respectively. Transient Gerstman’s syndrome was seen after left parietal resection under an awake operation in one. Postoperative epidural hemorrhage was detected in two patients and surgical infection in two. There was one case of delayed hydrocephalus development, which caused hemiparesis and was resolved with a shunt. There was no operative mortality, however, one patient expired 14 months after the operation due 96 J Korean Neurosurg Soc 36
Table 2. Pathologic classification (n=38) Pathology CD mild CD moderate CD severe PXA + CD mild ODG + CD mild ODG Chronic non-specific inflammation No biopsy
Number 14 4 13 1 1 1 1 3
CD : cortical dysplasia. ODG : oligodendroglioma. PXA : pleomorphic xanthoastrocytoma
Table 3. Cortical dysplasia and outcome Engel class I Mild Number 4 % of total 12.9 Moderate Number 2 % of total 6.5 Severe Number 9 % of total 29
II 1 3.2 0 0 1 3.2
III 7 22.6 2 6.5 2 6.5
IV 2 6.5 0 0 1 3.2
Total 14 45.2 4 12.9 13 41.9
to status epilepticus. With antiepileptic medication, her seizures had improved (Engel III). However, she had not taken her meications for 2 months before the onset of status epilepticus. Pathology and outcome Pathology was available in 34 patients (Table 2). Cortical dysplasia was the most common pathologic finding (33 of 35, 94.3%). The pathological severity of cortical dysplasia was classified according to Mischel15). Mild cortical dysplasia was present in 16, moderate in 4, and severe in 13. Among these 33, two cases showed mild cortical dysplasia around a tumorous lesion (pleomorphic xanthoastrocytoma and oligodendroglioma). One case showed oligodendroglioma without surrounding cortical dysplasia. Cortical dysplasia only occurred in 31 patients. Among these, only 17 patients (54.8%) showed an MRI abnormality. There was one case of chronic nonspecific inflammation, probably related to a previous head injury. Postoperative follow-up was possible in all patients and duration ranged from 14 to 81 months (mean, 50.7). The results of epilepsy surgery were grouped as seizure free, rare seizure, worthwhile improvement, and no worthwhile improvement, according to Engel’s classification’s I, II, III, and IV. At the last follow-up visit, seizures had disappeared in 15 patients (Engel’s classification I, 39.5%) and seizures were rare in 5 (Engel’s classification II, 13.5%). Thirteen patients showed worthwhile improvement (Engel’s classification III, at least a 90% improvement in seizure frequency versus preoperative status; 34.2%) and 5 showed no worthwhile improvement (Engel’s classification IV, 13.5%). Cortical dysplasia only was shown by 31 patients (Table. 3). In 3 patients with a tumor, one was Engel
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Table 4. Factors versus outcome (P
