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Neurosurgery:
doi: 10.1227/NEU.0000000000000241
Research-Human-Clinical Studies

Fifty Consecutive Hemispherectomies: Outcomes, Evolution of Technique, Complications, and Lessons Learned

Lew, Sean M. MD*; Koop, Jennifer I. PhD; Mueller, Wade M. MD*; Matthews, Anne E. PA-C*; Mallonee, Julianne C. BSN*

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Author Information

*Department of Neurosurgery, and

Department of Neurology, Medical College of Wisconsin, Milwaukee, Wisconsin

Correspondence: Sean M. Lew, MD, FACS, Children's Hospital of Wisconsin, 999 N 92nd St, Ste 310, Milwaukee, WI 53226. E-mail: slew@mcw.edu

Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.neurosurgery-online.com).

Received May 31, 2013

Accepted October 28, 2013

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Abstract

BACKGROUND: Techniques for achieving hemispheric disconnection in patients with epilepsy continue to evolve.

OBJECTIVE: To review the outcomes of the first 50 hemispherectomy surgeries performed by a single surgeon with an emphasis on outcomes, complications, and how these results led to changes in practice.

METHODS: The first 50 hemispherectomy cases performed by the lead author were identified from a prospectively maintained database. Patient demographics, surgical details, clinical outcomes, and complications were critically reviewed.

RESULTS: From 2004 to 2012, 50 patients underwent hemispherectomy surgery (mean follow-up time, 3.5 years). Modified lateral hemispherotomy became the preferred technique and was performed on 44 patients. Forty patients (80%) achieved complete seizure freedom (Engel I). Presurgical and postsurgical neuropsychological evaluations demonstrated cognitive stability. Two cases were performed for palliation only. Previous hemispherectomy surgery was associated with worsened seizure outcome (2 of 6 seizure free; P .005). The use of Avitene was associated with a higher incidence of postoperative hydrocephalus (56% vs 18%; P = .03). In modified lateral hemispherotomy patients without the use of Avitene, the incidence of hydrocephalus was 13%. Complications included infection (n = 3), incomplete disconnection requiring reoperation (n = 1), reversible ischemic neurological deficit (n = 1), and craniosynostosis (n = 1). There were no (unanticipated) permanent neurological deficits or deaths. Minor technique modifications were made in response to specific complications.

CONCLUSION: The modified lateral hemispherotomy is effective and safe for both initial and revision hemispherectomy surgery. Avitene use appears to result in a greater incidence of postoperative hydrocephalus.

ABBREVIATIONS: EEG, electroencephalography

FSIQ, Full Scale Intelligence Quotient

MCA, middle cerebral artery

MLH, modified lateral hemispherotomy

In 1938, the Canadian neurosurgeon K.G. McKenzie reported results from the first hemispherectomy performed for epilepsy.1 The first series of patients was reported by Krynauw2 in 1950, who described 12 children with infantile hemiplegia who underwent anatomic hemispherectomies for epilepsy or “mental changes.” In this series, all surviving patients with epilepsy demonstrated seizure freedom (there was 1 unexplained immediate postoperative death). Although effective for treating seizures, early hemispherectomy surgery was associated with significant morbidity and mortality.2-8 Over time, it became clear that a substantial number of patients were suffering long-term problems related to repeated hemorrhages into the large resection cavities and subsequent superficial cerebral hemosiderosis.3,4,6,9 By 1968, Rasmussen6,7 began to leave up to one-third of the epileptogenic hemisphere intact, which effectively eliminated superficial hemosiderosis at the cost of decreased seizure efficacy. This evolved into Rasmussen's7 initial description of functional hemispherectomy involving a combination of resection and disconnection of the diseased hemisphere in 1983.

Since that time, the evolutionary line for hemispherectomy surgery has branched considerably. Experienced epilepsy centers now perform a wide variety of techniques, including traditional anatomic hemispherectomies, Rasmussen-style functional hemispherectomies, perisylvian hemispherotomies, and hemicorticectomies, each with its own variations, twists, pros, and cons. There is no clear optimal technique, and comparing outcomes between techniques is fraught with difficulties because of variations in patient selection, surgical experience, and outcome metrics. Nevertheless, every published series adds to the common knowledge and moves the field forward. The purpose of this study is to share the results from the first 50 consecutive hemispherectomies from a single surgeon with an emphasis on outcomes, predictors of seizure control, postoperative hydrocephalus, complications, and how these results led to practice modifications.

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PATIENTS AND METHODS

Study Design

An institutional review board-approved review was undertaken of the first 50 consecutive pediatric hemispherectomy surgeries performed by the lead author (S.M.L.) between September 2004 and May 2012. For the first year of this time period, surgeries were performed with the senior author (W.M.M.) as a cosurgeon. A prospectively maintained database was used, as were individual chart reviews for additional data collection. Preoperative data included general demographics, seizure history, cause of epilepsy, prior surgical history, magnetic resonance imaging (MRI) findings, electroencephalography (EEG) findings, neuropsychological evaluations, and goals of surgery (palliative vs seizure freedom). Data were collected on surgical technique, time, and blood loss for each procedure. Follow-up data were available for all patients and included seizure outcome, neuropsychological evaluations, histology results, and complications. The follow-up time period and seizure outcome were determined from the last clinical encounter.

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Patient Selection

The preoperative workups were tailored to each patient. All patients underwent video-EEG monitoring and MRI. Noninfant patients had preoperative neuropsychological evaluations. Other diagnostic studies performed in some but not all patients included single-photon emission computed tomography, positron emission tomography (PET), magnetoencephalography, functional MRI, and Wada tests. All cases were formally reviewed at a multidisciplinary epilepsy conference before hemispherectomy surgery was offered. Two patients were identified preoperatively as palliative cases; for the remaining 48 patients, the goal of surgery was seizure freedom. One patient with cortical dysplasia underwent placement of intracranial electrodes before her resection; the remainder of the patients had single-stage procedures. One other patient with cortical dysplasia underwent a posterior quadrantectomy followed by intraoperative electrocorticography, which prompted conversion to a hemispherectomy (all done as a single surgical procedure). This was the only case that used intraoperative electrocorticography. Of note, 1 patient (who had not had prior epilepsy surgery) underwent a modified lateral hemispherotomy (MLH) that was deemed incomplete on her postoperative imaging (see Case Illustration 2) and during the same hospitalization returned to surgery to complete the procedure. This patient was categorized as not having prior epilepsy surgery for purposes of outcome analysis despite the 2 procedures.

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Neuropsychological Evaluations

To characterize cognitive outcomes related to hemispherectomy, presurgical and postsurgical neuropsychological evaluations were planned for each patient. When a patient's level of functioning allowed, a full battery of neuropsychological measures assessing general intellectual abilities, fine motor skills, attention, executive functioning, language skills, visual-spatial skills, memory, academic achievement, and adaptive functioning were administered. A measure of general intellectual abilities was administered to all patients within this sample. Because of the variability of functioning and age within the patient population, a number of different measures were used to assess each patient’s overall level of cognitive functioning. The measures used included a version of the Wechsler Intelligence Scale for Children (version III or IV),10,11 the Wechsler Adult Intelligence Scale (version III),12 a version of the Differential Abilities Scale (original or version II),13 Mullen Early Learning Scales,14 or the Stanford-Binet Intelligence Scales.15 Each of these measures provides an overall score consistent with the Full Scale Intelligence Quotient (FSIQ) calculated on Wechsler measures. Adaptive behavioral functioning was measured with the structured interview format of the Vineland Adaptive Behavior Scales,16 which also provides an overall composite score. The resulting composite score for both the FSIQ and adaptive behavior measures is a standard score with a mean of 100 and a standard deviation of 15.

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Surgical Techniques

The first 5 surgeries in this series were either Rasmussen-style hemispherectomies7,17 or anatomic hemispherectomies.2,8 As a result of a general dissatisfaction with these techniques, the MLH was adopted as the technique of choice. Aside from a single additional anatomic procedure performed for a revision hemispherectomy, all subsequent hemispherectomies, including 3 revision hemispherectomies, were done with the MLH technique. This technique was initially described by Cook et al18 in 2004 and is derivative of the peri-insular hemispherotomy techniques described by Schramm et al19,20 and Villemeure and Mascott21 in the 1990s. The features that distinguish this technique from peri-insular hemispherotomy techniques are sacrifice of the middle cerebral artery (MCA) to facilitate hemostasis, thus limiting blood loss; resection of a central opercular block of tissue to provide generous exposure of the ventricular system and removal of the insula with portions of the basal ganglia and thalamus; and resection of the anterior temporal lobe. At our institution, minor modifications have been made to the technique initially described by Cook et al.18 The osteoplastic craniotomy is considerably smaller, with the superior extent at the superior temporal line rather than the midpupillary line. We have found that we do not require visualization of anything outside the ventricular system. We forgo the orbitofrontal cortex resection that was performed as part of the deep frontal disconnection. The frontal disconnection is now made with the proximal anterior cerebral artery (visible through the arachnoid at the base of the genu of the corpus callosum) used as a landmark to create a disconnection sufficiently posterior to avoid leaving connected mesial basal posterior frontal tissue (Figure 1). A complete detailed description of the MLH procedure is included in Supplemental Digital Content 1, http://links.lww.com/NEU/A593. The same principles of this technique were applied to patients with previous epilepsy surgery, including 3 patients with previous hemispherectomies performed elsewhere. In these cases, preoperative imaging was scrutinized for evidence of retained connected ipsilateral brain, which was then targeted for disconnection. Frameless stereotactic navigation is not routinely used but is reserved for patients with a history of prior surgery affecting the normal anatomic landmarks or distorted baseline ventricular anatomy.

Figure 1
Figure 1
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Statistical Analysis

Associations between categorical variables were made by use of the Fisher test, exact Pearson χ2 test, or exact Mantel-Haenszel χ2 tests, and the Jonchheere-Terpstra test for ordinal-by-continuous comparisons (Engel score and age/time). Comparisons of continuous variables were made with the Wilcoxon rank-sum test (some exact), Spearman correlation, or paired t test for change in FSIQ scores. Multivariate logistic regression was performed to examine the simultaneous effect of variables on seizure outcome. For this analysis on dichotomized Engel score (I vs II, III, or IV), 2 palliative cases were excluded (because these surgeries were already expected to have poor seizure outcome). For the examination of risk factors related to the development of hydrocephalus, the 7 patients with preexisting hydrocephalus were excluded. A value of P < .05 was prospectively determined to indicate a significant difference. Standard deviations were presented with means as mean ± SD unless otherwise specified. The analysis was performed with SAS version 9.3 (SAS Institute, Cary, North Carolina).

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RESULTS

General

Causes of epilepsy, additional diagnoses, and previous epilepsy surgeries are listed in Table 1. The cause of epilepsy of the 1 patient listed as tumor/radiation therapy requires some explanation. This patient underwent resection of a large left hemisphere atypical teratoid/rhabdoid tumor at the age of 13 months. He underwent a second resection coupled with intracavitary radiation shortly thereafter. At the age of 2 years, he developed medically refractory epilepsy, and he underwent hemispherectomy surgery at the age of 3 years.

Table 1
Table 1
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The mean age at time of surgery was 9.1 years (range, 2.5 months-16.9 years). The mean age at onset of seizures was 2.1 years (range, 3 days-21.2 years), with a mean duration of seizures before surgery of 7.0 years (range, 7 months-20.2 years). The mean operative time was 260 minutes (range, 126-498 minutes) with a mean estimated blood loss of 340 mL (range, 25-1000 mL). There was a trend for decreased blood loss and operative time with experience. For the last 10 procedures (all MLH technique), the mean operative time was 208 minutes (range, 166-272 minutes) with a mean estimated blood loss of 218 mL (range, 50-650 mL). The mean follow-up period was 3.5 years (range, 3 months-7.5 years).

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Palliative Cases

Forty of the 50 patients (80%) achieved seizure freedom (Engel I). Two patients in this series were identified preoperatively as candidates for hemispherectomy for palliation only, without a chance of complete seizure freedom. Their families were counseled as such. Both patients had preexisting motor deficits, catastrophic epilepsy, and seizures predominantly (but not solely) arising from a single hemisphere. The first patient was a 10-year-old boy with a history of infantile spasms, Lennox-Gaustaut syndrome, microcephaly, cortical visual loss, spastic quadriparesis, status post—vagal nerve stimulator placement at the age of 22 months, and a complete corpus callosotomy at 8 years of age. At the time of surgery, he was on felbamate, valproic acid, and clorazepate, with >25 tonic seizures per day. Semiology for most of his seizures after the callosotomy involved tonic extension of the right upper extremity first. His workup demonstrated generalized ictal discharges, with >90% of interictal discharges from the left hemisphere. A left MLH was offered and performed. Histology revealed widespread diffuse dysplasia consistent with Palmini IIA and IIB changes but not focal. Hippocampal sclerosis was also present. At the last follow-up (9 months postoperatively), he was having 1 to 3 seizures a day (Engel IIIA).

The second palliative case involved a 5-year-old boy born prematurely at 33 weeks with a left MCA perinatal stroke. Long-term video-EEG monitoring revealed predominantly left-sided seizures but clear independent right-onset seizures as well. He also demonstrated severe developmental delays (nonverbal and nonambulatory) that suggested right hemispheric dysfunction. He was averaging 5 seizures a day on valproic acid, levetiracetam, clonazepam, lacosamide, and felbamate. A left MLH was performed for palliation. He had several generalized seizures in the first month after surgery. At his most recent follow-up, 12 months after surgery, he was having only rare simple partial seizures (Engel IIC) while on 3 antiepileptic medications.

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Nonpalliative Cases

Of the remaining 48 nonpalliative cases, 40 (83%) resulted in seizure freedom (Engel I). An additional 4 patients (8%) achieved an Engel II outcome, whereas 4 patients (8%) continue to have a significant seizure burden (3 Engel III, 1 Engel IV). Multiple variables were tested as possible determinants of seizure outcome. Age and duration of seizures did not correlate with seizure outcome (Table 2). Preoperative MRI findings can be found in Table 3. All reported findings are for MRIs that preceded any cranial surgeries. Presurgical imaging was not available for 1 patient who underwent a revision MRI after prior surgery elsewhere. The majority of patients had diffuse MRI abnormalities involving the affected side. However, none of the MRI findings were found to correlate with seizure outcome (Table 3). Preoperative EEG findings, seizure semiology, and their relation to seizure outcome are presented in Table 4. Although no correlations reached statistical significance, the presence of bilateral synchrony trended toward significance as a predictor of worsened seizure outcome (P = .07).

Table 2
Table 2
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Table 3
Table 3
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Table 4
Table 4
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The relationships between cause of epilepsy, prior surgical history, hemispherectomy technique, and outcome are demonstrated in Table 5. There was no significant correlation detected between cause and outcome (P = .67), with infarct (50%) and malformations of cortical development (25%) making up the majority. Within the malformations of cortical development group, 2 patients had hemimegalencephaly, both achieving Engel I outcomes.

Table 5
Table 5
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Twelve of the nonpalliative cases had prior cranial surgery. Six of them were prior hemispherectomy procedures performed by other surgeons. The first 3 revision hemispherectomies were performed as anatomic hemispherectomies (Engel outcomes: II, III, and IV), and the last 3 were done with the MLH technique with disconnections primarily of suspected connected tissue (Engel outcomes: I, I, II). Prior resective surgery was associated with worsened outcome (P = .005; Table 5). Pairwise comparisons indicated that the difference was likely related to the previous hemispherectomy group (previous hemispherectomy vs none, P = .006; nonhemispherectomy resection vs none, P > .99; Table 5). However, a clear significant difference could not be shown between the nonhemispherectomy resection group and the previous hemispherectomy group (P = .15; Table 5).

Hemispherectomy technique was a significant predictor of outcome, with anatomic hemispherectomies showing worsened outcome (P = .005; Table 5). However, 3 of the 4 anatomic hemispherectomies performed were revision procedures on patients with previous hemispherectomies. A multivariate analysis was performed that showed that neither bilateral synchrony (P = .11) nor hemispherectomy technique (P = .22) was a significant predictor when controlling for previous resective surgery. Previous resective surgery was the sole predictor of seizure outcome in the multivariate analysis.

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Unfavorable Seizure Outcomes

Eight of the 48 patients targeted for seizure freedom had persistent seizures (4 Engel II, 3 Engel III, 1 Engel IV). Four of these patients had previous hemispherectomies (2 Engel II, 1 Engel III, 1 Engel IV). Two of the remaining 4 had malformations of cortical development. The first was a 13-month-old girl status post—prior left temporal and parieto-occipital resections who achieved a class IIC outcome on 2 antiepileptic medications (follow-up, 5.0 years). The second patient was a 15-month-old boy with infantile spasms beginning at 4 months of age. He developed medically refractory complex partial right-sided seizures and a mild left hemiparesis. His brain MRI was normal, but PET imaging showed diminished signal in the right frontal and temporal lobes. He underwent a right MLH. Histology showed focal cortical dysplasia (type 1A). Postoperatively, he began to demonstrate left-sided seizures on EEG in addition to generalized events, although with markedly reduced frequency (follow-up, 1.5 years; Engel IIIA). The 2 remaining patients had infarcts as the cause of their epilepsy. The first patient was an 11-year-old girl with a congenital large right porencephalic cyst, shunted hydrocephalus, cortical blindness, spastic diplegia, and left hemiparesis. Seizure onset was at 16 months of age. Her preoperative video-EEG showed right-sided seizure onset but bilateral synchrony. She underwent a right MLH with a subsequent Engel IID outcome (nocturnal seizures only). Her postoperative MRI showed completed disconnections. A video-EEG study 6 years after surgery documented left-sided seizure onset. The second patient was a 12-year-old boy who suffered an anoxic/hypotensive injury associated with a home birth with a left MCA infarct. His preoperative video-EEG showed clinical symptoms that preceded bihemispheric slowing, leading to right greater than left bursts of 9- to 12-Hz activity. The activity would become more generalized over the right hemisphere and then engage the left. His right hemisphere appeared normal on MRI and PET. He underwent a left MLH, which resulted in improved but not absolute seizure control (follow-up, 6 months; Engel IIIA).

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Cognitive Evaluations and Outcomes

Preoperatively, forty-six children (92%) underwent presurgical neuropsychological evaluations at a mean age of 8.3 ± 4.9 years. Of the 46 patients tested, 22 (48%) were able to complete more comprehensive neuropsychological evaluations. Three patients were too low functioning for calculation of an FSIQ, with an estimated level of cognitive functioning at approximately a 2-year age equivalency level. The mean preoperative FSIQ for the remaining 43 patients was 59.3 ± 11.7, which is in the mild range of mental retardation or intellectual disability. However, there was significant variability in levels of functioning, with a range from 36 (profound intellectual disability) to 83 (low average). Of those who completed a Vineland Adaptive Behavior Scales (n = 28), the mean composite score was 58.2 ± 17.1, which also is within the mild range of intellectual disability (range, 24-84). Twenty-four patients (52%) demonstrated generalized cognitive dysfunction; however, the subset of the patients (n = 22, 48%) who were relatively higher functioning demonstrated a cognitive profile suggestive of lateralized cognitive dysfunction. That is, the pattern of strengths and weaknesses observed on testing indicated greater impairment in cognitive abilities that are typically attributed to the dominant/usually left (ie, language skills) or nondominant/usually right (ie, visual-spatial or nonverbal skills) hemispheres. This pattern of lateralized dysfunction was generally consistent with the side of seizure focus and planned surgery: Those with greater dysfunction lateralized to the right hemisphere underwent right hemispherectomies (10 of 10, 100%), and those with greater left-sided dysfunction underwent left hemispherectomies (11 of 12, 92%). Concordant cognitive lateralization did not correlate with seizure outcome (Spearman correlation, P = .47). It is important to note, however, that a significantly greater proportion of those with greater left-hemisphere dysfunction were also presumed to have undergone functional reorganization on the basis of their neuropsychological profiles (90.9% vs 0%; Fisher exact test, P < .001). Functional reorganization is presumed to have taken place if an individual demonstrates intact or stronger functioning within cognitive domains that typically are lateralized to the hemisphere of known greater dysfunction.

Twenty-nine patients underwent a postsurgical evaluation. One patient was too low functioning for calculation of an FSIQ, with an estimated level of cognitive functioning at approximately a 2-year age equivalency level. The mean FSIQ for the remaining 28 patients was 62.7 ± 15.4, which again was within the mild range of intellectual disability. There was significant variability with a range from 42 (severe intellectual disability) to 97 (average). Of those who completed a Vineland Adaptive Behavior Scales (n = 14), the mean composite score was 62.7 ± 17.7, which also is within the mild range of intellectual disability (range, 27-91).

Twenty-seven patients completed both the presurgical and postsurgical evaluations (Table 6). For this subset, the mean FSIQ was 63.9 ± 9.9 before hemispherectomy and 61.4 ± 14.1 after hemispherectomy. On an individual patient basis, 21 patients (78%) demonstrated relative stability of level of cognitive functioning (postoperative performance within 1 SD of preoperative), 1 (4%) demonstrated a significant gain (>1 SD), and 5 (19%) demonstrated a significant decline (>1 SD). (For individual presurgical and postsurgical changes, found in Supplemental Digital Content 2 (see Figure, http://links.lww.com/NEU/A594), which shows presurgical and postsurgical full-scale IQ scores in the patients who underwent testing for both [n = 27].) However, group-level analysis revealed that the difference between the presurgical and postsurgical FSIQ was not significant (P = .27). No preoperative variables were identified that correlated significantly with change in IQ after surgery (Table 6).

Table 6
Table 6
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Postoperative Hydrocephalus

Seven of the 50 hemispherectomy patients had preexisting hydrocephalus. Of the remaining 43 patients, 11 (26%) developed hydrocephalus and underwent subsequent shunt placement. Several variables were analyzed as possible factors contributing to hydrocephalus. Variables analyzed included cause of epilepsy, prior surgery, surgical technique, surgical time, use of Avitene (microfibrillar collagen hemostat; Davol, Warwick, Rhode Island) as a hemostatic agent, and cerebrospinal fluid profiles (cell counts and protein levels) sampled from external ventricular drains in the first 2 days after surgery (Table 7). The use of Avitene was the only significant predictor of future hydrocephalus, with an odds ratio of 5.8 (95% confidence interval, 1.2-28.4; P = .03). Hydrocephalus occurred in 56% of the cases (5 of 9) when Avitene was used and 18% of the cases (6 of 34) without Avitene. Within the MLH cohort, hydrocephalus occurred in 5 of 7 cases (71%) with Avitene and 4 of 31 cases (13%) without Avitene. Unfortunately, for the earlier cases in the series, including almost all of the non-MLH hemispherectomies, postoperative cerebrospinal fluid sampling was not performed. This and the limited sample size prevented meaningful multivariate analysis.

Table 7
Table 7
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Complications

There were no (unanticipated) permanent neurological deficits or deaths. One patient early in the series developed a reversible ischemic neurological deficit involving the contralateral hemisphere (Illustrative Case 1). One patient had a reoperation in the immediate postoperative period to address a missed disconnection (Illustrative Case 2). Three patients (6%) developed wound infections in the postoperative period. Two of these patients had prior craniotomies from previous resections and were treated with antibiotics and bone flap removal with subsequent cranioplasty. The third infection was in a patient without prior surgery who underwent an MLH (with an osteoplastic bone flap). This infection was successfully managed with drainage of a subgaleal abscess and antibiotics without removal of the bone flap.

The youngest patient (10 weeks old) in this series developed contralateral coronal craniosynostosis postoperatively. The details of this case have been previously reported.22 The patient had undergone a posterior quadrantectomy that was converted to a hemispherectomy under the same anesthesia after intraoperative electrocorticography revealed persistent epileptiform activity. The craniosynostosis was postulated to be due to the substantial volume loss created by the posterior quadrantectomy. As a result of this case, we have adopted disconnective procedures for posterior quadrantectomies.23

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ILLUSTRATIVE CASES

Case 1: Epidural Drainage

Patients undergoing MLH typically develop an epidural hematoma that is of no clinical significance. Early in this series, an epidural drain was attempted to prevent this occurrence, with unfavorable results. The patient was a 10-year-old girl born prematurely with grade IV intraventricular hemorrhage and subsequent shunted hydrocephalus, left hemiparesis, and intractable seizure onset during infancy. A comprehensive workup led to a right MLH. At the end of the procedure, in addition to the usual external ventricular catheter placed in the resection cavity, an epidural drain (10F) was placed to bulb suction. She emerged from anesthesia with seizures, new right-sided weakness, and increased tone. The epidural drain was removed from bulb suction and the seizures promptly ceased. An immediate MRI revealed increased T2 and fluid-attenuated inversion recovery signal in the contralateral thalamus with midline shift toward the resection cavity (Figure 2). She recovered to baseline status over the ensuing month with resolution of the thalamic T2/fluid-attenuated inversion recovery hyperintensity on a 6-month follow-up MRI. She has remained seizure free since the immediate postoperative period (follow-up, 7 years). We have since avoided the use of negative pressure drains in the epidural space in any craniotomy involving a sizeable resection cavity.

Figure 2
Figure 2
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Case 2: Use of Navigation

The patient was an 11-year-old girl born prematurely at 25 weeks with a large left grade IV intraventricular hemorrhage and subsequent shunted hydrocephalus and right hemiparesis. She developed seizures at 2 years of age with frequent simple and complex partial seizures and frequent bouts of status epilepticus, refractory to medical therapy. Video-EEG monitoring, PET scan, and seizure semiology implicated the left hemisphere. Her MRI demonstrated left cerebral atrophy, corpus callosum dysgenesis, and slit ventricles of atypical morphology (Figure 3). Intraoperatively, the left frontal horn was indistinct and the callosal disconnection was created too laterally, leaving mesial frontal tissue connected. She had seizures in the immediate postoperative period, and a reoperation was performed on postoperative day 5 to complete the callosal disconnection with the aid of frameless stereotactic navigation. She remains seizure free after this procedure (2.5-year follow-up, Engel IA). Since this case, our practice has been to use navigation in patients with distorted or atypical ventricular anatomy.

Figure 3
Figure 3
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DISCUSSION

Seizure Outcome and Relevant Prognostic Factors

Hemispherectomy surgery in the modern era is perhaps the most successful form of epilepsy surgery in terms of relief from seizure burden. The larger series published within the last decade reflect this success, with seizure freedom rates ranging from 54% to 90%.18,24-32 Our results follow a similar pattern, with 83% of nonpalliative cases (and 80% of all cases) resulting in seizure freedom (Engel I) and the majority of the remaining patients enjoying at least a significant reduction in their seizure burden.

Two patients were identified preoperatively who were felt not to have a chance at seizure freedom (but would still benefit from hemispherectomy surgery). These patients both had significant improvement (Engel IIIA and IIC). There is a precedent for palliative hemispherectomy surgery. Lupashko and colleagues33 reported a child with a terminal condition (Alper disease) and refractory status epilepticus who underwent hemispherectomy for palliation to allow extubation and hospital discharge. Ciliberto and colleagues34 reported 7 patients with clearly defined bilateral seizure onset undergoing hemispherectomy surgery, with 3 patients achieving seizure freedom (Engel I) and all patients having subjectively improved quality of life. In an attempt to better identify factors affecting seizure outcome, we excluded the 2 palliative cases from that subset of analyses. We felt that this would allow us to best determine factors associated with unexpectedly poor seizure outcome.

Although many publications have reported hemispherectomy outcome, in our review, only 6 have identified statistically significant preoperative factors correlating with seizure outcome, and their conclusions differ.24,29,35-38 This reflects the low statistical power afforded by the infrequency of this procedure at any single institution. Two of the 6 studies have implicated bilateral preoperative imaging abnormalities with adverse seizure outcome. In the largest series of hemispherectomy surgery published (n = 186), Moosa et al29 found that of all the preoperative variables assessed, only bilateral PET abnormalities had a significant correlation with seizure outcome. In 2010, Boshuisen et al35 reported the presence of contralateral MRI abnormalities as an adverse variable affecting outcome, a variable not found to be significant by Moosa et al. In our study, we reviewed MRI findings with regard to the presence of abnormalities, extent of lesions, laterality, and lesion type (Table 3). None of these variables approached significance. Of the remaining larger series reported (n > 40), imaging either was not assessed as a potential predictive factor18,24,27,28,30,31,37,39,40 or was not found to be significant.38 These somewhat conflicting findings regarding the relevance of bilateral MRI abnormalities may be a result of low-powered studies. As it stands, the relevance of bilateral MRI abnormalities is unclear.

Two of the 6 studies demonstrated age at the time of surgery as a significant predictive factor, with younger patients achieving higher levels of seizure freedom.24,38 This variable was not significant in our study (Table 2) or in any other series, including the 2 largest published series that examined age as a potential factor.27,29 If youth is a predictor for improved outcome, it appears not to be a strong one.

Many hemispherectomy series conclude that epilepsy origin is associated with seizure outcome,25,30,31,40,41 but only the final 2 of the 6 studies demonstrate statistically significant evidence of such.36,37 Devlin and colleagues36 reported a series of 33 cases, concluding that developmental pathology was associated with significantly worse outcome compared with acquired or progressive pathology. Kossoff et al37 reached a similar conclusion, finding that malformations of cortical development, hemimegalencephaly in particular, were associated with worsened outcomes. No such statistically significant correlations were found between origin and seizure outcome in our study (Table 5) or others examining the possibility.24,27,29,32,38,42,43 It would make sense that malformations of cortical development would be more likely to be associated with bilateral pathology compared with other causes (infarct, Rasmussen, Sturge-Weber) and thus more likely to result in contralateral seizures after surgery. It has been postulated that Rasmussen encephalitis and cortical dysplasia can involve the deeper hemispheric structures such as the basal ganglia and thalamus that are left behind with some techniques and that these affected structures may be a source of persistent seizures.18 Hemimegalencephaly also poses greater surgical challenges that may lead to less reliable disconnections/resections. It is unclear whether the failure of origin to be a significant predictor of seizure outcome in most studies is a result of low-powered studies or a true lack of effect.

In the present series, EEG findings did not correlate significantly with seizure outcome. Laterality of background abnormalities, interictal activity, and ictal onset were not significant. There was a trend toward significance with bilateral synchrony that was not significant in the multivariate analysis. Although 2 studies argue that preoperative EEG is predictive of outcome,44,45 both studies lack statistical power to bolster the assertion. Moosa et al29 identified lateralized ictal EEG onset as a significant predictor in their univariate analysis, but it was not an independent predictor in the multivariate analysis. Other studies investigating the possibility failed to show preoperative EEG parameters as significant predictors of seizure outcome.32,35,38,39,42,46

There is little evidence in our series that the chosen hemispherectomy technique affected seizure outcome. In the univariate analysis, technique was identified as a significant variable (P = .005) with worsened outcome with anatomic hemispherectomies. However, 3 of the 4 anatomic procedures were revision hemispherectomies, and this technique was not a significant factor when prior resective surgery was controlling for in the multivariate analysis. Comparing techniques is fraught with difficulty. Seizure outcome in this population is affected by patient selection, which cannot be controlled for in comparisons of results from various institutions. Within individual institutions, most series are similar to ours insofar as a specific technique became preferred over time without a satisfactory volume of cases using differing techniques to allow effective comparisons. One study has reported a fairly balanced distribution of cases between 2 hemispherectomy techniques with a demonstrably significant difference in outcome in their hands. Kwan et al28 reported 21 cases of hemidecortication vs 20 cases of peri-insular hemispherotomy. They found significant differences in operative time (5 hours for hemidecortication vs 7 hours for peri-insular hemispherotomy; P < .001) and a significantly higher reoperation rate with hemidecortication (6 of 21) for persistent seizures with residual cortex removed at all reoperations. After initial surgery, 85% of peri-insular hemispherotomy patients had Engel I or II outcomes vs 48% of the hemidecortication patients. The difference in efficacy in this study appeared to be related to persistent residual cortex left with the hemidecortication technique, which may be a reflection of experience with the technique or simply of the fact that it is more difficult to adequately isolate a hemisphere with hemidecortication. Three other centers with adequate volume (>20 cases per technique) comparing different hemispherectomy methods performed at a single institution did not find significant differences in seizure outcome.18,24,29

We identified a history of prior resective surgery as a risk factor for persistent seizures after hemispherectomy (P = .005). Pairwise comparisons suggest that it was the patients with a history of prior hemispherectomy who were likely responsible for this effect. This was an expected finding. Vadera et al47 recently published the largest series of revision hemispherectomy cases to date. They reported >90% seizure reduction in 64% of patients, but only 19% of patients achieved seizure freedom. They identified generalized ictal onset and cortical dysplasia as variables associated with poor outcome. The patient with persistent seizures after hemispherectomy can pose a diagnostic challenge. High-resolution MRI can demonstrate areas of residual connected tissue, but it can be difficult to confirm those areas as the definitive source of persistent seizures. The success rate in this population probably relates more to patient selection than to surgical technique. In our 6 revision hemispherectomy cases, all demonstrated areas of apparent residual connected ipsilateral cortex, and the remainder of their workups were consistent with ipsilateral seizures. Despite this, only 4 patients achieved Engel I/II outcomes. Nevertheless, our findings are consistent with those of Vadera et al47: There exists a subset of patients with prior hemispherectomies and persistent epilepsy who will benefit from revision surgery.

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Post-hemispherectomy Hydrocephalus

Hydrocephalus is a known adverse outcome of hemispherectomy surgery. Incidence rates vary dramatically in individual series, ranging from 9% to 81%.8,18,25,28,48-51 A recent multi-institutional review incorporated data on 690 hemispherectomy patients from 15 pediatric epilepsy centers (including ours).52 In that study, the overall incidence of hydrocephalus after hemispherectomy surgery was 23%. Prior cranial surgery and the anatomic hemispherectomy technique were identified as significant independent risk factors for developing hydrocephalus. In the present series, the overall incidence was 26%. When the MLH technique was initially adopted at our institution, Avitene was frequently used for hemostasis after removal of the opercular block of tissue. We noted in our early patients a high rate of postoperative hydrocephalus, with 5 of the first 9 MLH patients (56%) developing hydrocephalus. After reviewing our technique at length, we suspected the Avitene use was a factor. Since its use was discontinued, the hydrocephalus rate has dropped significantly to 13% (in MLH cases), and statistical analysis identified Avitene as the only independent risk factor for developing hydrocephalus in this series. In the multi-institutional review,52 the use of any hemostatic agent was a significant risk factor for developing hydrocephalus in the univariate analysis (but not the multivariate analysis). Avitene has been reported to induce granulomatous inflammatory responses after craniotomy in both patients and animal models.53,54 It is possible that this inflammation poses a risk for hydrocephalus similar to that seen in patients with intraventricular infection or hemorrhage. The lead author (S.M.L.) has since discontinued the use of hemostatic agents in all surgeries involving ventricular exposure.

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Neuropsychological Outcome

Hemispherectomy did not appear to have a detrimental effect on overall cognitive function in this series. This reassuring finding is consistent with those of prior studies.24,27,55-58 Despite the overall group-level stability, some individuals demonstrated significant changes in FSIQ. Other studies have identified differing preoperative factors significantly associated with pre-post cognitive improvement. These include lower presurgical intelligence,24 nonhemimegalencephalic cortical dysplasia,27 absence of contralateral MRI abnormalities,35 older age at seizure onset,59 shorter duration of seizures,59 and postoperative seizure freedom.24 In the present series, preoperative FSIQ, age at seizure onset, duration of seizures, age at hemispherectomy, and side of surgery failed to show significant correlations with change in FSIQ (Table 6).

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Surgical Technique

In the absence of clearly improved seizure outcome with 1 technique over another, the decision of which technique to use becomes a personal preference based on experience with differing techniques and perceptions regarding various advantages and disadvantages. Over the course of this series, the surgical technique evolved significantly. The major change was early in the series when the MLH technique was adopted. There are 2 distinguishing features of the MLH technique. The first is the early sacrifice of the middle cerebral artery. This allows excellent control of hemostasis during the remainder of the surgery, which in turn shortens the operative time. The second is the resection of the insular/basal ganglia/thalamic/opercular block of tissue lateral to the choroidal fissure. This provides excellent exposure of the ventricular system while ensuring complete removal of the insular cortex. With this exposure, the callosal, frontal, and posterior disconnections can be made with direct lines of sight without brain retraction, reducing the possibility of a missed disconnection. The facile nature of the disconnections also leads to shorter operative times. With this technique, we have found that surgery on infant brains does not pose any particular difficulties, and we do not recommend postponing surgery because of concerns of blood loss or other perceived difficulties with infant surgery if hemispherectomy surgery appears inevitable.

Since adopting the MLH technique, we have made minor modifications. We now use a significantly smaller osteoplastic craniotomy, extending superiorly only to the superior temporal line (the midpupillary line was initially described as the superior extent18), because this provides adequate access to the relevant anatomy. The frontal disconnection is now created by making a trough extending from the sylvian fissure to the inferior aspect of the rostrum of the corpus callosum with visualization of the ipsilateral anterior cerebral artery through the intact arachnoid. This minimizes any residual connected posterior mesial frontal lobe (Figure 1), a site implicated in hemispherectomy technical failures.47

Complications described in Illustrative Cases 1 and 2 further altered our practices. All patients undergoing MLH surgery develop blood in the epidural space that is transient and asymptomatic and does not cause midline shift. Nevertheless, as described in Illustrative Case 1, we attempted to use a negative suction epidural drain in 1 of the earlier cases. This resulted in a contralateral hemispheric ischemic injury that was fortunately temporary. There are multiple reports on the dangers associated with negative pressure drains in both the subgaleal and epidural spaces as a cause of remote hemorrhage, bradycardia, and diminished consciousness.60-63 We suspect that these risks are exacerbated in the setting of a large intracranial potential space that will allow migration of the midline structures toward the drain with associated distortion of the brain and its blood supply. Furthermore, the effectiveness of epidural drainage in preventing epidural and subgaleal collections is in doubt.64 We have abandoned the use of epidural drainage in such patients. Illustrative Case 2 highlights the utility of frameless stereotactic navigation in cases with distorted anatomic landmarks. It is now our practice to use navigation in all patients with prior resective surgery and in cases with markedly abnormal ventricular anatomy.

One potential disadvantage of the MLH technique is the incidence of postoperative hydrocephalus. The postoperative hydrocephalus rate for the technique is 24%. Since discontinuing the use of Avitene, the hydrocephalus rate with the MLH technique has been 13% (4 of 31 patients). This compares favorably with most larger series that report a hydrocephalus rate18,38,43 and with a recent multicenter study52 but is significantly higher than some peri-insular hemispherotomy series.30,40 It may be that the degree of brain resection involved or the greater exposure of the ventricular spaces increases the risk of hydrocephalus.

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CONCLUSION

The MLH is an effective method of achieving hemispherectomy, including revision hemispherectomy, with an acceptably low incidence of complications and stable cognitive functioning postoperatively. Avitene use correlated with the development of hydrocephalus and is now avoided. Negative pressure epidural drainage is unnecessary and dangerous in the setting of a large resection cavity. Frameless stereotactic navigation is not routinely used with this technique but is suggested for patients with atypical ventricular anatomy or prior resective surgery. Revision hemispherectomy carries a lower rate of success but should be considered in select cases. The origin of epilepsy did not correlate with seizure outcome. There is a lack of concordance between studies regarding prognostic factors for predicting seizure and neuropsychological outcomes after hemispherectomy. This is likely a byproduct of small sample sizes, and a meta-analysis or multi-institutional study is warranted.

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Disclosure

Statistical analysis for this project was supported, in part, by the National Center for Advancing Translational Sciences, National Institutes of Health, through grant 8UL1TR000055. The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article.

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Acknowledgment

We wish to thank Dr Gary Mathern, MD, for his generosity in sharing his expertise and the MLH technique. We also thank Daniel Eastwood, MS, for his data analysis, supported, in part, by the National Center for Advancing Translational Sciences, National Institutes of Health, through grant 8UL1TR000055.

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COMMENTS

The authors present a well-written report of a series of 50 consecutive children undergoing a hybrid hemispherectomy/hemispherotomy procedure for refractory epilepsy and achieved good overall results with respect to seizure freedom and unanticipated neurological and surgical complications. Overall seizure freedom was achieved in 80% (Engel class I), a number well within the range of most similar published series. The surgical technique used was well described (the so-called modified lateral hemispherotomy) in which a block of central opercular tissue, insula, and basal ganglia is resected after middle cerebral artery (MCA) sacrifice. The lateral temporal lobe is removed rather than disconnected. The remaining steps involve disconnection and not resection. The authors describe some minor modifications in surgical technique evolving over time based on an assessment of suboptimal outcomes as their experience grew. The use of Avitene as a hemostatic agent was abandoned when the postoperative hydrocephalus rate was recognized as high; the use of stereotactic navigation was introduced when ventricular anatomy was distorted; and the use of a negative pressure drain was abandoned after ipsilateral midline shift and acute neurological deterioration were noted in a patient early in their series.

The first 5 patients underwent Rasmussen-style or anatomic hemispherectomies. Thereafter, despite the minor adjustments in technique listed above, the majority of the patients seemed to have undergone a fairly uniform technique using resection and disconnection to achieve isolation of the diseased hemisphere (modified lateral hemispherotomy). Although their results are in line with the multiple other published series of hemispherotomy in children, their outcomes raise some questions. The series had a high proportion of patients with MCA infarctions (50%) and relatively few with hemimegalencephaly or Sturge-Weber syndrome. In this reviewer's experience, patients with MCA infarcts (generally an acquired, purely unilateral insult) have the best seizure control rates after hemispherotomy (approaching 100%).1 Patients with hemimegalencephaly and Sturge-Weber syndrome may have worse seizure control after hemispherotomy, and the relatively low proportions of these patients in the series prohibited meaningful statistical analysis of origin as a predictor of seizure outcome. In this report, 8% of the children with prior MCA infarcts were not rendered seizure free. One with an Engel class IIIA outcome was described (Unfavorable Seizure Outcomes section), and he suffered a more diffuse hypoxic injury to both hemispheres, along with the left MCA infarct. Another (Engel class IID) had contralateral seizure onset on postoperative electroencephalogram.

A postoperative hydrocephalus rate of 26% is relatively high. Although partially attributable to Avitene, it is possible that the technique used, with a significant amount of tissue resection rather than disconnection only, may also contribute. Thirteen percent of patients without preexisting hydrocephalus—and in whom Avitene was not used—still required cerebrospinal fluid shunts after surgery. The study was not powered or designed to determine whether hydrocephalus risk is linked to type of surgery. External ventricular drains were used, but they were weaned after 48 hours. At our center, we leave a drain in place for 5 days for continuous drainage to clear blood products and debris, and then it is removed without a weaning trial. With 5 days of postoperative ventricular drainage and a modified peri-insular technique, the postoperative hydrocephalus rate at our center is <5% to 10%.1

The authors should be commended for including analysis of preoperative and postoperative neuropsychological data and confirming stability in cognitive function after surgery in the overall cohort. Their data also suggest that some patients had significant improvements in cognitive function after surgery.

Matthew D. Smyth

St. Louis, Missouri

1. Limbrick DD, Narayan P, Powers AK, et al.. Hemispherotomy: efficacy and analysis of seizure recurrence. J Neurosurg Pediatr. 2009;4(4):323–332.

This is a very impressive series of 50 hemispherectomies performed by a single surgeon over a relatively short period of time for patients with medically refractory epilepsy. As in other aspects of neurosurgery, this paper highlights the value of consistency in neurosurgery, and how this consistency can foster improvements for patients based on lessons learned over the course of a consistent surgical experience. This is one of the relatively few reported series of 50 or more hemispherectomies from a single center. They favor a modification of the modern hemispherotomy technique, called the modified lateral hemispherotomy which, like other variations of hemispherotomy, is more of a disconnection than a resection. The seizure and neuropsychological results are impressive, even considering the relatively higher proportion of post-stroke patients (who tend to do better) and lower ratio of cortical malformation patients (who tend to do worse) in their cohort. The authors make a number of important contributions to the field, including their observation that Avitene use was a risk factor for subsequent hydrocephalus development in their patients, and that this operation may be a therapeutic option even when palliation is the goal, for select patients.

Howard L. Weiner

New York, New York

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CME QUESTIONS:

1. What is a well recognized complication after corpus callosotomy for epilepsy?

A. Hemiplegia

B. Gerstmann syndrome

C. Superficial cerebral hemosiderosis

D. Hemibalismus

E. Disconnection syndrome

2. Anatomic hemispherectomy historically is associated with what complication?

A. Gerstmann syndrome

B. Superficial cerebral hemosiderosis

C. Hemibalismus

D. Syndrome of the trephined

E. Callosal syndrome

3. Which syndrome is most likely to benefit from hemispherectomy?

A. Rasmussen's Encephalitis

B. Mesial temporal Sclerosis

C. Nonlesional Extratemporal Epilepsy

D. Lennox-Gastaut Syndrome

E. Drop attacks

Keywords:

Complications; Epilepsy; Hemispherectomy; Hydrocephalus; Modified lateral hemispherotomy; Outcomes

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