Resection from the Temporal Lobe

An international survey of pediatric epilepsy surgery centers revealed that temporal lobe resections (TLs) make up 23.2% of all resective procedures.6 Most of the literature on cognitive outcomes has been directed at children undergoing TL. A comprehensive review of the published studies before 2004 that examined children’s overall development before and after TL noted that only 3 of 16 studies that examined group outcome found evidence of a significant change (increase) in the IQ after surgery, suggesting that the overall rate of development does not change after surgery.7 These studies included seizure-free children, as well as children who had some ongoing residual seizures. In turn, it is possible that the rate of development progression after surgery was underestimated by the inclusion of children who had ongoing seizures. Indeed, two of the reviewed studies found that good seizure outcome was associated with an increase in IQ,8,9 but two other studies did not.10,11

Individual outcomes are examined in only some of the neuropsychological studies. One of the difficulties in reporting the neuropsychological individual outcomes is a lack of consensus on a method to be used to determine whether the change in the score is clinically significant. Some of the previously reviewed studies,7 however, did examine IQ changes in individual children after TL. Typically, the number of children who showed a significant increase tended to be greater than that of children who had a significant decline after TL. However, studies that have included a comparison group of children with intractable epilepsy in addition to a surgical group have found that the likelihood of change does not differ over time between the two,11,12 suggesting there is no advantage as a result of surgery.

In adults, TL surgery is associated with a neuropsychological morbidity; patients who undergo language-dominant (in most cases left) TL are at risk of a decline in anterograde verbal memory.13 In children, the outcome may differ because ongoing maturational changes, difference in etiology, and physiological and functional plasticity may have a significant role in determining the outcome.14 The review by Lah7 identified 13 studies that reported on the verbal memory outcome in children who underwent TL, and an additional study has since been published.10 Interestingly, only four found evidence of a significant decline, six found no evidence of a significant change, and four reported a significant improvement in memory after surgery. As with adults, a decline was more likely to be found after left rather than right TL, except in one study that found that a significant decline was independent of the side of the surgery.15 Of studies that found evidence of significant improvement, one showed increased verbal memory after right TL,8 and one found improved verbal memory after left or right TL.10 Improved visual memory was reported after either right or left TL in one study16 and after right TL in another.17

Of particular interest is a longitudinal study that compared child and adult memory outcome before surgery and at 3 and 12 months after TL.18 In short-term follow-up, both children and adults showed a significant declinein verbal memory. By the 12-month follow-up, however, children’s memory scores were comparable to their preoperative results, but adults’ scores were not, suggesting better functional outcome for children compared with adults. Smith, Elliot and Lach,5 conversely, found no evidence of a significant change in memory scores over time in children who underwent either temporal or extratemporal resection (regression analyses indicated that the site of excision did not have a significant impact on memory outcome). In this study, however, the first follow-up took place at 1 year after surgery, which was the time of the long-term follow-up in Gleissner et al’s18 study, at which point children’s results were much improved and comparable to their presurgical scores. Together, these findings suggest that, in children, memory reorganization after TL may occur rapidly.

In their unique longitudinal study, Smith, Elliot, and Lach5 examined objective and subjective memory in children who underwent temporal or extratemporal excisions and an epilepsy control group at baseline, 1-year follow-up, and 2- to 3-year follow-up. There was no significant change in objective memory scores over time in any of the groups. More importantly, low concordance between objective and subjective memory outcome was noticed. Qualitative analyses of children’s narratives indicated difficulty in aspects of everyday memory not measured by the objective memory tests, such as autobiographical and semantic memory. To date, only one case study19 directly examined autobiographical memory in a boy who was initially seen for a neuropsychological assessment at 9 years of age (some 1 1/2 years after the onset of temporal lobe epilepsy). His scores on memory tests fell in the age-appropriate range, but he had difficulty recalling autobiographical events. He underwent TL at 10 years of age, and follow-up 8 years later showed the same pattern of results. Evidence suggested that his problems in everyday memory may have been caused by impaired memory consolidation.

Clusmann and colleagues20 compared verbal memory outcome of 25 children who underwent left TLs that included one of the following surgical approaches: lesionectomy plus hippocampectomy (LX+HC), lateral temporal lesionectomy (lat. LX) and amygdalohippocampectomy (AH). Children who underwent left AH had an increased risk of developing more significant memory deficits after surgery compared with children who underwent left LX+HC or lat. LX. The authors warned, however, that this finding might be secondary to factors other than surgical techniques, because the type of procedure used in the surgery was guided by clinical reasons rather than patients being randomized to undergo different surgical procedures.

Outcomes in other cognitive areas, such as attention, language, and visuospatial skills have barely been examined. Improvements in attention have been reported after TL,18,20 which could be benefits secondary to favorable seizure outcome and reduction of antiepileptic medication. Nevertheless, Clusmann et al20 found the relationship between attention and seizure outcomes to be nonsignificant, although more than 80% of children were reported to be seizure free.

Adult literature suggests that dominant TL is also associated with a risk of language decline.21 In children, language-related cognitive decline after TL was first reported by Dlugos et al22 Nevertheless, Blanchette and Smith23 questioned the validity of this finding, as they pointed out that Dlugos et al22 did not use specific language-processing tasks. Instead, they used tasks (such as verbal learning) that involved language but assessed other cognitive skills (i.e., anterograde verbal memory). Blanchette and Smith23 found that children with left-sided (temporal, n = 10; or frontal, n = 9) lesions performed worse than children with right-sided lesions irrespective of the seizure site both before and after surgery (on category fluency and language comprehension tasks) but showed no evidence of a significant drop in their language scores after surgery. When changes in individual scores after TL were examined, however, significant changes were observed in several children, with declines most likely to be observed on the phonetic fluency task (5/10 children), irrespective of the side of resection. Subsequently, in a study that used one (combined) language score, Clusmann et al20 found a significant improvement in language score after right TL and no evidence of a drop after left TL. Gleissner et al,18 who reported on individual outcomes, found a significant increase (and no significant decline) in language scores in a small number of children after either right or left TL. The number of increases, however, was not significantly greater than could be expected by chance.

Finally, few studies used tasks to examine other specific visuospatial skills. One study found that the number of children who experienced losses in visuospatial skills after right TL was significantly greater than expected at 3 months after surgery.18 Nevertheless, only a small number of patients still demonstrated losses (relative to preoperative scores) at 12 months after surgery. Interestingly, Clusmann et al20 found a significant increase in visuospatial skills 1 year after left TL and pointed out that this improvement was in skills typically subserved by the hemisphere contralateral to the previous epilepsy focus.

Resection from the Frontal Lobe

Despite the fact that surgery in the frontal lobe accounts for 17.5% of pediatric resective procedures, which is not greatly different from the proportion of temporal lobe removals,6 the literature on the neuropsychological outcomes of frontal resections lags considerably behind that for temporal lobectomy, and only two studies were identified.

Twelve children with frontal lobe epilepsy (six left, six right) were compared preoperatively and 1 year after surgery with 12 children (matched for age and side of surgery) who underwent excision from the temporal lobe.24 The frontallobe group included six cases of lesionectomy, four cases of lesionectomy plus multiple subpial transactions (MST), and two cases of MST only. The outcomes included attention, executive function, memory, motor coordination, and language. Before surgery, the frontal group had higher IQ but was more impaired in motor coordination than the temporal lobe group. After surgery, there were improvements in attention and memory that were independent of site and side of surgery; the other functions examined did not change. Analysis of individual changes indicated that the majority of patients showed no significant changes over time. Postoperative improvements were not related to complete seizure relief after surgery.

Potential risk to the child’s language ability is of concern when undertaking resection in the language-dominant hemisphere. In the series described previously,24 two patients underwent surgery that involved area 44 in the left hemisphere. One case had bilateral language representation as determined by the intracarotid amobarbital test and had average language function before surgery. Extraoperative cortical stimulation in area 44 did not interfere with her language. Postoperatively, she showed a decrement in verbal fluency and comprehension. The second patient had right hemisphere language dominance, but electrical stimulation caused a speech arrest in a small left frontal region that was spared in surgery. Postoperative, verbal fluency and naming improved.

Verbal fluency, reading, spelling, vocabulary, and comprehension were examined in another study23 in which all children had left hemisphere language representation. No differences relating to site (frontal versus temporal lobe) were found before or after surgery, and none of these functions was significantly affected after excision from either the frontal or temporal lobes. Children with left hemisphere dysfunction had lower scores on measures of phonemic fluency and comprehension, but laterality, effects were not present for the other tasks.

Resection from the Parietal Lobe

Parietal lobe resections account for fewer than 3% of pediatric cases,6 and little has been written on either pre- or postoperative function among children who have undergone parietal lobe surgery. In one investigation of 15 children, a relatively high percentage had deficits in intelligence, memory, language, visuospatial processing, attention, executive function, and motor function before surgery.25 Differences between left- and right-sided cases were not observed; a large proportion had functional deficits discordant with the side of lesion. The most frequent impairment was in the realm of attention. After surgery, change was apparent only in the domain of attention, which was improved. By contrast to these findings, in a small case series of three patients with excisions from the postcentral gyrus, cognitive function was generally intact and was essentially unchanged in follow-up.26 Two of the patients had evaluation of fine motor dexterity on the hands; both showed declines bilaterally after surgery. In these two case series, the patients were quite heterogeneous in terms of the location of the excisions, which may explain the different pattern of findings.