Neuroimaging in the evaluation of children and adolescents with intractable epilepsy: II. Neuroimaging and pediatric epilepsy surgery

Association of magnetic resonance imaging identification of mesial temporal sclerosis with pathological diagnosis and surgical outcomes in children following epilepsy surgery

OBJECT

Mesial temporal sclerosis (MTS) is widely recognized as a significant underlying cause of temporal lobe epilepsy. Magnetic resonance imaging is routinely used in the preoperative evaluation of children with epilepsy. The purpose of this study was to evaluate the prevalence, reliability, and prognostic value of MRI identification of MTS and MRI findings indicative of MTS in a series of patients who underwent resection of the medial temporal lobe for medically refractory epilepsy.

METHODS

The authors reviewed the medical records and preoperative MRI reports of 25 patients who had undergone medial temporal resections (anterior temporal lobectomy or functional hemispherotomy) for medically intractable epilepsy. The preoperative MRI studies were presented for blinded review by 2 neuroradiologists who independently evaluated the radiographs for selected MTS features and provided a final interpretation. To quantify interrater agreement and accuracy, the findings of the 2 blinded neuroradiologists, the nonblinded clinical preoperative radiology report, and the final pathology interpretation were compared.

RESULTS

The preoperative MRI studies revealed MTS in 6 patients (24%), and histopathological analysis verified MTS in 8 (32%) of 25 specimens. Six MRI features of MTS were specifically evaluated: 1) increased hippocampal signal intensity, 2) reduced hippocampal size, 3) atrophy of the ipsilateral hippocampal collateral white matter, 4) enlarged ipsilateral temporal horn, 5) reduced gray-white matter demarcation in the temporal lobe, and 6) decreased temporal lobe size. The most prevalent feature of MTS identified on MRI was a reduced hippocampal size, found in 11 of the MRI studies (44%). Analysis revealed moderate interrater agreement for MRI identification of MTS between the 2 blinded neuroradiologists and the nonblinded preoperative report (Cohen κ 0.40-0.59). Interrater agreement was highly variable for different MTS features indicative of MTS, ranging from poor to near perfect. Agreement was highest for increased hippocampal signal and decreased temporal lobe size and was consistently poor for reduced gray-white matter demarcation. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and proportion perfect agreement were highest for increased hippocampal signal and reduced hippocampal size. An MRI finding of MTS was not predictive of seizure outcome in this small series.

CONCLUSIONS

Mesial temporal sclerosis identification on brain MRI in children evaluated for medial temporal resections has a PPV of 55%-67% and an NPV of 79%-87%. Increased hippocampal signal and reduced hippocampal size were associated with high predictive values, while gray-white differentiation and an enlarged temporal horn were not predictive of MTS. Seizure outcome following medial temporal resections was not associated with MRI findings of MTS or MRI abnormalities indicative of MTS in this small sample size.

99mTc-HMPAO single photon emission computed tomography (SPECT) in both asphyxiated and epileptic children with or without status epilepticus

In this study, technetium 99m hexamethylpropyleneamine oxime (99mTc-HMPAO) single photon emission computed tomography (SPECT) was performed on 18 asphyxiated and epileptic children who also had a status epilepticus episode, and the results were compared with those for 21 children without a status epilepticus episode. All patients underwent a detailed neurologic history, interictal electroencephalography, computed tomography, and/or magnetic resonance imaging. Visual evaluation of the SPECT study showed that 16 patients of group 1 had 56 hypoperfused regions in cerebral blood flow. However, in group 2, visual evaluation showed only six detectable hypoperfusion areas in five patients. When an asymmetric index value of 3 was considered as a cutoff point, 82 regions in group 1 and 57 regions in group 2 were above this value after the quantitative SPECT evaluation. The mean number of pathologic brain regions was found to be higher in group 1 (5.1 +/- 4.3) than in group 2 (2.7 +/- 2.4) (P = .014). The localization of hypoperfused regions that were observed in temporal and frontal regions was generally similar in both groups. In conclusion, the functional activities of the brain vary in both asphyctic and epileptic children, with and without status epilepticus. These children might be candidates for refractory convulsive disease, and interictal SPECT can be a reliable method for the detection of brain lesions in these patients.

Epilepsy surgery. Presurgical evaluation

The presurgical evaluation should result in a clear understanding of whether surgery can be undertaken and its associated risks and potential for benefit. The results of surgery are best when there is congruence in the seizure semiology, the irritative zone on interictal EEG, and the ictal onset zone with the epileptogenic lesion as defined on MRI and PET, and when there is a clear understanding of the ictal onset zone's relationship to eloquent cortex as defined by neuropsychologic evaluation, the intracarotid amobarbital test, and cortical functional mapping.

Pediatric epilepsy surgery: neuroimaging, neuropsychology, and anticonvulsants

Neuroimaging and the neuropsychological evaluation are important components of the presurgical evaluation for epilepsy surgery. Advances in neuroimaging over the last decade, to a large part, underlie improvements in pediatric epilepsy surgery outcomes. The neuropsychological evaluation plays an important role in the evaluation of the older child and adolescent, particularly in the evaluation of mesial temporal sclerosis. However, its role in the young child being considered for surgery remains to be defined. This section reviews the definition of medical intractability, issues related to medication withdrawal during video-EEG monitoring, recent neuroimaging advances, and the neuropsychological evaluation.

Transparahippocampal selective amygdalohippocampectomy in children and adolescents: efficacy of the procedure and cognitive morbidity in patients

OBJECT

Unilateral resection of the hippocampus and amygdala can be used to treat medically intractable mesial temporal lobe seizures. To date seizure outcome and the extent of cognitive morbidity have been unknown in children following the transparahippocampal variation of selective amygdalohippocampectomy (TSA), which prompted the present prospective study.

METHODS

Preoperative examinations and outcomes in 22 consecutive children and adolescents who underwent TSA were studied. Cognitive and psychological morbidity were assessed using standard neuropsychological instruments. The authors evaluated relationships between seizure control and cognitive morbidity and 13 and nine clinical variables, respectively. Seizure control was achieved in 11 (65%) of 17 patients (>2 years follow up). Among 13 clinical variables, the only preoperative finding that had a significant bearing on seizure control was the presence of unilateral hypometabolism, which could be observed on [18F]fluorodeoxyglucose-positron emission tomography scans (p<0.001). Patients with seizure control showed significant improvements in verbal and full scale intelligence quotients (both p = 0.05). Patients with longer preoperative durations of seizures exhibited more cognitive impairment that persisted postoperatively. Cognitive outcome analysis based on nine clinical factors revealed no significant difference in cognitive parameters postoperatively, except that significant improvement occurred in rote verbal memory scores among patients who underwent right-sided TSA (p = 0.01). Individually, 81% of the children achieved significant improvement in at least one of seven cognitive parameters, and 52% had stable or improved scores in all parameters.

CONCLUSIONS

The results indicate that TSA is a safe effective approach for the treatment of medically intractable mesial temporal lobe seizures in children with minimum effect on cognitive morbidity. Given that the literature suggests that children suffer progressive cognitive morbidity from persistent seizures, the results of this study support early surgical intervention for this group of children.

Cognitive deterioration associated with focal cortical dysplasia

Surgery for an area of focal cortical dysplasia in a critical region is reported in a right-handed female manifesting intractable focal epilepsy and verbal cognitive deterioration. She developed the first seizure at 2 years of age and was treated with phenytoin and zonisamide, with good control until 10 years of age. Although seizures did not occur at 9 years of age, she manifested dyscalculia, right-left disorientation, and finger agnosia, and N-isopropyl-p-iodoamphetamine single-photon emission computed tomography (SPECT) revealed focal hypoperfusion in the left parietal lobe. At 11 years of age, she developed regular nocturnal seizures and gradually lost the ability to understand the meaning of sentences. Verbal IQ declined from 94 to 63, and the area of hypoperfusion detected by interictal N-isopropyl-p-iodoamphetamine SPECT spread over the left parietotemporal lobes. Magnetic resonance imaging revealed focal cortical dysplasia mainly in the left parietal lobe, and ictal technetium-99m-ethyl cysteinate dimer SPECT images demonstrated an area of hyperperfusion around the focal cortical dysplasia, including the left precentral gyrus. Because of the overlap between the epileptogenic and functional cortex, the authors concluded that cortical resection, including focal cortical dysplasia, was inappropriate in this patient.