Epilepsy Surgery in Infants and Children

Ajay Gupta

Elaine Wyllie

William E. Bingaman

Surgery is now a well-established treatment for adults and children with medically intractable seizures (1, 2, 3, 4, 5). Several centers around the world have published their surgical experience and seizure outcome data after surgery in children, and results are encouraging from pediatric series involving infants and young children (1,3,6, 7, 8, 9, 10, 11, 12, 13, 14) and adolescents (10,15, 16, 17, 18, 19, 20, 21). However, identification of appropriate pediatric surgical candidates, especially infants and children, remains a challenge because of complex interactions of several unique and age-related factors (4,22).

This chapter focuses on these unique and age-related differences that interplay in the management of children who are likely to benefit from the surgical treatment of epilepsy. The step critical to surgical strategy in children as well as adults is the identification of a focal, resectable epileptogenic zone. Clues to the epileptogenic zone are found in seizure symptomatology, electroencephalography(EEG), and neuroimaging results. Some aspects of these features are similar to those in adult candidates, whereas others are unique to infants and children. Table 83.1 compares common findings during diagnostic evaluation of pediatric and adult patients for epilepsy surgery.

SEIZURE SEMIOLOGY DURING VIDEO-ELECTROENCEPHALOGRAPHY IN INFANTS AND CHILDREN

Clinical features of focal seizures may differ in pediatric and adult surgical candidates. Independent studies (23, 24, 25) of videotaped seizures from patients at separate institutions indicated that the classification of epileptic seizures of the International League Against Epilepsy (26), originally reflecting experience in older patients, was not applicable to infants younger than 3 years of age. In the study by Acharya and colleagues (23), only 3 of 21 patients had unmistakable characteristics of localized seizure onset, including clonic jerking of one extremity. In the remaining patients, seizures consisted of a decrease in behavioral motor activity with indeterminate level of consciousness and minimal or no automatisms, arising from temporal or temporoparietal regions, or bilateral tonic stiffening sometimes preceded by bilateral eyelid blinking, arising from frontal or frontoparietal regions. Other authors (24,27) have also noted bilateral motor phenomena during partial seizures in infants. The mechanism is unknown but may include ictal activation of subcortical regions or of the supplementary sensorimotor area. A localized electroencephalographic seizure pattern clarifies the focal nature of the epileptogenic process.

Seizure characteristics signaling localized onset in older patients may be absent or unidentifiable in infants. For example, an aura is an important clue to focal onset in older children and adults, but sensory phenomena are difficult to detect and are rarely observed during video-EEG studies in infants (23). Clinical seizure onset may be difficult to notice, especially in mentally impaired young children, and this may create a challenge during diagnostic evaluation like video-EEG and ictal single-photon-emission computer tomography (SPECT) (28,29). Complex gestural automatisms and altered awareness are hallmarks of many partial seizures in older patients, but assessment of the ictal level of consciousness in infants is fraught with problems, and automatisms, when present, tend to be simple, bland, and predominantly oral. In infants, distinguishing automatisms from normal background behavioral activity can be difficult (23,24).

TABLE 83.1 COMMONLY ENCOUNTERED DIFFERENCES DURING DIAGNOSTIC EVALUATION AND SURGICAL DECISION MAKING IN PEDIATRIC AND ADULT PATIENTS

Characteristic Findings		Infants/Young Children	Adult Patients
History, seizure semiology, and examination
	Specific auras	Rare (unable to communicate)	Common
	Seizure semiology	Stereotypic (like “epileptic spasms” or “bland stare”)	May indicate symptomatogenic zone
	Clinical seizure onset, ictal examination, postseizure recall	Unable or difficult to confirm	Easier
	Ictal lateralizing features	Uncommon or unreliable	Common and reliable
	Neurologic deficit on examination	Difficult to elicit (mild hemiparesis, visual fields)	Easy to elicit
	Neuropsychological testing for surgical risk	Less objective (because of age, severe cognitive and behavior difficulties)	Helpful in pointing to specific deficits
Scalp EEG patterns
	Confounding factor of developmental EEG evolution	Present	Absent
	Stereotypic and nonlocalizing interictal and ictal patterns	Common (hypsarrhythmia, generalized discharges)	Absent
Imaging and pathologic substrates
	Confounding factor of developmental brain MRI changes	Present	Absent
	Ictal SPECT	Difficult (brief frequent seizures, clusters, difficult ictal onset)	Easier
	Common location and extent of lesions	Extratemporal large lesions	Temporal, smaller lesions
	Common etiologies	Congenital (cortical dysplasia, malformation, tumor, perinatal stroke)	Hippocampal sclerosis, focal cortical dysplasia
Surgical considerations
	Morbidity and mortality	Higher (because of age, weight, larger resections, coexisting disabilities)	Lower
	Timing and best techniques for surgery	More controversial and require planning and experience	Less controversial
	Invasive mapping (intracranial grids or depth electrodes)	Not practical in most infants and young children	Possible
	Intraoperative neurophysiologic techniques	Limited utility, more challenging in infants	Very useful
	Goals of surgery/successful seizure control	Cognitive improvement, schooling, behavior, productive adult life	Job, driving, independence
Abbreviations: EEG, electroencephalographic; MRI, magnetic resonance imaging; SPECT, single-photon-emission computed tomography.

SCALP ELECTROENCEPHALOGRAPHY PATTERNS, INFANTILE SPASMS, AND FOCAL CORTICAL LESIONS

Within the first 2 years of life, focal cortical lesions may manifest as infantile spasms and hypsarrhythmia (7,14,30,32). The spasms may be intermixed with partial seizures (Fig. 83.1) or may replace a previous partial seizure type altogether, becoming the only active seizure type (Fig. 83.4). The mechanism is unknown, but a clue may be the relationship between age of onset of spasms and location of the lesion. Koo and Hwang (33) found that spasms began earliest in patients with occipital lesions (mean age, 3 months), appeared later in patients with centrotemporoparietal lesions (mean age, 6 months), and occurred latest in patients with frontal lesions (mean age, 10 months). This timing coincides with maturation in those regions; rapid increases in synaptic density and sequential myelination that proceed from the back to the front of the brain. Infantile spasms appear to result from an age-related pathologic interaction between a focal cortical lesion and normal developmental processes.

Chugani and colleagues (8,32, 33, 34) first emphasized the role of positron emission tomography (PET) and magnetic resonance imaging (MRI) in identifying focal cortical lesions in children with infantile spasms and hypsarrhythmia, describing several patients with cessation or dramatic reduction of seizures after cortical resection or hemispherectomy. Their experience has been replicated elsewhere (3,31). In that 65% of affected children are free of seizures after surgery (7), infantile spasms are not predictive of poor outcome. However, the identification of appropriate surgical candidates may be complicated by the absence of focal EEG seizure patterns in the setting of spasms with diffuse electrodecrements.

Figure 83.1 Case 1. (All images are of the same patient.) A: Axial magnetic resonance image from an 8-month-old boy, showing focal malformation of cortical development in the right temporo-occipital region (arrows). Findings were subtle and included decreased arborization of the white matter and thickened, poorly sulcated cortex. Seizures began 14 hours after an unremarkable term birth and occurred 20 to 30 times per day. The boy was otherwise normal except for developmental delay. B: 2-[¹⁸F]fluoro-2-deoxy-D-glucose positron emission tomography scan at age 8 months, showing glucose hypometabolism in the right temporo-occipital region (arrows). C: Interictal electroencephalogram at age 8 months, showing right posterior temporal sharp waves (maximum at the T8 and P8 electrodes), slowing, and decreased background activity. D: Ictal electroencephalogram at age 8 months with seizure pattern maximum in the right posterior temporal region (T8 electrode). Seizures involved bilateral clonic eyelid blinking, rhythmic interruption of crying, and bilateral clonic arm twitching. E: Ictal electroencephalogram at age 8 months, showing diffuse electrodecrement (arrow, preceded and followed by movement artifact) during an asymmetric spasm with extension and elevation of both arms (left more than right) and tonic closure of the left eyelid. F: Magnetic resonance image showing the right temporo-occipital resection performed at age 22 months. Fourteen months later, the child still has developmental delay but remains free of seizures off all antiepileptic medication. (A and C-F are from Wyllie E. Surgical treatment of epilepsy in infants and children. Can J Neurol Sci 2000;27:106-110, with permission.)

Figure 83.1 (continued)

The goal of the presurgical evaluation in patients with infantile spasms is to identify a region of cortical abnormality. Helpful EEG findings can include a predominance of interictal sharp waves over one region; localized slowing, decreased background activity, or absent sleep spindles over the affected region or hemisphere; unilateral electrodecremental events; asymmetric EEG seizures; or a history of partial seizures (4,14). Neurologic examination may show evidence of unilateral hemispheric dysfunction with decreased spontaneous movement of one arm (hemiparesis) or gaze preference to one side (homonymous hemianopia) (4,14). The generalized scalp EEG patterns in the presence of a focal lesion may not be limited to infants. Recently, Gupta and Wyllie (unpublished data, presented at the American Academy of Neurology meeting, 2004) described older children with a unilateral focal or hemispheric abnormality that presented with exclusively generalized interictal and ictal EEG patterns. Initially, these children were rejected for surgical treatment owing to the presence of exclusively generalized EEG findings. Because of a desperate situation with daily dreadful seizures, failure of all treatment modalities, and minimal risk of new postoperative side effects, surgical treatment was offered as a last resort. Of eight patients who underwent surgery, six were seizure free; one had more than 90% and one had a 50% seizure reduction at 1-year follow-up. However, in children, as in older patients, the location of the focal epileptogenic lesion must be defined, whenever possible, by a convergence of results from clinical examination, EEG, anatomic, and functional neuroimaging, and other testing (4).

ANATOMIC AND FUNCTIONAL NEUROIMAGING

Neuroimaging is a critical component of surgical strategy at every patient age. A focal epileptogenic lesion on the MRI seems to indicate a better prognosis for seizure-free outcome. In the Cleveland Clinic pediatric series from 1990 to 1996 (3), 54% of patients were seizure free and 19% had only rare seizures after extratemporal or multilobar resections. In contrast, in the Montreal Neurological Institute pediatric series (35) (excluding tumor cases) during the pre-MRI era between 1940 and 1980, only 27% had few or no seizures after frontal resection. The more favorable results from the Cleveland Clinic may be a result of identification of a focal epileptogenic lesion on preoperative MRI in 85% of patients. Almost identical results were reported in an adult series (36) of extratemporal resections performed in Bonn, Germany, from 1987 to 1993, with 54% of patients free of seizures after surgery. Seizure-free outcome in that series was significantly more common in lesional than nonlesional cases, with 82% of lesions identified preoperatively by MRI. The absence of MRI localization appears to be an unfavorable prognostic sign, although some patients may have good outcome after electroen-cephalogram-guided cortical resection. The yield of brain MRI, particularly in neocortical frontal and temporal lobe epilepsy, could be enhanced by use of high-resolution imaging, specialized protocols with thin sections, and experience of the reader (see Chapter 74) (37).

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