Laser ablation is an emerging, minimally invasive treatment for selected children with intractable focal epilepsy with improved procedural morbidity. Data for children lag similar studies in adults, but the hope is for near-equivalent seizure-control rates and improved neuropsychological outcome when compared with standard open surgical resection. The approach seems particularly beneficial when dealing with deep, focal lesions, such as hypothalamic hamartomas or hippocampal sclerosis.
Key points
- •
Laser ablation is a novel, minimally invasive technique for the surgical treatment of intractable epilepsy that involves MRI-guided thermal ablation of epileptogenic foci.
- •
Consider in patients with intractable epilepsy secondary to focal lesions, such as mesial temporal sclerosis, hypothalamic hamartomas, and possibly low-grade glioneuronal tumors.
- •
Early experience suggests less procedural morbidity, better neuropsychological outcomes, and similar short-term seizure freedom rates when compared with standard open surgical resection, but longer term study is needed.
Introduction
Pediatric epilepsy affects roughly 1 of every 100 children, of which as many of one-third have seizures that are incompletely controlled with medication alone. In children with medically intractable epilepsy who also have a radiographic and/or electrographic correlate for seizure origin, surgical resection is commonly considered. In appropriately selected patients, long-term seizure control rates will be in the 50% to 70% range after removal of the epileptogenic focus. Conventional surgical treatment consists of an open surgical procedure (craniotomy) and resection of the offending tissue. Although extensive experience supports the efficacy and safety of this approach, the attendant risks of open surgery with regard to procedural morbidity, incomplete resection, and damage to adjacent brain tissue cannot be completely eliminated. This supports a role for minimally invasive alternatives when treating certain epileptogenic lesions, especially those adjacent to or involving deep or eloquent brain structures, such as the dominant temporal lobe and deep brain structures (eg, hypothalamic hamartoma [HH]).
Laser ablation is a novel, minimally invasive surgical technique that is used in the treatment of focal, medically intractable pediatric epilepsy. Previous attempts with stereotactic lesioning for the treatment of epilepsy were limited due to the variability in thermal energy delivery and inability to achieve real-time feedback on the area of ablated tissue. Two systems, the Visualase device (Medtronic, Minneapolis, MN) and the Monteris device (Plymouth, MN), have recently been used for ablation of seizure foci. Generally, both systems consist of a laser catheter probe that is placed by the neurosurgeon into a previously identified epileptogenic focus via a small twist-drill cranial access site. The surgeon can then use real-time MRI thermal imaging to visualize treatment and tailor the ablation to encompass the entirety of the lesion while avoiding surrounding critical brain structures.
Early use of this approach in children with epilepsy shows its feasibility. It is particularly attractive for lesions such as HHs, in which the approach to the lesion can carry much of the morbidity. Deep heterotopia also may be targeted. Additionally, following the experience in adults, ablation of the dominant temporal hippocampus may provide improved neuropsychological outcomes compared with even selective resections.
Introduction
Pediatric epilepsy affects roughly 1 of every 100 children, of which as many of one-third have seizures that are incompletely controlled with medication alone. In children with medically intractable epilepsy who also have a radiographic and/or electrographic correlate for seizure origin, surgical resection is commonly considered. In appropriately selected patients, long-term seizure control rates will be in the 50% to 70% range after removal of the epileptogenic focus. Conventional surgical treatment consists of an open surgical procedure (craniotomy) and resection of the offending tissue. Although extensive experience supports the efficacy and safety of this approach, the attendant risks of open surgery with regard to procedural morbidity, incomplete resection, and damage to adjacent brain tissue cannot be completely eliminated. This supports a role for minimally invasive alternatives when treating certain epileptogenic lesions, especially those adjacent to or involving deep or eloquent brain structures, such as the dominant temporal lobe and deep brain structures (eg, hypothalamic hamartoma [HH]).
Laser ablation is a novel, minimally invasive surgical technique that is used in the treatment of focal, medically intractable pediatric epilepsy. Previous attempts with stereotactic lesioning for the treatment of epilepsy were limited due to the variability in thermal energy delivery and inability to achieve real-time feedback on the area of ablated tissue. Two systems, the Visualase device (Medtronic, Minneapolis, MN) and the Monteris device (Plymouth, MN), have recently been used for ablation of seizure foci. Generally, both systems consist of a laser catheter probe that is placed by the neurosurgeon into a previously identified epileptogenic focus via a small twist-drill cranial access site. The surgeon can then use real-time MRI thermal imaging to visualize treatment and tailor the ablation to encompass the entirety of the lesion while avoiding surrounding critical brain structures.
Early use of this approach in children with epilepsy shows its feasibility. It is particularly attractive for lesions such as HHs, in which the approach to the lesion can carry much of the morbidity. Deep heterotopia also may be targeted. Additionally, following the experience in adults, ablation of the dominant temporal hippocampus may provide improved neuropsychological outcomes compared with even selective resections.
Patient evaluation
Pediatric patients with focal, medically intractable epilepsy are considered for possible surgical treatment to include laser ablation. Children whose seizures are inadequately controlled on 2 or more antiepileptic medications meet criteria for intractable epilepsy and warrant additional workup for possible surgical treatment.
Initial evaluation of patients with new-onset epilepsy consists of assessment by a pediatric epileptologist with scalp electroencephalogram (EEG) and pharmacologic therapy, as deemed appropriate. High-resolution MRI is obtained to identify any potential underlying structural abnormalities, such as hippocampal sclerosis, HHs, gray matter heterotopia, cortical dysplasia, or masses that may represent the origin for the child’s seizures. All patients considered for surgery undergo long-term video EEG monitoring to provide additional information regarding seizure localization and semiology and attempt to correlate seizure origin with any relevant radiographic findings. Neuropsychological testing is performed to assist in identification of dysfunction that is relevant for localization, and preoperative consultations, especially for surgery in proximity to key structures involved in cognition, language, and memory, such as the dominant mesial temporal lobe. PET is frequently used and additional modalities are used as needed. Functional MRI is commonly used to assist in localization of function and assessment of reorganization from presumed seizure foci.
After evaluation in a multidisciplinary epilepsy conference, children with radiographic and electrographic correlation with a candidate epileptogenic focus amenable to surgery are referred for neurosurgical evaluation. Invasive monitoring may be needed to define the seizure-onset zone if the remainder of the evaluation is incongruent. In our pediatric population, the most common indications for laser ablation are mesial temporal sclerosis, HHs, and other focal lesions to include low-grade glioneuronal tumors, such as ganglioglioma and dysembryoplastic neuroepithelial tumor (DNET). Specific considerations regarding patient selection and evaluation are described for each of these in the following sections.
Mesial Temporal Sclerosis
Mesial temporal sclerosis (MTS) is of one of the most commonly encountered focal epilepsy pathologies. MTS may have a higher incidence of associated pathology (dual pathology) in the pediatric population. Radiographic findings consist of hippocampal signal change, loss of internal architecture, and/or volume loss on the affected side. Histopathologically confirmed MTS may have subtle imaging findings.
In these children, both open temporal lobectomy and laser ablation of the mesial temporal structures offer a reasonable approach to treatment, and they are used concurrently in our practice. Based on the adult experience of less cognitive decrement with laser ablation, we will typically offer laser ablation to those with suspected isolated dominant temporal lobe MTS foci. Semiology, EEG, or imaging features that suggest dual pathology would require either a larger resection or a limited treatment only after the use of invasive monitoring.
In adult patients with dominant mesial temporal lobe epilepsy, the experience at our and other institutions suggests that laser ablation offers improved neuropsychological outcomes when compared with standard open temporal lobectomy. A recent series of adult patients undergoing laser ablation for mesial temporal lobe epilepsy had significant preservation of famous face and common noun naming when compared with similar patients undergoing open temporal lobectomy.
In children, in whom there is concern for lateral temporal or extratemporal contribution to seizures on electrographic and/or radiographic evaluation, targeted laser ablation of the mesial temporal structures would be less effective in achieving acceptable seizure control. With nondominant temporal lobe involvement, the use of laser ablation would be balanced by the relatively good cognitive outcome with anterior temporal lobectomy and the concern of lower seizure control with a more limited treatment.
Laser ablation additionally offers patients and their families a less invasive approach to surgical management of intractable mesial temporal epilepsy. In patients in whom either laser ablation or standard open resection offers near equivalence in treatment benefits and risks, the preference of the child and his or her parents is a valid selection criterion. In our experience, the potential of a less-invasive treatment modality has allowed us to treat patients who would otherwise refuse open surgery.
Hypothalamic Hamartomas
HHs represent a rare congenital malformation involving the hypothalamus that present with a characteristic epilepsy syndrome. Seizures are classically gelastic type, which are characterized by spells of laughing and altered mental status. Gelastic seizures are notoriously medication-resistant and children with HHs can progress to epileptic encephalopathy with attendant impairments in behavior and cognition. Treatment of HHs with associated intractable epilepsy has been with open and endoscopic surgical resection. Based on their deep location and intimate association with the hypothalamus and other associated critical brain structures, surgery for these lesions carries not insignificant risks, to include endocrine dysfunction, weight gain, memory impairment, and even coma.
In children with HHs, we have moved to regarding laser ablation as first-line therapy. Laser ablation offers the benefit of minimal brain manipulation when compared with open and endoscopic surgical approaches. It additionally has the benefit of allowing real-time assessment of the area of thermal treatment; this provides the surgeon increased control, which is key when working adjacent to deep brain structures.
Low-Grade Glioneuronal Tumors
Low-grade glial neoplasms, such as ganglioglioma and DNET, represent an additional source of focal epilepsy in children. The most common presentation is seizures, which are commonly resistant to antiepileptic medication. Surgical management of these lesions is variable; children with intractable epilepsy usually undergo surgical management, which is effective in approximately 70% or more in providing seizure control.
Laser ablation is an alternative to standard open resection of these lesions. Recent literature supports the effectiveness of laser ablation in treating primary glial neoplasms and brain metastases in the adult population. We consider the use of laser ablation in children with these low-grade glial tumors and resultant intractable epilepsy in certain cases. The stereotactic frame used in placement of the laser catheter also can be used to obtain core tissue biopsies for pathology before thermal ablation. Also, the laser system can be used for treatment of multifocal lesions or in combination with a standard laser amygdalohippocampectomy in children with combined pathology.
Laser ablation
Surgical Technique
Anesthesia
A standard endotracheal intubation is performed with total intravenous anesthesia infusion of propofol and fentanyl with fine adjustment of sevoflurane, to allow for a motionless patient. An important aspect throughout the procedure is adequate analgesia and body temperature management, especially during patient transport. Important adjunct parts of anesthesia include the administration of preoperative antibiotics within 1 hour of incision. Other aspects of preoperative preparation include adequate placement of peripheral intravenous lines and insertion of urinary catheter for proper fluid management. Steroids are administered before performing the ablation to decrease treatment-associated edema, with dosing of dexamethasone at approximately 0.2 mg/kg up to 10 mg intravenously as a single dose, with a wide range of specific dosing possible based on practice preference. Active warming is used when the patient is not in transport or in the scanner.
Procedure
After endotracheal anesthesia is initiated, the Cosman-Roberts-Wells (CRW) frame is placed with the use of local anesthesia on pin sites ( Fig. 1 ). The patient is then transported to the radiology department for registration/planning study. For patients undergoing ablation on tumors or other similar lesions, a half-dose contrast-enhancing brain MRI is performed. Only half-dose contrast is administered on this initial brain MRI to be able to give contrast again on the posttreatment study. On patients with hamartomas or MTS, computed tomography (CT) of the head without contrast is performed and subsequently merged with a recent brain MRI. After the appropriated study has been performed, the patient is returned to the operating room (OR).
Related posts:
Hippocampal Transections for Epilepsy
Minimally Invasive Neurosurgery for Epilepsy Using Stereotactic MRI Guidance
The Role of Stereotactic Laser Amygdalohippocampotomy in Mesial Temporal Lobe Epilepsy
Stereo-Encephalography Versus Subdural Electrodes for Seizure Localization
Responsive Direct Brain Stimulation for Epilepsy
Neuromodulation for Epilepsy
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
