Stereotactic techniques in managing pediatric brain tumors

Utility of frameless stereotaxy in the resection of skull base and Basal cerebral lesions in children

Since 1991, we have performed nearly 300 stereotactic procedures using the ISG viewing wand on a variety of cranial lesions in patients under 22 years of age. Of these, 38 procedures were performed on 34 patients for basal cerebral and skull base lesions. Our patients ranged in age from 3.5 months to 22 years with a mean age of 9.45 years. There were 18 females and 16 males. Twenty-one patients had basal cerebral lesions located in the thalamus (10), basal ganglia (2), third ventricle (2), and hypothalamus (7). Thirteen patients had skull base lesions located within the anterior optic apparatus (3), sella turcica (4), middle and posterior cranial fossae (4), and craniocervical region (2). Preoperative CT and/or MRI scan images were taken as a volume acquisition and transferred to the computer workstation utilizing the ISG Wand software. This workstation was transferred to the operating room where it was calibrated to a faro Surgicom arm which interfaces with the patient and the three-dimensional radiological image. The ISG Wand was utilized to plan the scalp and bone flaps and to select the optional trajectory to lesion. The surgical approaches which were specifically used in this series with the ISG Wand included transcallosal (15), pterional (5), frontal (3), subtemporal (4), transsphenoidal (3), temporal (3), tumor cyst shunt insertion (1), burr hole drainage (1), transoral (2), bifrontal (1), bifrontal mid facial (1), and transnasal (1). Although brain shift occurred following craniotomy and with brain retraction, the relative immobility of these lesions at the skull or cerebral base permitted an accurate targeting of all lesions with an error range of 1.0-2.5 mm throughout the entire procedure. This relatively precise intraoperative feedback led to more accurate recognition of tumor landmarks. It is the authors' impression that a more aggressive resection of these lesions was achieved than could be without the device. We conclude that a frameless stereotactic device such as the ISG Wand is particularly valuable in the approach to skull base and basal cerebral tumors in children.

Endoscopic biopsy of brain tumors in children: diagnostic success and utility in guiding treatment strategies

OBJECT

Endoscopic biopsy is an important minimally invasive method of diagnosis in the initial management of lesions in children with intraventricular and periventricular tumors. The procedure can be performed in conjunction with CSF-diverting procedures for obstructive hydrocephalus. The authors present their single-institution experience in a predominantly pediatric series with respect to diagnostic efficacy, utility in guiding treatment plans, and safety.

METHODS

A retrospective review was conducted in a consecutive series of patients who underwent endoscopic biopsy of brain tumors during a 13-year period.

RESULTS

There were 33 endoscopic biopsies in 31 patients (16 males and 15 females). The average age of the patients was 11.3 years, with a mean follow-up duration of 2.4 years. The majority of biopsies were performed in conjunction with CSF-diverting procedures, such as endoscopic third ventriculostomy or fenestration of the septum pellucidum. Overall, 23 (70%) of 33 biopsies were diagnostic, with results that directed subsequent treatment. When stratified by tumor location, biopsy samples obtained in the lateral ventricle or pineal region were more favorable toward a successful diagnosis than those in the thalamus or tectal region. In 4 cases, elevated CSF tumor marker levels led to modification of the diagnosis and appropriate adjustment of treatment. The endoscopic third ventriculostomy success rate was 82.4%. There were 2 major complications (6.1%), which resulted in neurological deficits. There were no procedure-related deaths.

CONCLUSIONS

Endoscopic biopsy is an effective means of diagnosis of brain tumors in children. The diagnostic power may be more favorable with tumors in the lateral ventricle or pineal region. Collection of CSF during the procedure for tumor marker analysis is an integral component of diagnosis.

Pediatric arteriovenous malformation: University of Toronto experience using stereotactic radiosurgery

INTRODUCTION AND BACKGROUND

Arteriovenous malformations (AVMs) are congenital vascular lesions of the brain, which behave differently in pediatric population compared to adults. Treatment of pediatric AVMs includes a combination of microsurgery, embolization and radiation therapies. However, the role of radiosurgery in the treatment of pediatric AVMs is not fully accepted because of concerns regarding the long-term effects of radiation on the pediatric brain.

DISCUSSION

In this study, we review our experience at the University of Toronto with treating pediatric AVMs using linear accelerator-based (LINAC) radiosurgery over the past 15 years. We report our results, obliteration rates, and complications on a total of 40 patients. In addition, we provide a review of series published to date combined with our own results to determine whether radiosurgery is a safe and reasonable treatment modality for pediatric AVMs.

Stereotactic radiosurgery for pediatric intracranial arteriovenous malformations: the University of California at San Francisco experience

OBJECT

Stereotactic radiosurgery for arteriovenous malformations (AVMs) is an accepted treatment option, but few reports have been published on the results of this treatment in children. In this study the authors describe a series of pediatric patients with a minimum follow-up duration of 36 months.

METHODS

From 1991 to 1997, 40 children (26 boys and 14 girls) with AVMs were treated with radiosurgery at the University of California at San Francisco (UCSF). Follow-up information was available for 31 children (20 boys and 11 girls) in whom the median age at initial treatment was 11.2 years (range 3.4-17.5 years). The median follow-up duration was 60 months (range 6-99 months). Sixteen percent of the AVMs were Spetzler-Martin Grade II; 68%, Grade III; 10%, Grade IV; and 6%, Grade V. The mean volume of the AVMs was 5.37 cm3 and the median volume was 1.6 cm3. The mean marginal dose of radiation was 16.7 Gy and the median dose was 18 Gy (range 12-19 Gy). Angiography performed in 26 children confirmed obliteration of the AVM nidus in nine patients (35%), partial response in 16 patients (62%), and no response in one patient (4%). In five patients who refused angiography, magnetic resonance (MR) imaging revealed obliteration in two patients and partial response in three patients, bringing the overall obliteration rate associated with initial radiosurgery to 35%. Logistic regression analysis confirmed a significant correlation between marginal dose prescription and response (p = 0.025); in AVMs that received at least 18 Gy there was a 10-fold increase in the obliteration rate (63%) over AVMs that received a lower dose. Lesions smaller than 3 cm3 were associated with a six-fold increased obliteration rate (53%) over lesions larger than 3 cm3 (8%), but AVM volume was not a statistically significant predictor of response (p = 0.09). Twelve patients have since undergone repeated radiosurgery and are currently being followed up with serial MR imaging studies (in five cases, the AVM is now obliterated). During the follow-up period (1918 patient-months) there were eight hemorrhages in five patients, with a cumulative posttreatment hemorrhage rate of 3.2%/patient/year in the 1st year and a rate of 4.3%/patient/year over the first 3 years. There were two permanent neurological complications (6%) and no deaths in this study.

CONCLUSIONS

The lower overall obliteration rate reported in this series is most likely due to the larger mean AVM volumes treated at UCSF as well as conservative dose-volume prescriptions delivered to children. Significantly higher obliteration rates were observed when a marginal radiation dose of at least 18 Gy was delivered. The permanent complication rate is low and should encourage those treating children to use doses similar to those used in adults.

Technique of stereotactic biopsy in a 5-month-old child

We describe a technique of stereotactic frame-based biopsy in young children who have open fontanels and a deformable skull. A 5-month-old girl with a growing lesion in the right thalamus and basal ganglia underwent stereotactic biopsy, which disclosed an anaplastic astrocytoma. To avoid insertion of the four stereotactic frame fixation pins through the infant's skin and into bone, the pins were advanced into the hollowed end of rubber tops obtained from Vacutainer blood sampling tubes. The pressure applied to the skin was diffused through the rubber onto a wide skin surface, obviating skin puncture or bone deformation. This technique provided firm head fixation, and target accuracy was confirmed on post-operative imaging. This technique is safe and should permit use of conventional stereotactic techniques in young infants.

Malignant gliomas in children

Childhood supratentorial malignant gliomas, though less common than those in adults, are responsible for disproportionately high morbidity and mortality rates. Important advances have been made in our ability to diagnose these tumors by noninvasive neuroimaging techniques. In addition, progress has been made in our ability to correlate pathology and biological features with clinical outcomes to provide prognostic information. Neuroimaging and tissue prognostic factors now have important roles which directly affect clinical management. While surgery and radiation therapy are critical components of the treatment of childhood supratentorial gliomas, the role of chemotherapy is less clear. Significant responses have been demonstrated for chemotherapy regimens in infants with malignant gliomas and high-dose chemotherapy and ABMR regimens also produce encouraging response rates. The results of current clinical trials will help us determine if these response rates will translate into prolonged patient survival and allow us to identify subgroups of childhood malignant glioma patients that may benefit from adjuvant chemotherapy.