Functional brain mapping using positron emission tomography scanning in preoperative neurosurgical planning for pediatric brain tumors

Outcomes of tumour related epilepsy in a specialised epilepsy surgery unit

INTRODUCTION

Seizures are an important cause of morbidity in patients with low grade gliomas with approximately 40% of cases drug resistant. The pathogenesis is quite complex and poorly understood. The treatment aims vary between almost purely epilepsy considerations and those that are primarily oncologic.

AIM

To determine whether patients who present with seizures and are found to have a low grade glioma have better outcomes when managed through a specialized epilepsy unit compared to the general neurosurgical service.

METHODS

A review of the prospectively collected database was performed over a 10 year period to identify 48 adult patients who present with a seizure and were subsequently found to have a low grade glioma. These patients were analysed with respect to management through the specialized epilepsy service or the general neurosurgical service. The primary outcome was Engel classification between the two groups. Secondary outcomes included recurrence, postoperative deficits, delay to surgery, histology, grade and extent of resection.

OUTCOMES

The patients managed through the epilepsy service had significantly higher rate of favourable Engel outcomes (I and II) compared to the general neurosurgery service (OR: 13.2, 95% CI: 1.239-140.679; P = 0.033). The epilepsy surgery group patients had a significantly higher delay to surgery (P < 0.001). The patients in the epilepsy service had a significantly higher resection ratio compared to the general neurosurgery service (73% vs 127%, P = 0.014). Rates of recurrence were not different between the two groups.

CONCLUSION

Patients with tumour related epilepsy who undergo an intensive presurgical evaluation may obtain better seizure related outcomes.

Ability of (18)F-DOPA PET/CT and fused (18)F-DOPA PET/MRI to assess striatal involvement in paediatric glioma

PURPOSE

To assess the diagnostic performance of (18)F-DOPA PET/CT and fused (18)F-DOPA PET/MRI in detecting striatal involvement in children with gliomas.

METHODS

This retrospective study included 28 paediatric patients referred to our institution for the presence of primary, residual or recurrent glioma (12 boys, 16 girls; mean age 10.7 years) and investigated with (18)F-DOPA PET/CT and brain MRI. Fused (18)F-DOPA PET/MR images were obtained and compared with PET/CT and MRI images. Accuracy, sensitivity, specificity, negative predictive value (NPV) and positive predictive value (PPV) for striatal involvement were calculated for each diagnostic tool. Univariate and multivariate logistic analyses were applied to evaluate the associations between (18)F-DOPA PET/CT and fused (18)F-DOPA PET/MRI diagnostic results and tumour uptake outside the striatum, grade, dimension and site of striatal involvement (ventral and/or dorsal).

RESULTS

Accuracy, sensitivity, specificity, PPV, and NPV were 100 % for MRI, 93 %, 89 %, 100 %, 100 % and 82 % for (18)F-DOPA PET/MRI, and 75 %, 74 %, 78 %, 88 % and 58 % for (18)F-DOPA PET/CT, respectively. (18)F-DOPA PET/MRI showed a trend towards higher accuracy compared with (18)F-DOPA PET/CT (p = 0.06). MRI showed significantly higher accuracy compared with (18)F-DOPA PET/CT (p = 0.01), but there was no significant difference between MRI and (18)F-DOPA PET/MRI. Both univariate and multivariate logistic analyses showed a significant association (OR 8.0 and 7.7, respectively) between the tumour-to-normal striatal uptake (T/S) ratio and the diagnostic ability of (18)F-DOPA PET/CT (p = 0.03). A strong significant association was also found between involvement of the dorsal striatum and the (18)F-DOPA PET/CT results (p = 0.001), with a perfect prediction of involvement of the dorsal striatum by (18)F-DOPA PET/MRI.

CONCLUSION

Physiological striatal (18)F-DOPA uptake does not appear to be a main limitation in the evaluation of basal ganglia involvement.(18)F-DOPA PET/CT correctly detected involvement of the dorsal striatum in lesions with a T/S ratio >1, but appeared to be less suitable for evaluation of the ventral striatum. The use of fused (18)F-DOPA PET/MRI further improves the accuracy and is essential for evaluation of the ventral striatum.

Usefulness of PET Imaging to Guide Treatment Options in Gliomas

OPINION STATEMENT

Magnetic resonance imaging (MRI) is the gold standard guiding diagnostic and therapeutic management in glioma with its high resolution and possibility to depict blood-brain-barrier disruption when contrast medium is applied. In light of the shifting paradigms revealing distinct tumor subtypes based on the molecular and genetic characterization and increasing knowledge about the variability of glioma biology, additional imaging modalities such as positron emission tomography (PET) depicting metabolic processes gain further importance in the management of glioma.

The contribution of functional near-infrared spectroscopy (fNIRS) to the presurgical assessment of language function in children

Before performing neurosurgery, an exhaustive presurgical assessment is required, usually including an investigation of language cerebral lateralization. Among the available procedures, the intracarotid amobarbital test (IAT) was formerly the most widely used. However, this procedure has many limitations: it is invasive and potentially traumatic, especially for children. To overcome these limitations, neuroimaging techniques such as functional magnetic resonance imaging (fMRI) have been used. Again, these methods are difficult to use with children, who must remain motionless during data acquisition. Functional near-infrared spectroscopy (fNIRS) is a noninvasive functional imaging technique that is easily applied to pediatric and cognitively limited patients. It has been used recently in epileptic children for presurgical assessment of expressive and receptive language brain lateralization. The aim of this review is to present the contribution of fNIRS to the presurgical assessment of language function in children with neurological diseases.

Brain tumors

For most cancers, PET is essentially a diagnostic tool. For brain tumors, PET has got its main contribution at the level of the therapeutic management. Indeed, specific reasons render the therapeutic management of brain tumors, especially gliomas, a real challenge. Although some gliomas may appear well-delineated on conventional neuroimaging such as CT and MRI, they are by nature infiltrating neoplasms and the interface between tumor and normal brain tissue may not be accurately defined. Moreover, gliomas may present as ill-defined lesions for which various MRI sequences combination does not provide a unique contour for tumor delineation. Also, gliomas are often histologically heterogeneous with anaplastic areas evolving within a low-grade tumor, and contrast-enhancement on CT or MRI does not represent a good marker for anaplastic tissue detection. Finally, assessment of tumor residue, recurrence, or progression, may be altered by different signals related to inflammation or adjuvant therapies, and contrast enhancement on CT and MRI is not an appropriate marker at the postoperative or posttherapeutic stage. These limitations of conventional neuroimaging in detecting tumor tissue, delineating tumor extent and evidencing anaplastic changes, lead to potential inaccuracy in lesion targeting at different steps of the management (diagnostic, surgical, postoperative, and posttherapeutic stages). Molecular information provided by PET has proved helpful to supplement morphological imaging data in this context. F-18 FDG and amino-acid tracers such as C-11 methionine (C-11 MET) provide complementary metabolic data that are independent from the anatomical MR information. These tracers help in the definition of glioma extension, detection of anaplastic areas, and postoperative follow-up. Additionally, PET data have a prognostic value independently of histology. To take advantage of PET data in glioma treatment, PET might be integrated in the planning of image-guided biopsy, resection, and radiosurgery.

Clinical applications of PET and PET/CT in pediatric malignancies

The common childhood cancers are leukemia, CNS tumors, lymphomas, soft-tissue tumors (such as rhabdomyosarcoma and fibrosarcoma), neuroblastoma, malignant bone tumors, germ cell tumors with neoplasms of gonads and hepatic tumors. Usually the conventional imaging modalities, such as x-ray, ultrasound, computed tomography (CT) and MRI, are being routinely used for the management of these pediatric malignancies. However, most of these modalities provide structural information and are lacking in functional/metabolic status of these malignancies. Recently, PET and PET/CT have emerged as a functional diagnostic imaging modality for the management of various cancers in adult population. Up to now most of the data published in the literature are on PET alone. PET used in conjunction with CT is useful as it provides an enhanced view of the anatomical details and the malignant focus then can be located with highest accuracy. PET and PET/CT has been found to be useful in, for example, CNS tumors, lymphomas, soft-tissue tumors, neuroblastoma, malignant bone tumors and germ cell tumors. PET/CT has a limited role in early diagnosis, however, it plays an important role in initial staging, treatment response evaluation and detection of metastatic disease in these cancers. Despite the fact that PET/CT has better diagnostic value when compared with conventional imaging, such as CT and MRI, in the management of many pediatric cancers, there are certain limitations. PET/CT has a limited role in detection of lesions smaller than 5 mm, well-differentiated tumors and tumors with low metabolic rate. Many infections and inflammation can lead to false-positive PET/CT results. In the present review we will discuss the various clinical indications of PET and PET/CT in pediatric cancers.

PET imaging for pediatric oncology: an assessment of the evidence

Positron emission tomography (PET) has shown potential benefits when used in therapeutic clinical trials for children with cancer. However, existing trials are limited in scope with small numbers of patients and varied observations, making accurate conclusions about the usefulness of PET scanning impossible. This review examines PET and its applications in pediatric oncology. While evidence is limited, there appears to be a basis for rigorous evaluation of this imaging modality before widespread application without validation from clinical trials.

The value of positron emission tomography and proliferation index in predicting progression in low-grade astrocytomas of childhood

Astrocytomas are the most common brain tumors of childhood and adolescence. Low-grade astrocytomas (LGAs), in general, have favorable prognosis, but recurrence or progressive disease with dissemination, malignant transformation, and death occur in some cases. Current clinical and pathological measures including age, sex, imaging characteristics, location and size of the tumor, histopathology, and degree of resection cannot predict with certainty which tumors will demonstrate aggressive behavior. The objective of the study is to determine the predictive value of positron emission tomography (PET) and a proliferation index (PI) in identifying high risk LGAs. We reviewed 46 cases ages 5 months to 17 years with low-grade (WHO I-II) astrocytomas. All patients had PET scans utilizing [(18)F] fluorodeoxyglucose (FDG) and 24 cases had measurements with Ki-67/MIB-1 immunohistochemistry. Review of our data confirmed progressive disease (PD) in 18/46 (39%) of cases with 9/21 (42%) occurring after subtotal resection and 9/25 (36%) after gross total resection. The mortality rate was 5/46 (10.8%). Tumors with FDG hypermetabolism were significantly more likely to demonstrate aggressive behavior and PD. Increased PI values also suggested PD. Progression-free survival and time to progression were significantly longer for patients with hypometabolic scans. Time to progression was significantly longer with lower PI values. Results demonstrate that PET and PI are useful measures in the identification and stratification of high risk LGAs. The ability to identify a subset of progressive LGAs earlier may suggest the need for second-look neurosurgical procedures or more intensified adjuvant treatment that may ultimately improve outcome and survival.

POSITRON EMISSION TOMOGRAPHY-GUIDED VOLUMETRIC RESECTION OF SUPRATENTORIAL HIGH-GRADE GLIOMAS

OBJECTIVE

Integrating positron emission tomographic (PET) images into the image-guided resection of high-grade gliomas (HGG) has shown that metabolic information on tumor heterogeneity and distribution are useful for planning surgery, improve tumor delineation, and provide a final target contour different from that obtained with magnetic resonance imaging (MRI) alone in about 80% of the procedures. Moreover, PET guidance helps to increase the amount of tumor removed and to target image-guided resection to anaplastic tissue areas. The present study aims to evaluate whether PET-guided volumetric resection (VR) in supratentorial HGG might add benefit to the patient's outcome.

METHODS

PET images using [18F]fluorodeoxyglucose (n=23) and [11C]methionine (n=43) were combined with MRI scans in the planning of VR procedures performed at the initial stage in 66 consecutive patients (43 M/23 F) with supratentorial HGG according to the technique previously described. In all cases (35 anaplastic gliomas [20 astrocytomas, 10 oligoastrocytomas, 5 oligodendrogliomas] and 31 glioblastomas [GBM]), level and distribution of PET tracer uptake were analyzed to define a PET contour projected on MRI scans to define a final target contour for VR. Maximal tumor resection was accomplished in each case, with the intention to remove the entire abnormal metabolic area comprised in the surgical planning. Early postoperative MRI and PET assessed tumor resection. Survival analysis was performed separately in anaplastic gliomas and glioblastoma multiforme according to the presence or absence of residual tracer uptake on postoperative PET and according to the presence or absence of residual contrast enhancement on postoperative MRI.

RESULTS

Preoperatively, metabolic information helped the surgical planning. In all procedures, PET contributed to define a final target contour different from that obtained with MRI alone. Postoperatively, 46 of 66 patients had no residual PET tracer uptake (total PET resection), 23 of 66 had no residual MRI contrast enhancement. No additional neurological morbidity due to the technique was reported. A total PET tracer uptake resection was associated with a significantly longer survival in anaplastic gliomas (P = 0.0071) and in glioblastoma multiforme (P = 0.0001), respectively. A total MRI contrast enhancement resection was not correlated with a significantly better survival, neither in anaplastic gliomas (P = 0.6089) nor in glioblastoma multiforme (P = 0.6806).

CONCLUSIONS

Complete resection of the increased PET tracer uptake prolongs the survival of HGG patients. Because PET information represents a more specific marker than MRI enhancement for detecting anaplastic tumor tissue, PET-guidance increases the amount of anaplastic tissue removed in HGG.

Clinical Application of PET in Pediatric Brain Tumors

While rare in adults, central nervous system tumor is the most common solid tumor in childhood and is the leading cause of cancer death in children. Childhood brain tumors are different from those in adults in epidemiology, histologic features, and responses to treatment. Gliomas make up over one-half of all childhood brain tumors. Clinical application of PET imaging in brain tumors has demonstrated that it is helpful in tumor grading, establishing prognosis, defining targets for biopsy, and planning resection. This article emphasizes PET applications in childhood brain tumors, focusing on mainly gliomas with regard to tumor-grading and prognosis, distinguishing tumor recurrence from radiation necrosis, and PET guided diagnosis and treatment.

Nuclear Medicine in Pediatric Neurology and Neurosurgery: Epilepsy and Brain Tumors

In pediatric drug-resistant epilepsy, nuclear medicine can provide important additional information in the presurgical localization of the epileptogenic focus. The main modalities used are interictal (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) and ictal regional cerebral perfusion study with single-photon emission computed tomography (SPECT). Nuclear medicine techniques have a sensitivity of approximately 85% to 90% in the localization of an epileptogenic focus in temporal lobe epilepsy; however, in this clinical setting, they are not always clinically indicated because other techniques (eg, icterictal and ictal electroencephalogram, video telemetry, magnetic resonance imaging [MRI]) may be successful in the identification of the epileptogenic focus. Nuclear medicine is very useful when MRI is negative and/or when electroencephalogram and MRI are discordant. A good technique to identify the epileptogenic focus is especially needed in the setting of extra-temporal lobe epilepsy; however, in this context, identification of the epileptogenic focus is more difficult for all techniques and the sensitivity of the isotope techniques is only 50% to 60%. This review article discusses the clinical value of the different techniques in the clinical context; it also gives practical suggestions on how to acquire good ictal SPECT and interictal FDG-PET scans. Nuclear medicine in pediatric brain tumors can help in differentiating tumor recurrence from post-treatment sequelae, in assessing the response to treatment, in directing biopsy, and in planning therapy. Both PET and SPECT tracers can be used. In this review, we discuss the use of the different tracers available in this still very new, but promising, application of radioisotope techniques.

Predicting the location of mouth motor cortex in patients with brain tumors by using somatosensory evoked field measurements

Object

Before resective brain surgery, localization of the functional regions is necessary to minimize postoperative deficits. The face area has been relatively difficult to map noninvasively by using functional imaging techniques. Preoperative localization of face somatosensory cortex with magnetoencephalography (MEG) may allow the surgeon to predict the location of mouth motor areas.

Methods

The authors compared the location of face somatosensory cortex obtained with somatosensory evoked fields during preoperative MEG with the mouth motor areas identified during intraoperative electrocortical stimulation (ECS) mapping in 13 patients undergoing resection of brain tumor.

Results

In this group of patients, ECS mouth motor sites were usually anterior and lateral to MEG localizations of lip somatosensory cortex. The consistent quantitative relationship between results of these two mapping procedures allows the practitioner to predict the location of mouth motor cortex based on noninvasive preoperative MEG measurements.

Conclusions

Based on this result, the authors suggest that somatosensory mapping using MEG can be used to guide intraoperative mapping and neurosurgical planning.

PET imaging in the surgical management of pediatric brain tumors

OBJECTIVE

The present article illustrates whether positron-emission tomography (PET) imaging may improve the surgical management of pediatric brain tumors (PBT) at different steps.

MATERIALS AND METHODS

Among 400 consecutive PBT treated between 1995 and 2005 at Erasme Hospital, Brussels, Belgium, we have studied with (18) F-2-fluoro-2-deoxy-D-glucose (FDG)-PET and/or L-(methyl-(11)C)methionine (MET)-PET and integrated PET images in the diagnostic workup of 126 selected cases. The selection criteria were mainly based on the lesion appearance on magnetic resonance (MR) sequences. Cases were selected when MR imaging showed limitations for (1) assessing the evolving nature of an incidental lesion (n = 54), (2) selecting targets for contributive and accurate biopsy (n = 32), and (3) delineating tumor tissue for maximal resection (n = 40). Whenever needed, PET images were integrated in the planning of image-guided surgical procedures (frame-based stereotactic biopsies (SB), frameless navigation-based resections, or leksell gamma knife radiosurgery).

RESULTS

Like in adults, PET imaging really helped the surgical management of the 126 children explored, which represented about 30% of all PBT, especially when the newly diagnosed brain lesion was (1) an incidental finding so that the choice between surgery and conservative MR follow-up was debated, and (2) so infiltrative or ill-defined on MR that the choice between biopsy and resection was hardly discussed. Integrating PET into the diagnostic workup of these two selected groups helped to (1) take a more appropriate decision in incidental lesions by detecting tumor/evolving tissue; (2) better understand complex cases by differentiating indolent and active components of the lesion; (3) improve target selection and diagnostic yield of stereotactic biopsies in gliomas; (4) illustrate the intratumoral histological heterogeneity in gliomas; (5) provide additional prognostic information; (6) reduce the number of trajectories in biopsies performed in eloquent areas such as the brainstem or the pineal region; (7) better delineate ill-defined PBT infiltrative along functional cortex than magnetic resonance imaging (MRI); (8) increase significantly, compared to using MRI alone, the number of total tumor resection and the amount of tumor tissue removed in PBT for which a total resection is a key-factor of survival; (9) target the resection on more active areas; (10) improve detection of tumor residues in the operative cavity at the early postoperative stage; (11) facilitate the decision of early second-look surgery for optimizing the radical resection; (12) improve the accuracy of the radiosurgical dosimetry planning.

CONCLUSIONS

PET imaging may improve the surgical management of PBT at the diagnostic, surgical, and post-operative steps. Integration of PET in the clinical workup of PBT inaugurates a new approach in which functional data can influence the therapeutic decision process. Although metabolic information from PET are valid and relevant for the clinical purposes, further studies are needed to assess whether PET-guidance may decrease surgical morbidity and increase children survival.

SURGERY OF INTRINSIC CEREBRAL TUMORS

TUMORS AND OTHER structural lesions located with and adjacent to the cerebral cortex present certain challenges in terms of the overall management and design of surgical strategies. This comprehensive analysis attempts to define the current understanding of cerebral localization and function and includes the latest advances in functional imaging, as well as surgical technique, including localization of tumors and neurophysiological mapping to maximize extent of resection while minimizing morbidity. Finally, it remains to be seen whether or not stimulation mapping will be the most useful way to identify function within the cortex in the future. Another potential paradigm would be to actually record baseline oscillatory rhythms within the cortex and, following presentation of a given task, determine if those rhythms are disturbed enough to identify eloquent cortex as a means of functional localization. This would be a paradigm shift away from stimulation mapping, which currently deactivates the cortex, as opposed to identifying an activation function which identifies functional cortex.

Molecular Imaging of Brain Tumors: A Bridge Between Clinical and Molecular Medicine?

As the research on cellular changes has shed invaluable light on the pathophysiology and biochemistry of brain tumors, clinical and experimental use of molecular imaging methods is expanding and allows quantitative assessment. The term molecular imaging is defined as the in vivo characterization and measurement of biologic processes at the cellular and molecular level. Molecular imaging sets forth to probe the molecular abnormalities that are the basis of disease rather than to visualize the end effects of these molecular alterations and, therefore, provides different additional biochemical or molecular information about primary brain tumors compared to histological methods "classical" neuroradiological diagnostic studies. Common clinical indications for molecular imaging contain primary brain tumor diagnosis and identification of the metabolically most active brain tumor reactions (differentiation of viable tumor tissue from necrosis), prediction of treatment response by measurement of tumor perfusion, or ischemia. The interesting key question remains not only whether the magnitude of biochemical alterations demonstrated by molecular imaging reveals prognostic value with respect to survival, but also whether it identifies early disease and differentiates benign from malignant lesions. Moreover, an early identification of treatment success or failure by molecular imaging could significantly influence patient management by providing more objective decision criteria for evaluation of specific therapeutic strategies. Specially, as molecular imaging represents a novel technology for visualizing metabolism and signal transduction to gene expression, reporter gene assays are used to trace the location and temporal level of expression of therapeutic and endogenous genes. Molecular imaging probes and drugs are being developed to image the function of targets without disturbing them and in mass amounts to modify the target's function as a drug. Molecular imaging helps to close the gap between in vitro and in vivo integrative biology of disease.

Integrated positron emission tomography and magnetic resonance imaging–guided resection of brain tumors: a report of 103 consecutive procedures

Object

The aim of this study was to evaluate the integration of positron emission tomography (PET) scanning data into the image-guided resection of brain tumors.

Methods

Positron emission tomography scans obtained using fluorine-18 fluorodeoxyglucose (FDG) and l-[methyl-11C]methionine (MET) were combined with magnetic resonance (MR) images in the navigational planning of 103 resections of brain tumors (63 low-grade gliomas [LGGs] and 40 high-grade gliomas [HGGs]). These procedures were performed in 91 patients (57 males and 34 females) in whom tumor boundaries could not be accurately identified on MR images for navigation-based resection. The level and distribution of PET tracer uptake in the tumor were analyzed to define the lesion contours, which in turn yielded a PET volume. The PET scanning–demonstrated lesion volume was subsequently projected onto MR images and compared with MR imaging data (MR volume) to define a final target volume for navigation-based resection—the tumor contours were displayed in the microscope’s eyepiece. Maximal tumor resection was accomplished in each case, with the intention of removing the entire area of abnormal metabolic activity visualized during surgical planning. Early postoperative MR imaging and PET scanning studies were performed to assess the quality of tumor resection. Both pre- and postoperative analyses of MR and PET images revealed whether integrating PET data into the navigational planning contributed to improved tumor volume definition and tumor resection.

Metabolic information on tumor heterogeneity or extent was useful in planning the surgery. In 83 (80%) of 103 procedures, PET studies contributed to defining a final target volume different from that obtained with MR imaging alone. Furthermore, FDG-PET scanning, which was performed in a majority of HGG cases, showed that PET volume was less extended than the MR volume in 16 of 21 cases and contributed to targeting the resection to the hypermetabolic (anaplastic) area in 11 (69%) of 16 cases. Performed in 59 LGG cases and 23 HGG cases, MET-PET demonstrated that the PET volume did not match the MR volume and improved the tumor volume definition in 52 (88%) of 59 and 18 (78%) of 23, respectively. Total resection of the area of increased PET tracer uptake was achieved in 54 (52%) of 103 procedures.

Conclusions

Imaging guidance with PET scanning provided independent and complementary information that helped to assess tumor extent and plan tumor resection better than with MR imaging guidance alone. The PET scanning guidance could help increase the amount of tumor removed and target image-guided resection to tumor portions that represent the highest evolving potential.

Integration of [11C]Methionine-Positron Emission Tomographic and Magnetic Resonance Imaging for Image-guided Surgical Resection of Infiltrative Low-grade Brain Tumors in Children

OBJECTIVE:

To evaluate the interest of integrating positron emission tomography (PET) images with the radiolabeled tracer [11C]methionine (Met) into the image-guided navigation planning of infiltrative low-grade brain tumors (LGBTs) in children.

METHODS:

Twenty-two children underwent combined Met-PET with magnetic resonance imaging (MRI) scans in the planning of a navigation procedure. These children presented an LGBT (astrocytomas, 10; oligodendrogliomas, 4; ependymomas, 4; gangliogliomas, 4) located close to functional areas. Tumor boundaries were ill-defined on MRI (including T2-weighted and fluid-attenuated inversion-recovery scans) and could not be clearly identified for allowing a complete, or at least a large, image-guided resection. The PET tracer Met was chosen because of its higher sensitivity and specificity than MRI to detect tumor tissue. The level and extension of MET uptake were analyzed to define the PET contour, subsequently projected onto MRI scans to define a final target contour for volumetric resection. The quality of tumor resection was assessed by an early postoperative MRI and Met-PET workup.

RESULTS:

In 20 of the 22 children with ill-defined LGBTs, PET improved tumor delineation and contributed to define a final target contour different from that obtained with MRI alone. Met-PET guidance allowed a total resection of Met uptake in 17 cases that were considered total tumor resections because the operative margin left in place contained nontumor tissue.

CONCLUSION:

These data suggested that Met-PET guidance could help to improve the number of total resections and the amount of tumor removed in infiltrative LGBTs in children.

Positron emission tomography for the early postsurgical evaluation of pediatric brain tumors

OBJECT

The object was to study the value of postoperative positron emission tomography (PET) to assess the extension of brain tumor resection.

METHODS

Twenty children operated on for total resection of a glial tumor (18 low-grade, 2 anaplastic) presented a signal on postoperative magnetic resonance (MR) images raising the question of a possible tumor residue. PET was performed early ((18)F-Fluoro-deoxyglucose in 1, (11)C-methionine in 16, both in 3) to further characterize the nature of the abnormal MR signal in order to consider second-look surgery. An increased tracer uptake found in 14 children led to reoperation on 11 of them, confirming the tumor histologically. No (11)C-methionine uptake led to a conservative attitude in 6 children in whom MR imaging follow-up showed no tumor progression.

CONCLUSIONS

The early postoperative PET, especially with (11)C-methionine, appears to be a valid basis for complementary therapeutic decisions, especially second-look surgery, in glial tumors for which a radical resection is a key factor for prognosis.

The development of functional imaging in the diagnosis, management and understanding of childhood brain tumours

Imaging plays a fundamental role in the management of children with brain tumours. A series of new techniques, commonly grouped under the heading functional imaging, promise to give information on the properties and biological characteristics of tissues thereby adding to the structural information available from current imaging. The EPSRC funded a workshop to bring together clinicians from the UK Children's Cancer Study Group and scientific experts in the field to identify clinical problems in childhood brain tumours that may be addressed by functional imaging and to develop a clinical test bed for applying, evaluating and developing this new technology. The presentations and discussion sessions from the workshop are summarised and a review of the current 'state of the art' for this rapidly developing area provided. A key output of the workshop was agreement on a series of hypotheses which can be tested in carefully designed clinical studies.

Stereotactic biopsy guidance in adults with supratentorial nonenhancing gliomas: role of perfusion-weighted magnetic resonance imaging

OBJECT

The. diagnosis of low-grade glioma (LGG) cannot be based exclusively on conventional magnetic resonance (MR) imaging studies, and target selection for stereotactic biopsy is a crucial issue given the high risk of sampling errors. The authors hypothesized that perfusion-weighted imaging could provide information on the microcirculation in presumed supratentorial LGGs.

METHODS

All adult patients with suspected (nonenhancing) supratentorial LGGs on conventional MR imaging between February 2001 and February 2004 were included in this study. Preoperative MR imaging was performed using a dynamic first-pass gadopentate dimeglumine-enhanced spin echo-echo planar perfusion-weighted sequence, and the tumors' relative cerebral blood volume (rCBV) measurements were expressed in relation to the values observed in contralateral white matter. In patients with heterogeneous tumors a stereotactic biopsy was performed in the higher perfusion areas before resection. Among 21 patients (16 men and five women with a mean age of 36 years, range 23-60 years), 10 had diffuse astrocytomas (World Health Organization Grade II) and 11 had other LGGs and anaplastic gliomas. On perfusion-weighted images demonstrating heterogeneous tumors, areas of higher rCBV focus were found to be oligodendrogliomas or anaplastic astrocytomas on stereotactic biopsy; during tumor resection, however, specimens were characterized predominantly as astrocytomas. Diffuse astrocytomas were associated with significantly lower mean rCBV values compared with those in the other two lesion groups (p < 0.01). The rCBV ratio cutoff value that permitted better discrimination between diffuse astrocytomas and the other lesion groups was 1.2 (80% sensitivity and 100% specificity).

CONCLUSIONS

Perfusion-weighted imaging is a feasible method of reducing the sampling error in the histopathological diagnosis of a presumed LGG, particularly by improving the selection of targets for stereotactic biopsy.

Intraoperative electrical stimulation mapping as an aid for surgery of intracranial lesions involving motor areas in children

OBJECTIVE

We analysed the usefulness of intraoperative electrical stimulation mapping (ESM) for locating motor pathways in pediatric patients harboring cerebral lesions closely related to motor areas.

METHODS

We applied ESM in 17 consecutive pediatric patients operated on under general anesthesia. It was possible to locate motor function in 15 patients and in all children 5 years old and younger, as well as in all patients presenting with severe motor deficits, using relatively high current intensities. Intraoperative seizures occurred in 20% of our patients. A macroscopically complete removal of the lesion was carried out in 12 cases out of 17 with no definitive postoperative aggravation. Motor function improved for all patients presenting preoperatively with a severe paresis.

CONCLUSION

In our experience ESM revealed to be an useful tool for allowing us to push the resection of any lesion infringing on eloquent cortex up to the limit of functional areas, even in cases in very young and severely paretic children.

Magnetocephalography: a noninvasive alternative to the Wada procedure

Object. In this study the authors evaluated the sensitivity and selectivity of a noninvasive language mapping procedure based on magnetoencephalography (MEG), for determining hemispheric dominance for language functions.

Methods. Magnetic activation profiles of the brain were obtained from 100 surgical candidates (age range 8–56 years) with medically intractable seizure disorder by using a whole-head MEG system within the context of a word recognition task. The degree of language-specific activity was indexed according to the number of consecutive sources (modeled as single, moving current dipoles) in perisylvian brain areas. Only activity sources that were observed with a high degree of spatial and temporal overlap in two split-half data sets were used to compute the MEG laterality index. Independently, all patients underwent Wada testing for the determination of hemispheric dominance for language.

Independent clinical judgments based on MEG and Wada data showed a high degree of concordance (87%). Magnetoencephalography laterality judgments had an overall sensitivity of 98%, but a lower selectivity of 83%, which was due to the fact that MEG detected more activity in the nondominant hemisphere than was predicted based on the Wada test. A number of objective criteria were derived based on this large patient series to ensure data quality and bolster the clinical usefulness of MEG for language mapping.

Conclusions. Although the availability of MEG is still limited across epilepsy surgery centers, this study method may be substituted for the Wada procedure in assessing hemispheric dominance for language in select cases.

Pediatric brain tumors

Brain tumors in children vary with regard to histology, location, gender distribution, and age of onset. The past several decades have witnessed substantial improvements in the diagnosis and treatment. As a result, the number of long-term survivors also has increased continuously. Recent advances in neuroimaging facilitate tumor localization and mapping of brain function by noninvasive techniques and are becoming important in preoperative assessment for brain tumors. Surgery remains the mainstay of treatment of many tumor types. A role for chemotherapy is emerging, particularly for nonresectable tumors and in infants, for whom the adverse effects of radiation therapy are severe. Despite the improved treatments and prognostic data, however, many long-term survivors experience significant neurocognitive and developmental deficits.

Language lateralization in patients with temporal lobe epilepsy: a comparison of functional transcranial Doppler sonography and the Wada test

This study prospectively investigates whether noninvasive functional transcranial Doppler sonography (fTCD) is a useful tool to determine hemispheric language lateralization in the presurgical evaluation of patients with medically intractable temporal lobe epilepsy (TLE). fTCD results were compared with the Wada test as the gold standard. Wada test and fTCD were performed in 13 patients suffering from TLE. fTCD continuously measured blood flow velocities in both middle cerebral arteries, while the patient was performing a cued word generation task. During the Wada test, spontaneous speech, comprehension, reading, naming, and repetition were investigated. A laterality index (LI) was obtained by both procedures. Due to a lack of an acoustic temporal bone window, fTCD could not be performed in two patients (15%). In 9 of the remaining 11 patients hemispheric language dominance was found on the left side, in 1 patient on the right side, and 1 patient showed bihemispheric language representation. In all patients fTCD and the Wada test were in good agreement regarding hemispheric language lateralization, and the LI of both techniques were highly correlated (r = 0.776, P = 0.005). fTCD gives predictions of hemispheric language dominance consistent with the Wada test results even in children, patients with low IQ, and nonnative speakers. It is an alternative to the Wada test in determining language lateralization in patients with temporal lobe epilepsy.

Preoperative motor system brain mapping using positron emission tomography and statistical parametric mapping: hints on cortical reorganisation

OBJECTIVES

This study investigated the applicability of statistical parametric mapping (SPM) for analysing individual preoperative brain mapping studies in patients with cerebral mass lesions for neurosurgical planning. The study further investigated if hints on functional reorganisation processes can be found.

METHODS

Nine adult patients with cerebral mass lesions underwent activation [(15)O]water-PET under stimulation by finger (n=9) and foot (n=4) movement. Individual SPM-t-maps were computed without anatomical normalisation and coregistered to the individual magnetic resonance imaging. Relative cerebral blood flow change maps were calculated for comparison.

RESULTS

The spatial relation between the sensorimotor cortex and the lesion could be determined in all cases. Additional activations covered the ipsilateral sensorimotor cortex and the bilateral cerebellum, premotor cortices and supplementary motor areas. Patients with motor symptoms of the stimulated hand (paresis, focal seizures) activated the ipsilateral premotor cortices and contralateral cerebellum more often than patients without motor symptoms. The SPM results for p<0.005 and cerebral blood flow change maps showed considerably overlapping motor area activations. For p<0.001, SPM missed three sensorimotor cortex activations depicted by cerebral blood flow change maps and by SPM for p<0.005 in typical localisation. SPM analyses showed less activations probably unrelated to task performance.

CONCLUSION

It is concluded that SPM provides an efficient method for analysing individual preoperative PET activation studies. Activations of the ipsilateral premotor cortices and contralateral cerebellum may indicate an enhanced recruitment of ipsilateral motor pathways evoked by functional reorganisation processes. However, this changed activation pattern was not necessarily associated with a better neurological status.

Metabolic and electrophysiological validation of functional MRI

OBJECTIVES

Although functional MRI is widely used for preoperative planning and intraoperative neuronavigation, its accuracy to depict the site of neuronal activity is not exactly known. Experience with methods that may validate fMRI data and the results obtained when coregistering fMRI with different preoperative and intraoperative mapping modalities including metabolically based (18)F-fluorodeoxyglucose PET, electrophysiologcally based transcranial magnetic stimulation (TMS), and direct electrical cortical stimulation (DECS) are described.

METHODS

Fifty patients were included. PET was performed in 30, TMS in 10, and DECS in 41 patients. After coregistration using a frameless stereotactic system, results were grouped into overlapping (<1 cm distance), neighbouring (<2 cm), or contradictory (>2 cm).

RESULTS

Comparing fMRI with PET, 18 overlapping, seven neighbouring, and one contradictory result were obtained. In four patients no comparison was possible (because of motion artefacts, low signal to noise ratio, and unusual high tumour metabolism in PET). The comparison of TMS and fMRI showed seven overlapping and three neighbouring results. In three patients no DECS results could be obtained. Of the remaining 38 patients, fMRI hand motor tasks were compared with DECS results of the upper limb muscles in 36 patients, and fMRI foot motor tasks were compared with DECS results of the lower limb on 13 occasions. Of those 49 studies, overlapping results were obtained in 31 patients, and neighbouring in 14. On four occasions fMRI did not show functional information (because of motion artefacts and low signal to noise).

CONCLUSIONS

All validation techniques have intrinsic limitations that restrict their spatial resolution. However, of 50 investigated patients, there was only one in whom results contradictory to fMRI were obtained. Although it is not thought that fMRI can replace the intraoperatively updated functional information (DECS), it is concluded that fMRI is an important adjunct in the preoperative assessment of patients with tumours in the vicinity of the central region.

Task-related signal decrease on functional magnetic resonance imaging

An atypical pattern of signal change was identified on functional magnetic resonance (fMR) imaging in pathologic patients. Three normal volunteers and 34 patients with pathologic lesions near the primary motor cortex underwent fMR imaging with echo-planar imaging while performing a hand motor task. Signal intensities were evaluated with the z-score method, and the time course and changes of the signal intensity were calculated. Nine of the 34 patients with pathologic lesions displayed a significant task-related signal reduction in motor-related areas. They also presented a conventional task-related signal increase in other motor-related areas. The time courses of the increase and decrease were the inverse of each other. There was no significant difference between rates of signal increase and decrease. Our findings suggest that this atypical signal decrease is clinically significant, and that impaired vascular reactivity and altered oxygen metabolism could contribute to the task-related signal reduction. Brain areas showing such task-related signal decrease should be preserved at surgery.

New advances in brain tumor imaging

During the period of this review, there has been continued use and development of neuroimaging techniques in brain tumor diagnosis and management. Although no monumental developments or improvements in neuroimaging techniques or technology have occurred, important studies continue to be published showing the clinical impact and utility of various neuroimaging techniques to improve the care of patients with brain tumors. Several studies have shown the power of functional neuroimaging techniques with both magnetic resonance imaging (MRI) and positron-emission tomography (PET) to map eloquent cortex and assist in the planning of surgical and radiation therapy. New nuclear imaging radiopharmaceuticals, including various PET ligands and single photon emission computed tomography (SPECT) agents, have also been developed and show their potential power in the evaluation of brain tumor patients. New MRI pulse sequences to improve image quality and shorten imaging time have also been developed. Several excellent reviews of the use of fluorodeoxyglucose (FDG)-PET and MRI techniques were also published. This article reviews the relevant and important neuroimaging literature related to brain tumor that was published during the defined time period of November 1, 1999 to October 31, 2000. Discussion is organized by modality, including nuclear imaging techniques (SPECT and PET) and MRI (pulse sequence development, contrast agent development, functional MRI developments, and general MRI-related information).

Advances in pediatric neuro-oncology

A number of exciting advances have been reported over the past few years in the understanding and treatment of children with brain tumors. The present review highlights many of the publications from this period, focusing on their relevance within the major diagnostic and treatment domains of pediatric oncology (surgery, radiation therapy, chemotherapy, neuropathology, and neuroradiology). Although many of the publications cited provide confirmation of previously reported work, when taken together they form a good framework of the state of the field from the past few years.