Apparent diffusion and fractional anisotropy of diffuse intrinsic brain stem gliomas

Time-to-Event Endpoints in Imaging Biomarker Studies

Time-to-event endpoints are widely used as measures of patients' well-being and indicators of prognosis. In imaging-based biomarker studies, there are increasingly more studies that focus on examining imaging biomarkers' prognostic or predictive utilities on those endpoints, whether in a trial or an observational study setting. In this educational review article, we briefly introduce some basic concepts of time-to-event endpoints and point out potential pitfalls in the context of imaging biomarker research in hope of improving radiologists' understanding of related subjects. Besides, we have included some review and discussions on the benefits of using time-to-event endpoints and considerations on selecting overall survival or progression-free survival for primary analysis. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 3.

The performance of diffusion tensor imaging parameters for the distinction between medulloblastoma and pilocytic astrocytoma

BACKGROUND

The aim of this study was to evaluate the performance of diffusion tensor imaging (DTI) parameters for the distinction between pediatric medulloblastomas and pilocytic astrocytomas.

METHODS

DTI was performed in 36 patients, who were divided into two groups: group 1 consisted of 26 patients with medulloblastoma, whereas group 2 consisted of 10 patients with pilocytic astrocytoma. The Mann-Whitney U Test was utilized to compare the tumoral fractional anisotropy (tFA) and diffusivity (tMD) values and the tumor to parenchyma ratios for these values (rFA and rMD, respectively) between these two groups. Receiver operating characteristic (ROC) curve analysis and the Youden Index were applied to compute the cut-off point, and then the area under the curve (AUC), sensitivity, and specificity were calculated.

RESULTS

The tFA and rFA values of group 1 were significantly higher than those of group 2 (P<0.05). In contrast, the tMD and rMD values of group 1 were significantly lower than those of group 2 (P<0.05). Among the FA parameters, a cut-off tFA value of 0.37 provided the best ability to discriminate between medulloblastomas and pilocytic astrocytomas, producing a sensitivity value of 84.6%, a specificity of 80%, and an AUC of 81.7%. The cut-off values for MD and rMD were determined to be 1.06 × 10-3 mm2/s and 1.33, respectively, and were determined to be the most efficacious parameters for the differential diagnosis between medulloblastoma and pilocytic astrocytoma, which generated sensitivity, specificity, and AUC values of 100%.

CONCLUSIONS

DTI parameters can play pivotal roles in the discrimination between medulloblastoma and pilocytic astrocytoma.

NTMS based tractography and segmental diffusion analysis in patients with brainstem gliomas: Risk stratification and clinical potential

Introduction

Surgery on the brainstem level is associated with a high-risk of postoperative morbidity. Recently, we have introduced the combination of navigated transcranial magnetic stimulation (nTMS) and diffusion tensor imaging (DTI) tractography to define functionally relevant motor fibers tracts on the brainstem level to support operative planning and risk stratification in brainstem cavernomas.

Research question

Evaluate this method and assess it's clinical impact for the surgery of brainstem gliomas.

Material and methods

Patients with brainstem gliomas were examined preoperatively with motor nTMS and DTI tractography. A fractional anisotropy (FA) value of 75% of the individual FA threshold (FAT) was used to track descending corticospinal (CST) and -bulbar tracts (CBT). The distance between the tumor and the somatotopic tracts (hand, leg, face) was measured and diffusion parameters were correlated to the patients' outcome.

Results

12 patients were enrolled in this study, of which 6 underwent surgical resection, 5 received a stereotactic biopsy and 1 patient received conservative treatment. In all patients nTMS mapping and somatotopic tractography were performed successfully. Low FA values correlated with clinical symptoms revealing tract alteration by the tumor (p = 0.049). A tumor-tract distance (TTD) above 2 mm was the critical limit to achieve a safe complete tumor resection.

Discussion and conclusion

nTMS based DTI tractography combined with local diffusion analysis is a valuable tool for preoperative visualization and functional assessment of relevant motor fiber tracts, improving planning of safe entry corridors and perioperative risk stratification in brainstem gliomas tumors. This technique allows for customized treatment strategy to maximize patients' safety.

The Role of Advanced MRI Sequences in the Diagnosis and Follow-Up of Adult Brainstem Gliomas: A Neuroradiological Review

The 2021 WHO (World Health Organization) classification of brain tumors incorporated the rapid advances in the molecular, genetic, and pathogenesis understanding of brain tumor pathogenesis, behavior, and treatment response. It revolutionized brain tumor classification by placing great emphasis on molecular types and completely splitting adult-type and pediatric-type diffuse gliomas. Brainstem gliomas (BSGs) are the leading primary tumors of the brainstem, although they are quite uncommon in adults compared with the pediatric population, representing less than 2% of adult gliomas. Surgery is not always the treatment of choice since resection is rarely feasible and does not improve overall survival, and biopsies are not generally performed since the location is treacherous. Therefore, MRI (Magnetic Resonance Imaging) without and with gadolinium administration represents the optimal noninvasive radiological technique to suggest brainstem gliomas diagnosis, plan a multidisciplinary treatment and for follow-up evaluations. The MRI protocol encompasses morphological sequences as well as functional and advanced sequences, such as DWI/ADC (Diffusion-Weighted Imaging/Apparent Diffusion Coefficient), DTI (Diffusion Tensor Imaging), PWI (Perfusion-Weighted Imaging), and MRS (Magnetic Resonance Spectroscopy), which improve the accuracy of the diagnosis of BSGs by adding substantial information regarding the cellularity, the infiltrative behavior toward the v fiber tracts, the vascularity, and the molecular changes. Brainstem gliomas have been divided into four categories on the basis of their MRI radiological appearance, including diffuse intrinsic low-grade gliomas, enhancing malignant gliomas, localized tectal gliomas, and other forms. The aim of our review is to provide insight into the role of advanced MRI sequences in the diagnosis and follow-up of adult brainstem gliomas.

Correlation between Multiparametric MR Imaging and Molecular Genetics in Pontine Pediatric High-Grade Glioma

BACKGROUND AND PURPOSE

Molecular profiling is a crucial feature in the "integrated diagnosis" of CNS tumors. We aimed to determine whether radiomics could distinguish molecular types of pontine pediatric high-grade gliomas that have similar/overlapping phenotypes on conventional anatomic MR images.

MATERIALS AND METHODS

Baseline MR images from children with pontine pediatric high-grade gliomas were analyzed. Retrospective imaging studies included standard precontrast and postcontrast sequences and DTI. Imaging analyses included median, mean, mode, skewness, and kurtosis of the ADC histogram of the tumor volume based on T2 FLAIR and enhancement at baseline. Histone H3 mutations were identified through immunohistochemistry and/or Sanger or next-generation DNA sequencing. The log-rank test identified imaging factors prognostic of survival from the time of diagnosis. Wilcoxon rank-sum and Fisher exact tests compared imaging predictors among groups.

RESULTS

Eighty-three patients had pretreatment MR imaging and evaluable tissue sampling. The median age was 6 years (range, 0.7-17 years); 50 tumors had a K27M mutation in H3-3A, and 11, in H3C2/3. Seven tumors had histone H3 K27 alteration, but the specific gene was unknown. Fifteen were H3 wild-type. Overall survival was significantly higher in H3C2/3- compared with H3-3A-mutant tumors (P = .003) and in wild-type tumors compared with any histone mutation (P = .001). Lower overall survival was observed in patients with enhancing tumors (P = .02) compared with those without enhancement. H3C2/3-mutant tumors showed higher mean, median, and mode ADC_total values (P < .001) and ADC_enhancement (P < .004), with lower ADC_total skewness and kurtosis (P < .003) relative to H3-3A-mutant tumors.

CONCLUSIONS

ADC histogram parameters are correlated with histone H3 mutation status in pontine pediatric high-grade glioma.

Advanced Neuroimaging Approaches to Pediatric Brain Tumors

Simple Summary

After leukemias, brain tumors are the most common cancers in children, and early, accurate diagnosis is critical to improve patient outcomes. Beyond the conventional imaging methods of computed tomography (CT) and magnetic resonance imaging (MRI), advanced neuroimaging techniques capable of both structural and functional imaging are moving to the forefront to improve the early detection and differential diagnosis of tumors of the central nervous system. Here, we review recent developments in neuroimaging techniques for pediatric brain tumors.

Abstract

Central nervous system tumors are the most common pediatric solid tumors; they are also the most lethal. Unlike adults, childhood brain tumors are mostly primary in origin and differ in type, location and molecular signature. Tumor characteristics (incidence, location, and type) vary with age. Children present with a variety of symptoms, making early accurate diagnosis challenging. Neuroimaging is key in the initial diagnosis and monitoring of pediatric brain tumors. Conventional anatomic imaging approaches (computed tomography (CT) and magnetic resonance imaging (MRI)) are useful for tumor detection but have limited utility differentiating tumor types and grades. Advanced MRI techniques (diffusion-weighed imaging, diffusion tensor imaging, functional MRI, arterial spin labeling perfusion imaging, MR spectroscopy, and MR elastography) provide additional and improved structural and functional information. Combined with positron emission tomography (PET) and single-photon emission CT (SPECT), advanced techniques provide functional information on tumor metabolism and physiology through the use of radiotracer probes. Radiomics and radiogenomics offer promising insight into the prediction of tumor subtype, post-treatment response to treatment, and prognostication. In this paper, a brief review of pediatric brain cancers, by type, is provided with a comprehensive description of advanced imaging techniques including clinical applications that are currently utilized for the assessment and evaluation of pediatric brain tumors.

Imaging diagnosis and treatment selection for brain tumors in the era of molecular therapeutics

Currently, most CNS tumors require tissue sampling to discern their molecular/genomic landscape. However, growing research has shown the powerful role imaging can play in non-invasively and accurately detecting the molecular signature of these tumors. The overarching theme of this review article is to provide neuroradiologists and neurooncologists with a framework of several important molecular markers, their associated imaging features and the accuracy of those features. A particular emphasis is placed on those tumors and mutations that have specific or promising imaging correlates as well as their respective therapeutic potentials.

Meta-Analysis of Apparent Diffusion Coefficient in Pediatric Medulloblastoma, Ependymoma, and Pilocytic Astrocytoma

BACKGROUND

Medulloblastoma, ependymoma, and pilocytic astrocytoma are common pediatric posterior fossa tumors. These tumors show overlapping characteristics on conventional MRI scans, making diagnosis difficult.

PURPOSE

To investigate whether apparent diffusion coefficient (ADC) values differ between tumor types and to identify optimum cut-off values to accurately classify the tumors using different performance metrics.

STUDY TYPE

Systematic review and meta-analysis.

SUBJECTS

Seven studies reporting ADC in pediatric posterior fossa tumors (115 medulloblastoma, 68 ependymoma, and 86 pilocytic astrocytoma) were included following PubMed and ScienceDirect searches.

SEQUENCE AND FIELD STRENGTH

Diffusion weighted imaging (DWI) was performed on 1.5 and 3 T across multiple institution and vendors.

ASSESSMENT

The combined mean and standard deviation of ADC were calculated for each tumor type using a random-effects model, and the effect size was calculated using Hedge's g.

STATISTICAL TESTS

Sensitivity/specificity, weighted classification accuracy, balanced classification accuracy. A P value < 0.05 was considered statistically significant, and a Hedge's g value of >1.2 was considered to represent a large difference.

RESULTS

The mean (± standard deviation) ADCs of medulloblastoma, ependymoma, and pilocytic astrocytoma were 0.76 ± 0.16, 1.10 ± 0.10, and 1.49 ± 0.16 mm² /sec × 10^-3 . To maximize sensitivity and specificity using the mean ADC, the cut-off was found to be 0.96 mm² /sec × 10^-3 for medulloblastoma and ependymoma and 1.26 mm² /sec × 10^-3 for ependymoma and pilocytic astrocytoma. The meta-analysis showed significantly different ADC distributions for the three posterior fossa tumors. The cut-off values changed markedly (up to 7%) based on the performance metric used and the prevalence of the tumor types.

DATA CONCLUSION

There were significant differences in ADC between tumor types. However, it should be noted that only summary statistics from each study were analyzed and there were differences in how regions of interest were defined between studies.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 3.

Radiogenomics of diffuse intrinsic pontine gliomas (DIPGs): correlation of histological and biological characteristics with multimodal MRI features

OBJECTIVES

The diffuse intrinsic pontine gliomas (DIPGs) are now defined by the type of histone H3 mutated at lysine 27. We aimed to correlate the multimodal MRI features of DIPGs, H3K27M mutant, with their histological and molecular characteristics.

METHODS

Twenty-seven treatment-naïve children with histopathologically confirmed DIPG H3K27M mutant were prospectively included. MRI performed prior to biopsy included multi-b-value diffusion-weighted imaging, ASL, and dynamic susceptibility contrast (DSC) perfusion imaging. The ADC and cerebral blood flow (CBF) and blood volume (CBV) were measured at the biopsy site. We assessed quantitative histological data, including microvascular density, nuclear density, and H3K27M-positive nuclear density. Gene expression profiling was also assessed in the samples. We compared imaging and histopathological data according to histone subgroup. We correlated MRI quantitative data with histological data and gene expression.

RESULTS

H3.1K27M mutated tumors showed higher ADC values (median 3151 μm²/s vs 1741 μm²/s, p = 0.003), and lower perfusion values (DSC-rCBF median 0.71 vs 1.43, p = 0.002, and DSC-rCBV median 1.00 vs 1.71, p = 0.02) than H3.3K27M ones. They had similar microvascular and nuclear density, but lower H3K27M-positive nuclear density (p = 0.007). The DSC-rCBV was positively correlated to the H3K27M-positive nuclear density (rho = 0.74, p = 0.02). ADC values were not correlated with nuclear density nor perfusion values with microvascular density. The expression of gated channel activity-related genes tended to be inversely correlated with ADC values and positively correlated with DSC perfusion.

CONCLUSIONS

H3.1K27M mutated tumors have higher ADC and lower perfusion values than H3.3K27M ones, without direct correlation with microvascular or nuclear density. This may be due to tissular edema possibly related to gated channel activity-related gene expression.

KEY POINTS

• H3.1K27M mutant DIPG had higher apparent diffusion coefficient (p = 0.003), lower α (p = 0.048), and lower relative cerebral blood volume (p = 0.02) than H3.3K27M mutant DIPG at their biopsy sites. • Biopsy samples obtained within the tumor's enhancing portion showed higher microvascular density (p = 0.03) than samples obtained outside the tumor's enhancing portion, but similar H3K27M-positive nuclear density (p = 0.84). • Relative cerebral blood volume measured at the biopsy site was significantly correlated with H3K27M-positive nuclear density (rho = 0.74, p = 0.02).

MR imaging features of diffuse intrinsic pontine glioma and relationship to overall survival: report from the International DIPG Registry

BACKGROUND

This study describes imaging features of diffuse intrinsic pontine glioma (DIPG) and correlates with overall survival (OS) and histone mutation status in the International DIPG Registry (IDIPGR).

METHODS

Four hundred cases submitted to the IDIPGR with a local diagnosis of DIPG and baseline MRI were evaluated by consensus review of 2 neuroradiologists; 43 cases were excluded (inadequate imaging or alternative diagnoses). Agreement between reviewers, association with histone status, and univariable and multivariable analyses relative to OS were assessed.

RESULTS

On univariable analysis imaging features significantly associated with worse OS included: extrapontine extension, larger size, enhancement, necrosis, diffusion restriction, and distant disease. On central review, 9.5% of patients were considered not to have DIPG. There was moderate mean agreement of MRI features between reviewers. On multivariable analysis, chemotherapy, age, and distant disease were predictors of OS. There was no difference in OS between wild-type and H3 mutated cases. The only imaging feature associated with histone status was the presence of ill-defined signal infiltrating pontine fibers.

CONCLUSIONS

Baseline imaging features are assessed in the IDIPGR. There was a 9.5% discordance in DIPG diagnosis between local and central review, demonstrating need for central imaging confirmation for prospective trials. Although several imaging features were significantly associated with OS (univariable), only age and distant disease were significant on multivariable analyses. There was limited association of imaging features with histone mutation status, although numbers are small and evaluation exploratory.

The Role of Apparent Diffusion Coefficient in the Differentiation between Cerebellar Medulloblastoma and Brainstem Glioma

For certain clinical circumstances, the differentiation between cerebellar medulloblastoma and brainstem glioma is essential. We aimed to evaluate the role played by the apparent diffusion coefficient (ADC) values in the differentiation between cerebellar medulloblastomas and brainstem gliomas in children. The institutional review board approved this prospective study. Brain magnetic resonance imaging (MRI), including diffusion-weighted imaging (DWI) and ADC, was assessed in 32 patients (median age: 7.0 years), divided into two groups, a medulloblastoma group (group 1, n = 22) and a brainstem glioma group (group 2, n = 10). The Mann-Whitney U test was utilized to compare tumor ADCmax, ADCmin, ADCmean, and ADCsd values, and their ratios with the parenchyma values between the two groups. Receiver operating characteristic (ROC) curve analysis and the Youden index were used to calculate the cut-off value, along with the area under the curve (AUC), sensitivity, and specificity. The median ADCmax, ADCmin, and ADCmean values were significantly higher in group 2 than in group 1 (p < 0.05). The median ratios of ADCmin and ADCmean to the parenchyma were significantly higher in group 2 than in group 1 (p < 0.05). The ROC analysis showed that the AUC for the ADCmean ratio was the highest among these parameters, at 98.2%. The ADCmean tumor to parenchyma ratio was a significant and effective parameter for the differentiation between pediatric medulloblastomas and brainstem gliomas.

The Effects of Applying Apparent Diffusion Coefficient Parameters on the Differentiation between Fourth Ventricular Ependymoma and Diffuse Intrinsic Pontine Glioma

Distinguishing the fourth ventricular ependymoma from diffuse intrinsic pontine glioma (DIPG) is essential to improve the treatment strategy between these two tumor types. We attempted to evaluate the effects of applying apparent diffusion coefficient (ADC) values to the distinction between pediatric fourth ventricular ependymomas and DIPGs. Brain magnetic resonance imaging, including diffusion-weighted imaging and ADC, was assessed in 26 patients, who were divided into two groups: group 1 included 8 patients with fourth ventricular ependymoma and group 2 included 18 patients with DIPG. The Mann–Whitney U test was utilized to compare tumoral maximum (ADCmax), minimum ADC (ADCmin), mean ADC (ADCmean), and standard deviation (ADCsd) values, and the ratios between the tumor and parenchyma values for each of these parameters (rADCmax, rADCmin, rADCmean, and rADCsd, respectively) between the two groups. Cutoff values were calculated based on receiver operating characteristic curve analysis and the Youden index, and the area under the curve (AUC), sensitivity, and specificity were determined. The median ADCmax, ADCmin, ADCmean, rADCmax, rADCmin, and rADCmean values were significantly lower in group 1 than in group 2 (p < 0.05). For the differential diagnosis of ependymomas and DIPGs, a cutoff ADCmean value of 1.02 × 10−3 mm2/s was determined, which produced a sensitivity of 100%, a specificity of 88.9%, and an AUC of 95.8%. ADC parameters should be considered when performing a differential diagnosis between fourth ventricular ependymomas and DIPGs. Based on our findings, a cutoff ADCmean value of 1.02 × 10−3 mm2/s was the most significant and effective parameter for this purpose.

Pilocytic Astrocytoma: A Review of General, Clinical, and Molecular Characteristics

Pilocytic astrocytomas are the primary tumors most frequently found in children and adolescents, accounting for approximately 15.6% of all brain tumors and 5.4% of all gliomas. They are mostly found in infratentorial structures such as the cerebellum and in midline cerebral structures such as the optic nerve, hypothalamus, and brain stem. The present study aimed to list the main characteristics about this tumor, to better understand the diagnosis and treatment of these patients, and was conducted on search of the published studies available in NCBI, PubMed, MEDLINE, Scielo, and Google Scholar. It was possible to define the main histologic findings observed in these cases, such as mitoses, necrosis, and Rosenthal fibers. We described the locations usually most affected by tumor development, and this was associated with the most frequent clinical features. The comparison between the molecular diagnostic methods showed great use of fluorescent in situ hybridization, polymerase chain reaction (PCR), and reverse transcriptase-PCR, important techniques for the detection of BRAF V600E mutation and BRAF-KIAA1549 fusion, characteristic molecular alterations in pilocytic astrocytomas.

The role of diffusion tensor imaging metrics in the discrimination between cerebellar medulloblastoma and brainstem glioma

BACKGROUND

Differentiation between cerebellar medulloblastoma and brainstem glioma is necessary for certain clinical circumstances. We aimed to evaluate the function of diffusion tensor imaging (DTI) metrics in the differentiation between cerebellar medulloblastomas and brainstem gliomas in children.

PROCEDURE

The institutional review board approved this prospective study. Brain magnetic resonance imaging (MRI), including DTI, was assessed in 40 patients, who were divided into two groups: a medulloblastoma group (group 1, n = 25) and a brainstem glioma group (group 2, n = 15). The Mann-Whitney U test was utilized to compare tumoral fractional anisotropy (FA) and diffusivity (MD) values and tumor-to-parenchyma ratios for these values (rFA and rMD, respectively) between the two groups. Receiver-operating characteristic (ROC) curve analysis and the Youden index were exploited to calculate the cutoff value, along with the area under the curve (AUC), sensitivity, and specificity.

RESULTS

The FA value for medulloblastomas was significantly higher than that for brainstem gliomas (P < 0.05). In contrast, the MD and rMD values for medulloblastoma were significantly lower than those for brainstem gliomas (P < 0.05). A cutoff MD value of 0.97 was identified as the most effective factor for the differential diagnosis between medulloblastomas and brainstem gliomas, which reached a sensitivity of 96%, a specificity of 100%, and an AUC of 99.5%.

CONCLUSION

DTI metrics play a significant role in the differentiation between medulloblastoma and brainstem glioma in pediatric patients.

MR Imaging Correlates for Molecular and Mutational Analyses in Children with Diffuse Intrinsic Pontine Glioma

BACKGROUND AND PURPOSE

Recent advances in molecular techniques have characterized distinct subtypes of diffuse intrinsic pontine gliomas. Our aim was the identification of MR imaging correlates of these subtypes.

MATERIALS AND METHODS

Initial MRIs from subjects with diffuse intrinsic pontine gliomas recruited for a prospective clinical trial before treatment were analyzed. Retrospective imaging analyses included FLAIR/T2 tumor volume, tumor volume enhancing, the presence of cyst and/or necrosis, median, mean, mode, skewness, kurtosis of ADC tumor volume based on FLAIR, and enhancement at baseline. Molecular subgroups based on EGFR and MGMT mutations were established. Histone mutations were also determined (H3F3A, HIST1H3B, HIST1H3C). Univariate Cox proportional hazards regression was used to test the association of imaging predictors with overall and progression-free survival. Wilcoxon rank sum, Kruskal-Wallis, and Fisher exact tests were used to compare imaging measures among groups.

RESULTS

Fifty patients had biopsy and MR imaging. The median age at trial registration was 6 years (range, 3.3-17.5 years); 52% were female. On the basis of immunohistochemical results, 48 patients were assigned to 1 of 4 subgroups: 28 in MGMT-/epidermal growth factor receptor (EGFR)-, 14 in MGMT-/EGFR+, 3 in MGMT+/EGFR-, and 3 in MGMT+/EGFR+. Twenty-three patients had histone mutations in H3F3A, 8 in HIST1H3B, and 3 in HIST1H3C. Enhancing tumor volume was near-significantly different across molecular subgroups (P = .04), after accounting for the false discovery rate. Tumor volume enhancing, median, mode, skewness, and kurtosis ADC T2-FLAIR/T2 were significantly different (P ≤ .048) between patients with H3F3A and HIST1H3B/C mutations.

CONCLUSIONS

MR imaging features including enhancement and ADC histogram parameters are correlated with molecular subgroups and mutations in children with diffuse intrinsic pontine gliomas.

Cerebral blood flow changes after radiation therapy identifies pseudoprogression in diffuse intrinsic pontine gliomas

Background

The interval between progression and death in diffuse intrinsic pontine glioma (DIPG) is usually <6 months. However, reports of longer patient survival following radiotherapy, in the presence of radiological signs of progression, suggest that these cases may be comparable to pseudoprogression observed in adult glioblastoma. Our aim was to identify such cases and compare their multimodal MRI features with those of patients who did not present the same evolution.

Methods

Multimodal MRIs of 43 children treated for DIPG were retrospectively selected at 4 timepoints: baseline, after radiotherapy, during true progression, and at the last visit. The patients were divided into 2 groups depending on whether they presented conventional MRI changes that mimicked progression. The apparent diffusion coefficient, arterial spin labeling cerebral blood flow (ASL-CBF), and dynamic susceptibility contrast perfusion relative cerebral blood volume (DSCrCBV) and flow (DSCrCBF) values were recorded for each tumor voxel, avoiding necrotic areas.

Results

After radiotherapy, 19 patients (44%) showed radiological signs that mimicked progression: 16 survived >6 months following so-called pseudoprogression, with a median of 8.9 months and a maximum of 35.6 months. All 43 patients exhibited increased blood volume and flow after radiotherapy, but the 90th percentile of those with signs of pseudoprogression had a greater increase of ASL-CBF (P < 0.001). Survival between the 2 groups did not differ significantly. During true progression, DSCrCBF and DSCrCBV values increased only in patients who had not experienced pseudoprogression.

Conclusions

Pseudoprogression is a frequent phenomenon in DIPG patients. This condition needs to be recognized before considering treatment discontinuation. In this study, the larger increase of the ASL-CBF ratio after radiotherapy accurately distinguished pseudoprogression from true progression.

Quantifying radiation therapy response using apparent diffusion coefficient (ADC) parametric mapping of pediatric diffuse intrinsic pontine glioma: a report from the pediatric brain tumor consortium

BACKGROUND AND PURPOSE

Baseline diffusion or apparent diffusion coefficient (ADC) characteristics have been shown to predict outcome related to DIPG, but the predictive value of post-radiation ADC is less well understood. ADC parametric mapping (FDM) was used to measure radiation-related changes in ADC and compared these metrics to baseline ADC in predicting progression-free survival and overall survival using a large multi-center cohort of DIPG patients (Pediatric Brain Tumor Consortium-PBTC).

MATERIALS AND METHODS

MR studies at baseline and post-RT in 95 DIPG patients were obtained and serial quantitative ADC parametric maps were generated from diffusion-weighted imaging based on T2/FLAIR and enhancement regions of interest (ROIs). Metrics assessed included total voxels with: increase in ADC (iADC); decrease in ADC (dADC), no change in ADC (nADC), fraction of voxels with increased ADC (fiADC), fraction of voxels with decreased ADC (fdADC), and the ratio of fiADC and fdADC (fDM Ratio).

RESULTS

A total of 72 patients were included in the final analysis. Tumors with higher fiADC between baseline and the first RT time point showed a trend toward shorter PFS with a hazard ratio of 6.44 (CI 0.79, 52.79, p = 0.083). In contrast, tumors with higher log mean ADC at baseline had longer PFS, with a hazard ratio of 0.27 (CI 0.09, 0.82, p = 0.022). There was no significant association between fDM derived metrics and overall survival.

CONCLUSIONS

Baseline ADC values are a stronger predictor of outcome compared to radiation related ADC changes in pediatric DIPG. We show the feasibility of employing parametric mapping techniques in multi-center studies to quantitate spatially heterogeneous treatment response in pediatric tumors, including DIPG.

Arterial spin labelling and diffusion-weighted imaging in paediatric brain tumours

BACKGROUND

Diffusion- and perfusion-weighted MRI are valuable tools for measuring the cellular and vascular properties of brain tumours. This has been well studied in adult patients, however, the biological features of childhood brain tumours are unique, and paediatric-focused studies are less common. We aimed to assess the diagnostic utility of apparent diffusion coefficient (ADC) values derived from diffusion-weighted imaging (DWI) and cerebral blood flow (CBF) values derived from arterial spin labelling (ASL) in paediatric brain tumours.

METHODS

We performed a meta-analysis of published studies reporting ADC and ASL-derived CBF values in paediatric brain tumours. Data were combined using a random effects model in order to define typical parameter ranges for different histological tumour subtypes and WHO grades. New data were also acquired in a 'validation cohort' at our institution, in which ADC and CBF values in treatment naïve paediatric brain tumour patients were measured, in order to test the validity of the findings from the literature in an un-seen cohort. ADC and CBF quantification was performed by two radiologists via manual placement of tumour regions of interest (ROIs), in addition to an automated approach to tumour ROI placement.

RESULTS

A total of 14 studies met the inclusion criteria for the meta-analysis, constituting data acquired in 542 paediatric patients. Parameters of interest were based on measurements from ROIs placed within the tumour, including mean and minimum ADC values (ADC_ROI-mean, ADC_ROI-min) and the maximum CBF value normalised to grey matter (nCBF_ROI-max). After combination of the literature data, a number of histological tumour subtype groups showed significant differences in ADC values, which were confirmed, where possible, in our validation cohort of 32 patients. In both the meta-analysis and our cohort, diffuse midline glioma was found to be an outlier among high-grade tumour subtypes, with ADC and CBF values more similar to the low-grade tumours. After grouping patients by WHO grade, significant differences in grade groups were found in ADC_ROI-mean, ADC_ROI-min, and nCBF_ROI-max, in both the meta-analysis and our validation cohort. After excluding diffuse midline glioma, optimum thresholds (derived from ROC analysis) for separating low/high-grade tumours were 0.95 × 10^-3 mm²/s (ADC_ROI-mean), 0.82 × 10^-3 mm²/s (ADC_ROI-min) and 1.45 (nCBF_ROI-max). These thresholds were able to identify low/high-grade tumours with 96%, 83%, and 83% accuracy respectively in our validation cohort, and agreed well with the results from the meta-analysis. Diagnostic power was improved by combining ADC and CBF measurements from the same tumour, after which 100% of tumours in our cohort were correctly classified as either low- or high-grade (excluding diffuse midline glioma).

CONCLUSION

ADC and CBF values are useful for differentiating certain histological subtypes, and separating low- and high-grade paediatric brain tumours. The threshold values presented here are in agreement with previously published studies, as well as a new patient cohort. If ADC and CBF values acquired in the same tumour are combined, the diagnostic accuracy is optimised.

Multimodal Magnetic Resonance Imaging of Treatment-Induced Changes to Diffuse Infiltrating Pontine Gliomas in Children and Correlation to Patient Progression-Free Survival

PURPOSE

To use multimodal magnetic resonance imaging (MRI) to quantify treatment-induced changes in the whole volume of diffuse infiltrating pontine gliomas and correlate them with progression-free survival (PFS).

METHODS AND MATERIALS

This prospective study included 22 children aged 3.3 to 14.7 years (median, 5.9 years). Multimodal MRI was performed at 3 distinct time points: before treatment, the first week following radiation therapy (RT), and 2 months after RT. The imaging protocol included morphologic, multi b-value diffusion; arterial spin labeling; and dynamic susceptibility contrast-enhanced perfusion. Morphologic and multimodal data-lesion volume, diffusion coefficients, relative cerebral blood flow, and relative cerebral blood volume (rCBV)-were recorded at the 3 aforementioned time points. The Wilcoxon test was used to compare each individual parameter variation between time points, and its correlation with PFS was assessed by the Spearman test.

RESULTS

Following RT, the tumors' solid component volume decreased by 40% (P<.001). Their median diffusion coefficients decreased by 20% to 40% (P<.001), while median relative cerebral blood flow increased by 60% to 80% (P<.001) and median rCBV increased by 70% (P<.001). PFS was positively correlated with rCBV measured immediately after RT (P=.003), and in patients whose rCBV was above the cutoff value of 2.46, the median PFS was 4.6 months longer (P=.001). These indexes tended to return to baseline 2 months after RT. Lesion volume before or after RT was not correlated with survival.

CONCLUSIONS

Multimodal MRI provides useful information about diffuse infiltrating pontine gliomas' response to treatment; rCBV increases following RT, and higher values are correlated with better PFS. High rCBV values following RT should not be mistaken for progression and could be an indicator of response to therapy.

Correlation of 18F-FDG PET and MRI Apparent Diffusion Coefficient Histogram Metrics with Survival in Diffuse Intrinsic Pontine Glioma: A Report from the Pediatric Brain Tumor Consortium

The purpose of this study was to describe baseline ¹⁸F-FDG PET voxel characteristics in pediatric diffuse intrinsic pontine glioma (DIPG) and to correlate these metrics with baseline MRI apparent diffusion coefficient (ADC) histogram metrics, progression-free survival (PFS), and overall survival. Methods: Baseline brain ¹⁸F-FDG PET and MRI scans were obtained in 33 children from Pediatric Brain Tumor Consortium clinical DIPG trials. ¹⁸F-FDG PET images, postgadolinium MR images, and ADC MR images were registered to baseline fluid attenuation inversion recovery MR images. Three-dimensional regions of interest on fluid attenuation inversion recovery MR images and postgadolinium MR images and ¹⁸F-FDG PET and MR ADC histograms were generated. Metrics evaluated included peak number, skewness, and kurtosis. Correlation between PET and MR ADC histogram metrics was evaluated. PET pixel values within the region of interest for each tumor were plotted against MR ADC values. The association of these imaging markers with survival was described. Results: PET histograms were almost always unimodal (94%, vs. 6% bimodal). None of the PET histogram parameters (skewness or kurtosis) had a significant association with PFS, although a higher PET postgadolinium skewness tended toward a less favorable PFS (hazard ratio, 3.48; 95% confidence interval [CI], 0.75-16.28 [P = 0.11]). There was a significant association between higher MR ADC postgadolinium skewness and shorter PFS (hazard ratio, 2.56; 95% CI, 1.11-5.91 [P = 0.028]), and there was the suggestion that this also led to shorter overall survival (hazard ratio, 2.18; 95% CI, 0.95-5.04 [P = 0.067]). Higher MR ADC postgadolinium kurtosis tended toward shorter PFS (hazard ratio, 1.30; 95% CI, 0.98-1.74 [P = 0.073]). PET and MR ADC pixel values were negatively correlated using the Pearson correlation coefficient. Further, the level of PET and MR ADC correlation was significantly positively associated with PFS; tumors with higher values of ADC-PET correlation had more favorable PFS (hazard ratio, 0.17; 95% CI, 0.03-0.89 [P = 0.036]), suggesting that a higher level of negative ADC-PET correlation leads to less favorable PFS. A more significant negative correlation may indicate higher-grade elements within the tumor leading to poorer outcomes. Conclusion:¹⁸F-FDG PET and MR ADC histogram metrics in pediatric DIPG demonstrate different characteristics with often a negative correlation between PET and MR ADC pixel values. A higher negative correlation is associated with a worse PFS, which may indicate higher-grade elements within the tumor.

Posterior Fossa Tumors

Pediatric brain tumors are the leading cause of death from solid tumors in childhood. The most common posterior fossa tumors in children are medulloblastoma, atypical teratoid/rhabdoid tumor, cerebellar pilocytic astrocytoma, ependymoma, and brainstem glioma. Location, and imaging findings on computed tomography (CT) and conventional MR (cMR) imaging may provide important clues to the most likely diagnosis. Moreover, information obtained from advanced MR imaging techniques increase diagnostic confidence and help distinguish between different histologic tumor types. Here we discuss the most common posterior fossa tumors in children, including typical imaging findings on CT, cMR imaging, and advanced MR imaging studies.

Diffusion MRI in early cancer therapeutic response assessment

Imaging biomarkers for the predictive assessment of treatment response in patients with cancer earlier than standard tumor volumetric metrics would provide new opportunities to individualize therapy. Diffusion-weighted MRI (DW-MRI), highly sensitive to microenvironmental alterations at the cellular level, has been evaluated extensively as a technique for the generation of quantitative and early imaging biomarkers of therapeutic response and clinical outcome. First demonstrated in a rodent tumor model, subsequent studies have shown that DW-MRI can be applied to many different solid tumors for the detection of changes in cellularity as measured indirectly by an increase in the apparent diffusion coefficient (ADC) of water molecules within the lesion. The introduction of quantitative DW-MRI into the treatment management of patients with cancer may aid physicians to individualize therapy, thereby minimizing unnecessary systemic toxicity associated with ineffective therapies, saving valuable time, reducing patient care costs and ultimately improving clinical outcome. This review covers the theoretical basis behind the application of DW-MRI to monitor therapeutic response in cancer, the analytical techniques used and the results obtained from various clinical studies that have demonstrated the efficacy of DW-MRI for the prediction of cancer treatment response. Copyright © 2016 John Wiley & Sons, Ltd.

MRI Evaluation of Non-Necrotic T2-Hyperintense Foci in Pediatric Diffuse Intrinsic Pontine Glioma

BACKGROUND AND PURPOSE

The conventional MR imaging appearance of diffuse intrinsic pontine glioma suggests intralesional histopathologic heterogeneity, and various distinct lesion components, including T2-hypointense foci, have been described. Here we report the prevalence, conventional MR imaging semiology, and advanced MR imaging features of non-necrotic T2-hyperintense foci in diffuse intrinsic pontine glioma.

MATERIALS AND METHODS

Twenty-five patients with diffuse intrinsic pontine gliomas were included in this study. MR imaging was performed at 3T by using conventional and advanced MR imaging sequences. Perfusion (CBV), vascular permeability (v_e, K^trans), and diffusion (ADC) metrics were calculated and used to characterize non-necrotic T2-hyperintense foci in comparison with other lesion components, namely necrotic T2-hyperintense foci, T2-hypointense foci, peritumoral edema, and normal brain stem. Statistical analysis was performed by using Kruskal-Wallis and Wilcoxon rank sum tests.

RESULTS

Sixteen non-necrotic T2-hyperintense foci were found in 12 tumors. In these foci, ADC values were significantly higher than those in either T2-hypointense foci (P = .002) or normal parenchyma (P = .0002), and relative CBV values were significantly lower than those in either T2-hypointense (P = .0002) or necrotic T2-hyperintense (P = .006) foci. Volume transfer coefficient values in T2-hyperintense foci were lower than those in T2-hypointense (P = .0005) or necrotic T2-hyperintense (P = .0348) foci.

CONCLUSIONS

Non-necrotic T2-hyperintense foci are common, distinct lesion components within diffuse intrinsic pontine gliomas. Advanced MR imaging data suggest low cellularity and an early stage of angioneogenesis with leaky vessels resulting in expansion of the extracellular space. Because of the lack of biopsy validation, the underlying histoarchitectural and pathophysiologic changes remain unclear; therefore, these foci may correspond to a poorly understood biologic event in tumor evolution.

A Novel Methodology for Applying Multivoxel MR Spectroscopy to Evaluate Convection-Enhanced Drug Delivery in Diffuse Intrinsic Pontine Gliomas

BACKGROUND AND PURPOSE

Diffuse intrinsic pontine gliomas are inoperable high-grade gliomas with a median survival of less than 1 year. Convection-enhanced delivery is a promising local drug-delivery technique that can bypass the BBB in diffuse intrinsic pontine glioma treatment. Evaluating tumor response is critical in the assessment of convection-enhanced delivery of treatment. We proposed to determine the potential of 3D multivoxel (1)H-MR spectroscopy to evaluate convection-enhanced delivery treatment effect in these tumors.

MATERIALS AND METHODS

We prospectively analyzed 3D multivoxel (1)H-MR spectroscopy data for 6 patients with nonprogressive diffuse intrinsic pontine gliomas who received convection-enhanced delivery treatment of a therapeutic antibody (Phase I clinical trial NCT01502917). To compare changes in the metabolite ratios with time, we tracked the metabolite ratios Cho/Cr and Cho/NAA at several ROIs: normal white matter, tumor within the convection-enhanced delivery infusion site, tumor outside of the infused area, and the tumor average.

RESULTS

There was a comparative decrease in both Cho/Cr and Cho/NAA metabolite ratios at the tumor convection-enhanced delivery site versus tumor outside the infused area. We used MR spectroscopy voxels with dominant white matter as a reference. The difference between changes in metabolite ratios became more prominent with increasing time after convection-enhanced delivery treatment.

CONCLUSIONS

The comparative change in metabolite ratios between the convection-enhanced delivery site and the tumor site outside the infused area suggests that multivoxel (1)H-MR spectroscopy, in combination with other imaging modalities, may provide a clinical tool to accurately evaluate local tumor response after convection-enhanced delivery treatment.

Diffusion tensor imaging suggests extrapontine extension of pediatric diffuse intrinsic pontine gliomas

PURPOSE

To apply DTI to detect early extrapontine extension of pediatric diffuse intrinsic pontine glioma along the corticospinal tracts.

METHODS

In children with diffuse intrinsic pontine glioma, low-grade brainstem glioma, and age-matched controls, DTI metrics were measured in the posterior limb of the internal capsule and posterior centrum semiovale. Histological examination was available in one patient.

RESULTS

6 diffuse intrinsic pontine glioma, 8 low-grade brainstem glioma, and two groups of 25 controls were included. In diffuse intrinsic pontine glioma compared to controls, fractional anisotropy was lower in the bilateral posterior limb of the internal capsule, axial diffusivity was lower in the bilateral posterior centrum semiovale and posterior limb of the internal capsule, while radial diffusivity was higher in the bilateral posterior limb of the internal capsule. No significant differences were found between low-grade brainstem glioma and controls. In diffuse intrinsic pontine glioma compared to low-grade brainstem glioma, axial diffusivity was lower in the bilateral posterior limb of the internal capsule. Histological examination in one child showed tumor cells in the posterior limb of the internal capsule.

CONCLUSION

Reduction in fractional anisotropy and axial diffusivity and increase in radial diffusivity in diffuse intrinsic pontine glioma may reflect tumor extension along the corticospinal tracts as shown by histology. DTI may detect early extrapontine tumor extension in diffuse intrinsic pontine glioma before it becomes apparent on conventional MRI sequences.

Apparent diffusion coefficient histogram metrics correlate with survival in diffuse intrinsic pontine glioma: a report from the Pediatric Brain Tumor Consortium

BACKGROUND

Diffuse intrinsic pontine glioma (DIPG) is associated with poor survival regardless of therapy. We used volumetric apparent diffusion coefficient (ADC) histogram metrics to determine associations with progression-free survival (PFS) and overall survival (OS) at baseline and after radiation therapy (RT).

METHODS

Baseline and post-RT quantitative ADC histograms were generated from fluid-attenuated inversion recovery (FLAIR) images and enhancement regions of interest. Metrics assessed included number of peaks (ie, unimodal or bimodal), mean and median ADC, standard deviation, mode, skewness, and kurtosis.

RESULTS

Based on FLAIR images, the majority of tumors had unimodal peaks with significantly shorter average survival. Pre-RT FLAIR mean, mode, and median values were significantly associated with decreased risk of progression; higher pre-RT ADC values had longer PFS on average. Pre-RT FLAIR skewness and standard deviation were significantly associated with increased risk of progression; higher pre-RT FLAIR skewness and standard deviation had shorter PFS. Nonenhancing tumors at baseline showed higher ADC FLAIR mean values, lower kurtosis, and higher PFS. For enhancing tumors at baseline, bimodal enhancement histograms had much worse PFS and OS than unimodal cases and significantly lower mean peak values. Enhancement in tumors only after RT led to significantly shorter PFS and OS than in patients with baseline or no baseline enhancement.

CONCLUSIONS

ADC histogram metrics in DIPG demonstrate significant correlations between diffusion metrics and survival, with lower diffusion values (increased cellularity), increased skewness, and enhancement associated with shorter survival, requiring future investigations in large DIPG clinical trials.

Pediatric brainstem gliomas: new understanding leads to potential new treatments for two very different tumors

Pediatric brainstem gliomas include low-grade focal brainstem gliomas (FBSG) and high-grade diffuse intrinsic pontine gliomas (DIPG). These tumors share a crucial and eloquent area of the brain as their location, which carries common challenges for treatment. Otherwise, though, these two diseases are very different in terms of presentation, biology, treatment, and prognosis. FBSG usually present with greater than 3 months of symptoms, while DIPG are usually diagnosed within 3 months of symptom onset. Surgery remains the preferred initial treatment for FBSG, with chemotherapy used for persistent, recurrent, or inoperable disease; conversely, radiation is the only known effective treatment for DIPG. Recent developments in biological understanding of both tumors have led to new treatment possibilities. In FBSG, two genetic changes related to BRAF characterize the majority of tumors, and key differences in their biological effects are informing strategies for targeted chemotherapy use. In DIPG, widespread histone H3 and ACVR1 mutations have led to new hope for effective targeted treatments. FBSG has an excellent prognosis, while the long-term survival rate of DIPG tragically remains near zero. In this review, we cover the epidemiology, biology, presentation, imaging characteristics, multimodality treatment, and prognosis of FBSG and DIPG, with a focus on recent biological discoveries.

Pediatric brain tumors

Among all causes of death in children from solid tumors, pediatric brain tumors are the most common. This article includes an overview of a subset of infratentorial and supratentorial tumors with a focus on tumor imaging features and molecular advances and treatments of these tumors. Key to understanding the imaging features of brain tumors is a firm grasp of other disease processes that can mimic tumor on imaging. We also review imaging features of a common subset of tumor mimics.

Imaging of adult brainstem gliomas

Brainstem gliomas (BSGs) are uncommon in adults accounting for about 2% of all intracranial neoplasms. They are often phenotypically low-grade as compared to their more common paediatric counterparts. Since brainstem biopsies are rarely performed, these tumours are commonly classified according to their MR imaging characteristics into 4 subgroups: (a) diffuse intrinsic low-grade gliomas, (b) enhancing malignant gliomas, (c) focal tectal gliomas and (d) exophytic gliomas/other subtypes. The prognosis and treatment is variable for the different types and is almost similar to adult supratentorial gliomas. Radiotherapy (RT) with adjuvant chemotherapy is the standard treatment of diffuse low-grade and malignant BSGs, whereas, surgical resection is limited to the exophytic subtypes. Review of previous literature shows that the detailed imaging of adult BSGs has not received significant attention. This review illustrates in detail the imaging features of adult BSGs using conventional and advanced MR techniques like diffusion weighted imaging (DWI), diffusion tensor imaging (DTI), MR perfusion weighted imaging (PWI), MR spectroscopy (MRS), as well as 18F-fluoro-ethyl-tyrosine positron emission tomography (18F-FET/PET). We have discussed the pertinent differences between childhood and adult BSGs, imaging mimics, prognostic factors and briefly reviewed the treatment options of these tumours.

Radiation therapy and concurrent topotecan followed by maintenance triple anti-angiogenic therapy with thalidomide, etoposide, and celecoxib for pediatric diffuse intrinsic pontine glioma

BACKGROUND

Despite major treatment attempts, the prognosis for pediatric diffuse intrinsic pontine gliomas (DIPGs) remains dismal. Gliomas are highly vascularized tumors, suggesting that the prevention of vessel formation by anti-angiogenic treatment might be effective.

PROCEDURE

Forty-one pediatric patients with DIPG were treated according to the Angiocomb protocol, starting with radiotherapy combined with topotecan and followed by anti-angiogenic triple medication consisting of thalidomide, etoposide, and celecoxib. Overall survival, radiological response, quality of life, requirement of corticosteroids, and adverse effects were monitored. Eight patients treated with only radiotherapy were used as controls.

RESULTS

For study patients, the 12 and 24 months overall survival was 61% and 17%, respectively. The median overall survival was 12 months (range 4-60 months). Four radiological complete responses were seen, of which two were transient. Radiologically, 56% of the tumors reduced in size and 78% in signal intensity. Study patients were able to visit school or daycare and walk for a significantly longer time compared to controls (Log Rank 0.036 and 0.008, respectively). Adverse effects were generally minor.

CONCLUSIONS

The Angiocomb protocol created a noticeable share of long-term survivors and was well tolerated, suggesting that anti-angiogenic therapy for patients with DIPG should be studied more in the future.

18F-FDG PET and MR imaging associations across a spectrum of pediatric brain tumors: a report from the pediatric brain tumor consortium

The purpose of this study was to describe (18)F-FDG uptake across a spectrum of pediatric brain tumors and correlate (18)F-FDG PET with MR imaging variables, progression-free survival (PFS), and overall survival (OS).

METHODS

A retrospective analysis was conducted of children enrolled in phase I/II clinical trials through the Pediatric Brain Tumor Consortium from August 2000 to June 2010. PET variables were summarized within diagnostic categories using descriptive statistics. Associations of PET with MR imaging variables and PFS and OS by tumor types were evaluated.

RESULTS

Baseline (18)F-FDG PET was available in 203 children; 66 had newly diagnosed brain tumors, and 137 had recurrent/refractory brain tumors before enrolling in a Pediatric Brain Tumor Consortium trial. MR imaging was performed within 2 wk of PET and before therapy in all cases. The (18)F-FDG uptake pattern and MR imaging contrast enhancement (CE) varied by tumor type. On average, glioblastoma multiforme and medulloblastoma had uniform, intense uptake throughout the tumor, whereas brain stem gliomas (BSGs) had low uptake in less than 50% of the tumor and ependymoma had low uptake throughout the tumor. For newly diagnosed BSG, correlation of (18)F-FDG uptake with CE portended reduced OS (P = 0.032); in refractory/recurrent BSG, lack of correlation between (18)F-FDG uptake and CE suggested decreased PFS (P = 0.023). In newly diagnosed BSG for which more than 50% of the tumor had (18)F-FDG uptake, there was a suggestion of lower apparent diffusion coefficient (P = 0.061) and decreased PFS (P = 0.065).

CONCLUSION

(18)F-FDG PET and MR imaging showed a spectrum of patterns depending on tumor type. In newly diagnosed BSG, the correlation of (18)F-FDG uptake and CE suggested decreased OS, likely related to more aggressive disease. When more than 50% of the tumor had (18)F-FDG uptake, the apparent diffusion coefficient was lower, consistent with increased cellularity. In refractory/recurrent BSG, poor correlation between (18)F-FDG uptake and CE was associated with decreased PFS, which may reflect concurrent tissue breakdown at sites of treated disease and development of new sites of (18)F-FDG-avid malignancy.

Diffusion tensor histogram analysis of pediatric diffuse intrinsic pontine glioma

Purpose. To evaluate tumor structure in children with diffuse intrinsic pontine glioma (DIPG) using histogram analyses of mean diffusivity (MD), determine potential treatment and corticosteroid-related effects on MD, and monitor changes in MD distributions over time. Materials and Methods. DTI was performed on a 1.5T GE scanner. Regions of interest included the entire FLAIR-defined tumor. MD data were used to calculate histograms. Patterns in MD distributions were evaluated and fitted using a two-normal mixture model. Treatment-related effects were evaluated using the R² statistic for linear mixed models and Cox proportional hazards models. Results. 12 patients with DIPG underwent one or more DTI exams. MD histogram distributions varied among patients. Over time, histogram peaks became shorter and broader (P = 0.0443). Two-normal mixture fitting revealed large lower curve proportions that were not associated with treatment response or outcome. Corticosteroid use affected MD histograms and was strongly associated with larger, sharper peaks (R² = 0.51, P = 0.0028). Conclusions. MD histograms of pediatric DIPG show significant interpatient and intratumoral differences and quantifiable changes in tumor structure over time. Corticosteroids greatly affected MD and must be considered a confounding factor when interpreting MD results in the context of treatment response.

Localized high-resolution DTI of the human midbrain using single-shot EPI, parallel imaging, and outer-volume suppression at 7T

Localized high-resolution diffusion tensor images (DTI) from the midbrain were obtained using reduced field-of-view (rFOV) methods combined with SENSE parallel imaging and single-shot echo planar (EPI) acquisitions at 7T. This combination aimed to diminish sensitivities of DTI to motion, susceptibility variations, and EPI artifacts at ultra-high field. Outer-volume suppression (OVS) was applied in DTI acquisitions at 2- and 1-mm(2) resolutions, b=1000s/mm(2), and six diffusion directions, resulting in scans of 7- and 14-min durations. Mean apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured in various fiber tract locations at the two resolutions and compared. Geometric distortion and signal-to-noise ratio (SNR) were additionally measured and compared for reduced-FOV and full-FOV DTI scans. Up to an eight-fold data reduction was achieved using DTI-OVS with SENSE at 1mm(2), and geometric distortion was halved. The localization of fiber tracts was improved, enabling targeted FA and ADC measurements. Significant differences in diffusion properties were observed between resolutions for a number of regions suggesting that FA values are impacted by partial volume effects even at a 2-mm(2) resolution. The combined SENSE DTI-OVS approach allows large reductions in DTI data acquisition and provides improved quality for high-resolution diffusion studies of the human brain.

Pediatric brain tumors

Pediatric brain tumors are the most common solid tumor of childhood. This article focuses on the metabolic signature of common pediatric brain tumors using MR spectroscopic analyses.

Serial MR diffusion to predict treatment response in high-grade pediatric brain tumors: a comparison of regional and voxel-based diffusion change metrics

BACKGROUND

Assessment of treatment response by measuring tumor size is known to be a late and potentially confounded response index. Serial diffusion MRI has shown potential for allowing earlier and possibly more reliable response assessment in adult patients, with limited experience in clinical settings and in pediatric brain cancer. We present a retrospective study of clinical MRI data in children with high-grade brain tumors to assess and compare the values of several diffusion change metrics to predict treatment response.

METHODS

Eighteen patients (age range, 1.9-20.6 years) with high-grade brain tumors and serial diffusion MRI (pre- and posttreatment interval range, 1-16 weeks posttreatment) were identified after obtaining parental consent. The following diffusion change metrics were compared with the clinical response status assessed at 6 months: (1) regional change in absolute and normalized apparent diffusivity coefficient (ADC), (2) voxel-based fractional volume of increased (fiADC) and decreased ADC (fdADC), and (3) a new metric based on the slope of the first principal component of functional diffusion maps (fDM).

RESULTS

Responders (n = 12) differed significantly from nonresponders (n = 6) in all 3 diffusional change metrics demonstrating higher regional ADC increase, larger fiADC, and steeper slopes (P < .05). The slope method allowed the best response prediction (P < .01, η(2) = 0.78) with a classification accuracy of 83% for a slope of 58° using receiver operating characteristic (ROC) analysis.

CONCLUSIONS

We demonstrate that diffusion change metrics are suitable response predictors for high-grade pediatric tumors, even in the presence of variable clinical diffusion imaging protocols.

Can multiparametric MRI and FDG-PET predict outcome in diffuse brainstem glioma? A report from a prospective phase-II study

PURPOSE

To study the impact of multiparametric MRI and (18)F-FDG-PET on the outcome of children with diffuse intrinsic pontine gliomas (DIPG).

MATERIALS AND METHODS

Imaging data from a phase-II prospective therapeutic study in children with newly diagnosed DIPG were considered for evaluation. They included baseline MRI with contrast enhancement before treatment. Functional imaging included MR spectroscopy, MR perfusion and FDG-PET studies. All patients (n = 20) had baseline MRI and 11 patients had FDG-PET. Response was assessed by MRI and PET 4 weeks after therapy. Baseline imaging findings were correlated with survival. Presence or absence of adverse parameters on MRI (heterogeneous contrast enhancement, hyperperfusion or increased choline:NAA ratio) was used to develop a cumulative radiological prognostic index (RPI). Sensitivity and specificity of each imaging modality in tumour grading was estimated.

RESULTS

The cumulative RPI was able to classify the patients into different grades and was predictive of overall survival (p = 0.02). MR perfusion also predicted survival (p = 0.039). Sensitivity and specificity of MRI and FDG-PET to detect low-grade gliomas were low to moderate (33-66%), but moderate to high in detecting high-grade gliomas (50-100%). Baseline FDG uptake on PET scan did not correlate with survival (p = 0.7).

CONCLUSIONS

Cumulative RPI was able to classify tumours into different grades and predicted clinical outcome. At baseline, MR hyperperfusion indicated a shorter survival for DIPG patients. Sensitivity and specificity of imaging modalities to detect low-grade gliomas were poor.

Brain tumors in children--current therapies and newer directions

Brain tumors are the second most common malignancy and the major cause of cancer related mortality in children. Though significant advances in neuroimaging, neurosurgery, radiation therapy and chemotherapy have evolved over the years, overall survival rate remains less than 75%. Malignant gliomas, high risk medulloblastoma with recurrence and infant brain tumors continue to be a major cause of therapeutic frustration. Even today diffuse pontine gliomas are universally fatal. Though tumors like low grade glioma have an overall excellent survival, recurrences and progression in eloquent areas pose therapeutic challenges. As research continues to unravel the biology including key molecules and signaling pathways responsible for the oncogenesis of different childhood brain tumors, novel targeted therapies are profiled. Identification of major targets like the Epidermal Growth factor Receptor (EGFR), Platelet Derived Growth Factor Receptor (PDGFR), Vascular Endothelial Growth factor (VEGF) and key signaling pathways like the MAPK and PI3K/Akt/mTOR has enabled us over the recent years to better understand tumor behavior and design tailored therapy. These efforts have improved overall survival of children with brain tumors. This review article discusses the current status of common brain tumors in children and the newer therapeutic approaches.

Diffuse intrinsic pontine glioma-current status and future strategies

INTRODUCTION

Diffuse intrinsic pontine gliomas which constitute 15% of all childhood brain tumors are inoperable and response to radiation and chemotherapy has not improved long-term survival. Due to lack of newer effective therapies, mean survival after diagnosis has remained less than 12 months. Trials investigating chemotherapy and/or radiation have proven disappointing. As biopsy of these tumors are rarely performed due to the high eloquence of the brain stem, information about the pathology and biology remains elusive hindering development of novel biologic agents. Poor access of most chemotherapeutic agents to these tumors due to the blood-brain barrier continues to undermine therapeutic efficacy. Thus, to date, we remain at a virtual standstill in our attempts to improve the prognosis of children with these tumors.

METHODS

An extensive review of the literature was performed concerning children with diffuse brain stem gliomas including clinical trials, evolving molecular biology, and newer therapeutic endeavors.

CONCLUSION

A pivotal approach in improving the prognosis of these tumors should include the initiation of biopsy and encouraging families to consider autopsy to study the molecular biology. This will help in redefining this tumor by its molecular signature and profiling targeted therapy. Continued advances should be pursued in neuroimaging technology including identifying surrogate markers of early disease progression. Defining strategies to enhance local delivery of drugs into tumors with the help of newer surgical techniques are important. Exhaustive research in all these aspects as a multidisciplinary approach could provide hope to children with these fatal tumors.

Elevated citrate in pediatric astrocytomas with malignant progression

In vivo magnetic resonance spectroscopy (MRS) provides information about metabolite concentrations in tissue. Recently citrate was detected by MRS in subgroups of pediatric brain tumors. Citrate is an intermediate in the tricarboxylic acid (TCA) cycle and accumulates in tissue when the glycolytic rate exceeds the TCA cycle activity, a feature of malignant tumors. Currently, no practical indicators allow clinicians to predict risk for malignant progression of pediatric astrocytomas (World Health Organization [WHO] grade II). Medical records and citrate concentrations measured with in vivo MRS of 29 pediatric astrocytomas were reviewed. This included 6 patients with astrocytomas (WHO II) who had stable disease (indolent LGA) for >2 years, 7 with aggressive grade II astrocytomas (aggressive LGA), 13 with anaplastic astrocytomas (WHO III), and 3 with glioblastoma (WHO IV) with disease progression within 2 years. Citrate was observed in all patients with aggressive LGA, and the mean citrate concentration was significantly higher in this group than among those with indolent LGA (mean ± standard deviation, 4.1 ± 1.1 vs 0.6 ± 0.8 mmol/kg; P < .0001). There was no consistent pattern for citrate in anaplastic astrocytoma and glioblastoma, with citrate prominent in some lesions whereas undetectable in others. It is unclear whether citrate accumulation occurred because of fundamental defects of citrate regulation or was secondary to altered physiological conditions. Nonetheless, prominent citrate identified a subgroup of pediatric grade II astrocytomas destined for aggressive behavior. Citrate was not specific for poor outcome because it was not detectable in all high-grade astrocytomas. In high-grade astrocytoma, tumors with prominent citrate may constitute a metabolic subclass.

Diffusion differences between pilocytic astrocytomas and grade II ependymomas

BACKGROUND

The aim of our study was to differentiate between cerebellar pilocytic astrocytomas and grade II ependymomas on the basis of their diffusion properties.

PATIENTS AND METHODS

The study prospectively included 12 patients with pilocytic astrocytomas and 5 with ependymomas. Apparent diffusion coefficients (ADC) were compared between tumour types.

RESULTS

ADC values were significantly higher in pilocytic astrocytomas than ependymomas, with almost no overlapping of the range of measured ADCs between the two tumour types.

CONCLUSIONS

Significant diffusion differences between pilocytic astrocytomas and grade II ependymomas enable their preoperative distinction, in combination with conventional magnetic resonance images.

MRI as a central component of clinical trials analysis in brainstem glioma: a report from the Pediatric Brain Tumor Consortium (PBTC)

We report MRI findings from 2 pediatric clinical trials of diffuse intrinsic brainstem glioma (BSG) incorporating concurrent radiation therapy (RT) with molecularly targeted agents (gefitinib and tipifarnib). We determined associations of MRI variables with progression-free survival and overall survival and investigated effects of treatment on these variables. MRI (including diffusion and perfusion) was done before treatment, every 8 weeks (first year), every 12 weeks (thereafter), and at the end of treatment or disease progression. Reduced tumor volume (P < .0001) and tumor diffusion values (P <.0001) were apparent on the first post-RT/drug studies. Decreases in tumor volume correlated with pre-RT volume (P < .0001) and pre-RT diffusion values (P < .0001); larger decreases were noted for tumors with higher volumes and diffusion values. Patients with larger pre-RT tumors had longer progression-free survival (P < .0001). Patients with ≥ 25% decrease in tumor volume and diffusion values after RT had longer progression-free survival (P = .028) and overall survival (P = .0009). Enhancement at baseline and over time was significantly associated with shorter survival. Tumor diffusion values with baseline enhancement were significantly lower than those without (P = .0002). RT of BSG is associated with decreased tumor volume and intralesional diffusion values; patients with ≥ 25% decrease in values post-RT had relatively longer survival intervals, apparently providing an early imaging-based surrogate for relative outcomes. Patients with larger tumors and greater decreases in tumor volume and diffusion values had longer survival intervals. Tumor enhancement was associated with shorter survival, lower tumor diffusion values (increased cellularity), and a smaller drop in diffusion values after RT (P = .006). These associations justify continued investigation in other large clinical trials of brainstem glioma patients.

Evaluation of 18F-FDG PET and MRI associations in pediatric diffuse intrinsic brain stem glioma: a report from the Pediatric Brain Tumor Consortium

The purpose of this study was to assess (18)F-FDG uptake in children with a newly diagnosed diffuse intrinsic brain stem glioma (BSG) and to investigate associations with progression-free survival (PFS), overall survival (OS), and MRI indices.

METHODS

Two Pediatric Brain Tumor Consortium (PBTC) therapeutic trials in children with newly diagnosed BSG were designed to test radiation therapy combined with molecularly targeted agents (PBTC-007: phase I/II study of gefitinib; PBTC-014: phase I/II study of tipifarnib). Baseline brain (18)F-FDG PET scans were obtained in 40 children in these trials. Images were evaluated by consensus between 2 PET experts for intensity and uniformity of tracer uptake. Associations of (18)F-FDG uptake intensity and uniformity with both PFS and OS, as well as associations with tumor MRI indices at baseline (tumor volume on fluid-attenuated inversion recovery, baseline intratumoral enhancement, diffusion and perfusion values), were evaluated.

RESULTS

In most of the children, BSG (18)F-FDG uptake was less than gray-matter uptake. Survival was poor, irrespective of intensity of (18)F-FDG uptake, with no association between intensity of (18)F-FDG uptake and PFS or OS. However, hyperintense (18)F-FDG uptake in the tumor, compared with gray matter, suggested poorer survival rates. Patients with (18)F-FDG uptake in 50% or more of the tumor had shorter PFS and OS than did patients with (18)F-FDG uptake in less than 50% of the tumor. There was some evidence that tumors with higher (18)F-FDG uptake were more likely to show enhancement, and when the diffusion ratio was lower, the uniformity of (18)F-FDG uptake appeared higher.

CONCLUSION

Children with BSG for which (18)F-FDG uptake involves at least half the tumor appear to have poorer survival than children with uptake in less than 50% of the tumor. A larger independent study is needed to verify this hypothesis. Intense tracer uptake in the tumors, compared with gray matter, suggests decreased survival. Higher (18)F-FDG uptake within the tumor was associated with enhancement on MR images. Increased tumor cellularity as reflected by restricted MRI diffusion may be associated with increased (18)F-FDG uniformity throughout the tumor.

DTI assessment of the brainstem white matter tracts in pediatric BSG before and after therapy: a report from the Pediatric Brain Tumor Consortium

PURPOSE

To assess changes in apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values in brainstem gliomas (BSG) in children and to observe the temporal evolution of changes in the white matter tracts following therapy using diffusion tensor imaging (DTI) analysis.

METHODS

Serial ADC and FA measurements were obtained in three patients with newly diagnosed BSG on two approved treatment protocols. Values were compared with a set of normative ADC, FA, and eigenvalues of age-matched children of the corticospinal, transverse pontine and medial lemniscal tracts. Fiber tracking of the tracts coursing through the brainstem was performed using standard diffusion tractography analysis.

RESULTS

We found increased ADC values within tumor at baseline compared to age-matched controls, with subsequent drop following treatment and subsequent increase with recurrence. Correspondingly, FA values were reduced at presentation, but transiently recovered during the phase of tumor response to treatment, and finally decreased significantly during tumor progression. These changes were concordant with the tractography analysis of white matter tracts in the brainstem. Based on these results, we suggest that initial changes in ADC and FA values reflects tract infiltration by tumor, but not complete disruption, whereas tumor progression results in complete loss of anisotropy possibly due to tract disruption.

CONCLUSION

Serial changes in ADC and FA values and tractography data in pediatric BSG suggest initial tumor infiltration, with transient improvement on treatment and subsequent loss of tract anisotropy during tumor progression. This technique may have potential use in assessing response to treatment regimens for pediatric BSG.