Common Posterior Fossa Tumors Research Articles

IMG-18. DIFFERENTIAL DIAGNOSIS OF POSTERIOR FOSSA TUMORS USING RADIOMICS; A FIRST-LINE DIAGNOSTIC STEP REQUIRED FOR DOWNSTREAM ANALYSES

Abstract BACKGROUND Accurate radiographic diagnosis of pediatric brain tumors (PBTs) that originate in the brainstem and posterior fossa, including medulloblastoma (MB), pilocytic astrocytoma (PA), ependymoma (EPN), atypical teratoid/rhabdoid tumor (ATRT), and diffuse intrinsic pontine glioma (DIPG), is crucial for optimizing surgical approaches and enhancing neoadjuvant therapies. Existing research on the radiographic differential diagnosis of posterior fossa tumors has limitations, including small sample sizes, lack of inclusion of certain histologies especially rarer tumors such as ATRTs, and incomplete analysis of the whole tumor, including peritumoral edema. In this study, we aimed to perform a comprehensive analysis using radiomics and machine learning to differentiate among the common posterior fossa and brainstem tumors. METHODS We employed 927 radiomic features extracted from whole tumor regions within treatment-naïve, standard multiparametric MRI sequences (pre-/post-contrast T1-weighted, T2-weighted, FLAIR) of 264 patients (106 MBs, 78 PAs, 28 EPNs, 27 ATRTs, and 25 DIPGs), collected from the Children’s Brain Tumor Network (CBTN). We adopted a one-versus-rest classification strategy, employing Support Vector Machines combined with the Least Absolute Shrinkage and Selection Operator (LASSO) for feature selection, and implementing nested cross-validation for robustness. RESULTS The performances of the classifiers were evaluated using the Area Under the Receiver Operating Characteristic Curve, yielding values of 0.84 for MBs, 0.84 for PAs, 0.70 for EPNs, 0.75 for ATRTs, and 0.71 for DIPGs. CONCLUSIONS Our method effectively differentiates between various tumor types in the posterior fossa and brainstem, paving the path towards the development of comprehensive diagnostic and prognostic AI tools for pre-treatment histological diagnosis of these tumors. These AI tools can lead to more tailored, risk-adjusted treatments for PBTs, reducing morbidities and improving patient outcomes. Based on our promising initial results, we will expand our dataset to include more samples and incorporate rarer tumor types, as well as piloting in different molecular subclassifications.

What is Under the Tent? Posterior Fossa Tumors in Children, the Usual Suspects—Part 1

Pediatric posterior fossa tumors are a major cause of morbidity and mortality in children. In this 2-part series, we discuss the spectrum of posterior fossa tumors and their clinical and molecular characteristics. In Part 1, the authors discuss the 5 primary differential diagnoses of posterior fossa tumors: medulloblastoma, pilocytic astrocytoma, ependymoma, diffuse midline glioma, H3K27-altered, and atypical teratoid/rhabdoid tumors. Each posterior fossa tumor is clinically and histologically defined. Additionally, relevant epidemiology data, current genetics/molecular classification according to the fifth edition of the World Health Organization Classification of Tumors of the Central Nervous System, and imaging findings are reviewed. The new version of the international standard for the classification of central nervous system tumors introduces major changes that advance the role of molecular diagnostics in the pediatric central nervous system tumor classification, particularly in posterior fossa tumors, which may impact management and outcomes.Learning Objective: To recognize the imaging appearance of the most common posterior fossa tumors in children.

Differentiation of pilocytic astrocytoma, medulloblastoma, and hemangioblastoma on diffusion-weighted and dynamic susceptibility contrast perfusion MRI.

This study aimed to evaluate the diagnostic performance of dynamic susceptibility contrast (DSC) perfusion magnetic resonance imaging and apparent diffusion coefficient (ADC) for differentiating common posterior fossa tumors, pilocytic astrocytoma (PA), medulloblastoma (MB), and hemangioblastoma (HB). Between January 2016 and April 2022, we enrolled 23 (median age, 7 years [range, 2-26]; 12 female), 13 (10 years [1-24]; 3 female), and 12 (43 years [23-73]; 7 female) patients with PA, MB, and HB, respectively. Normalized relative cerebral blood volume and flow (nrCBV and nrCBF) and normalized mean ADC (nADCmean) were calculated from volume-of-interest and statistically compared. nADCmean was significantly higher in PA than in MB (PA: median, 2.2 [range, 1.59-2.65] vs MB: 0.93 [0.70-1.37], P < .001). nrCBF was significantly higher in HB than in PA and MB (PA: 1.10 [0.54-2.26] vs MB: 1.62 [0.93-3.16] vs HB: 7.83 [2.75-20.1], all P < .001). nrCBV was significantly different between all 3 tumor types (PA: 0.89 [0.34-2.28] vs MB: 1.69 [0.93-4.23] vs HB: 8.48 [4.59-16.3], P = .008 for PA vs MB; P < .001 for PA vs HB and MB vs HB). All tumors were successfully differentiated using an algorithmic approach with a threshold value of 4.58 for nrCBV and subsequent threshold value of 1.38 for nADCmean. DSC parameters and nADCmean were significantly different between PA, MB, and HB. An algorithmic approach combining nrCBV and nADCmean may be useful for differentiating these tumor types.

Common Histopathological spectrum of Posterior Fossa Tumors in Pediatric Age Group

Objective: To know about the common posterior fossa tumors in the pediatric age group on basis of Histopathology in Neurosurgery Department, Hayatabad Medical Complex Peshawar.&#x0D; Material and Methods: This descriptive cross-sectional study was conducted in the department of MTI Hayatabad medical complex Peshawar from January 2017 to January 2020. We included a total of 52 patients who operated for posterior fossa tumors and biopsy reports were observed to know the histological pattern of the tumor. We included all those patients who have posterior fossa tumors except those tumors which involved or arise from brain stem and infections. The data was collected and analyzed using SPSS version 21.&#x0D; Results: Our study shows that the mean age was 6 years with a standard deviation ± 2.81. Fifty-eight percent of children were male and 42% of children were female. Histopathologic patterns were analyzed as 48% of children had Medulloblastoma, 25% of children had Astrocytoma, 19% of children had Ependymoma, 8% of patients had other histopathologic patterns.&#x0D; Conclusion: Our study concludes that common histopathologic patterns of posterior fossa tumors in children were medulloblastoma (48%), Astrocytoma (25%), ependymoma (19%) respectively.

ROLE OF DIFFUSION WEIGHTED MRI IN DIFFERENTIAL DIAGNOSIS OF PAEDIATRIC POSTERIOR FOSSA TUMORS

Background: Infratentorial tumors accounts for 65% of all paediatric tumors, and most common infratentorial tumors in children include juvenile pilocytic astrocytoma (JPA), medulloblastoma, ependymoma and brainstem glioma. An accurate diagnosis has important clinical implications related to treatment and prognosis. DWI and ADC maps provide information regarding the cellularity of tumors and have an important role in the preoperative differentiation of different tumor types.&#x0D; Aim: To evaluate the role of DWI and ADC measurement in distinguishing between the most common pediatric posterior fossa tumors.&#x0D; Methods: In this study, we evaluated 25 paediatric patients aged between 1 to 15 years suspected to have posterior fossa mass on the CT referred from neurosurgery department to our department for MRI brain. All these patients subjected to conventional MRI followed by diffusion MR imaging and calculation of the ADC values. Written consent was taken from the guardians.&#x0D; Results: In juvenile pilocytic astrocytoma ( n = 10), ADC values ranged between 1.3 and 1.9 × 10?3 mm2/s, ependymoma (n = 8), ADC values ranged between 1.1 and 1.5 × 10?3 mm2/s and medulloblastoma (n = 7), ADC values ranged between 0.45 and 0.9 × 10?3 mm2/s. Statistically significant difference in ADC value was detected between JPA, ependymomas and medulloblastomas, while no statistically significant difference was detected between JPA and ependymomas.&#x0D; Conclusion: Diffusion Imaging plays an important role in demonstrating the features of posterior fossa brain tumours for appropriate diagnosis of medulloblastomas, ependymomas, and pilocytic astrocytoma.&#x0D; Keywords: DWI, MRI, Posterior fossa

Diagnostic accuracy of apparent diffusion coefficient ratio in distinguishing common pediatric CNS posterior fossa tumors

BackgroundPilocytic astrocytoma, medulloblastoma, and ependymoma are the most common pediatric CNS tumors seen at posterior cranial fossa and final diagnosis obtained by histopathology after surgical excision. Routine MRI study gives an idea about site and extension of the tumors but provide a little information about type and grade of tumors. ADC ratio had high sensitivity and specificity in differentiation between these tumors as regard type and grade according to tumor cellularity.Patients and methodsProspective study conducted on thirty pediatric patients (11 males and 19 females) with CNS posterior fossa masses, their ages ranged from 2 to 17 years (mean age of 8.7 years), conventional MRI, DWI, ADC value, and ADC ratio were done for all patients.ResultsADC values were significantly different between pilocytic astrocytomas (1.43 ± 0.28 × 10−3) and medulloblastomas (0.71 ± 0. 21 × 10−3) with a P value < 0.001, also there was a significant difference when comparing medulloblastomas (0.71 ± 0.21 × 10−3) with ependymomas (1.04 × 10−3 ± 0.21) with a P value < 0.001. ADC ratio at a cutoff > 1.7 showed significant good power of discrimination of astrocytoma (AUC = 0.85) from ependymoma with 87.5% sensitivity and 93.3% specificity. Similarly, at cutoff ≤ 1.6-> 1.2 was a significant good predictor of ependymoma (AUC = 0.85) with 87.8% sensitivity and 99.5% specificity. While, ADC ratio ≤ 1.2 was significant excellent discriminator of medulloblastoma (AUC = 0.99) with 100% sensitivity and 90% specificity.ConclusionADC ratio is a simple way used in distinguishing juvenile pilocytic astrocytoma, ependymoma, and medulloblastoma, which are the most frequent pediatric posterior fossa tumors. Cutoff ADC ratio of more than 1.7 characteristic of JPA with 87.5% sensitivity and 93.3% specificity, ADC ratio less than 1.1 characteristic of medulloblastoma with 100% sensitivity and 90% specificity. ADC ratios more than 1.1 and less than 1.7 characteristic of ependymoma with 87.8% sensitivity and 99.5% specificity. We recommended ADC ratio as a routine study in evaluation of pediatric CNS posterior fossa tumors.

Adult outcome after treatment of pediatric posterior fossa ependymoma: long-term follow-up of a single consecutive institutional series of 22 patients with more than 5 years of survival.

Ependymoma is the third most common posterior fossa tumor in children; however, there is a lack of long-term follow-up data on outcomes after surgical treatment of posterior fossa ependymoma (PFE) in pediatric patients. Therefore, the authors sought to investigate the long-term outcomes of children treated for PFE at their institution. The authors performed a retrospective analysis of outcome data from children who underwent treatment for PFE and survived for at least 5 years. The authors identified 22 children (median age at the time of surgery 3 years, range 0-18 years) who underwent primary tumor resection of PFE during the period from 1945 to 2014 and who had at least 5 years of observed survival. None of these 22 patients were lost to follow-up, and they represent the long-term survivors (38%) from a total of 58 pediatric PFE patients treated. Nine (26%) of the 34 children treated during the pre-MRI era (1945-1986) were long-term survivors, while the observed 5-year survival rate in the children treated during the MRI era (1987-2014) was 13 (54%) of 24 patients. The majority of patients (n = 16) received adjuvant radiotherapy, and 4 of these received proton-beam irradiation. Six children had either no adjuvant treatment (n = 3) or only chemotherapy as adjuvant treatment (n = 3). Fourteen patients were alive at the time of this report. According to MRI findings, all of these patients were tumor free except 1 patient (age 78 years) with a known residual tumor after 65 years of event-free survival.Repeat resections for residual or recurrent tumor were performed in 9 patients, mostly for local residual disease with progressive clinical symptoms; 4 patients underwent only 1 repeated resection, whereas 5 patients each had 3 or more resections within 15 years after their initial surgery. At further follow-up, 5 of the patients who underwent a second surgery were found to be dead from the disease with or without undergoing additional resections, which were performed from 6 to 13 years after the second procedure. The other 4 patients, however, were tumor free on the latest follow-up MRI, performed from 6 to 27 years after the last resection. Hence, repeated surgery appears to increase the chance of tumor control in some patients, along with modern (proton-beam) radiotherapy. Six of 8 patients with more than 20 years of survival are in a good clinical condition, 5 of them in full-time work and 1 in part-time work. Pediatric PFE occurs mostly in young children, and there is marked risk for local recurrence among 5-year survivors even after gross-total resection and postoperative radiotherapy. Repeated resections are therefore an important part of treatment and may lead to persistent tumor control. Even though the majority of children with PFE die from their tumor disease, some patients survive for more than 50 years with excellent functional outcome and working capacity.

The Diagnostic Value of MRI-Based Texture Analysis in Discrimination of Tumors Located in Posterior Fossa: A Preliminary Study.

ObjectivesTo investigate the diagnostic value of MRI-based texture analysis in discriminating common posterior fossa tumors, including medulloblastoma, brain metastatic tumor, and hemangioblastoma.MethodsA total number of 185 patients were enrolled in the current study: 63 of them were diagnosed with medulloblastoma, 56 were diagnosed with brain metastatic tumor, and 66 were diagnosed with hemangioblastoma. Texture features were extracted from contrast-enhanced T1-weighted (T1C) images and fluid-attenuation inversion recovery (FLAIR) images within two matrixes. Mann–Whitney U test was conducted to identify whether texture features were significantly different among subtypes of tumors. Logistic regression analysis was performed to assess if they could be taken as independent predictors and to establish the integrated models. Receiver operating characteristic analysis was conducted to evaluate their performances in discrimination.ResultsThere were texture features from both T1C images and FLAIR images found to be significantly different among the three types of tumors. The integrated model represented that the promising diagnostic performance of texture analysis depended on a series of features rather than a single feature. Moreover, the predictive model that combined texture features and clinical feature implied feasible performance in prediction with an accuracy of 0.80.ConclusionMRI-based texture analysis could potentially be served as a radiological method in discrimination of common tumors located in posterior fossa.

Role of Diffusion Mri In Differentiation Between The Common Pediatric Posterior Fossa Brain Tumors.

Background: Diffusion weighted imaging (DWI) and apparent diffusion coefficient (ADC) map provide information on MRI about the cellularity of the tumor and have an important role in the pre-operative differentiation of different tumor types. Objective: The aim of this work is to assess the role of diffusion MRI in differentiation between the most frequently encountered pediatric posterior fossa brain tumors. Materials and methods: Twenty-four patients were prospectively included in this study. They were referred from the Neurosurgery Department. All of them were suspected to have posterior fossa SOL according to the contrast enhanced CT. All patients were subjected to conventional MRI followed by diffusion MR imaging and calculation of the ADC values. Results: Twenty-four children (15 females) were included in the study. Their ages ranged between one and fifteen years old with a mean age of six years. Low-and high-grade tumors could be differentiated by using both absolute ADC values and ratios. Low-grade tumors showed statistically significantly higher ADC values (1.69±0.15 vs. 0.80±0.23) and ratios for tumor versus normal cerebellum (2.17±0.30 vs. 1.14±0.33) and tumor versus brain stem (1.88±0.35 vs. 1.06±0.24).The probability of error at 0.05 was considered significant, while at 0.01 and 0.001 was considered highly significant. Absolute ADC values and cerebellar and brainstem ratios were significantly higher in low-grade astrocytomas than in MBs. Overlap was found between ADC values of ATRTs and MBs.The sensitivity and specificity of a cutoff ADC value of > 1.083 x 10-3mm2/s for differentiation of pilocytic astrocytomas from MBs and ependymomas were 100%.The sensitivity and specificity of a cutoff ADC value of ≤ 0.847 x 10-3mm2/s for differentiation of medulloblastomas from PAs and ependymomas were 100%.The sensitivity and specificity of a cutoff ADC value of ≤ 1.083 x 10-3mm2/s and > 0.847 x 10-3mm2/s for ependymomas were 100%. Conclusion: The calculation of ADC value in the solid enhancing portion of a tumor is a simple and reliable technique for preoperative differentiation of the most common posterior fossa tumors.

Long noncoding RNA CCAT1 promotes cell proliferation and metastasis in human medulloblastoma via MAPK pathway.

Medulloblastoma is the most common posterior fossa tumor in children and one that easily metastasizes. The mechanisms of how the medulloblastoma develops and progresses remain to be elucidated. The present study aimed to assess the role of long noncoding colon cancer-associated transcript-1 (lncRNA CCAT1) in cell proliferation and metastasis in human medulloblastoma. Levels of CCAT1 were measured in samples and cell lines of medulloblastoma. Cell cycle progression, cell viability assay, colony formation assay, wound-healing and Transwell assays Corning, Cambridge, MA, USA were used to investigate the viability and motility of cells. Western blot assay was used to investigate the levels of CCAT1 and other proteins. The initial findings indicated that CCAT1 was significantly up-regulated in clinical cancerous tissues and expressed differently in a series of medulloblastoma cell lines. CCAT1 knockdown significantly slowed cell proliferation rates and inhibited cell clonogenic potential in Daoy cells and D283 cells. Cell cycle progression was disrupted with cell proportions in the G0/G1 phase decreased and the proportion in the S phase and G2/M phases increased, in Daoy cells and D283 cells. Concordantly, medulloblastoma tumor cell growth rates were found to be impaired in xenotransplanted mice. After CCAT1 knockdown, cell wound recovery ability was significantly inhibited. Furthermore, the phosphorylated levels of MAPK, ERK and MEK, but not their total levels decreased after the down-regulation of CCAT1 in Daoy and D283 cells. Our results suggested that the lncRNA CCAT1 promotes cell proliferation and metastasis in human medulloblastoma by possibly regulating the MAPK pathway.

Targeted Sequencing of Malignant Supratentorial Pediatric Brain Tumors Demonstrates a High Frequency of Clinically Relevant Mutations.

Pediatric brain tumors cause more deaths than any other childhood malignancy, and the identification of potentially actionable genomic alterations in this rare heterogeneous group of tumors may improve treatment and outcome. The genetic landscape of common posterior fossa tumors has been described in the past several years, yet the classification of malignant pediatric supratentorial tumors remains controversial. Next-generation sequencing (NGS) is a promising tool to evaluate multiple genes concurrently. The clinical utility of NGS has not been proven in pediatric brain tumors. We identified patients diagnosed with high-grade supratentorial pediatric brain tumors resected between 2008 and 2012 at our institution. DNA from 12 formalin-fixed paraffin-embedded tumor samples from 9 patients was analyzed, including 3 paired samples from diagnosis and relapse. A panel of 194 cancer-related genes was sequenced using targeted next-generation deep sequencing. Genetic findings were correlated with histology, immunohistochemistry, treatment, and survival. We found one or more pathologic genetic change (mutation, amplification, or deletion) in 8 of 9 (89%) of patients studied. Epidermal Growth Factor Receptor ( EGFR) mutations were found in 3 patients, 2 of which had an exon 20 insertion not previously described in pediatric malignancy. Additional genetic changes were found in EGFR and Platelet-Derived Growth Factor Receptor Alpha ( PDGFRA) at relapse not present in the initial samples. Familial cancer predisposition syndromes were suggested by mutations found in 3 genes in 4 patients, including TP53, MSH2, and CHEK2. Seven of 9 patients in this study died of their disease. In summary, targeted deep sequencing may be used in rare pediatric brain tumors to identify driver mutations for targeted therapy, suggest constitutional and familial testing for cancer predisposition syndromes, and select molecular targets worthy of further study.

Role of Dynamic Contrast-Enhanced Perfusion Magnetic Resonance Imaging in Grading of Pediatric Brain Tumors on 3T

Background/Aims: Perfusion magnetic resonance imaging (MRI) is useful for preoperative assessment of brain tumors. Dynamic susceptibility contrast perfusion MRI is commonly used for evaluation of brain tumors. Dynamic contrast-enhanced (DCE) MRI is an alternative method that has mainly been used in adult brain tumors. In this preliminary study, we report our initial experience with the DCE perfusion MRI in pediatric brain tumors. Methods: Sixty-four newly diagnosed pediatric brain tumor patients underwent DCE perfusion MRI on a 3-T scanner. Hemodynamic and kinetic parametric maps were generated and the regions with the highest values were measured on each map. Statistical differences were sought to differentiate between low-grade tumors, high-grade tumors, and medulloblastomas. The perfusion metrics of common posterior fossa tumors were also compared. Results: Relative corrected cerebral blood volume (rCBV) and fractional plasma volume measures differed significantly between high- and low-grade tumors (p < 0.05). High-grade tumors could be differentiated from low-grade tumors, with an rCBV cutoff value of 2.41 and 88.6% sensitivity and 65% specificity. There was no significant difference in K^trans, K_ep, V_e, or λ^tr between these 2 groups of tumors. rCBV, relative quantification of the cerebral blood flow, and permeability indices were found to be significantly different in various posterior fossa tumors, i.e., pilocytic astrocytoma, ependymoma, and medulloblastoma (p < 0.05). Conclusion: DCE-derived perfusion metrics are useful in differentiating high-grade tumors from low-grade ones and discriminating among various posterior fossa tumors in the pediatric age group.

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.

Relative ADC and Location Differ between Posterior Fossa Pilocytic Astrocytomas with and without Gangliocytic Differentiation.

Pilocytic astrocytomas, the most common posterior fossa tumors in children, are characterized by KIAA1549-BRAF fusions and shows excellent 5-year survival rates. Pilocytic astrocytoma with gangliocytic differentiation, a recently defined pilocytic astrocytoma variant that includes glial and neuronal elements similar to a ganglioglioma, may be distinguished from a classic ganglioglioma by molecular, radiologic, and histopathologic features. This study investigated whether imaging could distinguish posterior fossa pilocytic astrocytoma with and without gangliocytic differentiation. Preoperative MRIs (± CTs) of 41 children (age range, 7 months to 15 years; mean age, 7.3 ± 3.7 years; 58.5% male) with pilocytic astrocytoma with gangliocytic differentiation (n = 7) or pilocytic astrocytoma (n = 34) were evaluated; differences in tumor location, morphology, and minimum relative ADC between tumor types were compared (Wilcoxon rank sum test, Fisher exact test). Histopathology and BRAF fusion/mutation status were reviewed. Associations of progression-free survival with diagnosis, imaging features, and BRAF status were examined by Cox proportional hazards models. Pilocytic astrocytoma with gangliocytic differentiation appeared similar to pilocytic astrocytoma but had lower minimum relative ADC (mean, 1.01 ± 0.17 compared with 2.01 ± 0.38 for pilocytic astrocytoma; P = .0005) and was more commonly located within midline structures (P = .0034). BRAF status was similar for both groups. Non-total resection (hazard ratio, 52.64; P = .0002), pilocytic astrocytoma with gangliocytic differentiation diagnosis (hazard ratio, 4.66; P = .0104), and midline involvement (hazard ratio, 3.32; P = .0433) were associated with shorter progression-free survival. Minimum relative ADC and tumor location may be useful adjuncts to histopathology in differentiating pilocytic astrocytoma with gangliocytic differentiation from pilocytic astrocytoma. Shorter progression-free survival in pilocytic astrocytoma with gangliocytic differentiation is likely due to a propensity for involvement of midline structures and poor resectability.

Pediatric cerebellar astrocytoma: a review.

Cerebellar astrocytomas (CA) are one of the most common posterior fossa tumors in children. The vast majority is low grade, and prognosis for long-term survival is excellent. Recent literature about CA was reviewed to provide an up to date overview of the epidemiology, pathology, molecular and cell biology, diagnosis, presentation, management, and long-term outcomes. Surgical resection remains the first-line treatment with complete removal of the tumor the goal. However, even when only subtotal resection has been achieved, there is a significant chance that the tumor will remain stable or will regress spontaneously. Adjuvant chemotherapy is reserved for those tumors that progress despite surgery, and more personalized chemotherapy is being pursued with better understanding of the molecular genetics of this tumor. Radiotherapy has generally not been recommended, but stereotactic radiotherapy and conformal proton beam radiotherapy may be reasonable options in the setting of relapse or progression. In the long term, permanent neurologic deficits, mainly cerebellar dysfunction, are common, but quality of life and cognitive function are generally good. Low-grade CA remains primarily a surgical disease, with excellent survival rates. Care must be taken with surgery and adjuvant treatments to preserve neurologic function to allow for optimal outcomes in the long term.

Medulloblastoma in childhood-King Edward Memorial hospital surgical experience and review: Comparative analysis of the case series of 365 patients

Aim:Medulloblastoma is one of the most common posterior fossa tumors in childhood. The treatment-related side effects as well as predictive outcome still remain as a major challenge. The improved understanding of the disease and advances in molecular biology is changing the treatment paradigms from Chang's staging system to molecular risk stratification. However, surgery still remains as an important mainstay of therapy and is formidable. The role of radical surgery has always been a crucial factor in the outcome of these patients, the best survival being reported in patients who had total excision of the tumor and with no metastasis.Patient and Methods:An analysis of 365 patients (age<18 years) of medulloblastoma who underwent treatment at the Seth G.S. Medical College and King Edward VII Memorial hospital (KEM), Mumbai over a 25- year period (1985-2000 and 2001-2010) is presented. The clinical profile, radiological features, pathology and surgical nuances are discussed.Results:The most common age group affected was between 3 and 12 years. 75.3% presented with headaches, vomiting and 63.2% with papilledema. Sitting position was used in majority of cases. A total of 8 patients underwent shunting; all of them were in the postoperative period (5.19%). 92.2% (142 cases) had classical medulloblastoma, 5.1% (8 cases) had desmoplastic variant, 1.9% (3 cases) had anaplastic changes and 0.6% (1 case) had glial differentiation. The 5-year and 10-year progression free survival rate was 73 and 41% for average risk disease while for high risk disease rate it was 34%. The mortality rate was 2%. The quality of life was enhanced in patients who survived 5-10 years after treatment.Conclusion:Surgery for medulloblastoma is formidable. The option of sitting position for medulloblastoma surgery is still viable. A vigilant neuroanesthesiologist and a safe surgery are necessary to achieve a good postoperative result. Radiological characteristics are helpful adjuncts for determining effective surgical strategy. Permanent CSF drainage can be avoided in majority of patients and can be definitively considered in progressive symptomatic hydrocephalus. A safe maximal resection and a good Karnofsky score are paramount to ensure compliance with adjuvant therapy and contribute to an overall survival advantage.

Magnetic resonance spectroscopy findings in non-enhancing desmoplastic medulloblastoma

Medulloblasoma is a common posterior fossa tumor seen in children and presents with some typical features like midline vermian location and fairly homogeneous enhancment. Desmoplastic variety of medulloblastoma is usually seen in the adults and is known to show some atypical features like lateral cerebellar location, variable enhancement, and early meningeal infilteration. Therefore medulloblastoma should always be considered in differential diagnosis of posterior fossa mass in adults even when typical imaging findings are not that of medulloblastoma. Enhancement pattern can be variable in these tumors varying from mild to striking. Occasionally, totally non-enhancing tumors are encountered, which can cause further diagnostic confusion. We describe the magnetic resonance (MR) and MR spectroscopy findings in a case of midline vermian mass, which did not show any enhancement on post-contrast images, and was subsequently proven to be desmoplastic medulloblastoma. On MR spectroscopy, the mass showed elevated choline peak consistent with mitotic lesion. No significant lipid lactate leak was seen, which is also consistent with the ususally homogeneous nature of these tumors. Moreover, it displayed taurine peak at 3.4 ppm which is considered fairly specific for medulloblastoma. Therefore, MR spectroscopy findings can be helpful in the diagnosis of medulloblastoma in adults when MR imaging findings can be nonspecific.

Rosette-forming glioneuronal tumor of the fourth ventricle in an elderly patient

Rosette-forming glioneuronal tumor of the fourth ventricle (RGNT) is a rare condition, which previously has been described predominantly in middle-aged patients. There is limited experience with this kind of tumor in the elderly. Clinical, neuroimaging, and histological features of an example in a 70-year-old male who presented initially with vertigo are detailed and compared with published cases. Neuroimaging studies demonstrated a 4-cm cystic lesion in posterior fossa containing a 1-cm contrast-enhancing nodule on its lateral margin. The lesion was confined to the fourth ventricle and initially thought to be a hemangioblastoma until angiography clarified the minimal tumor vascularization. Gross total resection was achieved. Pathological examination showed a rosette-forming low grade tumor with a cell proliferation rate of 2% being consistent with RGNT. The postoperative course was uneventful and clinical symptoms resolved completely. There was no tumor recurrence after 2 years follow-up. We confirm that the rare and only recently characterized tumor entity of RGNT can also be found in elderly patients; furthermore, it can be associated with a benign course. The main differential diagnosis of RGNT resulting from CNS-imaging modalities in elderly patients are pilocytic astrocytoma and hemangioblastoma of the posterior fossa, which after metastasis are the most common primary adult intra-axial posterior fossa tumors. Therefore, a subtle preoperative radiological diagnosis is warranted and surgery should be performed by experienced hands to avoid neurological deterioration.

Treatment of posterior fossa tumors in children

The most common posterior fossa tumors in children are medulloblastoma, astrocytoma and ependymoma. Atypical rhabdoid teratoid tumors and brain stem gliomas are relatively rare. As the posterior fossa is a limited space, the tumors presenting in this region cause symptoms early on and require prompt treatment to avoid potential morbidity and mortality. Early detection and diagnosis of these tumors and prompt neurosurgical consultation is crucial in the optimum management of pediatric infratentorial brain tumors. Surgery is the mainstay of treatment, as it provides biopsy and decompression of the tumor. Adjuvant therapy is required in the majority of cases. Recent advances in the field of radiation biology and pharmacology have improved dose and delivery techniques of chemoradiation therapy. In the current era, advances in translational research and molecular genetics have assumed a major role in the pursuit of achieving a ‘cure’ for these potentially malignant tumors.

Magnetic resonance imaging of pediatric posterior fossa tumors.

MR detected abnormality in all 115 pediatric patients who subsequently had pathologically proven posterior fossa tumors. In 114, the initial magnetic resonance (MR) diagnosis was that of brain tumor. In 1, with less than 1-cm2 area of gadolinium enhancement, the significance of the initial finding was uncertain. Common posterior fossa tumor subgroups (brainstem gliomas, cerebellar astrocytomas, primitive neuroectodermal tumors, and ependymomas) have relatively consistent presentations on imaging studies. However, less common tumors mimic the MR appearance of more common ones, while common tumors may also have atypical appearances.