Anatomy of the posterior Fossa: a comprehensive description for pediatric brain tumors.

Posterior fossa tumors are the most common pediatric brain tumors, and present unique challenges in terms of their location and surgical management. The posterior fossa comprehends complex anatomy and represents the smallest and deepest of the three cranial base fossae. An in-depth understanding of posterior fossa anatomy is crucial when it comes to the surgical resection of pediatric brain tumors. Mastering the knowledge of posterior fossa anatomy helps the neurosurgeon in achieving a maximal and safe volumetric resection, that impacts in both overall and progression free survival. With the advancements in microsurgery, the telovelar approach has emerged as the workhorse technique for the resection of posterior fossa tumors in pediatric patients. This approach involves meticulously dissecting of the natural clefts present in the cerebellomedullary fissure, making a comprehensive understanding of the underlying anatomy key for its success.

Presurgical MRI-Based Radiomics Models for Predicting Cerebellar Mutism Syndrome in Children With Posterior Fossa Tumors.

BACKGROUND: Current studies have indicated that tumoral morphologic features are associated with cerebellar mutism syndrome (CMS), but the radiomics application in CMS is scarce. PURPOSE: To develop a model for CMS discrimination based on multiparametric MRI radiomics in patients with posterior fossa tumors. STUDY TYPE: Retrospective. POPULATION: A total of 218 patients (males 132, females 86) with posterior fossa tumors, 169 of which were included in the MRI radiomics analysis. The MRI radiomics study cohort (169) was split into training (119) and testing (50) sets with a ratio of 7:3. FIELD/SEQUENCE: All the MRI were acquired under 1.5/3.0 T scanners. T2-weighted image (T2W), T1-weighted (T1W), fluid attenuated inversion recovery (FLAIR), diffusion-weighted imaging (DWI). ASSESSMENT: Apparent diffusion coefficient (ADC) maps were generated from DWI. Each MRI dataset generated 1561 radiomics characteristics. Feature selection was performed with univariable logistic analysis, correlation analysis, and least absolute shrinkage and selection operator (LASSO) penalized logistic regression. Significant clinical features were selected with multivariable logistic analysis and used to constructed the clinical model. Radiomics models (based on T1W, T2W, FLAIR, DWI, ADC) were constructed with selected radiomics features. The mix model was based on the multiparametric MRI radiomics features. STATISTICAL TEST: Multivariable logistic analysis was utilized during clinical features selection. Models' performance was evaluated using the area under the receiver operating characteristic (AUC) curve. Interobserver variability was assessed using Cohen's kappa. Significant threshold was set as P < 0.05. RESULTS: Sex (aOR = 3.72), tumor location (aOR = 2.81), hydrocephalus (aOR = 2.14), and tumor texture (aOR = 5.08) were significant features in the multivariable analysis and were used to construct the clinical model (AUC = 0.79); totally, 33 radiomics features were selected to construct radiomics models (AUC = 0.63-0.93). Seven of the 33 radiomics features were selected for the mix model (AUC = 0.93). DATA CONCLUSION: Multiparametric MRI radiomics may be better at predicting CMS than single-parameter MRI models and clinical model. EVIDENCE LEVEL: 4. TECHNICAL EFFICACY: 2.

The use of the sodium fluorescein and YELLOW 560 nm filter for the resection of pediatric posterior fossa lesions.

PURPOSE: This study aimed to verify the feasibility, safety, and benefit of using fluorescein sodium (FL) and a YELLOW 560 nm filter in posterior fossa tumors in children. METHODS: All cases of pediatric posterior fossa tumors that have undergone surgery using fluorescein (2018-2022) have been included and were examined retrospectively. In those cases where resection of the tumor was planned, a blinded neuroradiologist distinguished gross total resection and subtotal resection according to the postoperative MRI findings. The surgical report and medical files were reviewed regarding the intraoperative staining grade and adverse events. The grade of fluorescent staining of the targeted lesion was assessed as described in the surgical reports. The screening was conducted for any reference to the degree of fluorescent staining: "intense," "medium," "slight," and "no staining." RESULTS: 19 cases have been included. In 14 cases, a complete resection was initially intended. In 11 of these cases, a gross total resection could be achieved (78.6%). Staining was described as intense in most cases (58.8%). Except for yellow-colored urine, no side effects obviously related to FL were found throughout the observation period. CONCLUSION: In combination with a specific filter, FL is a reliable, safe, and feasible tool in posterior fossa surgery in children.

Perioperative external ventricular drainage vs. no-EVD strategy in pediatric posterior fossa tumors-pilot study results.

INTRODUCTION: Pediatric brain tumors of the posterior fossa often present with occlusive hydrocephalus. Endoscopic third ventriculostomy (ETV) or ventriculoperitoneal shunting (VPS) has been established for definite hydrocephalus treatment. The aim of the study was to analyze the impact and safety of perioperative temporary external ventricular CSF drainage (EVD) placement on postoperative hydrocephalus outcome compared to a no-EVD strategy. PATIENTS AND METHODS: In a prospective database, 36 posterior fossa tumor patients of 2-18 years were included with a follow-up of 1 year. Fifty-eight percent presented with preoperative hydrocephalus. Patients were assigned to non-hydrocephalus group: group I (n = 15) and to preoperative hydrocephalus, group IIa with EVD placement (n = 9), and group IIb without EVD (n = 12). RESULTS: Median age of patients was 8.1 years (range 3.17 to 16.58 years). One-third of 21 hydrocephalus patients required ETV or VPS (n = 7). Occurrence of de novo hydrocephalus in group I after surgery was not observed in our cohort. Age and histology were no confounding factor for EVD placement between group IIa and IIb (p = 0.34). The use of EVD did not result in better control of hydrocephalus compared to no-EVD patients considering pre- and postoperative MRI ventricular indices (p = 0.4). Perioperative placement of an EVD resulted in a threefold risk for subsequent VPS or ETV (group IIa 55.5% vs group IIb 16.6%): relative risk for EVD patients compared to no-EVD patients with hydrocephalus was 3.3 (CI = 1.06-13.43, p = 0.09). CONCLUSION: Perioperative EVD placement appears to harbor a threefold relative risk of requiring subsequent permanent CSF diversion in children above 2 years. EVD was not more effective to control ventricular enlargement compared to tumor removal alone. The no-EVD strategy was safe and did not result in postoperative complications. Thus, to evaluate potential adverse effects on hydrocephalus outcome by EVD placement, a prospective study is warranted to falsify the results.

External ventricular drainage in the management of pediatric patients with posterior fossa tumors and hydrocephalus: a retrospective cohort study.

PURPOSE: To determine whether intraoperative adjunctive EVD placement in patients with a posterior fossa tumor (PFT) led to improved surgical, radiographic, and clinical outcomes compared to those who did not receive an EVD. METHODS: Patients were grouped as those who underwent routine intraoperative adjunctive EVD insertion and those who did not at time of PFT resection. Patients who pre-operatively required a clinically indicated EVD insertion were excluded. Comparative analyses between both groups were conducted to evaluate clinical, radiological, and pathological outcomes. Odds ratios (ORs) with corresponding 95% confidence intervals (CIs) were computed for post-operative outcomes. RESULTS: Fifty-five selected patients were included, 15 who had an EVD placed at the time of PFT resection surgery, and 40 who did not. Children without an EVD did not experience a higher rate of complications or poorer post-operative outcomes compared to those with an EVD placed during resection surgery. There was no significant difference in the degree of gross total resection (p = 0.129), post-operative CSF leak (p = 1.000), and post-operative hemorrhage (p = 0.554) between those with an EVD and those without. The frequency of new cranial nerve deficits post-operatively was higher in those with an EVD (40%) compared to those without (3%, p = 0.001). There was a trend towards more frequently observed post-operative hydrocephalus in the EVD group (p = 0.057). CONCLUSION: The routine use of EVD as an intraoperative adjunct in clinically stable pediatric patients with posterior fossa tumors and hydrocephalus may not be associated with improved radiological or clinical outcomes.

Placement of EVD in pediatric posterior fossa tumors: safe and efficient or old-fashioned? The Vienna experience.

PURPOSE: The perioperative treatment of hydrocephalus in pediatric posterior fossa tumors with an external ventricular drain (EVD) is the treatment of choice in our center. We analyzed our experience in using EVD concerning safety and effectivity. METHODS: This is a single-center retrospective cohort study of 100 consecutive pediatric patients who underwent resection for a newly diagnosed tumor in the posterior fossa between 2011 and 2022. RESULTS: Of the 100 patients with posterior fossa tumors, 80 patients (80%) had radiological signs of hydrocephalus at presentation, 49 patients (49%) of whom underwent placement of an EVD. In 40 patients, the EVD was inserted at a mean of 2.25 days prior to the tumor resection; 9 had the EVD inserted during tumor resection (frontal trajectory in 7 patients, occipital trajectory in 2 patients). Histology revealed pilocytic astrocytoma in 48 patients, medulloblastoma in 32, ependymoma in 11, and other histologic entities in 9 patients. Gross total/near-total resection was achieved in 46 (95.83%) of the 48 pilocytic astrocytomas, 30 (93.75%) of the 32 medulloblastomas, and 11 (100%) of the 11 ependymomas. The mean number of total days with the EVD in place was 8.61 ± 3.82 (range 2-16 days). The mean number of days with an EVD after tumor resection was 6.35 ± 3.8 (range 0-16 days). EVD-associated complications were seen in 6 patients (12.24%) including one infection. None of these resulted in a worse clinical course or any long-term sequelae. Permanent CSF diversion at 6 months after surgery was necessary in 13 patients (13%), including two VP shunt, two SD-shunt, six endoscopic third ventriculostomy (ETV), and three combined VP shunt and ETV procedures. Patients with a medulloblastoma or ependymoma had a higher rate of permanent CSF diversion needed than the group of pilocytic astrocytoma patients (27.9% versus 2.13%, p < 0.001). In patients with metastatic disease, 7 of 17 patients (41.18%) needed a permanent CSF diversion, compared to 6 of 83 patients (7.23%) in the group without metastasis (p = 0.001). CONCLUSION: The treatment of hydrocephalus in pediatric posterior fossa tumors with an EVD as a temporary measure is safe and effective, provided that a multi-professional understanding for its handling is given and there is no need for a long transport of the children.

Diffusion Tensor Imaging Technique Delineating the Prognosis for Cerebellar Mutism in Posterior Fossa Tumors: A New Tool.

AIM: Cerebellar mutism syndrome (CMS) is a morbid complication of posterior fossa surgery in children. This review focuses on the current understanding of pathophysiology in the white matter tracts (WMT) using diffusion tensor imaging (DTI). MATERIAL AND METHODS: A series of 38 patients operated on for posterior fossa tumors in our institute between December 2019 till May 2021 were evaluated neurologically along with characteristics of mutism and DTI imaging (fractional anisotropy) in preoperative and postoperative periods. We also noted tumor size, location, volume, brainstem compression, cerebellar peduncle involvement, extent of resection, surgical approach, and histopathology. RESULT: Cerebellar mutism developed in five patients. The mean age, male sex, tumor size >5 cm, superior cerebellar peduncle involvement, and vermian incision were found to have positive correlation with the development of CMS. They showed reduction in fractional anisotropy in superior cerebellar peduncle (SCP) following resection; however, others' WMT did not show any significant change in fractional anisotropy values pre- or post-surgery. CONCLUSION: Our study suggests that functional disruption of WMT, i.e., superior cerebellar peduncle and dentato-thalamo-cortical tract (DTC) is the underlying pathophysiological component of CMS. Taking this into consideration, we need to deploy techniques to limit the damage to the superior cerebellar peduncle and DTC using neurophysiological monitoring.

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.

Preoperative and postoperative high angular resolution diffusion imaging tractography of cerebellar pathways in posterior fossa tumors.

This study aimed to utilize high angular resolution diffusion magnetic resonance imaging (HARDI) tractography in the mapping of the pathways of the cerebellum associated with posterior fossa tumors (infratentorial neoplasms) and to determine whether it is useful for preoperative and postoperative evaluation. Retrospective data from 30 patients (age 2-16 yr) with posterior fossa tumor (17 low grade, 13 high grade) and 30 age-sex-matched healthy controls were used. Structural and diffusion-weighted images were collected at a 3-tesla scanner. Tractography was performed using Diffusion Toolkit software, Q-ball model, FACT algorithm, and angle threshold of 45 degrees. Manually assessed regions of interest were placed to identify reconstructed fiber pathways passing through the superior, medial, and inferior cerebellar peduncles for the preoperative, postoperative, and healthy control groups. Fractional anisotropy (FA), apparent diffusion coefficient (ADC), and track volume measures were obtained and analyzed. Statistically significant differences were found between the preop/postop, preop/control, and postop/control comparisons for the volume of the tracts in both groups. Displacement and disruption of the pathways seemed to differ in relation to the severity of the tumor. The loss of pathways after the operation was associated with selective resection during surgery due to tumor infiltration. There were no FA differences but significantly higher ADC in low-grade tumors, and no difference in both FA and ADC in high-grade tumors. The effects of posterior fossa tumors on cerebellar peduncles and reconstructed pathways were successfully evaluated by HARDI tractography. The technique appears to be useful not only for preoperative but also for postoperative evaluation.

Postsurgical geometrical variations of tumor bed and brainstem during photon and proton therapy for pediatric tumors of the posterior fossa: dosimetric impact and predictive factors.

PURPOSE: Brainstem radionecrosis is an important issue during the irradiation of tumors of the posterior fossa. The aim of the present study is to analyze postsurgical geometrical variations of tumor bed (TB) and brainstem (BS) and their impact on dosimetry. METHODS: Retrospective collection of data from pediatric patients treated at a single institution. Availability of presurgical magnetic resonance imaging (MRI) was verified; availability of at least two postsurgical MRIs was considered a further inclusion criterion. The following metrics were analyzed: total volume, Dice similarity coefficient (DSC), and Haudsdorff distances (HD). RESULTS: Fourteen patients were available for the quantification of major postsurgical geometrical variations of TB. DSC, HD max, and HD average values were 0.47 (range: 0.08;0.76), 11.3 mm (7.7;24.5), and 2.6 mm (0.7;6.7) between the first and the second postoperative MRI, respectively. Postsurgical geometrical variations of the BS were also observed. Coverage to the TB was reduced in one patient (D95: -2.9 Gy), while D2 to the BS was increased for the majority of patients. Overall, predictive factors for significant geometrical changes were presurgical gross tumor volume (GTV) > 33 mL, hydrocephaly at diagnosis, Luschka foramen involvement, and younger age (≤ 8 years). CONCLUSION: Major volume changes were observed in this cohort, with some dosimetric impact. The use of a recent co-registration MRI is advised. The 2-3 mm HD average observed should be considered in the planning target volume/planning organ at risk volume (PTV/PRV) margin and/or robust optimization planning. Results from wider efforts are needed to verify our findings.

Imaging pitfalls in paediatric posterior fossa neoplastic and non-neoplastic lesions.

Paediatric posterior fossa lesions can have much overlap in their clinical and radiological presentation. There are, however, a number of key imaging features that can help the reading radiologist to distinguish tumours from important tumour mimics which are often inflammatory or metabolic entities. This pictorial review provides a number of important cases that proved challenging on imaging and illustrates some common pitfalls when interpreting lesions in the posterior fossa in children. Not everything that is abnormal will be a tumour, but often other causes are overlooked and misinterpreted as tumours, leading to great morbidity for that child. This article highlights some lesions that were mistaken as tumours and will introduce the reader to less commonly seen pathologies which are important to consider on a differential list for this location.

Abnormal spindle-like microcephaly-associated (ASPM) gene expression in posterior fossa brain tumors of childhood and adolescence.

PURPOSE: In neurogenesis, ASPM (abnormal spindle-like microcephaly-associated) gene is expressed mainly in the ventricular zone of posterior fossa and is the major determinant in the cerebral cortex. Besides its role in embryonic development, ASPM overexpression promotes tumor growth, including central nervous system (CNS) tumors. This study aims to investigate ASPM expression levels in most frequent posterior fossa brain tumors of childhood and adolescence: medulloblastoma (MB), ependymoma (EPN), and astrocytoma (AS), correlating them with clinicopathological characteristics and tumor solid portion size. METHODS: Quantitative reverse transcription (qRT-PCR) is used to quantify ASPM mRNA levels in 80 pre-treatment tumor samples: 28 MB, 22 EPN, and 30 AS. The tumor solid portion size was determined by IOP-GRAACC Diagnostic Imaging Center. We correlated these findings with clinicopathological characteristics and tumor solid portion size. RESULTS: Our results demonstrated that ASPM gene was overexpressed in MB (p = 0.007) and EPN (p = 0.0260) samples. ASPM high expression was significantly associated to MB samples from patients with worse overall survival (p = 0.0123) and death due to disease progression (p = 0.0039). Interestingly, two patients with AS progressed toward higher grade showed ASPM overexpression (p = 0.0046). No correlation was found between the tumor solid portion size and ASPM expression levels in MB (p = 0.1154 and r = - 0.4825) and EPN (p = 0.1108 and r = - 0.3495) samples. CONCLUSION: Taking in account that ASPM gene has several functions to support cell proliferation, as mitotic defects and premature differentiation, we suggest that its overexpression, presumably, plays a critical role in disease progression of posterior fossa brain tumors of childhood and adolescence.

Pediatric takotsubo syndrome caused by hydrocephalus after posterior fossa tumor surgery.

Takotsubo syndrome (TTS) can develop after intense physical or emotional stress and is uncommon in children. We report a 2-year-old girl who developed TTS caused by acute hydrocephalus after posterior fossa tumor resection and required mechanical ventilation and administration of vasopressor/inotropic agents. Her cardiac function gradually recovered over the course of 2 weeks. Hydrocephalus after posterior fossa surgery can cause compression of the medulla oblongata, resulting in solitary nucleus dysfunction and TTS, a potentially life-threatening complication.

Neuroimaging of pediatric infratentorial tumors and the value of diffusion-weighted imaging (DWI) in determining tumor grade.

BACKGROUND: Diffusion-weighted imaging (DWI) provides information about the cellular density of tumors. This feature is useful in grading and identifying different tumor types. PURPOSE: To assess the value of diffusion restriction and apparent diffusion coefficient (ADC) values in differentiating pediatric infratentorial tumors. MATERIAL AND METHODS: This was a retrospective review of the magnetic resonance imaging (MRI) of 82 children (age range 1-16 years) with infratentorial tumors. Histopathological grading after surgical excision/biopsy was categorized as low grade (WHO grades I and II) (n = 31; 29 pilocytic astrocytomas, 2 ependymomas) and high grade (WHO grade III and IV) (n = 51; 40 medulloblastomas, 8 anaplastic ependymomas, 1 anaplastic astrocytoma, 2 atypical rhabdoid teratoid tumors [ATRT]). MRI features and ADC values were compared among tumor types and grades using a two-tailed t test, Mann-Whitney U test for continuous data and Chi-square test for categorical variables. RESULTS: Diffusion restriction and low ADC value was a feature of high-grade tumors (P<0.001). The mean ADC values of the low-grade and high-grade tumors were 1.567 × 10-3mm2/s and 0.661 × 10-3mm2/s, respectively. Using 0.9 × 10-3mm2/s as the cut-off value, the sensitivity, specificity, positive and negative predictive values for differentiating the grades was 87%, 100%, 100%, and 81.8%, respectively. Significant differences were found between the mean ADC values of the individual tumor types (P<0.05), except between medulloblastoma and ATRT. CONCLUSION: ADC values and visual assessment of diffusion restriction are useful in tumor grading. The individual tumor types can be identified by an algorithmic approach, using DWI in conjunction with other described MRI features.

Evolution of cerebellomedullary fissure opening: its effects on posterior fossa surgeries from the fourth ventricle to the brainstem.

Surgical approaches to the fourth ventricle and its surrounding brainstem regions have changed significantly in the previous 30 years, after the establishment of cerebellomedullary fissure (CMF) opening. With the development of CMF opening techniques, CMF opening surgeries have become widely used for the treatment of various pathologies and have contributed to the improvement of surgical results in posterior fossa surgeries. We here review the historical progress of CMF opening surgeries to help the future progression of neurosurgical treatments. The authors studied the available literature to clarify how CMF opening surgeries have developed and progressed, and how much the idea and development of CMF opening techniques have affected the advancement of posterior fossa surgeries. With the establishment of angiography, anatomical studies on CMF in the 1960s were performed mainly to clarify vascular anatomy on radiological images. After reporting the microsurgical anatomy of CMF in a cadaveric study in 1982, one of the authors (T.M.) first proposed the clinical usefulness of CMF opening in 1992. This new method enabled wide exposure of the fourth ventricle without causing vermian splitting syndrome, and it took the place of the standard approach instead of the conventional transvermian approach. Several authors reported their experiences using this method from the end of the twentieth century to the early twenty-first century, and the naming of the approach, "telovelar approach" by Mussi and Rhoton in 2000 contributed to the global spread of CMF opening surgeries. The approach has become widely applied not only for tumors but also for vascular and brainstem lesions, and has assisted in the development of their surgical treatments, and brought up the idea of various fissure dissection in the posterior fossa. Studies of microsurgical anatomy of the fourth ventricle, including the CMF, has led to new surgical approaches represented by the transCMF/telovelar approach. The CMF opening method caused a revolution in posterior fossa surgeries. The idea was developed based on the experience gained while dissecting the CMF (the roof of the fourth ventricle) in the laboratory. Anatomical studies using cadaveric specimens, particularly their dissection by surgeons themselves, together with a deep understanding of brain anatomy are essential for further advancements in neurosurgical treatments.

The clinical and imaging features of infratentorial germinomas compared with supratentorial ectopic germinomas.

BACKGROUND: Intracranial germinoma is very sensitive to chemoradiotherapy, while the risk of infratentorial operation is high. The accurate diagnosis can provide the more reasonable treatment, avoiding the unnecessary therapeutic risks. PURPOSE: To evaluate the clinical and imaging features of infratentorial germinomas. MATERIAL AND METHODS: The clinical and imaging data of 13 infratentorial germinomas were collected and compared with 17 supratentorial germinomas in the same period. The clinical and imaging findings were retrospectively analyzed. RESULTS: Infratentorial germinomas were more common in female patients than supratentorial ones (53.85% vs. 11.76%, P = 0.020). The mean age of the infratentorial group (23.0 ± 10.2 years) was significantly older than that of supratentorial group (12.4 ± 3.3 years, P = 0.003). Most infratentorial germinomas (12/13, 92.31%) underwent surgical resection, while stereotactic biopsy was more common in the supratentorial group (11/17, 64.71%, P = 0.002). Infratentorial germinomas were significantly smaller than supratentorial ones (25.85 ± 8.13 mm vs. 37.18 ± 18.11 mm, P = 0.031). Cystic lesions were more common in supratentorial germinomas (12/17, 70.59%), while most infratentorial germinomas were solid lesions (10/13, 76.92%, P = 0.025). On post-contrast T1-weighted imaging, obvious enhancement was more common in infratentorial germinomas than in supratentorial ones (100% vs. 64.71%, P = 0.024). CONCLUSION: In addition to the common findings with supratentorial germinomas, infratentorial lesions have some specific clinical and imaging features.

Pediatric age, posterior fossa meningioma.

Meningiomas are benign, slow-growing tumors originating from arachnoid gap cells. They constitute 15%-20% of all intracranial tumors in adults and 04%-4% in the pediatric age group. Meningiomas in the posterior fossa in the pediatric period do not initially come to mind. In the case presented here, there was a cystic meningioma showing heterogenous contrast and obstructive hydrocephaly was observed associated with 4th ventricle pressure. the tumor was totally removed, then the ventriculo peritoneal shunt was applied.

Radiology of post-operative paediatric cerebellar mutism syndrome.

BACKGROUND: Post-operative paediatric cerebellar mutism syndrome is a well-recognized complication following posterior fossa tumour resection in children. Over the past few decades, imaging has played an important role in understanding this disorder. AIM: This review article aims to focus on the disorder from a radiological perspective, summarizing the salient radiological evidence related to the anatomical structures, pathophysiology, and risk factors related to this disorder. CONCLUSION: Radiological studies have been integral to the improved understanding of this condition. Future large multicentre studies and quantitative analysis techniques will be vital in further refinement of our understanding of this complex condition.

Cerebral Vasospasm after Posterior Fossa Tumor Surgery: A Case Report and Literature Review.

INTRODUCTION: This report presents an unusual case of symptomatic vasospasm following resection of posterior fossa tumor in a 9-year-old female patient. To the best of our knowledge, only 6 pediatric cases of vasospasms as a complication of brain tumor surgery have been reported in the literature previously. CASE PRESENTATION: After an uneventful 12 days postoperatively, the patient suddenly presented with acute neurological deterioration on the 13th day and MR angiography showed bilateral narrowing of the supraclinoid segments of the internal carotid artery and the proximal parts of the A1 and M1 segments. Hypervolemia and vasospasm treatments were administered, and the patient exhibited no neurological deficit at the time of discharge, confirmed via normal MRI. CONCLUSION: Early diagnosis and intervention in case of suspected symptomatic cerebral vasospasm after pediatric posterior fossa tumor surgery are essential in order to achieve favorable outcomes.

The Use of 5-Aminolevulinic Acid to Assist Gross Total Resection of Paediatric Posterior Fossa Tumours.

BACKGROUND: 5-aminolevulinic acid (5-ALA) use is well established in the resection of adult high-grade gliomas. There is growing interest in its usefulness in the paediatric population. The potential benefit of 5-ALA-guided resection motivated our unit to offer the established adult protocol as off-label use. OBJECTIVE: to determine if 5-ALA guided resection was routinely useful and offered increased gross total resection (GTR) results. METHODS: Nineteen patients harbouring a posterior fossa tumour suggestive of either an ependymoma or medulloblastoma (MB) underwent surgery between January 2018 and October 2019. The mean age was 5 years (range 2-12 years). A dose of 20 mg/kg of 5-ALA (Gliolan®) was given 4 h preoperatively. Intraoperatively, the tumours were viewed under violet-blue light and the presence of fluorescence was recorded. Fluorescence status was compared with histopathological classification and grade, Ki-67 index, GTR rate, and a subjective determination of "usefulness" was determined. RESULTS: The case series included ependymoma grade II (n = 6), ependymoma grade III (n = 4), and MB grade IV (n = 9). For the combined cohort, the strong fluorescence rate was 68% (n = 13), the heterogenous fluorescence rate was 26% (n = 5), and the completely negative fluorescence rate was 5% (n = 1). The strong fluorescence rate of 90% found in the combined ependymoma group compared to the 45% strong fluorescence rate in the MB group was statistically significant (p = 0.05). Within the MB group the Ki-67 index was found to be significantly higher in the strongly fluorescent group as opposed to the patchy or non-fluorescent group (77.5 vs. 40%, p = 0.016). Fluorescence was determined to be useful in 63% of all cases. There was no significant relationship between fluorescence and GTR. The relationship between perceived usefulness and resection was not statistically significant. No adverse drug reactions were recorded. CONCLUSION: This case series adds to the growing body of evidence demonstrating the safety of 5-ALA in the paediatric population. 5-ALA guided resection was found to be useful in the majority of cases but this did not correlate with GTR status. Ependymomas reliably fluoresce in 90% of cases, and 5-ALA-guided resection should be considered when a preoperative diagnosis of ependymoma is suspected.