Chondro-Osseous Metaplasia in an Anaplastic Ependymoma: Diagnostic Challenges in an Uncommon Tumor Phenotype

There are a few studies regarding intracranial findings in neonates with Noonan syndrome (NS); however, there are no quantitative analyses in a pediatric population. The aim of this study was to find characteristic intracranial abnormalities and to quantitatively analyze the posterior fossa and cranium base in children with NS. A total of 30 patients (11 females and 19 males, mean age 13.1±4.3years) were retrospectively identified between July 2017 and June 2022. Twenty-one patients had MRI. Age at MRI examination, sex, genetic mutations, and clinical findings were noted. In patients with MRI, the presence of white matter lesions, basal ganglia lesions, corpus callosum abnormalities, sellar/parasellar lesions, and tonsillar ectopia was noted. For morphometric analysis, cerebellar diameter, vermis and clivus heights, cranial base, tentorial and infratentorial angles, and McRae's and Twining's lines were each measured twice by two radiologists individually. The most common lesions were focal white matter lesions, followed by abnormalities of the splenium of the corpus callosum. The cerebellar diameter, vermis and clivus heights, Twining's line, and infratentorial angle were significantly smaller; cranial base angle and tentorial angle were significantly larger in NS (p<.05). Interrater and intrarater agreements were the highest for cerebellar diameter and the lowest for tentorial angle measurements. Children with NS had characteristic callosal and tentorial findings and neuroimaging findings similar to other RASopathies. This study also shows that a small posterior fossa and flattening of the cranial base are present in children with NS, which may aid in diagnosis.

Demonstration of brain parenchyma at the base of the skull and in the cerebellum in CT studies is usually rendered difficult by the partial volume effect of adjacent bone structures. As a result, studies by a number of authors have shown the superiority of MRI over CT in demonstrating brain tumors at these locations in adults (8, 9, 10, 15, 16, 22, 23). Signal enhancement with paramagnetic contrast media has played an important role in this respect (6, 7, 17). The fact that there is no exposure to X-ray is an additional advantage of MRI in studies of children and adolescents. This important advantage has to be weighed against the long duration of the examination and necessity of sedation or general anesthesia in infants and young children. Since gadolinium cannot be administered to young children, we undertook to compare CT and MRI in children with tumors at the base of the skull and in the posterior fossa.

Background: The commonest malignancy in the pediatric age group is leukemia, followed by brain tumors. Pediatric brain tumors are usually seen in children below 10 years. The incidence ranges from 1 to 3 per 100,000 cases. Primary intracranial tumors most commonly occur in the posterior fossa in children while infratentorial tumors are predominant in children over 4 years. Infratentorial tumors are more common overall, accounting for 45-60% of all cases. Physiologic characteristics of the pediatric posterior fossa tumors are well represented in advanced MRI techniques, which results in better pre-operative tumor evaluation, and often better results. Objectives: Primary intracranial tumors most commonly occur in the posterior fossa in children. Treatment and prognosis rely heavily on correct diagnosis. The most important modality for early diagnosis is MRI of the brain. This study aims to evaluate the role of MRI in pediatric posterior fossa tumors. Materials and methods: Thirty-three patients in the pediatric age group (&lt;18 years) with a clinical suspicion of posterior fossa tumors, referred to the department of Radiology for undergoing MRI of the brain with contrast were included in the study. These patients underwent surgery followed by histopathological examination (HPE). Five parameters from conventional MRI were chosen and correlated with histopathology (gold standard). Statistical analysis was done subsequently. Results: Diffusion-weighted imaging (DWI) is the most accurate parameter (94%), followed by T2 weighted imaging (T2WI), gradient, and post-contrast sequence (91% each). Diffusion-weighted imaging and post-contrast sequence had the highest specificity (almost 96%) while DWI and T2WI had the highest sensitivity (90% each). All 5 parameters are useful in 85% of cases. Overall diagnostic accuracy of MRI was almost 94% compared to histopathology. Conclusion: DWI is the best parameter, followed by T2WI, gradient imaging, and post-contrast sequence. MRI is highly accurate in the evaluation of pediatric posterior fossa tumors. In centers where advanced MRI techniques cannot be performed, some parameters from conventional MRI can be selected that aid in diagnosis. Our study shows that judicious use of 5 parameters can increase sensitivity, specificity, and diagnostic accuracy of MRI for pediatric posterior fossa tumors.

Background: Various neoplastic and nonneoplastic lesions can involve posterior cranial fossa. Posterior fossa lesions are potentially fatal since they may result in compression of the brainstem. The objective of this study was to analyze the spectrum of posterior fossa lesions and their clinical presentations. Methods: A prospective cross sectional study was conducted over a period of one year. Thirty patients with clinical features of posterior fossa pathology, referred for cranial computed tomography, were evaluated in the study. Results: Posterior fossa lesions found in this study were cerebellar abscess- 4(13.3%), arachnoid cyst- 4(13.3%), brainstem glioma- 3(10%), cerebellar astrocytoma- 3(10%), acute cerebellar infarct- 2(6.7%), cerebellar metastasis- 2(6.7%), acoustic neuroma- 2(6.7%), meningioma- 2(6.7%), medulloblastoma- 2(6.7%), ependymoma- 1(3.3%), Dandy-Walker malformation- 1(3.3%), 4th ventricular bleed- 1(3.3%), brainstem haemorrhage- 1(3.3%), cerebellar haemorrhage- 1(3.3%), and neurocysticercosis- 1(3.3%). The maximum numbers of cases (23.3%) with posterior fossa lesions were in their first decade of life. Features of raised intracranial pressure (i.e. headache, nausea &amp; vomiting) were the commonest presenting symptoms. Other symptoms included altered sensorium, ataxia, fever, limb weakness, vertigo, seizure, hearing loss, neck stiffness, slurring of voice, ear discharge, tinnitus, loss of consciousness and macrocrania in decreasing order of frequency. Conclusion: There is wide spectrum of the lesions in posterior fossa in children and adults in this part of Nepal, requiring prompt diagnosis and intervention, and CT has a pivotal role in the management. Nepalese Journal of Radiology / Vol.3 / No.1 / Issue 4 / Jan-June, 2013 / 53.58 DOI: http://dx.doi.org/10.3126/njr.v3i1.8796

Choroid plexus papillomas (CPPs) are rare benign neoplasms which are particularly uncommon in the posterior fossa in children. We herein present a case series of five patients treated at a tertiary care hospital. A comprehensive literature review was also carried out. The patients treated at the tertiary care hospital were aged between 4 and 16 years. Gross total resection (GTR) was initially achieved in two patients. All patients showed clinical improvement. Moreover, 27 articles published between 1975 and 2021 were selected for the literature review, totaling 46 patients; with the 5 patients previously described, the total sample was composed of 51 cases, With a mean age was 8.2 years. The lesions were located either in the fourth ventricle (65.3%) or the cerebellopontine angle (34.7%). Hydrocephalus was present preoperatively in 66.7% of the patients, and a permanent shunt was required in 31.6% of the cases. The GTR procedure was feasible in 64.5%, and 93.8% showed clinical improvement. For CPPs, GTR is the gold standard treatment and should be attempted whenever feasible, especially because the role of the adjuvant treatment remains controversial. Neuromonitoring is a valuable tool to achieve maximal safe resection. Hydrocephalus is common and must be recognized and promptly treated. Most patients will need a permanent shunt. Though there is still controversy on its efficacy, endoscopic third ventriculostomy is a safe procedure, and was the authors' first choice to treat hydrocephalus.

Tumours in the posterior fossa in children only present minor problems in diagnosis since the introduction of the computerized tomogram, but in postoperative follow-up studies it is rather difficult to distinguish between the various findings in the posterior fossa. This holds true especially for medulloblastomas and ependymomas. Operative changes in the anatomical structures, metal-clips, scar-like changes, post-radiation sclerosis and other findings are reasons why it is almost impossible to diagnose early recurrence of these tumours. In order to obtain more information after operation, CT findings were studied in 36 children with tumours in the posterior fossa. The findings are summarized and discussed.

Surgical approach to the posterior fossa in children, including anesthetic considerations and complications: The prone and the sitting position. Technical note

The WHO Classification of Tumours of the Central Nervous System (2016) classifies nonmeningothelial malignant spindle cell tumors involving the extraaxial tissues of the posterior fossa as melanocytic tumors and malignant mesenchymal tumors (sarcomas). The objective of this study was to conduct a review of the literature pertaining to the management strategies of posterior fossa malignant spindle cell tumors in the pediatric population. The authors performed an institutional search of their pathology database for patients younger than 18 years of age who presented with posterior fossa malignant spindle cell tumors. A literature review was also performed using the PubMed database, with "posterior fossa" or "spindle cell tumors" or "Ewing sarcoma" or "high-grade" or "spindle cell sarcoma" or "leptomeningeal melanocytoma" as keywords. The database search was restricted to pediatric patients (age ≤ 18 years). Parameters reported from the literature review included patient age, tumor location, presenting symptoms, treatment modalities (resection, chemotherapy, and/or radiotherapy), leptomeningeal spread at or after the time of treatment, and follow-up length and resulting outcome. The authors report 3 rare cases of posterior fossa malignant spindle cell tumors, including Ewing sarcoma in a 13-year-old male; high-grade spindle cell sarcoma, not otherwise specified in a 10-year-old male; and primary leptomeningeal melanocytoma in a 16-year-old female. All 3 patients underwent resection and radiotherapy and either chemotherapy or targeted immunotherapy. At the last follow-up, all patients were alive with either resolution or stable disease. A review of these 3 cases and the existing literature support managing patients with intracranial malignant spindle cell tumors with multimodal therapy that can include a combination of resection, radiotherapy, and chemotherapy or immunotherapy to prolong progression-free and overall survival.

Cystic lesions of the posterior fossa cannot easily be classified according to etiology, location, symptoms and treatment. We are proposing a better classification mainly of the benign infratentorial lesions.

The authors sought to establish whether the volume of the posterior fossa in children suffering from Chiari malformation Type I (CM-I) is smaller than normal, as has been suggested previously. They also investigated the role of syringomyelia in posterior fossa development. Both posterior fossa volume (PFV) and intracranial volume (ICV) were measured using segmentation techniques on preoperative magnetic resonance images obtained in 42 children who underwent surgery for CM-I (mean age 127 months, range 36-204 months); 25 (59%) of the patients had syringomyelia. The PFV/ICV ratio was calculated to eliminate differential supratentorial growth. Patients who had deformities potentially interfering with skull growth or who had undergone a shunt insertion procedure prior to craniovertebral decompression were excluded. The results were compared with measurements of 51 healthy children using one-way analysis of variance. In patients with CM-I only, the mean PFV and PFV/ICV ratios were not statistically different than those for healthy children. In patients with both CM-I and syringomyelia (CM-S), the mean PFV and PFV/ICV ratios were statistically smaller than those for healthy children. The ICV was 1383 cm3 in the healthy group, 1459 cm3 in the CM-I only group, and 1400 cm3 in the CM-S group (p = 0.363); the PFV was 186 cm3 in the healthy group, 196 cm3 in the CM-I only group, and 171 cm3 in the CM-S group (p = 0.036); the PFV/ICV ratio was 0.135 in the healthy group, 0.134 in the CM-I only group, and 0.122 in the CM-S group (p = 0.004). These differences were more prominent in the first 10 years of life. Children with isolated CM-I do not have a PFV smaller than normal, whereas children with both CM-I and syringomyelia have a PFV significantly smaller than normal. This result indicates that the two subgroups may represent different phenotypic expression or even a different pathogenesis.

Aim: To determine the prevalence of posterior fossa tumors in children and adults, as well as their histological kinds. Study design: A cross-sectional study Place and duration: From February 2012 to January 2019, the Department of Neurosurgery at Riyadh Care Hospital Methodology: We undertook a descriptive analysis of patients with posterior fossa space-occupying lesions. The neurosurgical intervention was done in all of the instances due to the critical location. Specimens were sent for histological evaluation after surgery. The data from these patients, as well as histology reports, were examined. The data was analyzed using SPSS version 21. Results: Males made up 57.14 percent (n=48) of the 84 patients, while children made up 41.66 percent (n=35). The most common tumor was schwannoma, seen in 34.52 percent (n=29) of cases, 72.41 percent of adults, and 27.58 % of children. In 22.61 %, 15.47 %, and 14.28 % of cases, meningioma, pilocytic astrocytoma (PCA), and Meduloblastoma were found, respectively. Metastasis was only seen in adults, and malignant round blue cell tumors were only found in children. Astrocytoma and schwannoma were prevalent in adults. Children were more likely to develop Meduloblastoma, Pilocytic astrocytoma, and malignant round blue cell tumors. Conclusion: High-grade Astrocytoma and Schwannoma are dominantly present in adults. Malignant round blue cell tumor, Pilocytic astrocytoma Medulloblastoma is more prevalent in children. Metastasis was only observed in adults. Because of their location, risk of excision, and involvement of the brain stem structures and fourth ventricle, posterior fossa tumors are widely known for their significant morbidity and mortality. Early diagnosis is now possible due to modern diagnostic and therapy technologies, which help to lower mortality rates and improve postoperative prognosis. Keywords: posterior cerebral fossa tumors, children, adults

Medulloblastoma (MB) is the most common malignant brain tumor of the posterior fossa in children. Surgical excision followed by neuraxis radiation has been the mainstay of therapy for children with localized posterior fossa(PF) MB. This treatment has resulted in a 60-65% long term disease free survival. In an effort to improve the outcome of children with this chemosensitive tumor, some institutions have incorporated adjuvant chemotherapy into the initial therapeutic regimen. Between 5/92 and 1/97, 12 children (mean age 10 years 3 months) presented consecutively with localized PF MB. Magnetic resonance imaging of the spine showed no evidence of metastatic disease. All patients underwent gross total surgical excision of the primary tumor followed by total neuraxis irradiation, and then treatment with 6 cycles of multiagent chemotherapy. The median radiation doses to the spinal axis, brain, and tumor were 3600 cGy, 4000 cGy and 5450 cGy, respectively. Following radiation therapy, all patients were treated with cycles of vincristine 2 mg/m2 IV, methylprednisolone 300 mg/m2 IV every six hours for three doses, cisplatin 90 mg/m2 IV, and cyclophosphamide 1200 mg/m2 IV. G-CSF was subsequently administered until neutrophil recovery. Chemotherapy cycles were administered every 3-4 weeks. Nine of twelve (75%) patients received 6 of 6 scheduled cycles of chemotherapy with 68 of 72 planned cycles administered overall. At a mean duration from diagnosis of 3 years, all patients remain disease-free. Hematopoietic toxicity predominated with grade III/IV neutropenia and thrombocytopenia following 66% and 32% respectively, of administered cycles of chemotherapy. Infectious complications included 13 episodes of fever and neutropenia (4 with positive blood cultures), 2 episodes of cellulitis and 2 episodes of herpes zoster. GI and renal toxicities were minimal with one episode each of pancreatitis, ileus and hepatic enzyme elevation; 2 episodes of transient reduction in creatinine clearance (25-49%); and 6 episodes of electrolyte imbalance. One patient developed severe unilateral hearing loss. Transfusion support with packed red blood cells and platelets was required following 40% and 10%, of administered cycles of chemotherapy respectively. Dose modification due to toxicity occurred following 42% of cycles of therapy, and 50% of patients required nutritional support. This regimen was well tolerated with the major toxicity being hematopoietic. While longer follow up is necessary, this regimen shows promise for improved clinical outcome in children with PF MB.

OBJECTIVE We previously reported the resolution of syringohydromyelia without cerebellar tonsillar ectopia in five patients after posterior fossa decompression of the so-called Chiari 0 malformation. A sixth patient is described. In this study, the anatomy of the posterior fossa is analyzed using radiological imaging, enabling features of the posterior fossa in this uncommon subgroup of children to be characterized. METHODS Multiple measurements were made on magnetic resonance imaging studies in six children with Chiari 0 malformation to determine the position of the brainstem relative to the foramen magnum. Fifty children with normal magnetic resonance imaging studies of the brain were used as controls. RESULTS All children with a Chiari 0 malformation were found to have the following positive results: obices that were located more than 2 standard deviations below normal, an increase in the anteroposterior midsagittal distance of the spinomedullary junction at the level of the foramen magnum, an increase in the angle between the floor of the fourth ventricle and clivus, and an increase in the anteroposterior midsagittal distance of the foramen magnum. CONCLUSION The findings of this study suggest that the contents of the posterior fossa are indeed compromised and/or distorted in patients with syringohydromyelia but no tonsillar ectopia. In this group, the brainstem was caudally displaced more than 3 standard deviations below normal.

We previously reported the resolution of syringohydromyelia without cerebellar tonsillar ectopia in five patients after posterior fossa decompression of the so-called Chiari 0 malformation. A sixth patient is described. In this study, the anatomy of the posterior fossa is analyzed using radiological imaging, enabling features of the posterior fossa in this uncommon subgroup of children to be characterized. Multiple measurements were made on magnetic resonance imaging studies in six children with Chiari 0 malformation to determine the position of the brainstem relative to the foramen magnum. Fifty children with normal magnetic resonance imaging studies of the brain were used as controls. All children with a Chiari 0 malformation were found to have the following positive results: obices that were located more than 2 standard deviations below normal, an increase in the anteroposterior midsagittal distance of the spinomedullary junction at the level of the foramen magnum, an increase in the angle between the floor of the fourth ventricle and clivus, and an increase in the anteroposterior midsagittal distance of the foramen magnum. The findings of this study suggest that the contents of the posterior fossa are indeed compromised and/or distorted in patients with syringohydromyelia but no tonsillar ectopia. In this group, the brainstem was caudally displaced more than 3 standard deviations below normal.

Objective: The posterior fossa (PF) has been found to be small in various forms of Chiari malformation. Explanations involving a connection between growth hormone deficiency (GHD) and Chiari I malformation (CIM) have been proposed. However, to date, no quantitative analysis of the PF of patients with CIM and GHD has been performed. Our study was performed to determine the geometry of the PF in children with GHD and CIM. Methods: Morphometric analysis of the PF was performed in 10 children with GHD and CIM (group 1), 20 children with GHD and no CIM (group 2) and 50 controls. Results: PF volumes for group 1 ranged from 128 to 259 ± 33 ml, and for group 2, they ranged from 115 to 186.2 ± 25.4 ml. Lengths of the foramen magnum for groups 1 and 2 had means of 36 and 38 mm, respectively. The mean basiocciput length and tentorial angle for groups 1 and 2 were 20 and 19 mm and 89 and 87.5°, respectively. Conclusions: We have determined that children with GHD with or without CIM have no significant difference in their PF volume compared to controls. However, our data demonstrate significant underdevelopment of portions of the bony PF in both patients with GHD alone and in patients with GHD and CIM. Tentorial angles were elevated in noncontrol groups. We propose that this association is not due to an increased rate of ‘midline’ defects seen in GHD but rather a structurally distorted PF that is not capacious enough to house the entire developing rhombencephalon. These data will hopefully aid in the further understanding of the pathophysiology of CIM.