Case report: Gross total resection of a primary fourth ventricular meningioma using the telovelar approach in a dog.

An 11-year-old spayed female Maltese dog presented with a 2-month history of gait alterations, wide-based stance, and chronic vomiting. Neurological examination revealed cerebellovestibular signs, including head tilt, nystagmus, strabismus, intentional tremor, and hypermetric gait. MRI showed a mass with iso- to hypointensity on T1-weighted (T1W) images and heterogeneous hyperintensity on T2-weighted (T2W) images, with marked non-uniform contrast enhancement. The tumor was removed via a telovelar approach without intraoperative complications. Postoperatively, the dog developed non-ambulatory paraparesis with the rigidity of the pelvic limbs but recovered ambulation within 6 days. Preoperative neurological signs progressively improved, and the patient was discharged without complications 10 days after surgery. Histological examination revealed dense spindle cells with an abundant collagen matrix and oval-shaped nucleated cells with small whorls, leading to a diagnosis of transitional meningioma of the fourth ventricle. MRI follow-up at 8 months postoperatively showed no definitive evidence of recurrence. At the final follow-up, 15.4 months postoperatively, mild neurological signs, including a slight head tilt and subtle strabismus, remained, but the rest of the neurological examination was normal. This is the first reported case of a meningioma in the fourth ventricle of a dog successfully removed using the telovelar approach.

Primary Central Nervous System Lymphoma Presenting as a Solitary Fourth Ventricular Mass: A Case Report.

The occurrence of primary fourth ventricular lymphoma is an exceptionally uncommon phenomenon. Here, we present a case of lymphoma in the fourth ventricle in a 30-year-old male who presented with progressive headache and vertigo over the last one month of his presentation. Preoperative MRI revealed a space-occupying lesion of the fourth ventricle. Pathological analysis following complete resection confirmed the lesion as primary central nervous system lymphoma. The patient underwent chemotherapy following the MTR (methotrexate, temozolomide, and rituximab) protocol with four months of uneventful follow-up, indicating no disease recurrence. Therefore, clinicians are advised to consider the potential presence of lymphoma as part of the differential diagnosis for space-occupying lesions, especially when there is a combination of clinical deterioration and rapid imaging progression.

The tonsillouvular fissure approach to exophytic cavernous malformation in the lateral recess of the fourth ventricle: 2-dimensional operative video.

Cavernous malformations surrounding the fourth ventricle are challenging lesions to access and treat surgically owing to the complexity and eloquence of adjacent neural tissue [1] Long-standing practice included tissue transgression through the overlying cerebellar cortical surface of the hemisphere or vermis [1-3]. Using natural corridors such as tonsillobiventral fissure, cerebellomedullary fissure, and tonsillouvular fissure (TUF) offers elegant access to the fourth ventricle, avoiding traversing of neural tissue [4-7]. A 32-year-old male presented with headache, nausea, vomiting, double vision, and vertigo. Neuroimaging demonstrated a 17-mm diameter cavernous malformation protruding into the left lateral recess of the fourth ventricle. The patient consented for the procedure and underwent a middline suboccipital craniotomy in a prone position. TUF approach was performed by dissecting the arachnoid to the depth of the fissure, and after identifying the tonsillomedullary segment of the posterior inferior cerebellar artery, minimal white matter transgression was used to reach cavernous malformation. Complete removal of the lesion was achieved and confirmed on postoperative imaging. The postoperative course was uneventful. TUF approach with manipulation by ipsilateral and contralateral retraction of tonsills allows the widening of the surgical corridor and better exposure of lesions of the lateral recess of the fourth ventricle [1]. TUF approach is a valuable alternative to transvermian and transcerebellar approaches that minimize the division of neural tissue [6]. To the best of our knowledge this is the first case describing the TUF approach to exophytic cavernoma presenting in the lateral recess of the fourth ventricle. Under our institutional ethical review board regulations, approval was not necessary.

Atypical epidermoid cyst of the fourth ventricle with minimal diffusion-restriction.

BACKGROUND: Epidermoid cysts are benign, slow growing extra-axial lesions most commonly found in the cerebellopontine angle that have a characteristic imaging pattern of restricted diffusion on diffusion-weighted imaging (DWI). METHODS: A 10-year-old male with a history of asthma and diabetes was found to have a lesion within the fourth ventricle on a magnetic resonance imaging (MRI) brain study. MRI showed a well-circumscribed vermian lesion without contrast enhancement or restricted diffusion with mild hydrocephalus. He was referred to the neurosurgical service once he acutely developed symptoms of dizziness. He underwent a gross-total resection of the lesion on which histopathology confirmed an epidermoid cyst. RESULTS: Here, we report a case of an atypical epidermoid cysts found in the midline of the fourth ventricle without restricted diffusion on MRI. CONCLUSION: Avid restricted-diffusion on DWI is usually pathognomonic for an epidermoid cyst when evaluating an extra-axial lesion, yet we report the second case in the literature of an epidermoid cyst without this classical imaging characteristic.

Anatomical considerations and surgical manipulation of the rhomboid lip in microvascular decompression for hemifacial spasm.

BACKGROUND: In microvascular decompression (MVD) procedures for hemifacial spasm (HFS), surgeons often encounter a rhomboid lip which may obscure the root exit zone (REZ) of the facial nerve. This study aims to explore the anatomical variations of rhomboid lips and their surgical implications to improve safety and effectiveness in MVD surgeries. METHODS: A retrospective analysis was conducted on 111 patients treated for HFS between April 2021 and March 2023. The presence of a rhomboid lip was assessed through operative video records, and its characteristics, dissection methods, and impact on nerve decompression outcomes were further examined. Preoperative magnetic resonance imaging (MRI) scans were reviewed for detectability of the rhomboid lip. RESULTS: Rhomboid lips were identified in 33% of the patients undergoing MVD, with a higher prevalence in females and predominantly on the left side. Two distinct types of rhomboid lips were observed: membranous and cystic variations. The membranous type was noted for its smaller size and position ventral to the choroid plexus. In contrast, the cystic variation was distinguished by its larger size and a thin membrane that envelops the choroid plexus. Preoperative MRI successfully identified rhomboid lips in only 21% of the patients who were later confirmed to have them in the surgical procedures. Surgical approaches primarily involved incisions on the dorsal wall and along the glossopharyngeal nerve root, with only limited need for extensive dissection from lower cranial nerves. Immediate spasm relief was observed in 97% of the patients. One case exhibited a lower cranial nerve deficit accompanied by brainstem infarction, which was caused by the dissection from the lower cranial nerves. CONCLUSIONS: Recognizing the two variations of the rhomboid lip and understanding their anatomical structures are essential for reducing lower cranial nerve injuries and ensuring effective nerve decompression.

Rare Complications of CSF Diversion: Paradoxical Neuroimaging Findings in a Double, Chiasmic Case Report.

Two patients with CSF shunting systems exhibited symptoms of altered intracranial pressure. Initial neuroimaging led to misinterpretation, but integrating clinical history and follow-up imaging revealed the true diagnosis. In the first case, reduced ventricular size was mistaken for CSF overdrainage, while the actual problem was increased intracranial pressure, as seen in slit ventricle syndrome. In the second case, symptoms attributed to intracranial hypertension were due to CSF overdrainage causing tonsillar displacement and hydrocephalus. Adjusting the spinoperitoneal shunt pressure resolved symptoms and imaging abnormalities. These cases highlight the necessity of correlating clinical presentation with a deep understanding of CSF dynamics in shunt assessments.

Delayed symptomatic TFV in neonatal posthemorrhagic hydrocephalus-pathophysiology and therapeutic strategy: A case report and review of the literature.

INTRODUCTION: Trapped fourth ventricle (TFV), which is a rare neurosurgical condition with multifactorial etiology, requires a prompt diagnosis and appropriate therapeutic method selection. We report a case of post-hemorrhagic hydrocephalus and TFV incited/worsened by prematurity, sepsis, acute respiratory distress syndrome (ARDS), mechanical ventilation, and concomitant fourth ventricle outlets stenosis; which displayed a delayed onset. This article addresses the proposed pathophysiology and the clinical importance of appropriate therapeutic strategies with a mini-review of the literature. CASE PRESENTATION: We encountered a case involving a premature Asian male newborn with sepsis and posthemorrhagic hydrocephalus who required ventriculoperitoneal shunt surgery. However, after three years, the baby was diagnosed with a trapped fourth ventricle and subsequently underwent retrograde endoscopic surgery with stent insertion. DISCUSSION: TFV is traditionally known as a complication of lateral ventricle shunting. However, in rare cases such as our neonate patient, it develops as a consequence of multiple pathophysiological processes including ventricular system inflammation along with associated anatomic and physiologic alterations, which necessitates prompt diagnosis and a case-specific therapeutic strategy. CONCLUSION: Understanding the multifactorial pathophysiological mechanisms leading to the development of TFV is crucial. The presence of comorbidities such as prematurity, neonatal sepsis, and ARDS increased the risk of intraventricular hemorrhage and subsequent inflammation and further exacerbated obstructions in cerebrospinal fluid pathways. When posthemorrhagic TFV is accompanied by collapsed lateral ventricles, the optimal treatment approach is retrograde endoscopic fenestration with stent insertion. This treatment option has proven effective in alleviating the condition and restoring proper cerebrospinal fluid flow.

Bilateral abducens and facial nerve palsies following fourth ventriculoperitoneal shunt with laparoscopic-assisted abdominal catheter placement.

Introduction: Hydrocephalus, altering cerebrospinal fluid (CSF) dynamics, affects 175 per 100,000 adults worldwide. Ventriculoperitoneal shunts (VPS) manage symptomatic hydrocephalus, with 125,000 cases annually. Despite efficacy, VPS face complications, necessitating interventions. Research question: "What are the mechanisms and risk factors for bilateral VIth and VIIth lower motor neuron palsies in hydrocephalus patients with a fourth ventriculoperitoneal shunt?" Material and methods: This study details a 36-year-old female with a neonatal meningitis history, multiple shunt replacements, admitted for abdominal pain secondary to pelvic inflammatory disease. An abdominal shunt catheter removal and external ventricular drain placement occurred after consultation with a general surgeon. A cardiac atrial approach and subsequent laparoscopic abdominal approach were performed without complications. Results: After one month, the patient showed neurological complications, including decreased facial expression, gait instability, and bilateral VIth and VIIth lower motor neuron palsies, specifically upgazed and convergence restriction. Discussion: The complication's pathophysiology is discussed, attributing it to potential brainstem herniation from over-drainage of CSF. Literature suggests flexible endoscopic treatments like aqueductoplasty/transaqueductal approaches into the fourth ventricle. Conclusions: This study underscores the need for increased awareness in monitoring neurological outcomes after the fourth ventriculoperitoneal shunt, particularly in cases with laparoscopic-assisted abdominal catheter placement. The rarity of bilateral abducens and facial nerve palsies emphasizes the importance of ongoing research to understand pathophysiology and develop preventive and therapeutic strategies for this unique complication.

Telovelar vs. Transvermian approach for the fourth ventricle tumors: A systematic review and meta-analysis.

BACKGROUND: Tumors in the fourth ventricle can be critical due to the small size of the fourth ventricle, which causes symptoms to be detected even in the presence of lesser mass effects. A proper surgical approach to the fourth ventricle poses challenges due to its deep location and proximity to vital compartments within the brainstem. The two commonly used approaches to these tumors are the transvermian and telovelar approaches. METHODS: A comprehensive systematic study was conducted based on a literature search of the databases. All case controls, cohorts, and case series including patients with fourth ventricle tumors, who were operated on with either telovelar or transvermian approaches were considered eligible. The evaluated outcomes were comparative postoperative complications of the telovelar vs. transvermian approach. After screening and data extraction, a meta-analysis was performed whenever adequate quantitative data were available. RESULTS: Seven studies with a total number of 848 patients, discussed both telovelar and transvermian approaches, with comparative reporting of outcomes in each group. Postoperative outcomes including cranial nerve deficit, mutism, diplopia, CSF leak, need for CSF diversion, and postoperative gait disturbance were not significantly different between telovelar and transvermian approaches. CONCLUSION: Postoperative complications were not significantly different between telovelar and transvermian approaches. Moreover, it could be proposed that such complications would be more likely to be a multifactorial matter concerning the patient's clinical condition, tumor characteristics, and surgeon's experience, rather than the surgical approach alone.

Cerebellar ependymal cyst: a case report.

Rationale: Intracranial ependymal cysts are relatively rare. The current case report focuses on a patient who was diagnosed with an ependymal cyst and underwent surgical treatment. Postoperative pathological examination confirmed the presence of this lesion in the cerebellum. Chief complaint: A 32-year-old female patient presented with a chief complaint of dizziness and headache with no triggers for the past 1 year. She also reported an increase in the frequency and intensity of symptoms in the past 2 weeks. Diagnosis: Cranial magnetic resonance imaging (MRI) showed a rounded long T1 and T2 abnormal signal foci in the left posterior part of the brainstem under the cerebellar pallidum. The lesion had a clear boundary, was approximately 4.0 × 3.1 × 3.2 cm in size, and did not exhibit any definitive enhancement. Interventions: Total resection of the lesion was carried out after completion of the preoperative examination.Treatment outcomes. The patient was discharged from the hospital on postoperative day 11 once their symptoms had disappeared. The sensory and motor functions of the limbs remained unaffected by treatment. Experiences: Cerebellum ependymal cysts are rare, and most patients only experience discomfort due to cerebral edema. These lesions are also often difficult to differentiate from other intracranial cysts using imaging alone. The aim of this study was to report a rare case of ependymal cyst so that it may serve as a reference for diagnosis and treatment in the future.

Giant brainstem cavernoma in pediatrics: diagnosis and treatment-case report.

INTRODUCTION: Brain cavernomas or cavernous angiomas are a rare vascular malformation in the general population, even more so in pediatric patients. Their incidence in this group is less than 5% of all vascular malformations. They are typically found in the cerebral hemispheres in cortico-subcortical locations and, more rarely, in the brainstem. OBJECTIVE: To describe the diagnosis, treatment, and follow-up of a case involving a pediatric patient with a giant cavernoma in the brainstem at J.P. Garrahan Hospital. MATERIALS AND METHODS: The clinical history of the case was retrieved from the database of J.P. Garrahan Pediatric Hospital. Additionally, a literature search was conducted in high-impact factor journals using the PubMed database. CONCLUSION: Both the authors of this study and experts consulted through the literature agree that, given the eloquence of the affected area and its challenging accessibility, close monitoring and an expectant approach are advisable for such patients. Nevertheless, when the onset of the case warrants it, surgical intervention is deemed necessary in emergency situations and following the acute phase for complete resolution of the pathology.

Osteopathic Approach in the Stimulation of the Endocannabinoid System: A Case Report.

The endocannabinoid system is an important neuromodulatory system responsible for maintaining homeostasis in the biological system. Similarly, the autonomic nervous system is important to control involuntary bodily functions such as thermoregulation, regulation of heart rate and sleep latency. The endocannabinoid system and the autonomic nervous system can be modified by osteopathic manipulative techniques. In this report, we present a case of a 53-year-old patient with comorbidities, habitual cannabis use, and disorders associated with the endocannabinoid system and autonomic nervous system, on whom the cranial technique of the fourth ventricle (CV4) was performed. The results obtained from the Pittsburgh Questionnaire and the Health Survey 36 (SF-36) Questionnaire were encouraging. The patient decreased tetrahydrocannabinol (THC) consumption. Her sleep quality and health improved, thus improving her quality of life. CV4 aimed to influence the functioning of the patient's autonomic nervous system and consequently the endocannabinoid system. Further research using randomized controlled trials will be important to have measurable and objective data on this topic.

Anatomical Step-by-Step Dissection of Midline Suboccipital Approaches to the Fourth Ventricle for Trainees: Surgical Anatomy of the Telovelar, Transvermian, and Superior Transvelar Routes, Surgical Principles, and Illustrative Cases.

Introduction Safe, effective access to the fourth ventricle for oncologic resection remains challenging given the depth of location, restricted posterior fossa boundaries, and surrounding eloquent neuroanatomy. Despite description in the literature, a practical step-by step dissection guide of the suboccipital approaches to the fourth ventricle targeted to all training levels is lacking. Methods Two formalin-fixed, latex-injected specimens were dissected under microscopic magnification and endoscopic visualization. Dissections of the telovelar, transvermian, and supracerebellar infratentorial-superior transvelar approaches were performed by one neurosurgery resident (D.D.D.), under guidance of senior authors. The dissections were supplemented with representative clinical cases to highlight pertinent surgical principles. Results The telovelar and transvermian corridors afford excellent access to the caudal two-thirds of the fourth ventricle with the former approach offering expanded access to the lateral recess, foramen of Luschka, adjacent skull base, and cerebellopontine angle. The supracerebellar infratentorial-superior transvelar approach reaches the rostral third of the fourth ventricle, the cerebral aqueduct, and dorsal mesencephalon. Key steps described include positioning and skin incision, myofascial dissection, burr hole and craniotomy, durotomy, the aforementioned transventricular routes, and identification of relevant skull base landmarks. Conclusion The midline suboccipital craniotomy represents a foundational cranial approach, particularly for lesions involving the fourth ventricle. Operatively oriented resources that combine stepwise neuroanatomic dissections with representative cases provide a crucial foundation for neurosurgical training. We present a comprehensive guide for trainees in the surgical anatomy laboratory to optimize familiarity with fourth ventricle approaches, mastery of relevant microsurgical anatomy, and simultaneous preparation for learning in the operating room.

Craniovertebral and spinal adhesive arachnoiditis: a late complication of ruptured vertebral and posterior inferior cerebellar arteries aneurysms.

BACKGROUND: Adhesive arachnoiditis is a rare yet serious complication that may occur following subarachnoid hemorrhage (SAH). In this circumstance, it is mainly due to ruptured vertebral artery (VA) or posterior inferior artery (PICA) aneurysms. It disrupts cerebrospinal fluid (CSF) flow leading to complications such as spinal arachnoiditis, syringomyelia, trapped 4th ventricle, or a combination of these conditions. Evidence for effective treatment strategies is currently limited. We aimed to review the epidemiology, clinical characteristics, treatment, complications, outcomes, and prognosis of cranio-vertebral junction and spinal adhesive arachnoiditis resulting from ruptured VA and PICA aneurysms. METHODS: This study involved a comprehensive literature review and complemented by our own case. We focused on adult cases of arachnoiditis, syringomyelia, and trapped 4th ventricle with SAH caused by ruptured VA or PICA aneurysms, excluding cases unrelated to these aneurysms and those with insufficient data. RESULTS: The study included 22 patients, with a mean age of 52.4 years. Symptoms commonly manifest within the first year after SAH and timely diagnosis requires a high index of suspicion. Treatment approaches included lysis of adhesions and various shunt procedures. Most patients showed improvement post-treatment, though symptom recurrence is significant. CONCLUSION: Adhesive arachnoiditis is a critical complication following SAH, most commonly from ruptured VA and PICA aneurysms. Early detection and individualized treatment based on the type of arachnoiditis and CSF flow impact are crucial for effective management. This study underscores the need for tailored treatment strategies and further research in this field.

Experience in treating children with ocular dyskinesia and hemifacial spasm secondary to pontine tumours adjacent to the fourth ventricle and systematic review.

OBJECTIVE: To investigate the treatment plan and prognosis of children with ocular dyskinesia and hemifacial spasm secondary to pontine tumours adjacent to the fourth ventricle. METHODS: In this retrospective study, the clinical information of 10 consecutively collected children with ocular dyskinesia and hemifacial spasm secondary to pontine tumours adjacent to the fourth ventricle was analyzed. All 10 children underwent pontine tumour resection through a trans-cerebellomedullary fissure approach; 4 children underwent preoperative diffusion tensor imaging scans to determine the relationship between the tumour and facial nerve nucleus, and the other 6 children underwent intraoperative deep electroencephalography (EEG) tumour monitoring, in which the tumour electrical discharge activity of the tumour was recorded. A voxel distribution map was established to describe the distribution of the tumour location, and patient prognosis was evaluated through clinical and imaging follow-up. RESULTS: All 10 children achieved total tumour resection; 9 tumours were pathologically suggested to be ganglioglioma (WHO grade I), and 1 was a hamartoma. The symptoms of the original ocular dyskinesia and hemifacial spasm disappeared immediately after the operation. The children were followed up for 4-75 months, and none of the symptoms recurred; four cases with preoperative diffusion tensor imaging showed that the tumour was close to the facial nerve. Four in six intraoperative electrophysiological monitoring showed that the tumour had electrical discharge behaviour, and the tumour distribution map indicates a high density of tumour presence in the facial nerve nucleus and the nucleus of the abducens nerve. CONCLUSIONS: In paediatric patients, the facial symptoms are related to the location and abnormal electrical discharge of the tumour. There is no significant correlation between ocular dyskinesia and the location of the tumour. Conventional antiepileptic therapy for this disease is ineffective, and early surgical intervention for total tumour resection can achieve a clinical curative effect.

Occipital Sinus-Sparing Linear Paramedian Dural Incision: A Technical Note and Case Series for Median Suboccipital Approach.

BACKGROUND: Durotomies, traditionally used during the midline suboccipital approach, involve sacrificing the occipital sinus (OS) with consequent shrinking of the dura, risk of venous complications, difficulty performing watertight closure, and a higher rate of postoperative cerebrospinal fluid (CSF) leaks. The present technical note describes the OS-sparing linear paramedian dural incision, which leads to a decrease in the risk of complications during the median suboccipital approach in our case series. METHODS: The OS-sparing linear incision technique involves a dural incision placed 1 cm lateral to the OS. The angle of view of the microscope is frequently changed to overcome the narrowed exposure of the linear durotomy. Copious irrigation with saline prevents drying of the dura. A running watertight closure of the dura is performed. The overall results of 5 cases are reviewed. RESULTS: The cases were 3 tumors and 2 cavernomas. The OS was preserved in all 5, and no duraplasty was needed. The average dura closure time was 16.8 minutes. No CSF leak occurred, and no wound complications were observed. A gross total resection of the lesion was achieved in all the patients. The mean follow-up was 10.2 months, and there were no late complications related to the dura closure. CONCLUSIONS: In comparison to the types of durotomies conventionally used for the midline suboccipital approach, the OS-sparing linear paramedian dural incision entails lower risks of bleeding, venous complications, CSF leaks, and infections by avoiding duraplasty. Validation of this technical note on a larger patient cohort is needed.

Exoscopic removal of the fourth ventricle choroid plexus papilloma with use of a midline suboccipital osteoplastic craniotomy.

Choroid plexus papillomas are relatively rare vascular tumors. In this video, the authors present a pediatric patient who underwent exoscopic removal of the fourth ventricle choroid plexus papilloma with the use of a midline suboccipital osteoplastic craniotomy. The exoscope in the fourth ventricle lesion helps to improve visualization in all directions, with the surgeon being able to maintain a comfortable position throughout the procedure. In addition, the midline suboccipital osteoplastic craniotomy helps to reduce the potential risks of complications, in particular, CSF leak and craniovertebral junction instability. The video can be found here: https://stream.cadmore.media/r10.3171/2023.10.FOCVID23106.

Imaging features to distinguish posterior fossa ependymoma subgroups.

OBJECTIVES: Posterior fossa ependymoma group A (EPN_PFA) and group B (EPN_PFB) can be distinguished by their DNA methylation and give rise to different prognoses. We compared the MRI characteristics of EPN_PFA and EPN_PFB at presentation. METHODS: Preoperative imaging of 68 patients with posterior fossa ependymoma from two centers was reviewed by three independent readers, blinded for histomolecular grouping. Location, tumor extension, tumor volume, hydrocephalus, calcifications, tissue component, enhancement or diffusion signal, and histopathological data (cellular density, calcifications, necrosis, mitoses, vascularization, and microvascular proliferation) were compared between the groups. Categorical data were compared between groups using Fisher's exact tests, and quantitative data using Mann-Whitney tests. We performed a Benjamini-Hochberg correction of the p values to account for multiple tests. RESULTS: Fifty-six patients were categorized as EPN_PFA and 12 as EPN_PFB, with median ages of 2 and 20 years, respectively (p = 0.0008). The median EPN_PFA tumoral volume was larger (57 vs 29 cm3, p = 0.003), with more pronounced hydrocephalus (p = 0.002). EPN_PFA showed an exclusive central position within the 4th ventricle in 61% of patients vs 92% for EPN_PFB (p = 0.01). Intratumor calcifications were found in 93% of EPN_PFA vs 40% of EPN_PFB (p = 0.001). Invasion of the posterior fossa foramina was mostly found for EPN_PFA, particularly the foramina of Luschka (p = 0.0008). EPN_PFA showed whole and homogeneous tumor enhancement in 5% vs 75% of EPN_PFB (p = 0.0008). All mainly cystic tumors were EPN_PFB (p = 0.002). The minimal and maximal relative ADC was slightly lower in EPN_PFA (p = 0.02 and p = 0.01, respectively). CONCLUSION: Morphological characteristics from imaging differ between posterior fossa ependymoma subtypes and may help to distinguish them preoperatively. CLINICAL RELEVANCE STATEMENT: This study provides a tool to differentiate between group A and group B ependymomas, which will ultimately allow the therapeutic strategy to be adapted in the early stages of patient management. KEY POINTS: • Posterior fossa ependymoma subtypes often have different imaging characteristics. • Posterior fossa ependymomas group A are commonly median or lateral tissular calcified masses, with incomplete enhancement, affecting young children and responsible for pronounced hydrocephalus and invasion of the posterior fossa foramina. • Posterior fossa ependymomas group B are commonly median non-calcified masses of adolescents and adults, predominantly cystic, and minimally invasive, with total and homogeneous enhancement.