- Seen in young children (peak age 1–5 years, male:female 1.4:1; 70% of pediatric ependymomas arise within the posterior fossa; second peak in young adults at 30–40 years). Presents with subacute progressive morning headaches, vomiting, lethargy, torticollis, neck pain, and multiple cranial nerve palsies (CN VI, VII, IX, X) due to direct brainstem compression.
- Caused by neuroepithelial neoplasm arising from differentiated ependymal cells lining the ventricular system and central canal of the spinal cord:
- (1)Anatomical Origin: Floor of the fourth ventricle (rhomboid fossa) or lateral recess.
- (2)Biological Classification (DNA Methylation Framework):
- 1.Posterior Fossa Ependymoma Group A (PF-A): Infants and young children; lateral location; hypermethylated phenotype; highly aggressive with high recurrence rates and poor prognosis.
- 2.Posterior Fossa Ependymoma Group B (PF-B): Older children and adults; midline location; genome-wide chromosomal instability; favorable prognosis.
- (3)Pathological Hallmarks: Perivascular pseudorosettes (tumor cells radiating around central blood vessels with an anuclear fibrillary zone) and true ependymal rosettes/canals.
Imaging Findings
- Magnetic Resonance Imaging (Brain MRI - Diagnostic Gold Standard Framework):
- –Hallmark 'Plastic' / 'Pliable' Tumor: Soft, compliant tumor that characteristically molds to the shape of the fourth ventricle and squeezes out ('toothpaste tumor' sign) through anatomical egress pathways:
- 1.Laterally through the Foramen of Luschka into the cerebellopontine (CP) angle cistern.
- 2.Inferiorly through the Foramen of Magendie and foramen magnum into the dorsal cervical subarachnoid space (encasing the upper cervical spinal cord).
- –Floor of 4th Ventricle Origin: Arises directly from the ventricular floor (obex/rhomboid fossa), causing extensive encasement of posterior inferior cerebellar arteries (PICA), vertebral arteries, and lower cranial nerves.
- –Heterogeneous Signal Architecture:
- 1.T1WI: Hypointense to isointense, marked heterogeneous appearance.
- 2.T2WI: Markedly heterogeneous, mixed solid, cystic, and hemorrhagic components.
- 3.Blooming on SWI: Coarse, punctate calcifications (present in up to 50%, contrasting with <10–20% in medulloblastoma) and hemosiderin blood products.
- 4.Diffusion Characteristics: Intermediate diffusion.
- 5.Contrast Enhancement: Heterogeneous, patchy, moderate to intense enhancement post-gadolinium.
- –DWI / ADC: Demonstrates intermediate diffusivity, serving as a reliable quantitative discriminator among pediatric 4th ventricular tumors.
- –**SWI / T2* GRE: Prominent heterogeneous blooming artifact** in >50% of cases due to coarse intratumoral calcifications and hemorrhagic foci.
- Computed Tomography (CT Head):
- –Heterogeneous soft-tissue mass with coarse, punctate or clumped intratumoral calcifications (>50%) and extension into CP angle cisterns.
- Plain Radiograph (X-Ray) & Bone Findings:
- –Skull X-Ray: Pediatric skull radiographs may reveal cranial suture diastasis from obstructive hydrocephalus and punctate posterior fossa calcifications.
Differential Diagnosis
| Differential Diagnosis | Key Distinguishing Features |
|---|---|
Medulloblastoma (WHO Grade 4\) | Arises from the roof of the 4th ventricle (vermis); does not squeeze out through the foramina of Luschka; highly hypercellular with profound restricted diffusion; calcifications are rare. |
Pilocytic Astrocytoma (WHO Grade 1\) | Cyst with an intensely enhancing mural nodule; located in cerebellar hemisphere; lacks calcification and foraminal extrusion. |
Choroid Plexus Papilloma | Cauliflower-like lobulated mass with brilliant, homogeneous enhancement; highly mobile, causes dramatic CSF overproduction and generalized hydrocephalus. |
Atypical Teratoid/Rhabdoid Tumour (AT/RT) | Bulky, destructive, off-midline mass in infants <3 years; rapid progression with extensive necrosis and loss of INI1. |
Important Points to Remember
- Diagnostic Pitfall: Failing to check for extension through the foramina of Luschka and Magendie or missing PICA vascular encasement! Unlike medulloblastoma which remains encapsulated within the fourth ventricle, ependymoma characteristically 'creeps' out through the foramina of Luschka into the CP angles and down through the foramen magnum into the dorsal spinal canal. Complete surgical resection (GTR) is the single most powerful prognostic factor, but encasement of lower cranial nerves (CN IX, X, XI) and the PICA makes total resection challenging.
- Crucial Review Areas:
- 1.Foramina of Luschka and CP angle cisterns on axial T2WI for lateral extrusion ('toothpaste sign').
- 2.Foramen of Magendie and upper cervical spine on sagittal T2WI for downward extrusion into the spinal subarachnoid space.
- 3.Basilar, vertebral, and PICA arteries on contrast T1WI for circumferential vascular encasement.
- 4.Post-contrast whole-spine MRI to screen for leptomeningeal seeding (occurs in 10–15%).
- Radiologist Safe Practice & Management:
- 1.Urgent Neurosurgical Referral: Immediate consultation with a pediatric neurosurgeon for evaluation and management of hydrocephalus.
- 2.Complete Neuraxis Staging: High-resolution contrast-enhanced whole-spine MRI and post-operative CSF cytology to exclude drop metastases.
- 3.Maximal Safe Microsurgical Resection: Aggressive gross total resection (GTR); intraoperative neurophysiological monitoring of cranial nerves is mandatory to resect foraminal extensions safely.
- 4.Molecular Staging: Histopathological grading (WHO Grade 2 vs Grade 3\) and DNA methylation profiling (PF-A vs PF-B classification).
- 5.Post-Operative Conformal Radiation Therapy: High-dose localized conformal proton beam radiation therapy (or photon radiation) to the tumor bed for all patients >1 year of age, regardless of GTR status.