Definition
- Essential:
- Posterior fossa tumour with morphological and immunohistochemical features of ependymoma AND
- Global reduction of H3 p.K28me3 (K27me3) in tumour cell nuclei OR
- DNA methylation profile aligned with PFA ependymoma
- Desirable:
- Stable genome on genome-wide copy-number analysis
Origin
- Undifferentiated glial stem or progenitor cell in the developing hindbrain
Numbers
- Median age of presentation of 3 years
- >95% of posterior fossa ependymomas in children under 6 years of age, decreasing to 50% in the adolescent population and 5-11% in adults
- Male>female
Clinical features
- Mass effect on surrounding posterior fossa structures
- Cranial nerve deficits
- Obstructive hydrocephalus
- Headache
- Vomit
- Rapidly growing head circumference.
Origin
- Undifferentiated glial stem or progenitor cell in the developing hindbrain
Location
- Arise from the roof or lateral portions of the 4th ventricle as opposed to the floor
- This is important given that previous studies have demonstrated lower survival rates and challenges achieving a total surgical resection in laterally positioned tumours
- As if going out the foramen of Luschka
Molecular pathology
- DNA methylation patterns, including hypermethylation of CpG islands and global DNA hypomethylation
- Overexpression of EZHIP → Low global levels of histone H3 K27-trimethylation
- By DNA methylation profiling: 2 molecular subgroups and 9 molecular subtypes of PFA ependymomas
- Clinical implication not fully shown yet
Pathology
Macroscopic
- Circumscribed tumours
- Tan-coloured and are soft or spongy, with a gritty consistency if calcified
Microscopic
- High-grade features, including prominent mitotic activity and microvascular proliferation, were observed in 64% of PFA ependymomas
Radiology
- Same with PFB tumours
- A 14-month-old girl presented with 1-month history of progressive weakness and frequent falls; has been unwell, lethargic, and vomiting for 11 days; choking on food and right-sided torticollis; she was finally unable to sit or walk.
- Clinically, she showed quadriparesis and nystagmus.
- Coronal T2w (A), FLAIR (B), DWI (C), and T1w-CE (D) show a large tumour centred on the inferior aspect of the posterior fossa causing obstructive hydrocephalus.
- T2 signal intensity and enhancement are inhomogeneous.
- Prominent vessels are noted.
- DWI shows neither diffusion restriction nor increased diffusivity
Prognosis
- Overall outcome is related to the extent of surgical excision
- Worse prognosis vs PFB
- Gain of chromosome 1q is a reproducible adverse prognostic indicator across all posterior fossa ependymomas
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