Ependymoma

Ependymomas comprise of a relatively broad group of glial tumours which share common origin from differentiated ependymal cells lining the ventricles of the brain or the central canal of the spinal cord ³. They account for 3 – 9% of all neuroepithelial neoplasms, 6 – 12% of all paediatric brain tumours  ⁵ and up to 33% of brain tumours occurring in those less than 3 years of age ⁶ . 

Demographics and clinical presentation

There is no recognised gender predilection ³.  They can occur at any age. The posterior fossa tumours tend to present more commonly  in the paediatric age group with a second possible peak around the 3^rd decade.

Clinical presentation can vary according to location.

Location

Infratentorial location is commoner ( ≈ 60% ⁵)

Common locations include

• floor of the fourth ventricle (commonest location in children)
• spinal cord : conus medullaris 

Associations

• neurofibromatosis type 2 (NF2)

Pathology

They tend to be soft and frond like tumours which are moderately cellular. Perivascular pseudorosettes may be seen. The tumours arise from dedifferentiated ependymal cells that line the ventricles of the brain and central canal of the spinal cord.

Classification

Ependymomas can occur in both malignant and benign forms 

• WHO Grade I
  • myxopapillary ependymoma
• WHO Grade II
  • cellular ependymoma
  • papillary ependymoma
  • clear cell ependymoma
• WHO Grade III
  • anaplastic ependymoma

Radiographic features

Ependymomas are more apt to extend through the foramina of Luschka and Magendie, hence the term plastic ependymoma. This is a characteristic feature.

CT

Brain

• calcification is common on CT ( ≈ 50%) 
• often shows heterogenous enhancement 
• typically invaginates into ventricles
• cystic areas ( ≈ 50%) 
• a small proportion can have haemorrhage

Spinal cord

• homogenous enhancement

MRI

Brain

Signal heterogeneity is a feature useful in distinguishing ependymoma from the more homogeneous medulloblastoma. Calcification and hemorrhagic foci are more typical of ependymoma than medulloblastoma. Similarly, choroid plexus papilloma is more homogeneous than ependymoma and lacks the typical irregular margins and surrounding edema of ependymoma.

• T1 : solid portions of ependymoma typically are isointense to hypointense relative to white matter.
• T2 : hyper intense to white matter 
• as many as 50% of ependymomas demonstrate signal heterogeneity, which may indicate calcification, necrosis, methemoglobin, hemosiderin, or tumor vascularity.
• hypointense foci on both T1- and T2-weighted images suggest haemosiderin, calcium, or necrosis.
• cystic changes result in high signal intensity on T2-weighted images.
• C + (GAD) : shows enhancement

Enhancement with gadolinium is useful in differentiating tumour from adjacent vasogenic oedema and normal brain parenchyma. Without intravenous contrast enhancement, T2-weighted images are more reliable in differentiating tumour margins than are T1-weighted images.

Treatment and prognosis

Total or partial resection could be attempted +/- irradiation.

Prognosis is however relatively poor which is mainly due to tumours occuring in surgically challenging locations making complete resection difficult.

Differential diagnoses

The differential includes

• medulloblastoma : especially if around the 4^th ventricle and in the paediatric population
• sub ependymoma : tends to occur in older individuals
• astrocytoma : see ependymoma vs astrocytoma