Ependymomas represent a relatively broad group of glial tumours most often arising from the lining the ventricles of the brain or the central canal of the spinal cord. They account for ~5% of all neuroepithelial neoplasms, ~10% of all paediatric brain tumours and up to 33% of brain tumours occurring in those less than 3 years of age.
Ependymomas can occur anywhere, but certain locations are more typical. Overall distribution is 11:
- posterior fossa: 60%
- supratentorial ependymoma: 30%
- spinal cord/canal: 10%
The remainder of this article concerns itself with intracranial ependymomas.
There is no recognised gender predilection 3. Although they can occur at any age, the posterior fossa tumours tend to present more commonly in the paediatric age group (mean age at diagnosis is 6 years of age), with a smaller second peak for supratentorial tumours around the 3rd decade 7.
Clinical presentation can vary according to location. Initial presentation with signs and symptoms of raised intracranial pressure is common, particularly with tumours in the fourth ventricle. Other posterior fossa symptoms including ataxia are also encountered 7. Supratentorial ependymomas may also present with seizures or focal neurological deficits 2,5.
In the infrequent scenario of haemorrhage, the presentation will be hyper-acute.
- neurofibromatosis type 2 (NF2)
Ependymomas are glial tumours with ependymal differentiation which tend to arise within or abutting the ventricular system of the brain or central canal of the spinal cord 7,11. Although for many years ependymomas were believed to be tumours arising from dedifferentiated ependymocytes, it now appears fairly certain that in fact, they arise from radial glial stem cells 9-11.
Macroscopically, ependymomas tend to be well defined lobulated gray or tan-coloured soft and frond-like tumours which are moderately cellular. They may have focal areas of calcification.
Microscopically, these tumours are characterised by well-differentiated cells. Characteristic features include ependymal rosettes, which are uncommon but pathognomonic and perivascular pseudorosettes which are far more common and seen in most of ependymomas 8,11.
Dystrophic calcification, haemorrhage, myxoid degeneration and even rarely metaplasia (bone or cartilage) are sometimes encountered 11.
A number of immunohistochemical markers are useful, including 11,12:
- glial fibrillary acid protein (GFAP)
epithelial membrane antigen (EMA)
- positive in the luminal surface of the ependymal rosettes
- positive dot or ring-like perinuclear intracytoplasmic structure (intracytoplasmic microrosette)
- S100: positive
- vimentin: positive
- OLIG2: negative
Ependymomas are WHO grade II tumours, with more histologically aggressive tumours denoted WHO III (anaplastic ependymoma), although the reliability of histological features in grading these tumours and the prognostic significance is somewhat controversial, and recently there has been a shift towards molecular markers to subdivide ependymomas 11.
In the current (2016 update) WHO classification of CNS tumours the following entities are accepted as belonging to the ependymoma family of tumours 11:
- WHO grade I
- WHO grade II
- WHO grade III
Note: the 2016 update to WHO classification of CNS tumours has deleted the variant cellular ependymoma as it was felt that it overlapped that of a standard ependymoma too closely 11.
The majority of intracranial ependymomas (60%) are located in the posterior fossa (infratentorial), usually arising from the floor of the fourth ventricle 5-7. This is especially true in children. The remainder (40%) are located supratentorially and up to half of these are intraparenchymal 7.
Posterior fossa ependymomas are apt to extend through the foramina of Luschka and Magendie, hence the term plastic ependymoma. This is a characteristic feature and can be seen on both CT and MRI.
Ependymomas are typically heterogeneous masses with areas of necrosis, calcification, cystic change and haemorrhage frequently seen. This results in a heterogeneous appearance on all modalities.
Intraparenchymal lesions (usually supratentorial) are usually large and variable in appearance, ranging from completely solid, enhancing masses to cysts with a mural nodule, or more heterogeneous masses 7. They are believed to arise from trapping of embryonic rests of ependymal tissue in the developing cerebral parenchyma 5.
- coarse calcification is common (50%)
- cystic areas (50%)
- solid component iso to hypodense
- heterogeneous enhancement
- variable haemorrhage
- solid portions of ependymoma typically are isointense to hypointense relative to white matter 7
- hyperintense to white matter
- more reliable in differentiating tumour margins than non-contrast T1-weighted images (but less reliable than contrast enhanced T1)
T2* (e.g. SWI)
- foci of blooming from haemorrhage or calcification
T1 C+ (Gd)
- enhancement present but heterogeneous
- enhancement with gadolinium is useful in differentiating tumour from adjacent vasogenic oedema and normal brain parenchyma
- restricted diffusion may be seen in solid components, especially in anaplastic tumour
- diffusion should be interpreted with caution in masses with significant haemorrhage or calcification
Although it is uncommon when compared to tumours like medulloblastomas, careful examination of the entire neuraxis is required to assess for the presence of CSF seeding.
Treatment and prognosis
A total or partial resection could be attempted +/- irradiation.
Prognosis is, however, relatively poor, which is mainly due to tumours occurring in surgically challenging locations, making complete resection difficult.
Poor prognostic factors include a 4th ventricular location, anaplastic variant and incomplete resection. As such, children have a worse prognosis (both 4th ventricular location and anaplastic variant are more common in children). Overall, the 5-year survival rate in children ranges from 50 to 75% 7.
Once recurrence has occurred, the prognosis is very poor, with a mortality rate of 90% 7.
General imaging differential considerations include:
- similar demographic, especially if around the 4th ventricle
- arises from vermis
- less 'plastic', does not tend to extend through foramina
- enhancement more homogenous
- calcification less common
- tends to occur in older individuals
- usually not enhancing
choroid plexus papilloma
- in children usually in the trigone of the lateral ventricles
- in adults usually in the fourth ventricle (i.e opposite to ependymoma)
- more vividly and homogeneously enhancing
- lacks adjacent parenchymal oedema
- NB choroid plexus carcinoma can be heterogeneous and invade brain
choroid plexus metastasis
- can appear similar
- older individuals, usually with a history of malignancy
- difficult to distinguish from intraparenchymal supratentorial ependymoma
- usually older patients
- epicentre usually in the white matter
- usually arises from/in contact with septum pellucidum
- less vivid enhancement
- atypical teratoid/rhabdoid tumour
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