Subependymomas are uncommon, benign (WHO grade I) tumours which are slow growing and non-invasive. They tend to occur in middle-aged and older individuals and usually identified as an incidental finding.
These tumours were previously also known as subependymal astrocytomas, not to be confused with subependymal giant cell astrocytomas seen with tuberous sclerosis. They are also considered by some to be variants of ependymomas, with which they may co-exist (see below).
Subependymomas tend to present in middle-aged to older individuals (typically 5th to 6th decades 3). There is a slight male predilection (M:F 2.3:1) 6.
Typically patients are asymptomatic and small lesions are discovered incidentally. In some cases, especially when the tumours are larger, presentation is with symptoms of raised intracranial pressure due to obstructive hydrocephalus.
The histopathology of subependymomas is distinct comprising of a tumour arising from the subependymal glial layer with low cellularity and no high grade features (no mitoses, Ki-67/MIBI index > 1.5%, no necrosis). These lesions are hypovascular. Loose pseudorosettes are seen. Cells express GFAP 4-6. They are WHO grade I lesions (see WHO classification of CNS tumours).
Occasionally foci of cellular ependymoma are seen, although the effect on clinical behaviour is unclear 4-5. They are graded according to the ependymoma component and not surprisingly behave similarly to the higher grade (ependymoma) component 6.
Macroscopically they appear as well circumscribed masses attached to the ventricular wall by a narrow pedicle 6.
Subependymomas are most commonly seen in the fourth ventricle, but can arise anywhere where there is ependyma. They are therefore in the differential for other intraventricular masses. Distribution in the ventricular system is as follows 6:
- fourth ventricle: 50-60%
- lateral ventricles (usually frontal horns): 30-40%
- third ventricle: rare
- central canal of the spinal cord: rare
They are usually small, typically less than 2cm in size 6.
Isodense to somewhat hypodense intraventricular mass compared to adjacent brain, which does not usually enhance. If large, it may have cystic or even calcific (up to half of the cases 3) components. Surrounding vasogenic oedema is usually absent.
- iso-hypointense to white matter
- generally homogeneous but may be heterogeneous in larger lesions
- hyperintense to adjacent white and grey matter
- again, heterogeneity may be seen in larger lesions, with susceptibility related signal drop out due to calcifications occasionally seen
- no adjacent parenchymal oedema (as no brain invasion is present) 6
T1 C+ (Gd)
- usually no enhancement, although at times may demonstrate mild enhancement
As expected from the histology, subependymomas show no or little vascularity 6.
Treatment and prognosis
If appearances are characteristic, then follow up is a viable option.
Resection should be considered if the patient is symptomatic (hydrocephalus or mass effect), the mass has an atypical appearance or demonstrates growth. Local resection is curative.
General imaging differential considerations include:
- intraventricular meningioma
- central neurocytoma (particularly if close to 3rd ventricle)
- cerebral metastasis
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- 2. Russell JH, Gaillard F, Drummond KJ. A mass in the fourth ventricle. J Clin Neurosci. 2009;16 (3): 425, 482. Pubmed citation
- 3. Koral K, Kedzierski RM, Gimi B et-al. Subependymoma of the cerebellopontine angle and prepontine cistern in a 15-year-old adolescent boy. AJNR Am J Neuroradiol. 2008;29 (1): 190-1. doi:10.3174/ajnr.A0821 - Pubmed citation
- 4. Tonn J, Westphal M, Rutka JT. Oncology of CNS Tumors. Springer Verlag. (2009) ISBN:364202873X. Read it at Google Books - Find it at Amazon
- 5. Keating RF, Goodrich JT, Packer RJ. Tumors of the pediatric central nervous system. George Thieme Verlag. (2001) ISBN:0865778485. Read it at Google Books - Find it at Amazon
- 6. Smith A, Smirniotopoulos J, Horkanyne-Szakaly I. From the Radiologic Pathology Archives: Intraventricular Neoplasms: Radiologic-Pathologic Correlation. Radiographics. 2013;33 (1): 21-43. Radiographics (full text) - doi:10.1148/rg.331125192
- 7. Chiechi MV, Smirniotopoulos JG, Jones RV. Intracranial subependymomas: CT and MR imaging features in 24 cases. AJR Am J Roentgenol. 1995;165 (5): 1245-50. doi:10.2214/ajr.165.5.7572512 - Pubmed citation