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Subependymoma

Subependymomas are uncommon, benign (WHO grade I) tumours which are slow growing and non-invasive.

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).

Epidemiology

Supependymomas 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.

Clinical presentation

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.

Pathology

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 indes > 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.

Radiographic features

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: 30-40%
  • third ventricle: rare
  • central canal of the spinal cord: rare

They are usually small, typically less than 2cm in size 6.

CT

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 cases 3) components.  Surrounding vasogenic oedema is usually absent.

MRI
  • T1
    • iso - hypointense to white matter
    • usually homogenous but may be heterogenous in larger lesions
  • T2
    • hyper intense to adjacent white and grey matter
    • again, heterogeneity may be seen in larger lesions, with suceptibility 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
DSA - angiography

As expected from the histology, subependymomas demonstrate no or little vascularity 6.

Treatment and prognosis

If appearances are characteristic then followup 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.

Differential diagnosis

General imaging differential considerations include

See also

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