Supratentorial ependymoma

Supratentorial ependymomas are an uncommon type of ependymoma, found within the cerebral hemispheres, either remote to or abutting the ventricles. 

They have distinct molecular features compared to both posterior fossa ependymomas and spinal ependymomas. 

Epidemiology

Overall, supratentorial ependymomas affect primarily children and adolescents, but also adults to a lesser degree ¹⁰. 

The epidemiology varies according to molecular subtype ^7,9,10:

• supratentorial ependymoma, ZFTA fusion-positive

  • the majority of supratentorial ependymomas, especially in children

  • M:F = 2:1

  • age: older children

• supratentorial ependymoma, YAP1 fusion-positive

  • uncommon (<10% of all supratentorial ependymomas)

  • M:F = 1:3

  • age: <3 years of age

Clinical presentation

Supratentorial ependymomas usually present with headaches, seizures and focal neurological deficits compared to their infratentorial counterparts that mainly present with features of raised intracranial pressure.

Pathology

Although histologically similar, supratentorial ependymomas have a distinct molecular profile to the more common posterior fossa ependymomas. In the 5^th edition (2021) of the WHO classification of CNS tumors, supratentorial ependymomas are divided into ^9,10: 

• supratentorial ependymoma, ZFTA (RELA) fusion-positive

• supratentorial ependymoma, YAP1-MAMLD1 fusion

In the minority of cases when these two common molecular alterations are absent (17-30%), or testing is inconclusive or unavailable, then the term supratentorial ependymoma NEC or NOS should be used respectively ¹⁰. 

Radiographic features 

Radiologically these tumors have few characteristic features, appearing as heterogeneous parenchymal masses with calcification, cystic components, solid enhancing components and surrounding edema. 

Although they can be located anywhere in the hemispheres, they seem to have a predilection for the frontal and parietal lobes ¹⁰. 

CT

• coarse calcification is common (50%) 

• cystic areas (50%) 

• solid component iso to hypodense

• heterogeneous enhancement 

• a small proportion can have hemorrhage

• non-contrast CT appearances of an intraparenchymal ependymoma is said to resemble a periwinkle flower, thus periwinkle sign ⁸.

MRI

• T1

  • solid portions of ependymoma typically are isointense to hypointense relative to white matter ⁷

• T2

  • hyperintense to white matter

  • more reliable in differentiating tumor margins than non-contrast T1-weighted images (but less reliable than contrast-enhanced T1)

• T2* (e.g. SWI)

  • foci of blooming from hemorrhage or calcification

• T1 C+ (Gd)

  • enhancement present but heterogeneous

  • enhancement with gadolinium is useful in differentiating tumors from adjacent vasogenic edema and normal brain parenchyma

• DWI/ADC

  • restricted diffusion may be seen in solid components especially in grade 3 tumors

  • diffusion should be interpreted with caution in masses with significant hemorrhage or calcification

Mnemonic

The imaging findings can be remembered by the “1234 rule”:

• 1: a single large tumor common in the first decade

• 2P: Perilesional edema and Periwinkle sign

• 3L: Large Lobulated Lobar mass

• 4C: Central Chunky Calcification and large peripheral Cyst 

Treatment and prognosis

Treatment is primarily with maximal (hopefully complete) surgical resection ¹⁰. Recurrence is common and CSF spread is encountered fairly frequently, especially in grade 3 tumors ¹⁰.

Supratentorial ependymomas generally have a somewhat poorer prognosis than their more common posterior fossa counterparts ¹⁰. This is especially the case in children ⁷. 

ZFTA fusion-positive tumors have a poor prognosis, whereas YAP1 fusion-positive tumors appear to have a substantially better prognosis, despite their often large size at diagnosis ¹⁰. 

Differential diagnosis

Imaging differential considerations depend on whether the tumor is within the parenchyma (usually the case) or less commonly within the ventricle. 

For parenchymal tumors consider: 

• diffuse astroctyoma, oligodendroglioma and glioblastoma

• embryonal tumors with multilayered rosettes (ETMR)

• pilocytic astrocytoma

• cerebral metastasis

• astroblastoma

When the mass appears to be intraventricular, consider:

• central neurocytoma

• choroid plexus papilloma

• subependymal giant cell astrocytoma

• subependymoma