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Supratentorial ependymomas

Supratentorial ependymomas are uncommon intraparenchymal or periventricular tumors of the cerebral hemispheres presenting primarily in children and adolescents with headaches, seizures, and focal neurological deficits.

Key Images

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Ependymoma

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Look For First
  • Large heterogeneous parenchymal mass in frontal or parietal lobe with mixed solid and cystic components
  • Coarse calcification (periwinkle sign) visible on CT/MRI
  • Perilesional vasogenic edema surrounding a lobulated mass
  • Heterogeneous enhancement on contrast-enhanced T1 weighted imaging
Key Image Findings
  • Heterogeneous parenchymal mass with predilection for frontal and parietal lobes, typically abutting or remote from the ventricular system.
  • Coarse calcification present in approximately 50% of cases, classically described as the periwinkle sign on non-contrast CT.
  • Cystic components in approximately 50% of cases, often large peripheral cysts adjacent to the solid tumor core.
  • CT appearances show iso to slightly hyperdense solid components with heterogeneous enhancement and possible hemorrhage in a minority of cases.
  • On MRI, solid portions are isointense to hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging, with T2 more reliable than T1 for margin differentiation.
  • T2* sequences (SWI) demonstrate blooming artifact from hemorrhage or calcification, helpful for detecting these components.
  • Heterogeneous gadolinium enhancement on T1-weighted images distinguishes tumor from adjacent vasogenic edema and normal brain parenchyma.
  • Restricted diffusion may be present in solid components, particularly in grade 3 tumors, though diffusion interpretation requires caution with significant hemorrhage or calcification.
Differential Diagnosis
  • Diffuse astrocytoma, oligodendroglioma, and glioblastoma - distinguished by molecular subtype (ZFTA or YAP1 fusion in ependymomas), patient age, and location within hemispheric parenchyma rather than periventricular.
  • Pilocytic astrocytoma - typically more homogeneous enhancement, commonly located in cerebellum or optic pathway, lacks the coarse calcification and cystic architecture of ependymomas.
  • Embryonal tumors with multilayered rosettes (ETMR) - occur in very young children, often have more restricted diffusion, lack the characteristic periwinkle calcification pattern.
  • Cerebral metastasis - history of primary malignancy, often multiple lesions, typically at gray-white matter junction with smooth margins.
  • Central neurocytoma - if mass appears intraventricular, typically arises from septum pellucidum with characteristic heterogeneous appearance but different molecular markers.
  • Astroblastoma - rare tumor with similar heterogeneous appearance; molecular profiling (ZFTA/YAP1 fusion) distinguishes ependymoma.
Discussion

Supratentorial ependymomas are molecularly distinct from posterior fossa ependymomas, classified as ZFTA fusion-positive (majority, especially in older children) or YAP1 fusion-positive (uncommon, <10%, typically in children <3 years) by WHO 2021 classification.

ZFTA fusion-positive tumors carry poor prognosis while YAP1 fusion-positive tumors have substantially better prognosis despite often large size at presentation, making molecular subtyping clinically significant.

Clinical presentation differs from infratentorial ependymomas, which present with raised intracranial pressure; supratentorial tumors present with headaches, seizures, and focal neurological deficits.

The 1234 rule mnemonic aids recognition: one single large tumor in first decade, two perilesional edema and periwinkle sign, three large lobulated lobar mass, four central chunky calcification and peripheral cyst.

CSF spread occurs fairly frequently, especially in grade 3 tumors, requiring baseline and surveillance neuraxis imaging including spine imaging.

Treatment requires maximal surgical resection, with recurrence being common; molecular subtype predicts risk and may guide adjuvant therapy decisions.

Reporting Pearls

Describe supratentorial ependymomas as heterogeneous lobulated parenchymal masses (most common in frontal/parietal lobes) with characteristic coarse calcification (periwinkle sign), large peripheral cysts, restricted enhancement, and surrounding vasogenic edema; specify molecular subtype (ZFTA vs YAP1 fusion) if available and note complete/partial resection status post-operatively, as this critically impacts prognosis.

Pitfalls
  • Misidentifying the tumor as a low-grade glioma (astrocytoma or oligodendroglioma) due to parenchymal location and heterogeneous enhancement; molecular profiling with ZFTA or YAP1 fusion is essential for accurate diagnosis.
  • Overinterpreting restricted diffusion as indicating high-grade malignancy without considering that grade 3 ependymomas may show restricted diffusion; clinical correlation and molecular data are necessary for prognostication.
  • Failing to recognize the periwinkle sign of coarse calcification as a characteristic feature; this should prompt consideration of ependymoma in the differential diagnosis of parenchymal masses.
  • Misattributing hemorrhagic or calcified foci as tumor enhancement rather than susceptibility artifact on T2*/SWI, potentially leading to overestimation of enhancing tumor volume; always correlate with contrast-enhanced T1 imaging.
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