Infratentorial Ependymoma

KEY FACTS

Terminology

• Posterior fossa ependymoma (PF-EPN)

Imaging

• Ependymoma can occur anywhere in neuraxis

• Most common site: Posterior fossa (2/3 of cases)

  • Lobulated mass in body/inferior 4th ventricle

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      Soft or “plastic” tumor

      • □

        Accommodates to shape of ventricle

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        Squeezes through foramen of Magendie into cisterna magna

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        ± extension through foramina of Luschka into cerebellopontine angle cisterns

• NECT

  • Ca++ common (50%)

  • ± cysts, hemorrhage

  • Obstructive hydrocephalus common

• MR

  • Variable enhancement; usually does not restrict on DWI

Top Differential Diagnoses

• Most common DDx in children

  • Primitive neuroectodermal tumor-medulloblastoma (PNET-MB)

  • Cerebellar pilocytic astrocytoma

  • Atypical teratoid-rhabdoid tumor

• Most common DDx in adults

  • Metastasis

  • Choroid plexus papilloma

  • Hemangioblastoma

Pathology

• 3 posterior fossa ependymoma molecular subtypes

  • Posterior fossa ependymoma subtype A (PF-EPN-A)

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      Most common (50%)

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      Predominately infants

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      Poor prognosis

  • PF-EPN-B

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      10% of PF-EPNs

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      Older children, adults

    • –

      Better prognosis

  • Subependymoma (PF-SE)

Clinical Issues

• Signs of increased intracranial pressure

• 3-17% cerebrospinal fluid dissemination

Diagnostic Checklist

• Much less common than primitive neuroectodermal tumor-medulloblastoma or pilocytic astrocytoma

• “Plastic” tumor that expands 4th v, squeezes extends through outlet foramina

• Indistinct tumor/brain interface?

  • With floor of 4th ventricle = ependymoma

  • With roof of 4th ventricle = PNET-MB

TERMINOLOGY

IMAGING