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Ependymomas and Subependymoma


Ependymoma

Definition

  • A slowly growing tumor generally arising in the central region of the spinal cord in adults or a ventricle in children and adults

  • Most correspond to World Health Organization (WHO) Grade II; anaplastic ependymomas are WHO Grade III

Clinical Features

Epidemiology

  • Comprise 5% to 7% of all CNS tumors; no gender predilection

  • Bimodal age distribution with first peak in childhood (2 to 16 years) and second peak at 30 to 40 years

  • Infratentorial tumors predominate in children; typically arise from floor of the fourth ventricle

  • Third most common posterior fossa tumor in children

  • Supratentorial tumors have no age predilection

  • Ependymomas are the most common intra-axial spinal cord tumors in adults

Presentation

  • Obstructive hydrocephalus with fourth ventricular tumors; headache, nausea, and vomiting; may have ataxia or visual disturbances

  • Focal neurologic deficits, seizures, and intracranial hypertension with supratentorial lesions

  • Spinal cord lesions present with motor and sensory deficits

Prognosis and Treatment

  • 60% to 70% overall 5-year survival

  • Best prognosis with spinal cord tumors of adults; usually treated with surgery

  • Recurrences common in children with fourth ventricular tumors; gross total resection

Imaging Characteristics

  • Well-demarcated masses with variable enhancement on MRI

  • Hemorrhage and calcifications in some cases

Pathology

Gross

  • Soft pink-tan, well-demarcated tumor

  • Occasional hemorrhage or necrosis

  • Fourth-ventricular tumors may extend out of foramina of Luschka into subarachnoid space

Histology

  • Uniform appearance of tumor cells with round to oval nuclei having salt-and-pepper–like chromatin

  • Perivascular pseudorosettes composed of radially arranged, tapering cell processes extending to intratumoral blood vessels

  • Ependymal rosettes or ependymal canal-like structures with central lumen are less common

  • Tumor blood vessels occasionally hyalinized

  • Papillary ependymomas: rare variant with uniform epithelial surfaces along CSF exposures with papillary or pseudopapillary architecture

  • Clear cell ependymomas: mimic of oligodendroglioma but has well-demarcated border with adjacent brain; usually located in cerebral hemisphere of young adults; may behave more aggressively

  • Tanycytic ependymomas; usually arise in the spinal cord as a discrete mass that is well demarcated from the adjacent neural tissue; forms fascicles of highly fibrillated bipolar spindle cells; mimic of diffuse astrocytoma; ependymal rosettes usually absent with only vague pseudorosettes

Immunopathology/Special Stains

  • GFAP is strongly reactive in tapering perivascular cell processes

  • Dotlike epithelial membrane antigen (EMA) reactivity especially along inner lumina of ependymal rosettes

  • CD99 reactive (but nonspecific)

  • Ki-67 (MIB1) labeling typically low (<5%)

Electron Microscopy

  • Cilia (including basal bodies—“blepharoplasts”) and microvilli found along luminal surfaces of ependymal rosettes

  • Zipperlike junctional complexes

  • Deep nuclear invaginations in the clear cell variant

Genetics

  • 30% incidence of aberration involving chromosome 22

  • Associated with neurofibromatosis type 2 involving tumor suppressor NF2 gene

  • NF2 gene is located at 22q12, which is distinct from the 22q mutation found in many incidental ependymomas of the spinal cord

Main Differential Diagnoses

  • Fourth ventricle—child: medulloblastoma, pilocytic astrocytoma, choroid plexus tumor

  • Intra-axial spinal cord—adult: diffuse astrocytoma

  • Supratentorial: central neurocytoma, choroid plexus tumor, astroblastoma

  • Papillary variant: choroid plexus tumor, metastasis

  • Clear cell ependymoma: oligodendroglioma

  • Tanycytic ependymoma of spinal cord: diffuse astrocytoma

Fig 1, Ependymoma. The MRI shows a contrast-enhancing tumor within the cervical spinal cord.

Fig 2, Ependymoma. This contrast-enhancing fourth ventricular tumor focally extends into the foramen of Luschka ( right ).

Fig 3, Ependymoma. Low-magnification view showing a sharp demarcation between the tumor and adjacent neural tissue along the top of the image.

Fig 4, Ependymoma. These tumors display a rather uniform appearance with perivascular pseudorosettes as a distinctive feature that is usually present.

Fig 5, Ependymoma. Some tumors may form ependymal canal-like structures or have ependymal rosettes.

Fig 6, Ependymoma. GFAP immunoreactivity is particularly evident in tapering perivascular tumor cell processes.

Fig 7, Ependymoma. EMA is typically reactive along the luminal borders of ependymal canals ( left ) and rosette-like structures ( right ).

Fig 8, Papillary ependymoma. This variant forms linear epithelial-like surfaces along the border with CSF. Pseudopapillary structures may be seen in other examples.

Fig 9, Clear cell ependymoma. This rare supratentorial variant maintains a sharply circumscribed border with adjacent brain tissue and is an important mimic of oligodendroglioma.

Fig 10, Tanycytic ependymoma. Such tumors show no ependymal rosettes, and perivascular pseudorosettes are subtle findings. This variant is an important mimic of astrocytoma in the spinal cord. Tanycytic ependymomas are typically well demarcated from the adjacent cord.

Anaplastic Ependymoma

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