= in majority benign slow-growing neoplasm of mature well-differentiated ependymal cells lining the ventricles

Incidence: most common in children; 5–9% of all primary CNS neoplasms; 15% of posterior fossa tumors in children; 63% of spinal intramedullary gliomas

Histo: benign aggregates of ependymocytes in form of perivascular pseudorosettes; may have papillary pattern (difficult DDx to choroid plexus papilloma)

Age:

1. supratentorial: at any age (atrium / foramen of Monro)
2. posterior fossa: age peaks at 5 + 34 years; M÷F = 0.8÷1

Associated with: neurofibromatosis

• increased intracranial pressure (90%)

Location:

1. infratentorial: floor of 4^th ventricle (70% of all intracranial ependymomas)
2. conus medullaris: 40–65% of all spinal intramedullary gliomas
3. supratentorial: in frontal >parietal >temporoparietal juxtaventricular region (uncommonly intraventricular), lateral ventricle, 3^rd ventricle

in children: infratentorial÷supratentorial = 7÷3

• small cystic areas in 15–50% (central necrosis)
• fine punctate multifocal calcifications (25–50%)
• intratumoral hemorrhage (10%)
• frequently grows into brain parenchyma with extension to cortical surface (particularly in frontal + parietal lobes)
• may invaginate into ventricles
• expansion frequently through foramen of Luschka into cerebellopontine angle (15%) or through foramen of Magendie into cisterna magna (up to 60%) (CHARACTERISTIC)
• direct invasion of brainstem / cerebellum (30–40%)
• insinuation around blood vessels + cranial nerves
• communicating hydrocephalus (100%) ← protein exudate elaborated by tumor clogging resorption pathways

CT:

• sharply marginated multilobulated iso- / slightly hyperdense 4^th ventricular mass
• thin well-defined low-attenuation halo (= distended effaced 4^th ventricle)
• heterogeneous / moderately uniform enhancement of solid portions (80%)

MR:

• low to intermediate heterogeneous SI on T1WI
• hypointense tumor margins on T1WI + T2WI in 64% (= hemosiderin deposits)
• foci of high-signal intensity on T2WI (= necrotic areas / cysts) + low signal intensity (= calcification / hemorrhage)
• fluid-fluid level within cysts
• homogeneous Gd-DTPA enhancement of tumor

Cx: subarachnoid dissemination via CSF (rare) (DDx: malignant ependymoma, ependymoblastoma)

Rx: surgery (difficult to resect due to adherence to surrounding brain) + radiation (partially radiosensitive) + chemotherapy

DDx of cerebellar ependymoma:

1. Astrocytoma (hypodense, displaces 4^th ventricle from midline, cystic lucency, intramedullary)
2. Medulloblastoma (hyperdense, calcifications in only 10%)
3. Trapped 4^th ventricle (no contrast enhancement)