Subependymoma

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Done

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Gliomas, Glioneuronal Tumors, and Neuronal Tumors

Definition

• Essential:
• Circumscribed glioma with clustering of tumour cell nuclei within expansive, focally microcystic fibrillary matrix AND
• Lack of conspicuous nuclear atypia AND
• Absent or minimal mitotic activity AND (for unresolved lesions)
• DNA methylation profile aligned with subependymoma

Numbers

• 8% of all ependymal tumours

• Rare: 0.51% of all CNS tumours

• Middle age and elderly patients

• Male:female 2.3:1

CNS WHO grading

• Grade 1

Origin

• Mixture of astrocytes and ependymal cells
• Subependymal glia
• Astrocytes of the subependymal plate
• Ependymal cells

Localization

• Intraventricular (mainly)
• 4th ventricle: Most common (60%)
• Lateral ventricle: 30%
• Ventricular wall

• Rare:
• Cerebrum
• 3rd ventricle
• Spinal cord
• Cervical and cervicothoracic intramedullary or extramedullary masses

Histopathology

Macroscopic

• A slow growing

• Exophytic intraventricular glial neoplasm

• A, Subependymoma filling the right lateral ventricle, with displacement of the septum pellucidum to the contralateral hemisphere.
• The tumour is sharply delineated and only focally attached to the ventricular wall;
• The cut surface is greyish-white with some small haemorrhages;
• Note the old cystic infarct in the left corpus caudatum (arrowhead).

• B, Large subependymoma filling the left ventricle and a smaller one in the right ventricle.

• C, Posterior fossa subependymoma in the caudal region of the fourth ventricle. Note the compression of the dorsal medulla (arrowheads).

• D, Third ventricle subependymoma (arrowheads).

Microscopic

• Characterized by clusters of bland to mildly pleomorphic mitotically inactive cells embedded in an abundant fibrillary matrix with fq microcystic change

• Small cultures of uniform nuclei embedded in a dense fibrillary matrix of glial cell processes with occurrence of small cyst

• Can have calcification and haemorrhage

• Occasionally form ependymal pseudo rosettes: cell processes oriented around vessels

• Supratentorial ependymomas do not show chromosome 6 copy number alterations but other locations eg spinal and posterior fossa have chr 6 copy number alterations

• Some tumours have admixed histological features of both subependymoma and ependymoma

• Staining
• GFAP positive
• Unlike ependymomas EMA is rarely expressed in subependymomas

Genetic susceptibility

• Rare but well documented

• Mainly for tumours in 4th ventricle

Clinical presentation

• 50% have symptoms (associated with larger size or specific locations)
• Obs(X) HCP

• Often asymptomatic
• Incidental finding on neuroimaging

Molecular pathology

• Identifiable by methylome studies but further molecular classification does not provide added clinicopathological utility

• No known chromosomal or genetic abnormalities that contribute to its growth

Radiology

• Sharply demarcating nodular masses

• Non-enhancing

• Calcification and haemorrhage may be present

• Intramedullary lesions are eccentrically positioned

• T1/T2: hypo to hyperintense

• Minimal to moderate enhancement

Images

Management

Conservative

• Indicated for
• Older patients
• If the patient is elderly and presents with obstructive hydrocephalus without brain-stem compression from a mass with radiologic appearance consistent with subependymoma, insertion of a ventriculoperitoneal shunt and observation with MRI may be a good alternative to removing the tumor surgically.
• Asymptomatic patients

Surgical

• Indicated
• Symptomatic
• Progressive on imaging.

• Technique
• Location
• Lateral ventricle
• Complete excision and surgical cure can be usually achieved.
• 4th ventricle
• Deliberate subtotal resection to avoid injury to floor
• Respiratory failure from brain-stem manipulation is the most common perioperative cause of death in patients with subependymoma.
• Internal debulking with ultrasonic aspiration or laser, the tumor is gradually folded in on itself and dissected from the surrounding brain.
• Usually a well-defined plane between the tumor and normal brain, but occasionally the tumor will be infiltrative and adherent, presumably due to an ependymal component of the tumor.

Prognosis

• Good prognosis

• Virtually no recurrence if gross total resection

• Residual tumour takes decades to grow

• Assessments of chromosome 19 status and DNA methylation profiling may prove useful in the risk stratification of patients with mixed or morphologically ambiguous lesions

• Occurrence of НЗ p.K28M (K27M) mutation in brainstem gliomas exhibiting subependymoma histology has not been associated with rapidly fatal progression