Subependymoma

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Sujit Routray, M.D. [2]

Synonyms and keywords: Protoplasmic astrocytomas; Diffuse astrocytoma; Low grade astrocytoma

Overview

Subependymoma is a type of the brain tumor; specifically, it is a rare form of ependymal tumor. Subependymoma is a benign (WHO grade I) tumor, which is slow growing and non-invasive.

Pathophysiology

Gross Pathology

• Subependymoma is most commonly seen in the fourth ventricle, but can arise anywhere where there is ependyma. The distribution in the ventricular system is as follows:
  • Fourth ventricle: 50-60%
  • Lateral ventricles (usually frontal horns): 30-40%
  • Third ventricle: rare
  • Central canal of the spinal cord: rare

Microscopic Pathology

• On microscopic histopathological analysis, subpendymoma is characterized by microcystic spaces and bland appearing cells without appreciable nuclear atypia or mitoses. The nuclei tend to form clusters.

Immunohistochemistry

• Subependymoma is demonstrated by positivity to tumor marker such as GFAP.

Differentiating Protoplasmic Astrocytoma from other Diseases

• Subependymoma must be differentiated from:
  • Neoplasms of the ventri­cular wall and septum pellucidum
    • Ependymoma
    • Central neurocytoma
    • Subependymal giant cell astrocytoma
  • Neoplasms of the choroid plexus
    • Choroid plexus papilloma and carcinoma
  • Others
    • Intraventricular meningioma
    • Intraventricular metastasis
    • Oligodendroglioma
    • Pilocytic astrocytoma
    • Glioblastoma multiforme
    • Medulloblastoma
    • Intraventricular teratoma

Epidemiology and Demographics

Age

• Subependymoma is a rare disease that tends to affect middle-aged adults and the elderly population (typically 5th to 6th decades).

Gender

• Males are more commonly affected with subependymoma than females. The male to female ratio is approximately 2.3 to 1.

Natural History, Complications and Prognosis

Natural History

• If left untreated, patients with subependymoma may progress to develop seizures and obstructive hydrocephalus.
• Subependymoma is a slow growing tumor with an indolent course.

Complications

• Common complication of subependymoma include:

• Obstructive hydrocephalus

History and Symptoms

History

• When evaluating a patient for subependymoma, you should take a detailed history of the presenting symptom (onset, duration, and progression), other associated symptoms, and a thorough family and past medical history review.

Symptoms

• Typically patients of subependymoma are asymptomatic and small lesions are discovered incidentally.
• Symptoms of subependymoma include:
  • Symptoms due to elevated intracranial pressure
    • Headache
    • Nausea
    • Vomiting
  • Neurological symptoms
    • Seizures
    • Sudden loss of awareness
    • Transient loss of memory

CT

• Head CT scan is helpful in the diagnosis of protoplasmic astrocytoma. On CT scan, protoplasmic astrocytoma is characterized by:

• Hypodense mass
• Positive mass effect
• No enhancement
• Cystic or fluid attenuation, due to the aforementioned prominent mucinous microcystic component

MRI

• Brain MRI is helpful in the diagnosis of subependymnoma. On MRI, subependymoma is characterized by:

MRI component	Findings
T1	Iso - hypointense compared to white matter Homogeneous but may be heterogeneous in larger lesions
T2	Hyperintense compared to adjacent white and grey matter Heterogeneity may be seen in larger lesions, with susceptibility related signal drop out due to calcifications No adjacent parenchymal edema (as no brain invasion is present)
Fluid-attenuated inversion recovery (FLAIR)	Large areas of T2 hyperintensity suppress on FLAIR These are not macrocystic, but rather represent the areas with abundant microcystic change)
T1 with contrast	Little or no enhancement

Other Imaging Findings

Magnetic Resonance Spectroscopy

• MR spectroscopy may be helpful in the diagnosis of protoplasmic astrocytoma, which demonstrates elevated choline/creatine ratio.

Magnetic Resonance Perfusion

• MR perfusion may be helpful in the diagnosis of protoplasmic astrocytoma, which demonstrates no elevation of relative cerebral blood volume (rCBV).

Electroencephalogram

• Electroencephalogram (EEG) is performed in cases of protoplasmic astrocytoma to record the continuous electrical activity of the brain and locate the seizure activity.

Biopsy

• Biopsy of the protoplasmic astrocytoma tumor, taken through a needle during a simple surgical procedure, helps to confirm the diagnosis.

Treatment

• The treatment of protoplasmic astrocytoma depends on the clinical presentation, tumor size, and location.

• Surgery: The predominant therapy for protoplasmic astrocytoma is surgical resection.
• Radiotherapy: Radiotherapy may be used in protoplasmic astrocytoma post-operatively or at the time of recurrence or progression.
• Chemotherapy: Chemotherapy may have a role in recurrent and de-differentiated tumors.

Treatment of protoplasmic astrocytoma

Surgery

Radiotherapy

Chemotherapy