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: Subependymomas; Subependymal astrocytoma; Subependymal astrocytomas

Overview

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

Pathophysiology

Pathogenesis

• Subependymoma arises from subependymal glial cells, although it can also arise from astrocytes from the subependymal plate, ependymal cells, and mixed ependymal and astrocytic cells.

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
• On gross pathology, subependymoma is characterized by a small, white to grey, firm, well circumscribed, solid, avascular mass attached to the ventricular wall by a narrow pedicle.

Microscopic Pathology

• On microscopic histopathological analysis, subependymoma is characterized by microcystic spaces and bland appearing cells without appreciable nuclear atypia or mitoses. The nuclei tend to form clusters. No high grade features (no mitoses, Ki-67 / MIBI index > 1.5%, no necrosis) are present. Loose pseudorosettes are observed.

Immunohistochemistry

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

Differentiating Subependymoma 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

Prevalence

• Subependymoma constitutes approximately 1% of all intracranial tumors.

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

• Obstructive hydrocephalus is a common complication of subependymoma.

Prognosis

• The prognosis of subependymoma is excellent wih complete excision of the tumor.

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 subependymoma. On CT scan, subependymoma is characterized by:

• Iso- and hypodense intraventricular mass
• Positive mass effect
• No enhancement
• If large, it may have cystic or even calcific components
• No vasogenic edema

MRI

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

MRI component	Findings
T1 weighted image	Iso - hypointense compared to white matter Homogeneous but may be heterogeneous in larger lesions
T2 weighted image	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)
T1 weighted image with contrast	Little or no enhancement

Biopsy

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

Treatment

• The predominant therapy for subependymoma is surgical resection.