Subependymoma

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Mohamadmostafa Jahansouz M.D.[2]Sujit Routray, M.D. [3]

Historical Perspective

• Subependymomas was first discovered by Ilya Mark Scheinker a Russian physician in 1945.

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 (mitoses, Ki-67 / MIBI index > 1.5%, necrosis) are present. Loose pseudorosettes are observed.

Immunohistochemistry

• Subependymoma is demonstrated by positivity to tumor marker such as GFAP.
• Also mixed populations of cells may be variably positive for:
  • Olig2
  • NHERF1
  • Sox2
  • CD44

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

Frequency and incidence

• The frequency of asymptomatic subependymomas was 0.4% in 1,000 serial routine necropsies and 0.7% in symptomatic subependymomas from 1,000 serial surgical specimens of intracranial neoplasms.
• The incidence of subependymoma was estimated to be 0.7 incidence cases per 100,000 of patients with pathologically proven intracranial neoplasms.

Age

• Patients of all age groups may develop subependymoma.

• 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.

Risk Factors

• The risk factors in the development of subependymoma are not well defined.

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 with complete excision of the tumor.

• The majority of patients with [disease name] remain asymptomatic for [duration/years].
• Early clinical features include [manifestation 1], [manifestation 2], and [manifestation 3].
• If left untreated, [#%] of patients with [disease name] may progress to develop [manifestation 1], [manifestation 2], and [manifestation 3].
• Common complications of [disease name] include [complication 1], [complication 2], and [complication 3].
• Prognosis is generally [excellent/good/poor], and the [1/5/10­year mortality/survival rate] of patients with [disease name] is approximately [#%].

Diagnosis

Diagnostic Criteria

• The diagnosis of [disease name] is made when at least [number] of the following [number] diagnostic criteria are met:

• [criterion 1]
• [criterion 2]
• [criterion 3]
• [criterion 4]

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

Physical Examination

• Patients with [disease name] usually appear [general appearance].
• Physical examination may be remarkable for:

• [finding 1]
• [finding 2]
• [finding 3]
• [finding 4]
• [finding 5]
• [finding 6]

Laboratory Findings

• There are no specific laboratory findings associated with [disease name].

• A [positive/negative] [test name] is diagnostic of [disease name].
• An [elevated/reduced] concentration of [serum/blood/urinary/CSF/other] [lab test] is diagnostic of [disease name].
• Other laboratory findings consistent with the diagnosis of [disease name] include [abnormal test 1], [abnormal test 2], and [abnormal test 3].

Imaging Findings

• 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

Other Diagnostic Studies

• [Disease name] may also be diagnosed using [diagnostic study name].
• Findings on [diagnostic study name] include [finding 1], [finding 2], and [finding 3].

Treatment

Medical Therapy

• There is no treatment for [disease name]; the mainstay of therapy is supportive care.

• The mainstay of therapy for [disease name] is [medical therapy 1] and [medical therapy 2].
• [Medical therapy 1] acts by [mechanism of action 1].
• Response to [medical therapy 1] can be monitored with [test/physical finding/imaging] every [frequency/duration].

Surgery

• Surgery is the mainstay of therapy for [disease name].
• [Surgical procedure] in conjunction with [chemotherapy/radiation] is the most common approach to the treatment of [disease name].
• [Surgical procedure] can only be performed for patients with [disease stage] [disease name].

Prevention

• There are no primary preventive measures available for [disease name].

• Effective measures for the primary prevention of [disease name] include [measure1], [measure2], and [measure3].

• Once diagnosed and successfully treated, patients with [disease name] are followed-up every [duration]. Follow-up testing includes [test 1], [test 2], and [test 3].

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.