Subependymoma

# Historical Perspective
Subependymoma was first discovered by Ilya Mark Scheinker, a Russian physician, in 1945.

# Classification
There is no established system for the classification of subependymoma.

# 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 it 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 the following features:
- 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 characterized by positive tumor marker GFAP. Mixed populations of cells may be variably positive for:
- Olig2
- NHERF1
- Sox2
- CD44

# Causes
The cause of the development of subependymoma has not been identified.

# 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
- Ependymoma
- Central neurocytoma
- Subependymal giant cell astrocytoma
- Neoplasms of the choroid plexus
Choroid plexus papilloma and carcinoma
- Choroid plexus papilloma and carcinoma
- Others
Intraventricular meningioma
Intraventricular metastasis
Oligodendroglioma
Pilocytic astrocytoma
Glioblastoma multiforme
Medulloblastoma
Intraventricular teratoma
- 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 cases per 100,000 individuals 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 in the 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
- If left untreated, patients with subependymoma may progress to develop seizures and obstructive hydrocephalus.
- Subependymoma is a slow-growing tumor with an indolent course.
- Obstructive hydrocephalus is a common complication of subependymoma.
- The prognosis of subependymoma is excellent with complete excision of the tumor.
- Common complications of subependymoma are hydrocephalus and focal neurological deficits due to mass effect.

# Diagnosis

## 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
- Symptoms due to elevated intracranial pressure
Headache
Nausea
Vomiting
- Headache
- Nausea
- Vomiting
- Neurological symptoms
Seizures
Sudden loss of awareness
Transient loss of memory
- Seizures
- Sudden loss of awareness
- Transient loss of memory

## Physical Examination
- Patients with subependymoma usually appear normal.
- Physical examination may be remarkable for:
- Abnormal pupillary reflex
- Visual field defects
- Gait changes
- Bilateral Babinski sign
- Depressed Glasgow coma score (GCS)
- Decreased muscle strength
- Decreased deep tendon reflexes
- Sensation defects
- Hearing problems and abnormal Rinne and Weber tests

## Laboratory Findings
There are no specific laboratory findings associated with subependymoma.

## Electrocardiogram
There are no ECG findings associated with subependymoma.

## X-ray
There are no x-ray findings associated with subependymoma.

## Echocardiography or Ultrasound
There are no echocardiography/ultrasound findings associated with sybependymoma.

## CT scan
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:

## Other Imaging Findings
There are no other imaging findings associated with subependymoma.

## Other Diagnostic Studies
There are no other diagnostic studies associated with subependymoma.

## Medical Therapy
There is no medical therapy available for the treatment of subependymoma.

## Surgery
Surgery is the mainstay of therapy for subependymoma. Incidental intraventricular subependymoma can be managed conservatively through MRI surveillance. Surgical resection is indicated for:
- Symptomatic tumors
- Tumors without a clear imaging diagnosis

## Primary Prevention
There are no established measures for the secondary prevention of subependymoma.

## Secondary Prevention
There are no established measures for the primary prevention of subependymoma.