Subependymal giant cell astrocytoma

Subependymal giant cell astrocytomas (SGCAs or alternatively SEGAs) are benign tumours (WHO grade I), seen almost exclusively in young patients with tuberous sclerosis. They can be either asymptomatic or symptomatic due obstructive hydrocephalus, surgery treatment is often curative. 

On imaging, they classically appear as an intraventricular mass near the foramen of Monro, larger than 1 cm, showing calcifications, heterogenous MRI signal, and marked contrast enhancement. 

Epidemiology

Subependymal giant cell tumours are a well-known manifestation of tuberous sclerosis, affecting 5-15% of patients with the condition ⁸. They are principally diagnosed in patients under 20 years of age, only occasionally found in older individuals.  

Clinical presentation

Subependymal giant cell tumours are often asymptomatic. When symptoms occur, they are usually a result of obstructive hydrocephalus because of mass effect around the ventricular system at the level of the interventricular foramen (of Monro).

Pathology

Subependymal giant cell astrocytomas are considered WHO grade I lesions in the current (2016) WHO classification of CNS tumours ⁸. 

Macroscopic appearance

These tumours are multilobulated well-circumscribed tumours arising from the wall of the lateral ventricles near the foramen of Monro. They frequently contain cysts and calcification ⁸. 

Microscopic appearance

Subependymal giant cell astrocytomas are believed to arise from a subependymal nodule present in the ventricular wall in a patient with tuberous sclerosis, although this has yet to be categorically established ^4,8.

Histologically, subependymal nodules and subependymal giant cell tumours are essentially indistinguishable, and the distinction lies in the potential of a SEGA for growth and mass effect ⁵. The cells that appear astrocytic, usually resemble gemistocytes; large polygonal cells with prominent eosinophilic cytoplasm. A smaller number of ganglionic appearing giant pyramidal-like cells ⁸. 

The ependymal lining over SGCAs remains intact making CSF seeding highly unlikely ⁷.

Current evidence suggests that they are of a mixed neuronal and glial lineage, although they continue to be classified as astrocytomas ⁵. 

Immunophenotype

Immunohistochemical examination of these tumours demonstrates the following reactivity ⁸: 

• S100: positive
• GFAP: variable
• synaptophysin: variable
• CD34: negative
• additional variable and focal reactivity: class III beta-tubulin, NeuN, SOX2

Radiographic features

The foramen of Monro is the classic location, and the tumour arises when a subependymal nodule transforms into SGCA over a period of time.

CT

• typically appears as an intraventricular mass near the foramen of Monro
• they are usually larger than 1 cm
• lesions are iso- or slightly hypoattenuating to grey matter 
• calcification is common and haemorrhage is possible
• accompanying hydrocephalus may be present
• often shows marked contrast enhancement (subependymal nodules also enhance)

MRI

• T1: heterogeneous and hypo- to isointense to grey matter 
• T2: heterogeneous and hyperintense to grey matter; calcified components can be hypointense
• T1 C+ (Gd): can show marked enhancement

Treatment and prognosis

Young children who have tuberous sclerosis may be offered to screen because of the increased risk of developing subependymal giant cell astrocytomas.

The main treatment is surgery, which is indicated if a tumour is symptomatic, or growth is demonstrated on MRI. Surgery is often curative. Oral sirolimus has also been trialled ³.

Differential diagnosis

In the clinical context of known tuberous sclerosis, the appearance is virtually pathognomonic, and the main differential is between a subependymal nodule and SGCA. Serial imaging is most helpful here, as growth implies SGCA.

Other general considerations include:

• central neurocytoma
• choroid plexus papilloma (CPP)
• choroid plexus carcinoma (CPC)

See also

• differential for intraventricular tumours
• intraventricular masses - an approach