Subependymal giant cell astrocytoma

Subependymal giant cell astrocytomas (SEGA)  are benign tumours, seen almost exclusively in tuberous sclerosis (TS). 

Epidemiology

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

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.  Common sites of obstruction include the interventricular foramen (of Monro), the cerebral aqueduct (of Sylvius) and the third or fourth ventricles.

Pathology

Subependymal giant cell tumours  are believed to arise from a subependymal nodule present in the ventricular wall in a patient with TS ⁴.  Histologically, subependymal nodules and subependymal giant cell tumours are indistinguishable, and the distinction lies in the potential of a subependymal giant cell tumour for growth and mass effect ⁵.

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

Current evidence suggests that SGCAs are of a mixed neuronal and glial lineage, although they continue to be classified as astrocytomas ⁵. They are considered WHO grade I lesions (see WHO classification of CNS tumours). 

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

Treatment and prognosis

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

The main treatment is surgery, which is indicated if the tumour is symptomatic, or growth is demontrated on MRI. Surgery is often curative. Oral Rapamycin™ (sirolimus) has also been trialled ³.

Differential diagnosis

In the clinical context of known TS, 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 SCGA.

Other general considerations include:

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

See also

• differential for intraventricular tumours
• intraventricular masses - an approach