Subependymal Giant Cell Astrocytoma

Subependymal giant cell astrocytomas (SEGAs) are the most common cerebral neoplasm in patients with tuberous sclerosis, being found in up to 15% of patients. They are thought to arise from subependymal nodules in the ventricular wall.

Subependymal giant cell astrocytomas are almost always found near the foramen of Monro, are slowly-growing, and are WHO grade I tumors. The majority of cases occur during the first two decades of life.

CT reveals a heterogeneously low to iso attenuation lesion with or without calcifications in the region of the foramen of Monro with avid and heterogeneous enhancement. T1- and T2-weighted images reveal the mass to be hypo- to isointense to gray matter. The mass is heterogeneously hyperintense on FLAIR images. T2^* images may show punctate hypointensities corresponding to calcium. Similar to CT, there is avid enhancement.

Differential considerations include:

• Subependymoma: Most common location is the lower fourth ventricle and the frontal horns of the lateral ventricles. Found in older patients. Typically none to mild enhancement, which is more commonly seen in fourth ventricle subependymomas
• Central neurocytoma: May also arise near foramen of Monro or septum pellucidum. Found in young adults (SEGAs typically occur during the first two decades). Look for necrosis and cyst formation.
• Choroid plexus tumors: For example, papillomas or carcinomas. These demonstrate avid enhancement and may have seeding via cerebrospinal fluid. The latter is not seen with subependymal giant cell astrocytoma. In addition, carcinomas may invade the brain parenchyma
• Astrocytoma: May arise from the fornices of the septum pellucidum or the medial basal ganglia. Enhancement is variable and calcifications are rare.
• Germinoma: These often arise near the third ventricle, seed via the cerebrospinal fluid.

References

• Koeller KK, Sandberg GD. Cerebral intraventricular neoplasms: radiologic-pathologic correlation. Radiographics. 2002 Nov-Dec;22(6):1473-505.
• Hedlund GL. Subependymal Giant Cell Astrocytoma. STATdx. Amirsys, Inc.