Epidemiology of Subependymal Giant Cell Astrocytomas in Children
Incidence and Prevalence
5–15% of patients with TSC have SEGAs: SEGA is a well-known manifestation of tuberous sclerosis and affects 5–15% of patients with this condition. In a large series of TSC (28) SEGAs were found in 6.1% of 345 patients, but the true incidence of SEGA in TSC may eventually be found higher because some patients may harbor a tumor that does not yet produce symptoms. SEGAs accounted for only 1.4% of 733 pediatric brain neoplasms in one series (29).
Prevalence of 1 in 100,000: The prevalence of TSC is roughly 1 in 10,000 in the US, so the calculated prevalence of SEGAs should be around 1 in 100,000 (25).
Presence of a SEGA equals TSC: SEGAs without any other TSC manifestation are usually considered to be an initial manifestation of TSC with somatic mosaicism or forme fruste.
Typically found during childhood: SEGAs occur in young patients with TSC and generally display slow growth. Although SEGAs are usually found in patients under 20 years of age, occasionally they are first identified in older patients (3, 5, 8, 10, 22, 28). Young children who have TSC may be offered screening because of the increased risk of developing SEGA.
Slight male > female: Clinical series show a mild male predominance, with a mean age at surgery of 11 years (5, 7, 8).
No variance in distribution: There is no variance in the incidence as a function of geographic location.
Subependymal nodules: There may be a continuum from subependymal nodules to SEGA, which has been discussed in the literature, and it has been shown that subependymal nodules can transform to SEGAs. Subependymal nodules, however, are much more common. Some characteristics of subependymal nodules predispose to the development of SEGAs, including diameter greater than 5 mm, incomplete calcification, and enhancement by gadolinium. Subependymal nodules with these characteristics have been shown, when near to the foramen of Monro, to have a higher probability of evolving into a tumor, especially when family members have TSC (23).
Relationships to Other Disease States and Syndromes
Tuberous sclerosis: Patients diagnosed with TSC often have brain tumors (tumor = mass, not necessarily neoplasm). SEGA is the least common of the three types, occurring in only 5–15% of cases. In studies based on radiological evidence, SEGAs were found in up to 20% of patients with TSC, generally higher than the proportion found in studies based on histopathological evidence. The other two types of tumors associated with TSC, subependymal nodules and cortical tubers, are hamartomas, benign growths that are more common than SEGAs in patients with TSC. Radiographic evidence shows that 88–95% of patients with TSC have subependymal nodules, whereas SEGA is diagnosed in 2–14% (28).