Population-based analysis of sporadic and type 2 neurofibromatosis-associated meningiomas and schwannomas.

OBJECTIVE: To estimate the incidence of meningiomatosis and schwannomatosis, and their familial occurrences and relation to type 2 neurofibromatosis (NF2) in a well-defined population.
METHODS: Patients with histologically verified intracranial, spinal, or peripheral schwannomas or meningiomas, who were residents of the Helsinki University Hospital catchment area (population, 1,713,000) from January 1, 1985, to December 31, 1995, were included in the study. The Population Register Center was used to identify relatives of all the patients, and their data were linked further to the Finnish Cancer Registry to find NF2-related tumors. Detailed pedigrees were constructed for the patients with NF2, schwannomatosis, meningiomatosis, patients with relatives with histologically verified schwannomas or meningiomas, and patients younger than 25 years of age at the time of diagnosis.
RESULTS: Approximately 3% (12 of 455) of the schwannoma patients had multiple schwannomas in association with NF2, and 2% (11 of 455) had schwannomatosis without NF2. Two of the patients with schwannomatosis (2 of 11) had familial schwannomatosis. Approximately 1% (7 of 823) of the patients with meningioma had multiple meningiomas in association with NF2, and 4% (29 of 823) had meningiomatosis without NF2. No families with meningiomatosis were found among the 823 patients with meningioma studied. The birth occurrence of NF2 was 1 in 87,410.
CONCLUSIONS: The current diagnostic criteria of type 2 neurofibromatosis (NF2) seem valid because NF2 patients were differentiated rather easily from patients with sporadic schwannomatosis and meningiomatosis. Familial meningiomatosis, if it truly exists, is very rare, and familial schwannomatosis is uncommon.