Nonunited ossification center of the presphenoid bone: pseudomeningioma.

Three patients are described; in two of them initial plain skull films at an outside institution were interpreted as demonstrating an anterior clinoid meningioma. Evaluation of these films along with further study of the skull base with complex motion tomography demonstrated a separate and well corticated bony structure posterior and superior to each anterior clinoid in all three cases. After review of the developmental anatomy of this region, it was concluded that these bone centers represent failure of the posterior accessory centers of the presphenoid to fuse with the orbitosphenoid. The features of these nonunited centers appear to be characteristic and should allow distinction of this developmental anomaly from a pathologic process.