Morphologic study of 120 skull base defects in frontoethmoidal encephalomeningoceles.

Frontoethmoidal encephalomeningocele is a herniation of brain and meninges through a congenital bone defect in the skull at the junction of the frontal and ethmoidal bones. From 1992 to 1996, 120 cases of frontoethmoidal encephalomeningocele were seen in our institutes, and the morphology of the skull defects was studied. The patients underwent thorough physical examinations and radiographic investigations including spiral three-dimensional computed tomography scan. Together with intraoperative findings, we found more types of the defects than previously reported. Our findings were categorized into the following types: type I, a single external opening between frontal, nasal, ethmoidal, and orbital bones; type IA, opening is limited between two bones of the area; type IB, opening is extended transversely or cephalad to involve adjacent structures; type II, multiple external openings in the region; type IIA, all of the openings are limited types; type IIB, one or more of the openings is/are extended type(s) that involve adjacent structures. There are 14 subtypes in these two types: 3 in type IA, 6 in type IB, 3 in type IIA, and 2 in type IIB. This classification is helpful in understanding the herniation pathway and in keeping informative records.