Frontoethmoidal encephaloceles, a study of their pathogenesis.

A prospective clinical study of 30 patients with frontoethmoidal encephaloceles was performed in order to find support for a proposed theory concerning its pathogenesis, based on a previously performed embryological study and relevant findings in the literature. According to this proposed theory the pathogenesis of frontoethmoidal encephaloceles is primarily based on a disturbance in separation of neural and surface ectoderm at the site of final closure of the rostral neuropore during the final phase of neurulation in the 4th week of gestation. An insufficient occurrence of apoptosis might cause this disturbance in separation. The nonseparation of neural and surface ectoderm will result secondarily in a midline mesodermal defect. This mesodermal defect is reflected in the median skull defect at the site of the foramen caecum. The outgrowth of the nasal septum with the concomitant forward displacement of epidermis (surface ectoderm) and attached brain tissue (neural ectoderm) may act as herniating force. The patient study consisted of a clinical investigation, radiological investigations (X skull and CT scans), and surgical treatment in order to obtain specimens which were examined histologically. Clinical findings supportive of the proposed hypothesis are (1) the consistency in the location of the internal skull defect, (2) the close relationship between epidermal structures and glial tissue in 15 out of 29 specimens, and (3) the presence of a normally developed nose in combination with interorbital hypertelorism in all patients. A discussion of these findings is presented with special reference to the embryological aspects.