Anterior Transorbital Meningoencephaloceles: A Defect in the Pars Orbitalis of the Frontal Bone

Anterior encephaloceles have been extensively reported and classified. Most have occurred at the juncture of the anterior part of the sphenoid with the pars orbitalis of the frontal bone. This corresponds to the region of either the crista galli or the cribriform plate. Encephaloceles in this location are seen in the region of the glabella, medial orbit, or in the nasal cavity or nasopharnyx and have been described in detail [1]. Posterior orbital defects also occur and appear in conjunction with partial agenesis of the greater wing of the sphenoid bone, most frequently associated with neurofibromatosis [2, 3]. A more lateral anterior defect in the roof of the orbit involving the pars orbital is of the frontal bone is extremely rare, and to our knowledge only one case has been briefly mentioned in the literature [4]. This form of anterior encephalocele has not been included in the comprehensive classification formulated by Suwanwela and Suwanwela [5]. We recently encountered two patients with congenital defects in the anterior part of the pars orbitalis of the frontal bone. This structure, derived from membranous bone, forms most of the roof of the orbit and the floor of the anterior fossa. On the basis of the embryogenesis of the orbital roof defects and the radiologic and gross anatomic features in these patients, we believe that this lesion should be considered an additional although rare form of anterior encephalocele. Thorough radiologic evaluation , including tomography, is necessary for correct diagnosis and for planning appropriate surgical management.