Importance: Frontoethmoidal encephalomeningocele (FEEM) is a congenital anomaly with a skull base defect at the foramen caecum and a protrusion of meninges and brain tissue through an external defect on the face. The external defect was classified to nasofrontal, nasoethmoidal, naso-orbital, combined, and abortive type.
Objective: The aim of our study was to present a newly discovered internasal type (IN) of FEEM.
Design, setting, participants: Ninety-six FEEM patients' preoperative 3-dimensional computer tomography scans were studied in the Department of Surgery, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand followed by treatment from 2006 to 2016.
Findings: Sixteen patients had an external bony defect between the nasal bone that could not be classified in any previous classification. We suggest a new type of FEEM called "IN." The bony defect of this IN can be located on the upper nasal bone (4 cases), middle nasal bone (5 cases), or combined with naso-orbital type (7 cases) counted in the combined type.
Conclusions and relevance: Our study presents a newly discovered IN of FEEM. This IN can cause hypertelorism when the nasofrontal type could not. Preoperative 3-dimensional computer tomography scans are very helpful for surgical planning.