Ethmoid pneumatization and a large frontal-orbital-ethmoid mucocele

Frontal-orbital-ethmoid mucocele is a slow-growing retention cyst of the fronto-ethmoid complex secondary to blockage of the sinus ostia. It may produce significant disfigurement of the periorbital region necessitating surgical intervention. Prior to surgery, it is imperative to study the mucocele's extent through the variable patterns of ethmoid pneumatization as evident from clinical, imaging (computed tomogram) and endoscopic evaluation. This is illustrated in a case study of a 41-year-old woman presenting with fullness below the right eyebrow, progressive proptosis, and gaze restriction. The provisional diagnosis of frontal-orbital-ethmoid muco(pyo)cele was confirmed at endoscopic surgery, when it was drained and marsupialized through ethmoidectomy and frontal sinusotomy. Understanding the relationship of an enlarging mucocele with the inconsistent pattern of ethmoid pneumatization is the primary determinant for an uneventful and complete surgery, and to minimize recurrence. The gradually expanding mucocele occupies the path of least resistance and encroaches into the available spaces of ethmoid labyrinth, distorting key anatomic landmarks and making surgical intervention potentially challenging. Thus, preoperative imaging corroborated with naso-endoscopy is of paramount importance to trace the lesion along ethmoid pneumatization, and determine the relative positions of structures vulnerable to surgery. This often requires a comparative study of the contralateral side because the mucocele generally obscures the pneumatization pattern and vital landmarks on its side. The present imaging tutorial studies the extent of a large frontal-orbital-ethmoid mucocele through interpretation of multiplanar computed tomography cuts, keeping in mind the unpredictable nature of its expansion as a function of the highly individualistic ethmoid pneumatization.