This article presents a rare and interesting case of isolated mucocoele of haller cell (Infraorbital ethmoid cell) presenting with extensive proptosis and visual disturbances in the absence of facial pain and symptoms of sinusitis. CT PNS with contrast revealed a heterogeneous non enhancing soft tissue lesion in the roof of the left maxillary sinus/floor of left orbit with severe thinning of the floor of the left orbit and not filling the maxillary sinus. This is the fourth reported case of isolated mucocoele of haller cell and the first case to present with significant proptosis and visual disturbances. Treatment opted was endonasal endoscopic surgical removal and restoring the appropriate orbital function and cosmesis. Early diagnosis and prompt surgical management can help avoid dangerous visual complications in these kind of rare presentations.

Keywords: Maxillary sinus mucocele; Proptosis; Haller cell mucocele; Infraorbital ethmoidal cell; Haller cell.