Recently at the Royal Victoria Hospital a mucocele of the frontal sinus was operated on, and the sinus was found to be empty. This was the second such case in the past two years, and the finding has aroused considerable interest. In the better known reviews on the subject of mucocele no reference has been made to any similar finding. The records of the Royal Victoria Hospital for the past twenty years include 11 cases in which mucocele was diagnosed. In 3 cases the ethmoid sinus alone was involved; in 1 case the diagnosis is doubtful because no operation was performed; in 2 cases the finding was pyocele, whereas the 5 cases to be reported in this article fulfil the requirements generally accepted for a diagnosis of mucocele.
A complete survey of the literature has not been attempted. Among the more comprehensive reviews on this subject which we consulted but