In Reply .—I believe that there may very well be some confusion over the precise definition of a paranasal sinus pneumocele. As it was defined by Noyek, Zizmor, Bryce, Schaffer, Morrison, Tchang, Maber, Vines, Bonstelle, Floyd, Meyers, Burtschi, Sachdev, Biller and myself, 1 there was no localized sinus wall defect other than a postulated trap-valve mechanism at the sinus ostium. In none of these cases was there a history of trauma, surgery, infection, or tumor. The sinus recesses were expanded and the sinus walls were in part thinned secondary to pressure expansion of the sinus cavity. Three of the six patients had symptoms exacerbated by airplane rides and thus they clearly had a demonstrable relationship to air pressure. This differs from the condition of pneumosinus dilatans, which is also well described and has involved several sinuses at once. In these cases, the sinus walls were normal and not thinned and there was