Oil-on-water: proposed method for intraoperative identification of perilymphatic fistula

The intraoperative diagnosis of a perilymphatic fistula is usually subjective and controversial. Unless there is profuse gushing of fluid, there is no reliable, objective, intraoperative indicator of a perilymphatic fistula. The authors suggest a technique for the real-time determination of the existence and location of a perilymphatic fistula: visualization of clear perilymphatic fluid beneath a layer of mineral oil. Mineral oil is transparent to visible light, hydrophobic, and lighter than perilymphatic fluid. The oil traps the aqueous fluid, and tends to keep it contained in a droplet. With standard otomicroscopic viewing, a droplet of less than 1 microL of fluid is readily visible through the oil. In vitro temporal bone studies showing the utility and objectivity of identifying the aqueous fluid in the mesotympanum are reported. Mineral oil floats on saline and is readily removed with suction-irrigation techniques. The authors consider the oil-on-water technique to increase the resolution of identifying minute aqueous droplets and recommend in vivo study in patients.