VENTILATION SCINTIGRAPHY OF THE MIDDLE-EAR

In this study, an attempt was made to administer radioactive gas into the tympanic cavity to measure initial gas trappings as well as cleara nce from the middle ear to evaluate eustachian tube function. Methods: Twenty-eight patients were administered 50 MBq Xe-133 gas. Three diff erent methods for gas application were tested: (a) direct injection th rough a tympanostomy tube in two patients, (b) administration through a nasopharyngeal catheter combined with Valsalva maneuvers in six subj ects without middle ear dysfunction and (c) insufflation into the phar yngeal space through a nose olive performed in 12 patients with normal eustachian tube function and in eight patients with one-sided tube dy sfunction. Results: All three approaches were successful in visualizin g middle ear ventilation, demonstrating tracer trapping within the tym panic cavities in 20 of 28 patients. Semiquantitative evaluation by re gion of interest techniques revealed a left-to-right uptake ratio of 4 8.4%-51.6% in 13 patients without tube dysfunction. Five patients with one-sided tube dysfunction showed a significantly lower median uptake of 31.6% (p = 0.01). The clearance half-lives ranged from 9 to 283 mi n in normal subjects and 37-64 min in patients with one-sided tube mal function, demonstrating no statistically significant difference betwee n the two groups and a trend towards increased washout in patients wit h tympanic dysfunction. Conclusion: Middle ear ventilation scintigraph y with Xe-133 through a nose olive is an easy-to-perfom test to evalua te eustachian tube function and has a success rate of about 70%, thus, reflecting the complex physiological mechanisms involved.