Perilymphatic and endolymphatic pressure in the guinea pig after distal dissection of the endolymphatic sac

Hypothesis: The study was designed to investigate whether endolymphatic pre ssure exceeds perilymphatic pressure in an endolymphatic hydrops model with a partially functioning endolymphatic sac. Background: Previous investigations of perilymphatic and endolymphatic pres sure measurements during endolymphatic hydrops were done in a classic endol ymphatic hydrops model. with a surgically blocked endolymphatic duct and sa c. This model, in contrast to the clinical situation of Meniere's patients. totally lacks the functional contribution of the endolymphatic sac. Methods: In the guinea pip, a partially functioning endolymphatic sac was c reated via dissection of the distal portion of the sac from the sigmoid sin us. Three (n = 5) and 6 months (n = 3) later, perilymphatic and endolymphat ic pressures were measured consecutively using a WPI 900A micropressure sys tem. Results: It was observed that damage to the distal part of the endolymphati c sac caused endolymphatic hydrops in 58% of the casts. The hydrostatic pre ssure in hydropic ears did not differ from that of control ears. There was no pressure difference between the perilymphatic and endolymphatic compartm ents in ears with endolymphatic hydrops. The endocochlear potential in ears with hydrops was statistically significantly decreased (p < 0.002). Conclusion: In a hydrops model developed to be more comparable to the histo pathologic appearance of Meniere's disease in the inner ear. no hydrostatic pressure difference was measured between the perilymphatic and endolymphat ic spaces. The only functional difference from control ears we found was a decreased endocochlear potential.