Fine Structure of the round Window Membrane

Abstract

The round window membrane serves as the only soft tissue barrier separating the middle and inner ear. Its participation in the phase differential permitting the labyrinthine fluids to move under the influence of the stapes is better understoodi-P than its permeability characteristics in allowing certain chemical constituents to reach the inner ear fluids. 3 ,14 ,16 The purpose of this study is to report a description of submicroscopic morphologic details in animals (monkeys and guinea pigs). It is hoped that such information will be relevant to a better understanding of the physiologic and clinical implications of round window function. METHOD AND MATERIALThe temporal bones of adult male squirrel monkeys and guinea pigs were employed in these experiments. After the middle ear cavity was perfused with chilled 4% paraformaldehyde buffered with phosphate (pH 7.4) containing 1% sucrose, by means of injection through the tympanic membrane, the animals were decapitated and the temporal bones were opened. With the aid of an operating microscope, a small dental burr was used to make a hole between the round and oval windows. A second hole was made in the stapedial footplate. Through these holes the fixative was injected into the inner ear at low pressure. The temporal bones were then immersed in fresh fixative for two hours at 4 0 C, after which they were washed in cold phosphate buffered (pH 7.2) with added 1% sucrose. In the washing solution, the round window membrane was dissected free from the surrounding bone under the operating microscope. The specimens were postfixed in 1% osmium tetroxide buffered with phosphate (pH 7.4) for one hour at 4 0 C. They were then dehydrated with an ascending series of ethyl alcohol and embedded in Epon 812.Ultrathin sections were obtained with an LKB ultratome and Porter Blum microtome. The sections were double stained with uranyl acetate and lead acetate. Some sections were stained in 1% aqueous phosphotungstic acid for demonstration of elastic fibers. Micrographs were obtained using an RCA-EMU-3G electron microscope.OBSERVATIONS

Ultrastructural Organization of the Round Window Membrane in the Infant Human Middle Ear

“…The thickness of the round window membrane was foud to be 30-35 pm. Similarly to the round window membrane of various animals [Kawabata and Paparella, 1971;Richardson et al, 1971;Miriszlai et al, 1978] the round window membrane of human infants consists of three layers. The outer epithelial layer, in contrast to the round window membrane of animals, is wider, having 3-4 layers ( fig.…”

“…The ultrastructural organization of the round window membrane of various experimental animals (guinea pig, cat, monkey) has been described by Richardson et al [1971], Kawabata and Paparella [1971], and by Mir iszlai et al [1978], It is known that the round window membrane of man is considered as having an important role in the mechanism of hearing. It is also known that Menière's syndrome may be treated by placing NaCl crys tals onto the round window membrane [Arslan.…”

Targeted Delivery of Contrast Agents to the Tympanic Medial Wall at Minimum Amount and the Efficient Uptake in the Inner Ear through Oval and Round Windows

“…The inner layer consists of mesothelial cells continuous with the lining of the scala tympani. The cellular extensions are connected by gap junctions [23,24]. A histologic study in rats demonstrated that the annular ligament across the stapediovestibular joint is a porous structure composed of fibdllin, 36 kD microfibdl-associated glycoprotein, and hyaluronic acid [25].…”

Gas Permeability of Round Window Membrane

“…Therefore, the round window, with its thin membrane, is the main 'window' between the inner ear and the middle ear cavity, in terms of the possible exchange of small molecules. Sev eral studies have described the structures of the round window membrane, including microstructures [1][2][3][4][5]. Various features of the round window membrane have been demonstrated, such as an excretory channel of perilymph [6], a passage of inflammation from the middle ear to the inner ear [7], and a favored route of infiltration of locally ad ministered drugs to the inner ear [8].…”