The theory of the trigger, the bridge and the transmigration in the pathogenesis of acquired cholesteatoma.

The purpose of the study was to evaluate factors in the otitis media process that could play a role in the pathogenesis of acquired cholesteatoma. The study was divided in two parts: firstly the temporal bones of 75 cats and 15 chinchillas with induced otitis media, and 78 human bones with otitis media were evaluated. Special emphasis was placed on epithelial breaks. These breaks were commonly observed, leaving areas of connective tissue of the mucoperiostium in direct contact with the middle ear effusion. As these changes progressed, the effusion became organized, serving as a bridge for granulation tissue. In later stages these areas became totally or partially covered with epithelium. Areas of epithelial breaks became connected to each other through the organized effusion. Cholesteatomas in humans seem to spread using the connective tissue as scaffolding. Secondly, we reviewed 15 chinchillas in which a chemically modified membrane was placed leading from the external auditory canal to the promontory, through a tympanic membrane perforation. Squamous epithelial migration with cholesteatoma formation occurred through the tympanic membrane perforation, collagen membrane, organized effusion and granulation tissue in 53.5% of the experimental animals. The authors propose the theory that for transmigration of squamous epithelium to occur, a trigger (inflammatory process) and a bridge (granulation tissue and organized effusion) are needed in a predisposed subject.

Sustained release of antimicrobials in the middle ear using a biodegradable support.

The ototoxicity of a poly-L-lactic acid biodegradable support incorporating a therapeutically releasable amount of ampicillin was studied. This device has a shape that allows placement in the middle ear via a myringotomy incision. Once in the middle ear, it expands without mechanical interference and provides extended release of ampicillin. In vitro studies documented sustained release of ampicillin, and in vivo efficacy was demonstrated in otitis media induced in chinchillas and cats. Previous histopathologic studies showed a lack of inflammatory reaction from the device itself and documented its biodegradable characteristics. There was no evidence of ototoxicity on morphometry of the organ of Corti (hair cell counts) in chinchillas exposed to these devices for 3 weeks with and without ampicillin.

In search of missing links in otology. III. Development of a new animal model for cholesteatoma.

An experimental study was conducted in chinchillas regarding the pathogenesis of acquired cholesteatoma (keratoma). The placement of a chemically modified gelatin membrane from the external auditory canal to the promontory through a tympanic membrane perforation stimulated squamous epithelial cell migration. Cholesteatoma formation with the presence of keratin debris and inflammatory reactions was observed in the middle ear and anterior bulla in 53.5% of the experimental animals. These experimental findings show for the first time the presence of epithelial migration and true cholesteatoma formation in the middle ear of chinchillas in an experimental model with deliberate perforation of the tympanic membrane. Erosion of the cochlear walls was observed in areas with granulation tissue and cholesteatoma. The importance and significance of the migration of squamous epithelium and of the middle ear inflammatory reaction in the genesis of acquired cholesteatomas are discussed.

Extended middle ear drug delivery. A new concept; a new device.

The authors present the development of a new device that consists of a biodegradable support matrix incorporating a therapeutically releasable amount of ampicillin. This device is in an insertable shape that allows easy placement into the middle ear. Once in the middle ear cavity it expands, contacts the walls, and provides extended sustained release of ampicillin. In vitro studies over three months documented the consistent release of therapeutically effective levels of ampicillin. In vivo efficacy was demonstrated in the cat otitis media induced by eustachian tube obstruction. Cultures of normal cat middle ear cavities prior to obstruction revealed no microflora. Cultures after obstruction of the middle ears of animals treated with this device had no growth of bacteria as early as one week after obstruction (10 out of 12 cats). The contralateral untreated ears became culture negative at two weeks post obstruction, suggesting that the effect of the device is not limited to the treated ear. Histopathological studies showed the effect of the device as early as one week post obstruction in treated ears and after two weeks in the contralateral ear. Both ears became normal at three months, while obstructed untreated animals (controls) developed chronic irreversible otitis media changes. In addition, histopathological findings documented a lack of inflammatory reaction from the device itself, and its capacity of being biodegradable. Topical extended middle ear drug delivery can become a significant form of treatment for middle ear disease and has the potential of being useful as a source for inner ear drug delivery.

Otitis media. 16 years of pathogenesis approach.

The authors describe 16 years of their approach to research in otitis media, their rationale, and the concepts that have evolved from their experiments and clinical work. The authors suggest that interest is the key to progress and not laboratory facilities. They extend an invitation to individuals with different backgrounds but common interest in otitis media to work together from the standpoint of pathogenesis.

In search of missing links in otology. I. Development of a collagen-based biomaterial.

Experiments leading to the development and use of a biomaterial based on reconstituted collagen for use in tympanoplasty are presented. A stable, even membrane with optimal strength and an organized matrix of collagen protein strands has been obtained. Biocompatibility was documented by subcutaneous implantation, cytotoxicity with agar overlay, cell contact, and cell-growth inhibition studies. Experimental grafting in chinchillas with perforated tympanic membranes demonstrated that the collagen membrane performed well in all cases. Histopathological studies in chinchillas showed that the collagen membrane compared favorably with fascia grafts. Of significance is that: 1. The membrane has a matrix of microperforations that enhance tissue ingrowth, allow stable anchoring, and permit aeration of the middle ear cavity. 2. The membranes obtained are not exposed to aldehyde cross-linking; therefore, tissue reaction due to aldehydes is avoided.

In search of missing links in otology. II. Development of an implantable middle ear drug delivery system: initial studies of sustained ampicillin release for the treatment of otitis media.

The development of a new device that consists of a biodegradable support incorporating a therapeutically releasable amount of ampicillin is presented. This device is in an insertable shape that allows placement into the middle ear via a myringotomy incision. Once in the middle ear cavity, it expands, contacts the walls, and provides extended release of ampicillin. In vitro studies (3 months) documented the consistent release of therapeutic levels of ampicillin. In vivo efficacy was demonstrated in otitis-induced chinchillas (bacterial inoculation). The device compared favorably with topical and systemic treatment and prophylaxis of otitis media. The device was also efficient in repeated bacterial challenges. Topical extended middle ear drug delivery can become a significant form of treatment for middle ear disease, and has the potential of being useful as a source for inner ear drug delivery.

Anatomical perspective, approach, and experience with multichannel intracochlear implantation.

An overall review of the authors' anatomical perspective, approach, and experience with multichannel intracochlear implantation is presented. This report includes pertinent anatomical observations and experimental surgical procedures on fresh temporal bones. Although the scala tympani in the basal turn of the cochlea has an adequate space laterally for the insertion of electrodes, in the upper turns the adequate space is located medially. This is, in practice, the single-most limiting factor for an electrode, inserted via the round window, to reach the apical turns without damaging the basilar membrane. An experimental surgical procedure is described in which a second electrode is inserted in the middle turn via a mastoidotomy-tympanotomy approach and reaches a point near the apex. Studies of horizontal sections of human temporal bones include a review of potential structures that could be stimulated by the electrical currents generated by electrodes. The wall of the carotid artery, located at 750 microns from the basal turn at the level of the round window niche, is considered a potential structure to be affected by long-term stimulation. Anatomical principles and surgical considerations for the mastoidotomy-tympanotomy approach are described as an alternative to the facial recess approach. In the authors' experience, this procedure is technically easier, eliminates the possibility of postauricular flap complications, provides a better angle for insertion of electrodes, requires shorter hospitalization, and permits faster recovery than the facial recess approach. The authors' clinical approach, results, and observations are reviewed. Of note is a successful home-based rehabilitation program.

Ultrastructural studies of the peripheral extensions (dendrites) of type I ganglion cells in the cat.

An ultrastructural study of peripheral extensions (dendrites) of type I ganglion cells in seven healthy adult cats and one cat that underwent bilateral cochlear injection of neomycin was undertaken. Morphologic evidence revealed that the peripheral process (dendrite) consistently has a smaller diameter than the central process. As the dendrite reaches the cell body, there is a constricted segment with a length that ranges from 10 to 30 microns, and a diameter of 0.5 microns. This region is covered by a continuous myelin sheath that does not thin. The central process (axon) does not have a corresponding constriction, and consists of a myelin covered, smoothly tapered segment that extends to the first axonal node of Ranvier. In the deafened cat, some cell bodies of the surviving ganglion cells appeared to have a residual portion of dendrite. These morphologic characteristics might have physiologic implications both in the mechanisms of normal hearing and in cochlear implantation.

Ultrastructural studies of the human round window membrane.

An ultrastructural study of 14 round window membranes of seven human ears disclosed three basic layers: an outer epithelium lining the middle ear, a middle core of connective tissue, and an inner epithelium bordering the inner ear. Morphological evidence suggests that these layers participate in absorption and secretion of substances to and from the inner ear. A comparison of morphological features of round window membranes suggests that the average thickness of 70 microns does not change with advancing age. However, in the elderly, the connective tissue has a looser arrangement; there is an increase in ground substance; and elastic fibers thicken. Fibroblast nuclei become larger, rounder, and less uniform and have extensions. The ultrastructure of the "false round window membranes," with epithelial cells of the same type bounding both sides, suggests that these membranes consist of juxtaposed epithelial folds of the overlying promontory.

Permeability of the human round-window membrane to cationic ferritin.

An ultrastructural study was done in three sequential steps to determine if the human round-window membrane was permeable to macromolecules. Cationic ferritin was first placed for one hour in the round-window niche of two live rhesus monkeys. The same tracer was then placed in the same manner in two rhesus monkeys that had been dead for one hour. In both groups, cationic ferritin was observed to traverse the round-window membrane through pinocytotic vesicles into the scala tympani. After establishing that the transport capabilities of the round-window membrane of the monkey remained present one hour after death, cationic ferritin was placed for one hour in the round-window niche of two humans who had been dead for 30 minutes and one hour. The tracer was observed to traverse the round-window membrane through pinocytotic vesicles into the scala tympani in both humans. This report may be the first to document morphologically the permeability of human round-window membranes to macromolecules.

Experimental studies on round window structure: function and permeability.

Current research and an overall review of 12 years of round window membrane studies is presented. The approach, rationale, and concepts that have evolved from the studies are described. An ultrastructural study of the round window membrane of rhesus monkeys disclosed three basic layers: an outer epithelium, a middle core of connective tissue, and an inner epithelium. Morphologic evidence in monkeys, cats, and chinchillas suggests that these layers of the round window participate in absorption and secretion of substances to and from the inner ear, and that the entire membrane could play a role in the defense system of the ear. Cationic ferritin, horseradish peroxidase, 1-micron latex spheres, and neomycin-gold spheres placed in the middle ear of these experimental animals were observed to traverse the round window membrane through pinocytotic vesicles. Three-micron latex spheres and anionic ferritin were not incorporated by the membrane. Cationic ferritin and 1-micron latex spheres placed in perilymph were incorporated by the inner epithelial cells, suggesting absorptive capabilities of the round window membrane. Cationic ferritin was observed within the mesothelial cells underlying the scala tympani side of the basilar membrane, suggesting a role for these cells in the inner-ear defense system. A review of the subject and a general perspective from the author's viewpoint are discussed.

Ultrastructural studies of the round-window membrane of the cat.

An ultrastructural study of eight round-window membranes of four normal cats disclosed three basic layers: an outer epithelium (middle ear), a middle core of connective tissue, and an inner epithelium (inner ear). Morphologic evidence suggests that these layers participate in absorption and secretion of substances to and from the inner ear, such that the entire membrane could play a role in an inner ear "defense system." A comparison of morphologic features of round-window membranes from cats, rodents, and human beings suggests that the cat is a superior animal model for experimental studies. Cationic ferritin, placed for two hours in the round-window niche of four normal cats, was observed to traverse the round-window membrane through pinocytotic vesicles into the connective tissue layer. Evidence of exocytosis of tracer by the inner epithelial layer into the scala tympani is presented. When placed in perilymph, this same tracer was incorporated by inner epithelial cells, suggesting absorptive capabilities of the round-window membrane.

Methohexital-reinforced responding in rats: effects of fixed ratio size and injection dose.

The rate and pattern of lever pressing were studied in nine rats during daily 6-hr sessions in which responding led to the i.v. injection of sodium methohexital. Level pressing was shown to be established and maintained by the response-drug contingency in the absence of physiological dependence or aversive stimulation. Effects of 1.0, 2.0, 3.0 and 4.0 mg/kg/injection of methohexital and fixed ratio schedules of 1, 5, 10, 15 and 20 responses per injection were determined on response rate and drug intake. At 1.0, 2.0 and 3.0 mg/kg/injection, increases in fixed ratio value produced systematic decreases in drug intake; the magnitude of the effect was dose-dependent. More total drug was taken at each fixed ratio value as injection dose was increased. At 4.0 mg/kg/injection, drug intake remained relatively stable over 1, 5, 10 and 15 responses per injection, and decreased at 20 responses per injection. Response rate was inversely related in injection dose at 1 and 5 responses per injection and directly related to injection dose at 15 and 20 responses per injection.

Morphometry of the chinchilla organ of Corti and stria vascularis.

This research describes a procedure for a morphometric analysis of the organ of Corti and stria vascularis in the chinchilla. In nine normal cochleae the length of the basilar membrane and the stria vascularis measured 18.47 and 25.22 mm, respectively. An average of 1910 inner and 7501 outer hair cells were present while an average of 15 inner and 90 outer hair cells were absent. In all cochleae examined there were always some missing hair cells in varying numbers even though the animals had no known ototoxic exposure. Stria area, width and thickness increased from the cochlear apex toward the base. Consistency of changes in stria dimensions among animals was enhanced by expressing position in terms of percentage stria length rather than distance as such. Total stria volume was estimated at 0.15 microliter.