Effects of middle ear ventilation on cholesteatoma development in experimental animals

Pathogenesis of Retraction Pocket of the Tympanic Membrane-A Narrative Review

Several theories describe the development of the retraction pocket of the tympanic membrane (RP). Many authors suggest that the negative middle ear pressure is the main reason responsible for developing this condition. A narrative review has been undertaken, and conclusions are drawn reflecting a current knowledge with our new observations in the histological and immunohistochemical study. Recent studies show the important role of inflammation in the development and progression of RP. A review of the available literature shows that the inflammation plays a key role in pathogenesis of the RP and its progression to the cholesteatoma. We support this statement with our new results from histological and immunohistochemical analysis of the RPs.

A new theory interprets the development of a retraction pocket as a natural self-healing process

PURPOSE

The thesis that cholesteatoma evolves from a retraction pocket is widely accepted today. Yet, its prime etiology, the question of what triggers the invagination of healthy skin, still remains unclear despite centuries of investigations into the origin of cholesteatoma. A new idea interprets the horizontal migration of skin into the middle ear cavities as a self-healing process, curing an underlying inflammation in the tympanic cavity, through the overgrowth and contact with immunologically active tissue.

METHODS

A retrospective analysis of the interrelation of retraction pockets and underlying granulation tissue was conducted in 209 second-look cholesteatoma surgeries over the last decade.

RESULTS

A stable tympanic membrane over aerated, healthy middle ear mucosa was found in 71.3% of cases. In 11%, small retractions with air in other parts of the middle ear cleft (epitympanic, sinus or anterior mesotympanum) were described. In 6.2%, granulations under a retraction were found. Only 3.8% of the reports revealed air behind a retraction or did not provide enough information on the mucosa situation behind the drum membrane.

CONCLUSIONS

A new hypothesis interprets the origin of a retraction pocket-the precursor of a cholesteatoma-as a natural attempt by the body to cure an underlying inflammation in a cavity. Analogous phenomena exist, e.g. the migration of the omentum towards a local inflammation in the abdomen. This idea, which is supported by the findings in our 209 second-look surgeries, is the first explanation of the origin of retraction pockets that is compatible with the various characteristics of original or recurrent cholesteatoma. A prophylaxis against a recurrent cholesteatoma might be attained by securing free drainage of the mucosa into the tubal orifice with the use of thin silicone foils in an attempt to prevent any granulation in the middle ear cleft, similar to the principles of modern rhinosinusoidal surgery with its emphasis on unblocked mucosa clearance. This allows gas production in the healed middle ear mucosa to recover, reducing the risk of a recurrent retraction.

Tympanic Membrane Metalloproteinase Inflammatory Response

OBJECTIVE: The goal of this study was to determine whether expression of matrix metalloproteinases (MMP) in tympanic membranes (TM) is stimulated by host tumor necrosis factor-± (TNF-±) and bacterial toxin (lipopolysaccharide, LPS), which may play a role in the pathogenesis of cholesteatoma.

STUDY DESIGN: Gerbil TMs (n = 48) were cultured in the presence of either TNF-± or LPS. Quantitative analysis of TNF-± and MMPs was performed on both the homogenized TMs and the culture media supernatant.

RESULTS: Levels of TNF-± and MMPs did not increase significantly in TMs with exposure to inflammatory mediators. TNF-± levels in supernatant were elevated ( P < 0.007) with more concentrated LPS exposure. Supernatant levels of MMP2 were increased ( P < 0.007) at most concentrations of LPS and TNF-±.

CONCLUSION: Cultured TMs expressed MMPs in response to bacterial and host inflammatory mediators. These findings support a link between inflammation and the secretion of potentially destructive MMPs in the TM, which may contribute to the pathogenesis of cholesteatoma.

Effect of topical hyaluronic acid on experimental cholesteatoma

PURPOSE

Inflammation and connective tissue hyperplasia are believed to be important etiological factors in cholesteatoma pathogenesis. Previous work has shown that topically applied hyaluronic acid can reduce connective tissue proliferation in healing wounds and accelerate healing of tympanic membrane perforations. This study was undertaken to determine whether the antiproliferative effect of hyaluronic acid may inhibit propylene glycol-induced cholesteatoma in an animal model.

MATERIALS AND METHODS

A 60% propylene glycol solution was injected bilaterally into the middle ear cavities of 20 adult chinchillas. The control group (N = 10) received propylene glycol alone. In addition to propylene glycol injections, the experimental group (N = 10) received repeated bilateral topical applications of 1.5% hyaluronic acid onto the tympanic membranes. Animals were killed at 4 weeks for gross and light microscopic examination.

RESULTS

Seven control and 10 experimental animals survived the full 1-month study period. At the end of that time, cholesteatoma was found in 71% (10/14) of control ears and 70% (14/20) of experimental ears. Tympanic membrane structure did not differ significantly between groups by light microscopy and, in all animals, cholesteatomas originated by migration of hyperplastic epidermis through the tympanic membrane, as has been observed in previous studies using this animal model.

CONCLUSION

Under the conditions of this study, topical hyaluronic acid had no significant effect on cholesteatoma formation.

Effect of 5-fluorouracil in cholesteatoma development in an animal model

This investigation was designed to evaluate the effects of the antimetabolite 5-fluorouracil (5-FU) on cholesteatoma formation in a chinchilla model. The animals received middle ear applications of propylene glycol according to a procedure previously shown to produce cholesteatomas in 60% to 70% of animals. A 5% solution of 5-FU was then applied to the lateral surface of the tympanic membrane (TM) and, after 1 month, temporal bones were taken for histologic study. No macroscopically visible cholesteatomas were present in any of the 16 temporal bones included in the study. However, microscopic invasion of epidermis to the medial side of the TM was observed in four specimens; perforations were present in three of these. Although there was considerable variability in the response to 5-FU application, the majority of specimens showed little or no proliferation of connective tissue in the lamina propria of the TM. In the four specimens in which epidermis reached the medial side of the TM, it did so either by migration through microscopic breaks in the fibrous layer or via TM perforations. Thus, 5-FU did not completely inhibit migration of epidermis into the middle ear. However, the results of this study indicate that it does tend to reduce the proliferation of TM epidermis and connective tissue, thereby reducing the likelihood of cholesteatoma formation in the experimental model.

Tympanic membrane microstructure in experimental cholesteatoma

This study assessed changes in tympanic membrane microstructure associated with cholesteatoma development following middle ear application of 50% propylene glycol in chinchillas. Although the epidermal layer of the tympanic membrane (TM) was destroyed immediately after propylene glycol application, the epidermal basal lamina remained intact and appeared to serve as a substrate for regrowth of epidermis over the TM. During the initial phase of epidermal repair (4 to 7 days after propylene glycol administration), pseudopodial processes from the epidermal cells occasionally penetrated the basal lamina; however, no migration of epidermis into the lamina propria occurred at that time. The basal lamina remained largely intact until about 2 weeks, when it became fragmented in some areas, so that sizable gaps appeared. Hyperplastic epidermal cells then migrated through the gaps into the rapidly proliferating connective tissue of the lamina propria. At 2 to 4 weeks, degenerative changes were observed in portions of the fibrous layer, which underwent phagocytosis by foreign body giant cells. This process created defects in the fibrous layer which permitted invasion of epidermis to the medial portion of the lamina propria. The epidermis subsequently reached the medial side of the TM in areas where there was incomplete repair of the mucosal layer.