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The causes or pathogenesis are usually multiracial. Several risk factors can predispose to infection or initiate inflammation and subsequently the infectious process. Intact canal skin and cerement production have a protective effect against infections. This is secondary to the fact that cerement produces a pH in the ear canal that is slightly acidic. On the other hand, breakdown of skin integrity, insufficient cerement production, or blockage of the ear canal with cerement (which promotes water retention) can predispose to Infection.
Skin Integrity can be Injured by direct aroma, heat, and moisture or persistent water In the ear canal. Such damage Is thought to be necessary for initiation of the inflammatory process. Subsequently, edema may result, followed by bacterial inoculation and overgrowth. In Otis External, the infection is caused by bacteria or fungi. Scratching, inserting objects into the ear canal, or moisture (from swimming, for example can make the ear canal vulnerable to Infection.
The external auditory canal is a cylinder measuring approximately 2. 5 CM in length and 7. 0 to 9. 0 mm in width, extending from the conchs’ cartilage of the auricle to the humanity membrane . It Is divided Into a lateral (outer) cartilaginous portion that occupies approximately one-third of the canal and a medial (Inner) bony portion that occupies the remaining two-thirds. Their junction is termed the isthmus and is the narrowest region of the ear canal.
The outer cartilaginous portion is lined by thicker skin with numerous addenda structures including cerement glands, sebaceous glands, and hair follicles. The inner bony portion of the canal contains thin skin without subcutaneous tissue. The dermis In this area Is In direct contact with the underlying peritoneum. Thus, minimal Inflammation or Instrumentation of the bony canal causes significant pain and/or Injury. The Inferior tympanis recess Is a small depression In the inferior medial aspect of the ear canal, adjacent to the tympanis membrane.
Debris can collect in this area and cause or perpetuate infection. The lining of the ear canal is a exaggerating exogamous epithelium that undergoes continual sloughing. Epithelial migration is a naturally occurring cleaning process for the ear canal that allows egress of keratin debris and cerement. Epithelial migration begins in the center of the tympanis membrane and continues out to the medial, then lateral aspects of the ear canal.
The ear canal is bound superiorly by the middle cranial Foss, interiorly by the temporariness’s Joint and paranoid region, medially by the tympanis membrane, posterior by the mastoid cavity, and inferiorly by the skull base and soft tissues of the neck. These boundaries have particular importance when considering the potential complications of external Otis. The fissures of Sanatoria are a series of embryological fissures In the anterior aspect of the fissures also allow potential spread of ear canal disease to the paranoid region, temporariness’s Joint, and soft tissue of the upper neck.