Cholesteatoma either by metaplasia of the middle ear mucosa or by traumatic implantation of ear canal or tympanic membrane skin. In addition, cholesteatoma inadvertently left by a surgeon usually regrows as an epidermal cyst. Some authors have also suggested hereditary factors. More commonly, keratin accumulates in a pouch of tympanic membrane which extends into the middle ear space. This abnormal folding or 'retraction' of the tympanic membrane arises in one of the following ways: Cholesteatoma may also arise as a result of metaplasia of the middle ear mucosa or implantation following trauma. Cholesteatoma is diagnosed by a doctor by physical examination
Membrane technology utilized for gas separations (removal of CO from natural gas, separating N from air, organic vapor removal from air or a nitrogen stream) and sometimes in membrane distillation. The later process helps in the separation of azeotropic compositions reducing the costs of distillation processes. The pore sizes of technical membranes are specified differently depending on the manufacturer. One common distinction is by "nominal pore size". It describes the maximum pore size distribution and gives only vague information about the retention capacity of a membrane. The exclusion limit or "cut-off" of the membrane is usually specified in the form of "NMWC"