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
Semipermeable membrane the rate and the permeability. Many natural and synthetic materials thicker than a membrane are also semipermeable. One example of this is the thin film on the inside of the egg. Note that a semipermeable membrane is not the same as a selectively permeable membrane. Semipermeable membrane describes a membrane that allows some particles to pass through (by size), whereas the selectively permeable membrane "chooses" what passes through (size is not a factor). An example of a biological semi-permeable membrane is the lipid bilayer, on which is based on the plasma membrane that surrounds all biological cells. A group of