Cholesteatoma of the middle ear is a cystic structure that is not a true tumor. They are usually classified according to their pathogenesis as congenital cholesteatoma, acquired primary cholesteatoma and acquired secondary cholesteatoma. In patients with congenital cholesteatoma, the tympanic membrane is normal, so it is often difficult to be detected in the early stage, and it is not until hearing loss occurs that the patient will go to the hospital for consultation, and the diagnosis can be basically confirmed if the examination reveals a white mass shadow behind the tympanic membrane (Figure 1). Acquired primary cholesteatoma is the most common, patients often have a history of long-term obstruction of the Eustachian tube in childhood, due to the formation of negative pressure in the upper tympanic chamber of the middle ear, which eventually leads to the flaccid part of the tympanic membrane bag-like invagination, shed epithelium in the internal capsule bag gradually aggregated, and ultimately the formation of cholesteatomas (Figure 2); the clinical manifestations of this type of patients vary greatly, and some of them may have ear pus and a history of hearing loss, but some of the patients can be completely without any obvious symptoms. Some patients may have a history of pus and hearing loss, but others may be completely asymptomatic. Acquired secondary cholesteatoma often occurs in patients with marginal perforation of the tympanic membrane due to the growth of the epithelium of the external auditory canal into the tympanic cavity along the margin of the perforation (Fig. 3), and the patient presents early with symptoms, often manifesting as ear drainage and hearing loss; acquired secondary cholesteatomas can also occur as a result of trauma to the ear and surgery. Cholesteatoma consists of a capsule wall with a complex layer of squamous epithelium and a capsule content consisting of exfoliated squamous epithelium and keratinized material. Although cholesteatomas are not true tumors, they have characteristics similar to those of tumors, such as gradual growth, destruction of bone, and residual and recurrent growth. Due to the above characteristics of cholesteatoma, patients can experience destruction of the auditory tuberosity and even certain serious complications such as facial paralysis, labyrinthitis, meningitis and brain abscess. Therefore, the treatment principle of cholesteatoma is to operate as early as possible once found. Figure 1 Congenital cholesteatoma Figure 2 Acquired primary cholesteatoma Figure 3 Acquired secondary cholesteatoma