Cholesteatomas are bone destructive expansions of keratinizing squamous epithelium in the middle ear and temporal bone. Today, surgery is the only treatment. There are several controversies regarding cholesteatomas, including the definition, the pathogenesis and the surgical method. Intense efforts have been made searching for a comprehension of the cholesteatoma process at a cellular and molecular level. Recurrent infections and inflammation seem to be contributing factors for the cholesteatomas to expand. The innate immunity, essential to keep a healthy middle ear environment and to protect the middle ear from intruding pathogens, is therefore a matter of interest.

In this thesis, results are presented from a cohort of cholesteatoma surgeries in Östergötland from a 16-year period. A group of patients also filled in a questionnaire to assess changes in health-related quality of life (HRQoL) after surgery. According to the findings in this thesis, the residual and recurrence frequencies are low, and the hearing and HRQoL are improved in the majority of cases.

This thesis also presents an investigation of the innate immunity in ears with acquired cholesteatoma, in comparison with healthy controls. The expression of mRNA of toll-like receptors 2 and 4, participants of the Janus kinase/signal transducer and activator of transcription pathway, and nitric oxide synthases in middle ear mucosa, were investigated with quantitative polymerase chain reaction. An investigation of nitric oxide (NO) in the middle ear, with chemiluminescence measurements, is also presented.

A derangement of the innate immune system is seen in ears with cholesteatoma, which supports the idea that the innate immunity participates in the cholesteatoma process, though the underlying mechanisms are still unclear. The suggestion of NO production in the middle ear sheds light on NOs possible participation in the healthy middle ear environment.