Progressive erosion of the bone exposes the dura, the facial nerve, and the labyrinth to damage. Extradural abscess may be caused by direct extension of granulation tissue. The most common site of occurrence in cases of CSOM is the tegemen tympani but this condition is frequently associated with other complications, the most frequent of which is sinus thrombosis. Meningitis is the most common intracranial complication in the majority of cases. Dissemination of infection occurs through bone erosion, bacteremia, and congenital dehiscence.
Granulation tissue seems to play a bigger role in spread of the disease than does cholesteatoma.
Physical examination using the otoscope remains the gold standard for the initial evaluation. Pathogens may enter the middle ear cleft from the external auditory canal or from the nasopharynx via the eustachian tube. In contrast to the acute forms of otitis media, the most common organisms isolated in CSOM without cholesteatoma are P. aureginosa, Staphylococcus aureus, gram-negative bacilli and anaerobes. Material should be obtained directly from the middle ear cavity through the perforation and sent for aerobic, anaerobic, and fungal culture. The diagnosis of chronic mastoiditis is clinical.