Primary and secondary cholesteatomas, cholesterol granuloma, and mucocele of the temporal bone: Role of computed tomography and magnetic resonance imaging with emphasis on diffusion-weighted imaging

Cholesteatomas of the temporal bone may be congenital (primary) or acquired (secondary). Congenital cholesteatomas (epidermoid cysts) fall into the category of maldevelopmental cysts, arising owing to inclusion of ectodermal elements at the time of closure of the neural tube. Secondary cholesteatomas of the middle ear are most often related to prior infection and most frequently occur in the epitympanic cavity. Primary cholesteatomas of the temporal bone most often occur in the mesotympanum, but can be seen in the mastoid, facial nerve canal, and petrous apex. Primary cholesteatomas of the petrous apex on computed tomography have similar imaging features as cholesterol granulomas and mucoceles of the petrous bone. Magnetic resonance imaging is the study of choice to differentiate cholesteatomas from cholesterol graulomas and mucoceles. This article reviews computed tomography and magnetic resonance imaging characteristics of choleateatomas, cholesterol graulomas, and mucoceles.