What does "isthmus" denote in the context of the ear canal?

In the context of the ear canal, the term "isthmus" refers specifically to a narrowing or constricted portion of the canal. The ear canal, also known as the auditory canal, can have different parts, and the isthmus is the section where the diameter is reduced compared to the surrounding areas. This anatomical feature is important for various reasons, including its role in sound conduction and potential implications for the fitting of hearing aids. Understanding the isthmus is crucial for hearing aid dispensers and audiologists, as it impacts the selection and placement of devices within the ear canal.