"A mastoid bowl or mastoid cavity refers to a post surgical cavity that is created from the resection of mastoid air cells and intervening septae, usually during complex mastoidectomies such as canal wall up or canal wall down mastoidectomies, or other surgeries such as cochlear implantations. The cavity can be filled with bone, cartilage, fat, or hydroxyapatite to minimise its size 2, but may also account for a site of potentially recurrent soft tissue lesions, such as cholesteatomas."