Juxtaposition lipoma to the mastoid seventh nerve

The precise embryological source for fat in juxtaposition to the vertical portion of the seventh nerve in the mastoid is unknown. Seventeen percent of 240 temporal bones disclosed various amounts of fat adjacent to this portion of the nerve. Shiny areas of fat granules are occasionally seen around, and perhaps at first glance mistaken for, the seventh nerve during mastoid surgery. The radiographic appearance of fat in this area has not been described. Bilateral 1-cm ovoid images were interpreted in a 16-year-old girl as seventh nerve neuromas or perhaps hemangiomas, but were surgically proven to be a lipoma in the only ear operated on. Lipoma should be considered in the differential diagnosis for a mass in this location which demonstrates increased T1 signal, progressive decreased signal on T2-weighted images, and has signal intensity isodense with that of fat.