Is the human round window really round? An anatomic study with surgical implications.

Human round window (RW) presents anatomic variations that may influence surgical approach. The true shape of the human RW has been divisive since its first description in 1772 by Antonio Scarpa. Introduction of novel surgical strategies in recent years have raised its significance. Here, the human RW size and shape variations were documented in microdissected human temporal bones. An archival collection of human microdissected temporal bones was analyzed. RW rim could be delineated and photographed from the labyrinthine aspect and its topography assessed. Human RW is seldom round but ovoid or orthogonal, skewed, and nonplanar (saddlelike). Membrane is fan shaped or conical with an anteroinferior and a posterosuperior part. The mean longest diameter was 1.90 mm, and the smallest one is 1.54 mm. The mean diameter from the crista fenestra was 1.31 mm. The mean area of the RW was 2.08 mm, which varied between 0.99 and 3.20 mm. The crista fenestrae of the anterior component form a "doorstep" that may limit the entry to the scala tympani from the RW niche. The alternate anatomic features of the human RW may influence its surgical access and designs of implants aimed at targeting this region.