The appendix is a worm-like blind-ended structure.

The average length of the appendix is 8-10 cm (range 2-20 cm).

Normal appendix does not exceed 6 mm in maximal outer diameter (MOD) and should be compressible. 

The normal appendix consists of 5 distinct layers; the innermost echogenic layer which represents the interface of mucosa and lumen, the hypoechoic mucosal layer, the echogenic submucosal layer, the hypoechoic muscularis propria layer and the outermost echogenic serosal layer.