The intestinal muscularis propria is organized into discrete inner circular and outer longitudinal layers of muscle fibers that are oriented perpendicular to one another, except in the appendix, where the arrangement is more haphazard. The myenteric plexus of ganglia and nerves is sandwiched between the 2 muscle layers and is required for peristaltic activity. Maldevelopment or disruption of the neural or muscular elements can impair intestinal motility and cause intestinal pseudo-obstruction. This term refers to a malformation of the muscularis propria, with supernumerary and/or haphazard orientation of muscle fibers.