Innominate grooves of the colon: morphological characteristics and etiologic mechanisms.

The morphological characteristics of innominate lines and grooves of the colonic mucosa are described. There are three basic mucosal patterns: linear circumferential, network, and mixed. Lymphoid collections occur at frequent and regular intervals along the course of the lines. These collections split the muscularis mucosa, producing a series of perforations in this thin sheet of muscle. Where contractions of the muscle layer are predominantly longitudinal, those occurring between two rows of lymphoid tissue elevate the overlying mucosa to form ridges and grooves. Barium tends to accumulate in the grooves, particularly since the mucosa is thinner in these regions.