Figure 1d. Drawings illustrate the spectrum of anomalies resulting from incomplete atrophy of the omphalomesenteric duct. (a) Umbilicoileal fistula is a completely patent omphalomesenteric duct connecting the ileum to the anterior abdominal wall at the umbilicus. (b) Umbilical sinus results from failure of the umbilical end of the omphalomesenteric duct to close. (c) Umbilical cyst occurs when the midportion of the duct remains patent and each end obliterates. (d) A persistent fibrous cord occurs when the duct obliterates but is not absorbed. (e, f) Meckel diverticulum results when the ileal end of the duct remains patent and the umbilical end atrophies. The diverticulum remains connected to the umbilicus by a fibrous band if the obliterated duct fails to be absorbed (e).