The “Omega sign”: a new radiological sign for a rare type of internal hernia involving the sigmoid mesocolon

The transmesosigmoid hernia is a rare type of sigmoid mesocolon hernia. Its presentation is non-specific and thus hardly ever preoperatively diagnosed. Its diagnosis often requires surgical corroboration. This case report aims to improve on the preoperative diagnosis with a proposed observed sign on CT. All literature reviewed described radiological findings related to the small bowel; thus, features of small bowel obstruction was the “hallmark” of internal hernias. This paper intends to describe the features of the sigmoid mesocolon internal hernias, illustrate and propose a never reported configuration of the sigmoid colon. This sigmoid colon configuration has a resemblance to the omega sign. We intend to present a new hallmark sign, which may serve as a clue in the identification of internal hernias involving the sigmoid mesocolon.