The Greater Omentum-A Vibrant and Enigmatic Immunologic Organ Involved in Injury and Infection Resolution

Abstract

Once thought of as an inert fatty tissue present only to provide insulation for the peritoneal cavity, the omentum is currently recognized as a vibrant immunologic organ with a complex structure uniquely suited for defense against pathogens and injury. The omentum is a source of resident inflammatory and stem cells available to participate in the local control of infection, wound healing, and tissue regeneration. It is intimately connected with the systemic vasculature and communicates with the central nervous system and the hypothalamic pituitary adrenal axis. Furthermore, the omentum has the ability to transit the peritoneal cavity and sequester areas of inflammation and injury. It contains functional, immunologic units commonly referred to as "milky spots" that contribute to the organ's immune response. These milky spots are complex nodules consisting of macrophages and interspersed lymphocytes, which are gateways for the infiltration of inflammatory cells into the peritoneal cavity in response to infection and injury. The omentum contains far greater complexity than is currently conceptualized in clinical practice and investigations directed at unlocking its beneficial potential may reveal new mechanisms underlying its vital functions and the secondary impact of omentectomy for the staging and treatment of a variety of diseases.

Fig. 1.

Intraoperative photo of the human omentum (A) joining an inflamed appendix at the tip (B), demonstrating its great capacity for tissue adhesion. Other organs within the picture correspond to the cecum (C), and small bowel (D).

Fig. 2.

Scheme displaying the different composition of immune cells within the Milky spots. Milky spots are made up of a variety of immune cells, mainly macrophages, B and T cells with different proportions and localized in an apparent orderly manner with B and T cells in the center surrounded by macrophages. The relative composition of immune cells within the Milky spots showed some degree of discrepancy between various reports. Thus, macrophages have been reported to vary between 68 to 12%, T cells between 46 to 12% and B cells between 29 to 10% (32, 14, 25).