Sentinel or Selective Omentectomy in Epithelial Ovarian Cancer: New Perspective

Dear editor,

Omentectomy is commonly to be performed in ovarian cancer. We are aiming here to show its role and if it is needed to be preserved. Omentum is poorly understood regarding its function till now.

Omentum is derived from the ancient Egyptian who exams this organ while embalming bodies after death to detect good or bad “omens” for the dead. Greater omentum is made up of four layers. The anterior two layers descend from the greater curvature of the stomach and the proximal part of the duodenum, folded on itself and ascend again and attached to the transverse colon. It covers the greater sac. The right and the left gastroepiploic vessels provide the omental blood supply. The right one arises from the branches of the celiac artery and left one arises from the splenic artery. They run along the greater curvature of the stomach, a finger breadth or more below the curvature  [1].

The omentum consists of fat pads and histological entities, called the milky spots with no lymph nodes. The “milky spots” are areas containing macrophages, B and T cells. They are small white-colored areas of lymphoid tissue, found in the peritoneal, pleural, and pericardial cavities. Milky spots are in the greater omentum than anywhere else. They are like Peyer’s patches in the intestine. They play an immunologic role in defending the peritoneal cavity. These have been shown to be cytotoxic to cancer cells. The omental fat induces angiogenesis through the release of fibroblast growth factors and so has a role in healing of the inflamed or ischemic tissue and preventing adhesion formation. Furthermore, it is an energy source. The role of omentum in cancer is the capability of killing tumor cells. When overrun by cancer cells, there will be omental caking. The adipocyte composition of the omentum provides energy and provides angiogenesis to cancer cells, allowing them to grow and spread. Cancer cells have an affinity for the omentum, as reflected by omental caking in advanced ovarian cancer and microscopic spread in early cancer [2, 3].

The most widely accepted explanation is that tumor cells become detached from the primary tumor and transported throughout the peritoneal cavity by peritoneal fluid before seedling intraperitoneally. The flow of intraperitoneal fluid is directed by gravity to most dependent sites and then drawn in a cephalad direction clockwise direction along the paracolic gutters to the diaphragm by the negative intra-abdominal pressure during respiration. Metastasis preference sites are dependent on areas directed by the flow of fluid ranging from the cul-de-sac (gravity), right infracolic space (the termination of the small intestine), left infracolic space (sigmoid colon), right paracolic gutter (the ascending colon and peritoneal wall), omentum (trapping), and left paracolic space (upwards). The preferential growth of metastatic tumor cells is in the omentum, on the diaphragm, and in the paracolic gutters over Ther serosa surfaces. Cells accumulate in the milky spots of the greater omentum as well as the lymphatic lacunae of the diaphragm where the peritoneal fluid is absorbed and can lead to the development of malignant ascites if obstructed by cells [4–6].

Another possible explanation for peritoneal metastasis is coelomic metaplasia. The omentum and the ovarian epithelium may be synchronous malignant transformation. If the metaplasia hypothesis is correct, then lesions would be distributed randomly throughout the peritoneum and not at specific sites. If the theory of dissemination via peritoneal is true, then the shed tumor cells would first implant in the pouch of Douglas by gravity followed by sites along the peritoneal fluid circulation and this what usually happens. And this is the most accepted theory [7, 8].

The inclusion of omentectomy in ovarian cancer staging appears at 1960s as it was a frequent site of metastasis and affects survival. By the 1980s, cytoreductive surgery including omentectomy is introduced as the standard procedure including those without gross omental tumor involvement. In 1988, FIGO introduced stage IIIA with microscopic metastases to the upper abdominal cavity including the omentum. In 1999, FIGO introduced omental biopsy and did not specify how extensive it is. In 2012, guidelines recommended “infracolic omentectomy.” On surgical staging, visual examination and palpation cannot detect occult microscopic metastasis. So, it is recommended that supracolic or infracolic omentectomy should be performed. Although the lesser omentum can be affected, it is usually the greater omentum that is involved. Omentectomy is divided into infracolic, supracolic, and total. Infracolic omentectomy is the removal of the greater omentum below the transverse colon. Supracolic omentectomy includes the addition of the greater omentum between the transverse colon and the stomach. Total omentectomy is the removal of the lesser omentum and supracolic omentectomy [9–11].

Questions regarding omentectomy including the following: does detection of microscopic metastasis require total omentectomy or a limited one? What is the frequency of omental microscopic metastasis? What are the factors that can predict omental metastasis? Is there a risk from omentectomy? What about recurrence after omentectomy? Does it has a therapeutic affect?

Removal of the omentum has some side effects as the omentum provides a defense against intra-abdominal infection and it has a tumoricidal role. So, omentectomy, especially total omentectomy, may be associated with transverse colon or stomach injury, hemorrhage, or possible splenic injury. Regarding recurrence after surgery, the fibrin produced in response to the surgical trauma entraps the cancer cells, protecting them from the immune system. After entrapped in the fibrin, they benefit from the release of growth factors, that can be stimulating and promoting cancer growth. Furthermore, it may not be affected by chemotherapy. This can cause recurrence at stomach and bowel surface increasing morbidity. So recurrence can occur at margins of resection. If there is no omentum, there will be large peritoneal spread, generalized disease not localized. So it is better to reserve the omentum as thin omentum with low fat content and previous omentectomy can lead to more peritoneal affection as it traps cancer cells for food and for destruction so disease is localized at sites of resection [12, 13].

The extent of omentectomy is not well defined nor the visual suspicious appearance. It is not clear that removing a normal appearing omentum has therapeutic benefit even in local omental affection especially after adjuvant chemotherapeutic agents. Predictors of omental metastasis are higher stage (IC–IIC), higher tumor grade (G2, G3), serous cancer, presence of ascites, and elevated serum CA 125 [9–11].

In early stage ovarian cancer, occult metastatic foci in the apparently normal omentum could be in 30% of patients converting stage 1a and b to stage 3a. Because of the low incidence of omental metastases in early stage ovarian cancer and the efficacy of chemotherapy, total omentectomy may not be necessary and 3–5 random omental biopsies or infracolic omentectomy can be used. Supracolic omentectomy should be postponed until macroscopic disease is present or suspicion in appearance [11–13]. We are supposing suspicious omentum as omental panniculitis where there is tightly packed omentum fats that are friable on spreading of omentum and tear easily on manipulation. It is a sign of early inflammation from omental infiltration with local response. It should be investigated further regarding what to do if encountered or will it be suitable to proceed with limited or total omentectomy. It will be better to have a sentinel omentectomy with resection guided with the dye uptake. Panniculitis can be suspicious and widely affecting the omentum; there is no strict criteria for diagnosis, so till now if it is widespread in the omentum, we can proceed with limited resection or biopsy as it can be considered as a microscopic disease till now and needs a proof with biopsy for chemotherapy [12, 13].

Current practice and guidelines include omentectomy in advanced cases with or without macroscopic lesions in advanced cancer. If adjuvant chemotherapy is used, it is unclear whether removal of the normal appearing omentum has significant therapeutic advantage.

The peritoneum is not totally removed in advanced cancer but only biopsied or removal of the grossly affected areas so why is it different from the omentum in face of its advantage and disadvantages of its removal [9–12].

Our suggested sentinel or selective omentectomy proposal is as follows. In cases of microscopic disease, chemotherapy seems to eradicate it, so performing omental biopsies rather than infracolic or total omentectomy of the grossly normal omentum may be more better. Directed omental biopsy or sentinel or selective omentectomy in early and advanced ovarian cancer can be proposed in the case of advanced and early cancer. In early cancer, it can be used to guide biopsy, and in advanced cancer, it will guide biopsy and resection to microscopic affected areas to be removed with the macroscopic affected areas. It can be done using Indian ink installation in the peritoneum as it has been done on rats. It needs further research regarding technique and dose or alternatives. Furthermore, we are considering omental panniculitis as a suspicious omentum finding for omentectomy. If this is not available, we can proceed with a preferred multiple omentum biopsies or infracolic omentectomy in normal looking omentum and local resection for gross affected areas. In advanced cancer, we can proceed with infracolic omentectomy or supracolic one according to the area affected by the gross lesion, and if it is not affected which is rarely encountered as it is an early site of peritoneal spread as mentioned earlier, we can proceed with preservation as chemotherapy is given later. No biopsy is needed as in early cancer as chemotherapy will be given later [12, 13].

Regarding future research, we are proposing some ideas as role of omentum thickness, abundance or absence of fat as a predictor for spread, suspicious pathological gross findings of the omentum for omentectomy, and use of dyes for trapping in milky spots for selective surgery.

Conclusion

This highly vascularized organ is a storage site for lipids as a fuel and for immune cells. It has a tumor killing function and immune function. Cancer cells have the affinity for it so it can capture and localize cancer even recurrence. Selective or limited omentectomy in early and advanced cancer without gross involvement is proposed.

Authors’ Contributions

Author had done the diagnoses and surgery along with writing the article.

Compliance with Ethical Standards

Conflict of Interest

The author declares that he has no conflict of interest.

Ethical Approval

All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Informed Consent

Informed consent was obtained from the patient included in the study.