greater omentum

ANATOMY - Structure: Double-layered fold of peritoneum that folds back on itself, giving 4 layers total. Contains abundant adipose tissue, lymphatics, and macrophage/lymphocyte aggregates ("milky spots"). - Attachments: Superiorly to the greater curvature of the stomach and the first part of the duodenum; inferiorly it hangs freely over the small bowel and transverse colon (the posterior layers fuse with the transverse mesocolon). - Named ligaments (parts of the greater omentum, derived from the embryonic dorsal mesogastrium): - Gastrocolic ligament: stomach to transverse colon (the part most commonly entered during surgery to access the lesser sac). - Gastrosplenic (gastrolienal) ligament: stomach to spleen; carries short gastric and left gastro-omental vessels. - Gastrophrenic ligament: stomach to diaphragm. - Splenorenal ligament: derived from the dorsal mesogastrium, carries splenic artery/vein and the tail of the pancreas (often grouped with these structures). - Embryology: Derived from the dorsal mesentery (dorsal mesogastrium) of the foregut. Stomach rotation during development pulls the dorsal mesogastrium to the left, creating the lesser sac (omental bursa) behind the stomach. In contrast, the lesser omentum derives from the ventral mesentery (septum transversum). - Blood supply: Right and left gastro-omental (gastroepiploic) arteries run along the greater curvature within the omentum. The right gastro-omental artery comes from the gastroduodenal artery (from the common hepatic, a celiac branch). The left gastro-omental artery comes from the splenic artery (celiac). Venous drainage goes to the portal system: the right gastro-omental vein drains to the superior mesenteric vein, and the left drains to the splenic vein. Lymphatics drain to gastroepiploic nodes, then celiac nodes. - Peritoneal relationship: Intraperitoneal structure that forms the anterior boundary of the lesser sac's inferior recess.

FUNCTIONS 1. Immune/defense: milky spots with macrophages and lymphocytes clear peritoneal pathogens and bacteria; "policeman of the abdomen." 2. Walls off infection or inflammation (e.g., perforated appendix or diverticulitis), limiting spread and forming adhesions/abscess containment. 3. Fat storage and energy reserve; thermal insulation and cushioning of viscera. 4. Promotes angiogenesis and healing; used surgically as a vascularized pedicle flap (omental flap) to cover wounds, repair perforations (Graham patch for perforated peptic ulcer), fill sternal or mediastinal defects, and reconstruct chest wall or perineal defects.

CLINICAL SIGNIFICANCE / HIGH-YIELD ASSOCIATIONS - Omental caking: Diffuse thickening/infiltration of the omentum on CT, classically due to peritoneal carcinomatosis from ovarian cancer, but also gastric, colon, pancreatic cancers, lymphoma, and peritoneal tuberculosis. Pseudomyxoma peritonei (mucinous appendiceal tumor) is another peritoneal disease. - Ovarian cancer commonly metastasizes to the omentum (omentectomy is part of staging/debulking). - Omental infarction: Rare cause of acute right-sided abdominal pain that can mimic appendicitis or cholecystitis; due to torsion or vascular compromise. CT shows a "whorled" fatty mass. - Peritoneal adhesions: Omentum adheres to inflamed sites and can cause small bowel obstruction from adhesive bands after surgery. - Hernias: Omentum is a common content of hernias (inguinal, umbilical, incisional); may become incarcerated or strangulated. - Laparoscopic access to the lesser sac: Through the gastrocolic ligament. - Lesser sac pathology: Pancreatic pseudocysts commonly collect in the lesser sac, posterior to the stomach and bounded anteriorly by the lesser omentum and gastrocolic ligament. - Ligation of gastro-omental arteries: The right gastro-omental artery is used as a conduit in coronary artery bypass grafting (CABG) in some cases (gastroepiploic artery graft). - Spleen: Gastrosplenic ligament contains short gastric vessels; injury during splenectomy or gastric surgery can cause bleeding.

COMPARISON WITH LESSER OMENTUM (commonly tested) - Lesser omentum (hepatogastric + hepatoduodenal ligaments): connects the liver to the lesser curvature of the stomach and proximal duodenum. The hepatoduodenal ligament contains the portal triad (hepatic artery proper, portal vein, common bile duct) and forms the anterior border of the epiploic foramen of Winslow. Compressing the hepatoduodenal ligament (Pringle maneuver) controls hepatic bleeding. The lesser omentum is derived from the ventral mesentery. - Greater omentum: from the dorsal mesentery (dorsal mesogastrium); hangs from the greater curvature.

MNEMONIC/PEARL - "Policeman of the abdomen": it migrates to sites of inflammation. - Greater omentum = Greater curvature, Gastro-omental arteries, Gastrocolic/gastrosplenic ligaments. - Dorsal mesentery gives rise to greater omentum; ventral mesentery gives rise to lesser omentum, falciform ligament, and the liver's peritoneal coverings.