T cells in the peritoneum.

The peritoneal cavity is a fluid-packed area that houses most of the abdominal organs, including the omentum, a visceral adipose tissue with milky patches or groups of leukocytes organized in the same way to those observed in typical lymphoid tissues. A distinct population of leukocytes patrols the peritoneal cavity and travels in and out of the milky spots, facing antigens or pathogens in the peritoneal fluid and responding appropriately. T cells may play a crucial function in regulating adaptive immune responses to antigens in the peritoneal cavity to ensure tissue homeostasis and healing. When peritoneal homeostasis is interrupted by inflammation, infection, obesity, or tumor metastasis, the omentum's dedicated fibroblastic stromal cells and mesothelial cells control peritoneal leukocyte recruitment and activation in unique ways. T cells, which employ their T cell receptor to target specific antigens, are an important component of the acquired immune response since they are present in the peritoneal cavity. The peritoneum provides a different environment for T cells to respond to pathogens. This chapter outlines the anatomy relevant to T cell function and biology, such as antigen processing/presentation, T cell activation, and the many T cell subpopulations in the peritoneal cavity, as well as their role in cancer or other infection.

Morphological hallmarks facilitating distinction of omental milky spots and lymph nodes: an exploratory study on their discriminative capacity.

BACKGROUND: Omental milky spots (OMSs) are the primary lymphoid structures of the greater omentum. However, the presence of lymph nodes (LNs) has occasionally been mentioned as well. Understanding which lymphoid structures are present is of significance, especially in gastric tumor metastasis; tumor deposits in omental LNs suggest local lymphatic spread, whereas tumor deposits in OMSs suggest peritoneal spread and hence extensive disease. Since LNs and OMSs share morphological characteristics and OMSs might be wrongly identified as LNs, reliable hallmarks facilitating easy discrimination are needed. MATERIALS AND METHOD: A series of microscopic morphological hallmarks unique to LNs were selected as potential candidates and were assessed for their discriminative capacity: 1) capsule, 2) trabeculae, 3) subcapsular sinus, 4) afferent lymphatic vessels, 5) distinct B- and T cell regions, and 6) a layered organization with, from the outside in a capsule, cortex, paracortex, and medulla. These hallmarks were visualized by multiple staining techniques. RESULTS: Hallmarks 1, 2 5 and 6 were shown to be the most efficient as these were consistent and discriminative. They were best visualized by Picrosirius red, smooth muscle actin and a B-cell / T-cell double staining. CONCLUSION: The presence of a capsule, trabeculae, distinct B- and T-cell regions and a layered organization represent consistent and reliable morphological features which allow to easily distinguish LNs from OMSs, especially when applied in combination.

The omentum harbors unique conditions in the peritoneal cavity to promote healing and regeneration for diaphragm muscle repair in mdx mice.

Although the primary cause of Duchenne muscular dystrophy (DMD) is a genetic mutation, the inflammatory response contributes directly to severity and exacerbation of the diaphragm muscle pathology. The omentum is a lymphoid organ with unique structural and immune functions serving as a sanctuary of hematopoietic and mesenchymal progenitors that coordinate immune responses in the peritoneal cavity. Upon activation, these progenitors expand and the organ produces large amounts of growth factors orchestrating tissue regeneration. The omentum of mdx mouse, a DMD murine model, is rich in milky spots and produces growth factors that promote diaphragm muscle regeneration. The present review summarizes the current knowledge of the omentum as an important immunologic structure and highlights its contribution to resolution of dystrophic muscle injury by providing an adequate environment for muscle regeneration, thus being a potential site for therapeutic interventions in DMD.

Omental Vascularized Lymph Node Flap: A Radiographic Analysis.

BACKGROUND: Vascularized lymph node transfer is an increasingly popular option for the treatment of lymphedema. The omental donor site is advantageous for its copious soft tissue, well-defined collateral circulation, and large number of available nodes, without the risk of iatrogenic lymphedema. The purpose of this study is to define the anatomy of the omental flap in the context of vascularized lymph node harvest. METHODS: Consecutive abdominal computed tomography angiography (CTA) images performed at a single institution over a 1-year period were reviewed. Right gastroepiploic artery (RGEA) length, artery caliber, lymph node size, and lymph node location in relation to the artery were recorded. A two-tailed Z-test was used to compare means. A Gaussian Mixture Model confirmed by normalized entropy criterion was used to calculate three-dimensional lymph node cluster locations along the RGEA. RESULTS: In total, 156 CTA images met inclusion criteria. The RGEA caliber at its origin was significantly larger in males compared with females (p < 0.001). An average of 3.1 (1.7) lymph nodes were present per patient. There was no significant gender difference in the number of lymph nodes identified. Average lymph node size was significantly larger in males (4.9 [1.9] × 3.3 [0.6] mm in males vs. 4.5 [1.5] × 3.1 [0.5] mm in females; p < 0.001). Three distinct anatomical variations of the RGEA course were noted, each with a distinct lymph node clustering pattern. Total lymph node number and size did not differ among anatomical subgroups. CONCLUSION: The omentum is a reliable lymph node donor site with consistent anatomy. This study serves as an aid in preoperative planning for vascularized lymph node transfer using the omental flap.

Earlobe-like peritoneal appendage near the angle of His: a useful landmark for demarcating the lateral margin of the gastric cardia.

The gastric cardia-the small area around the cardiac orifice including the abdominal esophagus-is an important target area for abdominal and thoracic surgeries, especially for laparoscopic procedures. In this study of 28 cadavers, a peritoneal earlobe-like appendage near the angle of His was identified as a useful indicator of the lateral margin of the abdominal esophagus, which is otherwise obscure because the peritoneum continues to the diaphragm without definite demarcation of this margin. This structure, which appears equivalent to the epiploic appendages, was commonly found to be present (in 22/28, 78.6 % of the 28 cadavers) and was 4-21 mm × 6-40 mm × 1-4 mm in size, triangular, round, or leaf-like in shape, contained fat, and was on an imaginary line along which the lesser omentum adheres to the lesser curvature and continues to the diaphragm (18/22, 81.8 %). This indicator is associated with the lesser omentum and is part of the gastrophrenic ligament, and could serve as a useful indicator of the margin of the gastric cardia, thus aiding surgeons performing laparoscopic surgery in this region.

Imaging of the pediatric peritoneum, mesentery and omentum.

The normal peritoneal structures, including the mesenteries and the omenta, are only a few cell layers thick and are visible on imaging based upon the tissues (e.g., fat) and structures (e.g., blood vessels and lymph nodes) contained within them. These structures become more visible and change in appearance when involved by pathological processes. In this pictorial essay, we discuss the normal anatomy of the various abdominopelvic peritoneal structures and illustrate numerous developmental and acquired diagnoses that involve these structures in the pediatric and young adult population.

The Omental Pedicle Flap in Dogs Revised and Refined: A Cadaver Study.

OBJECTIVE: To expand current knowledge on the canine omental vasculature and refine the existing lengthening technique of the canine omentum. STUDY DESIGN: Ex vivo study. ANIMALS: Canine cadavers (n=20). METHODS: In 10 canine cadavers the omental arteries were mapped using intravascular latex injection and these results were used to create an omental pedicle flap based on the splenic artery in 10 additional cadavers. The operating range of the flap was recorded with particular attention to the main regions of interest for omental transposition in dogs (axillary and inguinal regions). RESULTS: The superficial and deep omental leaves were each predominantly supplied by a left and a right marginal omental artery that anastomosed near the caudal omental border into a superficial and a deep omental arch, respectively. Anastomoses between arteries of the superficial and the deep omental leaves were weak and inconsistent, except for 1 anastomosis that was found in 8 of 10 dogs. By transposing the intact omentum, the right axilla could be reached in 3 dogs, both axillae in 1 dog, and both groins in all cadavers. In all cases, the omental pedicle reached to and beyond the axillary and inguinal regions. By unfolding the pedicle leaves, the width of the pedicle tip could be doubled. CONCLUSION: When lengthening the omentum is necessary to reach extra-abdominal structures, the omental pedicle flap based on the splenic artery appears to preserve the omental vascular supply. These observations warrant further clinical trials to evaluate this new omtental flap technique in vivo.

The Microscopic Structure of the Omentum in Healthy Dogs: The Mystery Unravelled.

The canine omentum has many valuable properties but is still an underestimated organ. It contributes in many ways to the protection of the peritoneal cavity through its versatility on immunological level, but also through its role during angiogenesis, absorption, adhesion and fat storage. Despite a wide range of applications, the basic structure of the omentum is not well documented. This study provides an insight in the microscopic structure of the canine omentum through both light microscopic and electron microscopic investigations. Two regions could be distinguished in the canine omentum: translucent and adipose-rich regions. The translucent regions were composed of two different layers: a continuous flattened mesothelium on top of a submesothelial connective tissue matrix. The adipose-rich regions consisted of a substantial layer of adipocytes on which a flattened continuous mesothelium was present. Between those two layers, a few strands of collagen fibres could be detected. Large aggregates of immune cells, the so-called milky spots, were not observed in the omentum of healthy dogs. Only a limited number of leucocytes, macrophages and neutrophils were found, scattered throughout the connective tissue in the translucent regions. At the level of the adipose-rich regions, the immunological population was virtually non-existent.

Morphology of the Canine Omentum Part 2: The Omental Bursa and its Compartments Materialized and Explored by a Novel Technique.

The canine omental bursa is a virtual cavity enclosed by the greater and lesser omentum. While previous representations of this bursa were always purely schematic, a novel casting technique was developed to depict the three-dimensional organization of the omental bursa more consistently. A self-expanding polyurethane-based foam was injected into the omental bursa through the omental foramen in six dogs. After curing and the subsequent maceration of the surrounded tissues, the obtained three-dimensional casts could clearly and in a reproducible way reveal the omental vestibule, its caudal recess and the three compartments of the splenic recess. The cast proved to be an invaluable study tool to identify the landmarks that define the enveloping omentum. In addition, the polyurethane material can easily be discerned on computed tomographic images. When the casting technique is preceded by vascular injections, the blood vessels that supply the omentum can be outlined as well.

Morphology of the Canine Omentum Part 1: Arterial Landmarks that Define the Omentum.

Although the omentum remains an enigmatic organ, research during the last decades has revealed its fascinating functions including fat storage, fluid drainage, immune activity, angiogenesis and adhesion. While clinicians both in human and veterinary medicine are continuously exploring new potential omental applications, detailed anatomical data on the canine omentum are currently lacking, and information is often retrieved from human medicine. In this study, the topographic anatomy of the canine greater and lesser omentum is explored in depth. Current nomenclature is challenged, and a more detailed terminology is proposed. Consistent arteries that are contained within folds of the superficial omental wall are documented, described and named, as they can provide the anatomical landmarks that are necessary for unambiguous scientific communication on the canine omentum. In an included dissection video, the conclusions and in situ findings described in this study are demonstrated.

Gross anatomy of the ringed seal (Pusa hispida) gastro-intestinal tract.

The gross anatomical structure of the ringed seal (Pusa hispida) gastrointestinal tract is poorly described and often veterinary anatomical terminology is not used. Although the basic abdominal visceral pattern corresponded to domestic carnivores, significant differences were noted. The stomach was an elongated sharply bent tube (u-shaped) with the pylorus and fundus juxtaposed. The elongated jejunum measured up to 15.6 times body length and had 37 jejunal arteries from the cranial mesenteric artery. The pancreas was asymmetrical with a small right lobe and a large left lobe. The unusually short greater omentum negated formation of deep and superficial leaves. The most remarkable difference was the separation of the liver parenchyma into three physically separate masses, held together by hepatic ducts, veins and arteries. The topography and position of the liver was dependent on the amount of blood in the hepatic sinus (distended hepatic veins and hepatic portion of vena cava). Thus, as the hepatic sinus filled, the lateral liver masses separate from the central mass by moving caudolaterally. This was facilitated by modified coronary and triangular ligaments which did not attach directly to the liver, but instead to the hepatic sinus. These anatomical adaptations are apparently advantageous to ringed seal's survival in a deep marine environment.

Ultrasonographic examination of the small intestine, large intestine and greater omentum in 30 Saanen goats.

The small and large intestine of 30 healthy Saanen goats were examined ultrasonographically using a 5.0 MHz-linear transducer. The goats were examined on the right side, from the eighth rib to the caudal aspect of the flank. The small and large intestine could be easily differentiated. The descending duodenum could be imaged in 19 goats, and the jejunum and ileum seen in all goats. The jejunum and ileum were most often seen in cross-section and rarely in longitudinal section in the ventral region of the right flank. The intestinal contents were usually homogenously echoic, and active motility was observed in all the goats. The diameter of the small intestine was 0.8-2.7 cm (1.6 [0.33] cm). The spiral ansa of the colon was imaged in all the goats, and in 21 the caecum was also seen. Both these sections of large intestine were most commonly seen in the dorsal region of the right flank. The spiral ansa of the colon was easily identified by its spiral arrangement of centripetal and centrifugal gyri, which had a garland-like appearance. Because of intraluminal gas, only the wall of the colon closest to the transducer could be imaged. The diameter of the spiral colon ranged from 0.8 to 2.0 cm (1.1 [0.24] cm). Usually only the wall of the caecum closest to the transducer could be imaged and it appeared as a thick, echoic, slightly undulating line. The greater omentum could be seen in all the goats.

Cystoduodenal ligament as an abnormal fold and the accompanying anatomical and clinical implications.

This paper reports two cases of cadaveric cystoduodenal ligament in the lesser omentum, different from the commonly known hepatoduodenal and hepatogastric ligaments. Cystoduodenal ligament was occasionally reported and implies a variation in the anatomy of the omental bursa and its foramen. The omental foramen which has been commonly described to provide communication between the greater and the lesser sacs, and located posterior to the free egde of the lesser omentum, is not so in these cases. The knowledge of abnormal peritoneal folds like this may be important to surgeons, prosectors and radiologists.

Analysis of human omentum-associated lymphoid tissue components with S-100: an immunohistochemical study.

Milky spots are opaque patches in the greater omentum. They were first described by von Recklinghausen (1863) in the omentum of rabbits. In man, milky spots are relatively uniform, highly vascularized accumulations of mononuclear cells. The objective of this study was to describe in human omental lymphoid tissue components with S-100. Tissue samples (greater omentum) were collected from 14 patients operated with different reasons in our Department of General Surgery, in order to histologically present the presence of S-100 in the cells making up the milky spots in human omentum tissue. Tissue samples were cut approximately 5-8 micrometer thick with frozen-sections and stained with an indirect immunoperoxidase technique, as described previously. Then milky spots were examined by light microscopy. These data indicate that unstimulated milky spots in the human greater omentum are to a great extent just a preformed specific accumulation of primarily macrophages within the stroma of the greater omentum, secondarily B- and T-lymphocytes. In addition to these cells, we observed that a few mast and reticular cells were seen in the milky spots by S-100 reactive cross-sections of greater omentum. In the human omentum tissue that was stained with indirect immunoperoxidase method using anti S-100 monoclonal antibody, an arteriole cross-section in the center, reactive nerve cross-sections in the adjacent stroma and endogenic peroxidase reactivity in a few granulocytes in omental tissue were observed.

Release of inflammatory mediators by human adipose tissue is enhanced in obesity and primarily by the nonfat cells: a review.

This paper considers the role of putative adipokines that might be involved in the enhanced inflammatory response of human adipose tissue seen in obesity. Inflammatory adipokines [IL-6, IL-10, ACE, TGFbeta1, TNFalpha, IL-1beta, PAI-1, and IL-8] plus one anti-inflammatory [IL-10] adipokine were identified whose circulating levels as well as in vitro release by fat are enhanced in obesity and are primarily released by the nonfat cells of human adipose tissue. In contrast, the circulating levels of leptin and FABP-4 are also enhanced in obesity and they are primarily released by fat cells of human adipose tissue. The relative expression of adipokines and other proteins in human omental as compared to subcutaneous adipose tissue as well as their expression in the nonfat as compared to the fat cells of human omental adipose tissue is also reviewed. The conclusion is that the release of many inflammatory adipokines by adipose tissue is enhanced in obese humans.

Catheter patency and peritoneal morphology and function in a rat model of citrate-buffered peritoneal dialysis.

BACKGROUND: Single-dwell studies in rats and humans have shown that supplementing citrate for lactate in peritoneal dialysis (PD) fluids improves ultrafiltration (UF). ♢ METHODS: The long-term effects of citrate-substituted PD fluids on PD catheter patency, UF, and peritoneal morphology were evaluated in a rat model over 5 weeks of daily PD fluid exposure. A standard 2.5% glucose 40 mmol/L lactate PD fluid and a corresponding 10/30 mmol/L citrate/lactate PD fluid were compared. In a control group, rats with catheters received no PD fluid. ♢ RESULTS: The average patency time (% of 36 days) of silicone rubber PD catheters was significantly longer in the citrate PD group (98.8% ± 1.2%) and the control group (100% ± 0%) compared to the lactate PD group (54.7% ± 9.5%). In a separate experiment, heparin-coated polyurethane catheters were used to study peritoneal morphology and fluid transport. The citrate group had a higher net UF than the lactate group at the beginning and at the end of the 5 weeks. During the experiment, both fluid-treated groups suffered from UF loss; the control group showed the highest net UF at the end of the 5 weeks. Peritoneal vascular density and submesothelial thickness, indicators of angiogenesis and fibrosis, were not significantly different among the groups. Fibrosis was significantly negatively correlated to osmotic UF. ♢ CONCLUSION: A positive acute effect of citrate on UF was confirmed and conserved over time. Citrate PD strongly improved PD catheter patency time compared with lactate. Both citrate PD and lactate PD induced negative long-term effects on UF compared with control animals.

Association of adipocyte genes with ASP expression: a microarray analysis of subcutaneous and omental adipose tissue in morbidly obese subjects.

BACKGROUND: Prevalence of obesity is increasing to pandemic proportions. However, obese subjects differ in insulin resistance, adipokine production and co-morbidities. Based on fasting plasma analysis, obese subjects were grouped as Low Acylation Stimulating protein (ASP) and Triglyceride (TG) (LAT) vs High ASP and TG (HAT). Subcutaneous (SC) and omental (OM) adipose tissues (n = 21) were analysed by microarray, and biologic pathways in lipid metabolism and inflammation were specifically examined. METHODS: LAT and HAT groups were matched in age, obesity, insulin, and glucose, and had similar expression of insulin-related genes (InsR, IRS-1). ASP related genes tended to be increased in the HAT group and were correlated (factor B, adipsin, complement C3, p < 0.01 each). Differences between LAT and HAT group were almost exclusively in SC tissue, with little difference in OM tissue. Increased C5L2 (p < 0.01), an ASP receptor, in HAT suggests a compensatory ASP pathway, associated with increased TG storage. RESULTS: HAT adipose tissue demonstrated increased lipid related genes for storage (CD36, DGAT1, DGAT2, SCD1, FASN, and LPL), lipolysis (HSL, CES1, perilipin), fatty acid binding proteins (FABP1, FABP3) and adipocyte differentiation markers (CEBPalpha, CEBPbeta, PPARgamma). By contrast, oxidation related genes were decreased (AMPK, UCP1, CPT1, FABP7). HAT subjects had increased anti-inflammatory genes TGFB1, TIMP1, TIMP3, and TIMP4 while proinflammatory PIG7 and MMP2 were also significantly increased; all genes, p < 0.025. CONCLUSION: Taken together, the profile of C5L2 receptor, ASP gene expression and metabolic factors in adipose tissue from morbidly obese HAT subjects suggests a compensatory response associated with the increased plasma ASP and TG.

Dexamethasone and the inflammatory response in explants of human omental adipose tissue.

Dexamethasone is a synthetic glucocorticoid that is a potent anti-inflammatory agent. The present studies examined the changes in gene expression of 64 proteins in human omental adipose tissue explants incubated for 48h both in the absence and presence of dexamethasone as well as the release of 8 of these proteins that are putative adipokines. The proteins were chosen because they are inflammatory response proteins in other cells, are key regulatory proteins or are proteins with known functions. About 50% were significantly up-regulated while about 10% were unchanged and the remaining 40% were down-regulated. Dexamethasone significantly up-regulated the expression of about 33% of the proteins but down-regulated the expression of about 12% of the proteins. We conclude that dexamethasone is a selective anti-inflammatory agent since it inhibits only about one-fourth of the proteins up-regulated during in vitro incubation of human omental adipose tissue.

Sonographic anatomy of the gastrohepatic ligament.

OBJECTIVE: The purpose of this presentation is to illustrate anatomic and pathologic features of the gastrohepatic ligament (GHL) and to show its usefulness for precise localization of abnormalities, particularly in relation to the lesser peritoneal cavity and diseases occurring within the confines of the ligament itself. METHODS: Cases were selected that illustrate the objectives above. RESULTS: Illustrations show various anatomic and pathologic features meant to enhance interpretation of left upper quadrant sonograms. CONCLUSIONS: Illustrations seen in the sonographic literature vaguely interpret the relationships of the GHL. Misunderstanding has led not only to improper nomenclature but also to the use of inappropriate indicators of lesser omental diseases. With a clear understanding of the anatomy of the GHL and its use as a pivotal marker for structures around and within it, one can avoid these pitfalls and better evaluate adult and pediatric lesser omental anatomy.