Lesser sac: Anatomy and non-neoplastic processes Poster No.: C-0027 Congress: ECR 2013 Type: Educational Exhibit Authors: E. Papadaki, R. Moschona, S. Paschalidou ; Rethymno, CR/ 1 2 2 3 1 3 GR, Rethymno/GR, Rethymno, CRETE/GR Keywords: Contrast agent-intravenous, CT, Anatomy, Abdomen, Contrast agent-oral, Education and training DOI: 10.1594/ecr2013/C-0027 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 26
Learning objectives 1. To provide a comprehensive review of the anatomy of the lesser sac, as studied by computed tomography (CT). 2. To overview the spectrum of the non-neoplastic processes that may affect this sac, with emphasis on the role of CT. Background The peritoneal cavity contains a series of communicating but compartmentalized potential spaces, that are not visualized on CT scans, unless they are distended by pathologic processes. This cavity is divided into two parts - greater sac and lesser sac. The greater sac is further divided into supracolic and infracolic compartments by the transverse colon. The lesser sac, also known as the omental bursa, is the largest recess of the peritoneal cavity and is bound anteriorly by the lesser omentum and stomach, and posteriorly by the transverse mesocolon, pancreas, upper part of the left kidney, the left adrenal gland and the diaphragm. The lesser sac is empty and collapsed so that only parts of its boundaries, such as the posterior gastric wall and pancreatic body, are observed on axial CT scans (4). To the right, the lesser sac opens into the greater sac via the epiploic foramen or foramen of Winslow. The epiploic foramen is bound anteriorly by the free border of the lesser omentum, with the common bile duct, hepatic artery, and the portal vein between its two layers, posteriorly by the inferior vena cava, superiorly by the caudate process of the liver, and inferiorly by the first part of the duodenum (2,3). In patients with intraperitoneal inflammation, this foramen may seal, separating the lesser sac from the greater peritoneal cavity (4). A prominent fold of peritoneum, elevated from the posterior abdominal wall by the left gastric artery, divides the lesser sac into two compartments - a large lateral on the left and a smaller medial on the right (fig.1). The lesser sac has three recesses: the superior (fig.2, fig.3), splenic (fig.4) and inferior recess (fig.5). The medial compartment contains the superior recess which surrounds the medial aspect of the caudate lobe. The splenic recess extends across the midline to the splenic hilum, attached by the gastrosplenic and splenorenal ligaments. The inferior recess extends inferiorly between the stomach, pancreas, and transverse mesocolon, between the two layers of the greater omentum, although this space is usually obliterated (2,3,4). Page 2 of 26
Disease processes producing generalized ascites or those involving the pancreas, transverse colon, posterior wall of the stomach, posterior wall of the duodenum and caudate lobe of the liver can produce pathologic changes in the lesser sac (4). Non neoplastic processes involving the lesser sac include the following: (a) fluid collections of ascitic transudate, inflammatory exudate, bile, or blood; (b) solid or cystic mass lesions including inflammatory processes; and (c) internal hernias (1). A fluid collection within only the lesser sac should be considered an inflammatory exudate from pancreatitis, cholecystitis, or gastric perforation. Fluid collections involving the lateral compartment of the lesser sac displace the stomach anteriorly and sometimes medially, whereas medial compartment collections cause lateral displacement of the stomach. Occasionally, inflammation involving the medial compartment may extend via the aortic or diaphragmatic hiatus into the lower mediastinum (4). Non-neoplastic space- occupying processes include pancreatic pseudocysts or abscesses and enlarged lymph nodes. Lesser sac hernias make up only about 1-4% of all internal hernias. The entrance of herniation into the lesser sac is usually through the foramen of Winslow, and less commonly, via the transverse mesocolon or trans-omental (often iatrogenic) (1). Images for this section: Page 3 of 26
Fig. 1: CT sections in a patient with ascitic transudate. The lesser sac, distended with ascites, is traversed by the stretched peritoneal fold (black arrows) in which the left gastric artery courses to reach the lesser curvature of the stomach and divides the lesser sac into two compartments - a large lateral on the left and a smaller medial on the right Page 4 of 26
Fig. 2: Normal anatomy of the lesser sac, which consists of a superior recess (blue arrow) (fig.2,fig.3), a splenic recess (white arrow) (fig.4), and an inferior recess (yellow arrow) (fig.5) in axial CT images. Note a large amount of air in greater sac (black straight arrow) in a patient with pneumoperitoneum. Page 5 of 26
Fig. 3: Normal anatomy of the lesser sac, which consists of a superior recess (blue arrow) (fig.2,fig.3), a splenic recess (white arrow) (fig.4), and an inferior recess (yellow arrow) (fig.5) in axial CT images. Note a large amount of air in greater sac (black straight arrow) in a patient with pneumoperitoneum. Page 6 of 26
Fig. 4: Normal anatomy of the lesser sac, which consists of a superior recess (blue arrow) (fig.2,fig.3), a splenic recess (white arrow) (fig.4), and an inferior recess (yellow arrow) (fig.5) in axial CT images. Note a large amount of air in greater sac (black straight arrow) in a patient with pneumoperitoneum. Page 7 of 26
Fig. 5: Normal anatomy of the lesser sac, which consists of a superior recess (blue arrow) (fig.2,fig.3), a splenic recess (white arrow) (fig.4), and an inferior recess (yellow arrow) (fig.5) in axial CT images. Note a large amount of air in greater sac (black straight arrow) in a patient with pneumoperitoneum. Page 8 of 26
Imaging findings OR Procedure details This exhibit describes and illustrates the anatomy of the lesser sac. We present a comprehensive review of non-neoplastic processes of lesser sac including: air collection after gastric perforation (fig.6,7,8,9) or surgery (fig.11,12,13), inflammatory exudate from pancreatitis (fig.15,16), pancreatic pseudocysts (fig.17,18), ascitic transudate (fig.1), bile peritonitis after blunt liver trauma (fig.10,11,12,13,14) and hematoma (fig.19,20,21,22). Images for this section: Page 9 of 26
Fig. 6: Depiction of lesser sac anatomy by air - fluid collection, in a case of neglected, sealed - off, gastric perforation. CT images depict air collection in the superior recess of lesser sac (blue arrow )(fig.6,7), in liver hilum (green arrow) (fig.8) and in the inferior recess (yellow arrow) (fig.9), while fluid collection is present within the splenic recess (white arrow) (fig.6). Axial CT image in the level of Winslow foramen shows a small air collection delineating the foramen (black arrow) (fig.7). Fig. 7: Depiction of lesser sac anatomy by air - fluid collection, in a case of neglected, sealed - off, gastric perforation. CT images depict air collection in the superior recess of lesser sac (blue arrow )(fig.6,7), in liver hilum (green arrow) (fig.8) and in the inferior recess (yellow arrow) (fig.9), while fluid collection is present within the splenic recess Page 10 of 26
(white arrow) (fig.6). Axial CT image in the level of Winslow foramen shows a small air collection delineating the foramen (black arrow) (fig.7). Fig. 8: Depiction of lesser sac anatomy by air - fluid collection, in a case of neglected, sealed - off, gastric perforation. CT images depict air collection in the superior recess of lesser sac (blue arrow )(fig.6,7), in liver hilum (green arrow) (fig.8) and in the inferior recess (yellow arrow) (fig.9), while fluid collection is present within the splenic recess (white arrow) (fig.6). Axial CT image in the level of Winslow foramen shows a small air collection delineating the foramen (black arrow) (fig.7). Page 11 of 26
Fig. 9: Depiction of lesser sac anatomy by air - fluid collection, in a case of neglected, sealed - off, gastric perforation. CT images depict air collection in the superior recess of lesser sac (blue arrow )(fig.6,7), in liver hilum (green arrow) (fig.8) and in the inferior recess (yellow arrow) (fig.9), while fluid collection is present within the splenic recess (white arrow) (fig.6). Axial CT image in the level of Winslow foramen shows a small air collection delineating the foramen (black arrow) (fig.7). Page 12 of 26
Fig. 10: Bile peritonitis in a patient with grade V liver trauma. Axial CT images, 15 days following the trauma, demonstrates bile collection within the inferior recess of lesser sac (blue arrow) (fig.10). Postoperative air bubbles into the lesser sac (white arrows) (fig.11,12) and the winslow foramen (light blue arrow) (fig.13). Page 13 of 26
Fig. 18: Pancreatic pseudocysts (white arrows) projecting into the lesser sac in CT sections of an alcoholic patient with multiple episodes of pancreatitis (fig.17,18). Page 14 of 26
Fig. 19: Lesser sac hematoma, with mass-like configuration, in the splenic recess (white arrow) (fig.19) and in the inferior recess of the lesser sac (blue arrow) (fig.20). A small amount of hemoperitoneum surrounding the liver. The hematoma, which was initially misinterpreted with GIST, was disclosed at surgery. Page 15 of 26
Fig. 20: Lesser sac hematoma, with mass-like configuration, in the splenic recess (white arrow) (fig.19) and in the inferior recess of the lesser sac (blue arrow) (fig.20). A small amount of hemoperitoneum surrounding the liver. The hematoma, which was initially misinterpreted with GIST, was disclosed at surgery. Page 16 of 26
Fig. 21: Hematoma in the superior recess of lesser sac (black arrows) (fig.21) in CT sections of a trauma patient with grade IV pancreatic injury. CT scan depicts a proximal pancreatic transection (white arrow) (fig.22) with a peripancreatic hematoma (light green arrow). Page 17 of 26
Fig. 17: Pancreatic pseudocysts (white arrows) projecting into the lesser sac in CT sections of an alcoholic patient with multiple episodes of pancreatitis (fig.17,18). Page 18 of 26
Fig. 16: Axial CT images in a patient with acute pancreatitis depict the inflammatory exudate in the lesser sac (white arrow) (fig.15). The exudate extends into the inferior recess of the lesser sac (light blue arrow) and the splenic recess (green arrow) (fig.16). Page 19 of 26
Fig. 15: Axial CT images in a patient with acute pancreatitis depict the inflammatory exudate in the lesser sac (white arrow) (fig.15). The exudate extends into the inferior recess of the lesser sac (light blue arrow) and the splenic recess (green arrow) (fig.16). Page 20 of 26
Fig. 14: Axial CT image in a patient with grade V liver trauma, complicated with intrahepatic biloma. A small amount of free bile collection extends into the superior recess of the lesser sac (black arrow) (fig.14), surrounding the medial aspect of the caudate lobe. Page 21 of 26
Fig. 13: Bile peritonitis in a patient with grade V liver trauma. Axial CT images, 15 days following the trauma, demonstrates bile collection within the inferior recess of lesser sac (blue arrow) (fig.10). Postoperative air bubbles into the lesser sac (white arrows) (fig.11,12) and the winslow foramen (light blue arrow) (fig.13). Page 22 of 26
Fig. 12: Bile peritonitis in a patient with grade V liver trauma. Axial CT images, 15 days following the trauma, demonstrates bile collection within the inferior recess of lesser sac (blue arrow) (fig.10). Postoperative air bubbles into the lesser sac (white arrows) (fig.11,12) and the winslow foramen (light blue arrow) (fig.13). Page 23 of 26
Fig. 11: Bile peritonitis in a patient with grade V liver trauma. Axial CT images, 15 days following the trauma, demonstrates bile collection within the inferior recess of lesser sac (blue arrow) (fig.10). Postoperative air bubbles into the lesser sac (white arrows) (fig.11,12) and the winslow foramen (light blue arrow) (fig.13). Page 24 of 26
Fig. 22: Hematoma in the superior recess of lesser sac (black arrows) (fig.21) in CT sections of a trauma patient with grade IV pancreatic injury. CT scan depicts a proximal pancreatic transection (white arrow) (fig.22) with a peripancreatic hematoma (light green arrow). Page 25 of 26
Conclusion 1. CT is the method of choice in defining pathology involving the lesser sac. 2. Pathological processes and their pathway of spread are easily diagnosed after a thorough appreciation of the anatomy, including the ligaments and mesenteries, which subdivide the peritoneal cavity. References 1 Eunhye Yoo, MD, Joo Hee Kim, MD, Myeong-Jin Kim, MD, Jeong-Sik Yu, MD, Jae-Joon Chung, MD, Hyung-Sik Yoo, MD and Ki Whang Kim, MD. Greater and Lesser Omenta: Normal Anatomy and Pathologic Processes, RadioGraphics 2007; 27:707-720 2 Badri M. Shrestha, Peter W.G. Brown, Martin E. Wilkie, and Andrew T. Raftery. THE ANATOMY AND PATHOLOGY OF THE LESSER SAC: IMPLICATIONS FOR PERITONEAL DIALYSIS, PeritDialysis International, Vol. 30, pp. 496-501 3 Mathias Prokop,Michael Galanski. Spiral and Multislice Computed Tomography of the Body, pp. 596-601 4 Joseph K. Lee, Stuart S. Sagel, Robert Stanley, Jay Heiken. Computed Body Tomography with MRI correlation, pp975-1010 Personal Information Page 26 of 26