Abstract
The peritoneal cavity is subdivided into supracolic and infracolic compartments by transverse colon and its mesocolon. The supracolic compartment contains the liver, spleen, stomach, and lesser omentum. The infracolic compartment contains the coils of small bowel surrounded by ascending, transverse, and descending colon and the paracolic gutters. The imaging of different compartments is possible by various methods such as ultrasound (US) and computerized tomography. The treating physicians should be familiar with the relevant radiological anatomy of different compartments and spaces as accurate localization of fluid collection/lymph node in peritoneal cavity greatly aids in selection of a treatment strategy. The role of endoscopic US (EUS) is emerging for detail evaluation of all parts of peritoneal cavity as it provides an easy access for fine-needle aspiration from different compartments of peritoneal cavity. In this review, we describe the techniques of evaluation of different parts of supracolic compartments of peritoneum by EUS.
Keywords: Endoscopic ultrasound, liver, peritoneal ligaments, peritoneal spaces, retroperitoneum, spleen, stomach
Introduction
The abdominal cavity contains three potential spaces, i.e., the peritoneal cavity, subperitoneal space, and retroperitoneum.[1] The subperitoneal space, which is enclosed by double-layered peritoneal folds, subdivides the peritoneal cavity into different compartments.[2] These peritoneal folds (known as ligaments, mesentery, or omentum) also connect the intraperitoneal organs to the abdominal wall and act as conduits for the passage of neurovascular structures from the retroperitoneum.[3] The potential space between the peritoneal folds can provide a pathway for subperitoneal spread of disease processes.[4] Slow fluid collection in the retroperitoneal, subperitoneal, or peritoneal space may be localized, but rapid accumulation of fluid, such as occurs in cases of trauma or acute pancreatitis, may overcome the natural boundaries and spill into multiple spaces.[5,6,7] The treating physicians should be familiar with the relevant radiological anatomy of these ligaments and spaces as accurate localization of fluid collection and lymph node in the peritoneal cavity, subperitoneal space, and retroperitoneum greatly aids in the selection of a treatment strategy.[8] The fat, lymph nodes, and blood vessels within ligaments act as radiological landmarks of identification for imaging by ultrasound (US), computerized tomography (CT), and magnetic resonance imaging.[9,10,11,12,13] Endoscopic US (EUS) provides an additional modality for assessment of peritoneal ligaments.[14] The transverse mesocolon, which attaches the transverse colon to the posterior wall of the abdomen, subdivides the peritoneal cavity into supracolic and infracolic compartments located above and below the transverse colon and its mesocolon. The supracolic compartment contains the liver, spleen, stomach, and lesser omentum. The infracolic compartment contains the coils of the small bowel surrounded by the ascending, transverse, and descending colon and the paracolic gutters. In this review, we describe the normal EUS anatomy of the peritoneal spaces and the recesses of the supracolic compartments of the peritoneum with supportive images by US/CT scan. Most of the images have been taken with the presence of fluid in some compartment of the abdominal cavity to facilitate clear description [Figure 1].
APPLIED EMBRYOLOGY OF THE PERITONEAL LIGAMENTS
Most peritoneal ligaments arise from the ventral or dorsal mesentery of the gut. The liver and its ligaments arise in the ventral mesentery (ventral mesogastrium), whereas the stomach, spleen, pancreatic tail, and their corresponding ligaments develop in the dorsal mesentery of the foregut (dorsal mesogastrium). The ventral part of the ventral mesentery becomes the falciform ligament, and the dorsal part of the ventral mesentery becomes the lesser omentum (hepatogastric and hepatoduodenal parts). At the level of the spleen, the ventral part of the dorsal mesentery becomes the gastrosplenic ligament, and the dorsal part of the dorsal mesentery becomes the splenorenal ligament. Above the level of the spleen, the dorsal mesentery gives rise to the gastrophrenic ligament (GPL), and below the level of the spleen, it gives rise to the gastrocolic ligament.
Applied anatomy of the liver
The ligaments of the liver
The ligaments of the liver include the suspensory ligaments of the liver (falciform) and the lesser omentum. The falciform ligament and lesser omentum contribute to the formation of the right and left coronary (crown-like) ligaments. The falciform ligament is continuous with the superior layer of the right coronary ligament to the right and with the anterior layer of the left coronary ligament to the left. The gastrohepatic ligament (GHL) (part of the lesser omentum) is continuous with the inferior layer of the right coronary ligament to the right and with the posterior layer of the left coronary ligament to the left. On both sides, the coronary ligaments continue as triangular ligaments. On the right side, the coronary ligament has superior and inferior layers (as it lies more toward the posterior surface of the liver) while on the left side, it has anterior and posterior layers (as it lies more toward the superior surface of the liver). The superior and inferior layers of the right coronary ligament are long, widely separated, and enclose the bare area of the liver. The left triangular ligament is a short ligament [Figure 2].
The perihepatic spaces
The left and right suprahepatic spaces lie between the diaphragm and the liver and are separated by the falciform ligament [Figures 3, 4 and Video 1]. The left and right infrahepatic spaces lie between the liver, the transverse colon, and the transverse mesocolon and are separated by the ligamentum teres [Figure 5]. The superior coronary ligament separates the bare area from the right suprahepatic space, and the inferior coronary ligament (hepatorenal ligament) separates the bare area from the hepatorenal recess. The inferior coronary ligament has a membranous extension, which reaches up to the inferior vena cava (IVC), and the extended ligament separates the superior recess of the lesser sac from the bare area of the liver on the right side [Figure 6]. The lateral part of the left triangular ligament separates the posterior and anterior left suprahepatic spaces.
Communications
The right suprahepatic spaces communicate with the right subhepatic space around the right triangular ligament and the inferior border of the liver [Figures 3–5 and Video 2]. The hepatorenal space communicates medially with the superior recess of the lesser sac through the foramen of Winslow, is limited inferiorly by the right flexure of the colon, and has free lateral communication with the right paracolic gutter [Figures 1, 7 and 8]. The left infrahepatic space is separated from the superior recess of the lesser sac by the GHL and communicates with the left suprahepatic and perisplenic spaces.
Applied anatomy of the stomach
The ligaments of the stomach
The lesser omentum contains the GHL and the hepatoduodenal ligament (HDL) and extends from the L-shaped (truly a reverse L) attachment on the visceral surface of the liver to the lesser curvature of the stomach. This L-shaped ligament has vertical and horizontal parts [Figures 9 and 10]. The GHL (pars condensa) is the vertical part, which extends from the lesser curvature into the fissure for the ligamentum venosum [Figures 11 and 12]. The superior recess of the lesser sac can extend along the ligament up to the caudate lobe of the liver [Figure 13]. The HDL (pars vasculosa) is the horizontal part, which extends from the porta hepatis to the upper border of the first part of the duodenum [Figure 9]. The three ligaments that are attached to the greater curvature are confluent but described as the gastrophrenic (above the level of spleen) [Figures 9 and 14], gastrosplenic (at the level of spleen) [Figures 9 and 15], and gastrocolic ligaments (below the level of spleen) [Figures 9 and 16]. Strictly speaking, of the three ligaments attached to the greater curvature, only the gastrocolic ligament is referred to as the greater omentum. The GPL forms the boundary of the bare area of the stomach, and the gastrosplenic ligament forms the left boundary of the splenic recess of the lesser sac. The gastrocolic ligament has two anterior layers that fold upon themselves to continue as two posterior layers extending up to the transverse colon. During fetal life, the inferior recess of the lesser sac extends in between the anterior and posterior layers of the gastrocolic ligament. However, the space is usually obliterated in adults. If the layers are not obliterated, fluid collection can occur in the inferior recess of the lesser sac between the anterior and posterior layers.
The perigastric spaces
The lesser sac lies posterior to the stomach [Figure 17]. It can be subdivided into superior and inferior compartments, above and below the level of the plane of the pancreas, by the gastropancreatic folds. The left and right folds project into the lesser sac and are raised by the anterior course of the left gastric artery and the common hepatic artery, respectively [Figures 18 and 19]. The superior recess is related to the inferior and left sides of the caudate lobe of the liver [Figures 20 and 21]. The left lateral margin of the superior recess near the fundus of the stomach is related to the GPL, which is contiguous inferiorly with the gastrosplenic and splenorenal ligaments, which form the left lateral boundary of the lesser sac. The space between the anterior margin of the gastropancreatic fold and the posterior layer of the GHL is the only direct pathway between the superior and inferior compartments of the lesser sac. The superior compartment is separated from the splenic recess by the course of the left gastric artery [Figures 22–24 and Video 3]. The splenic recess, which is an extension of the inferior compartment toward the splenic hilum, extends between the gastrosplenic and splenorenal ligaments and lies anterior to the upper part of the left kidney, the left suprarenal gland, and the diaphragm [Video 4]. The inferior recess is significantly larger and mainly located to the left of the midline. It separates the stomach from the body of the pancreas. Generally, the caudal extent of the inferior recess is at the level of the transverse colon and the transverse mesocolon [Figure 25 and Video 5]. The boundaries of the inferior recess include the gastropancreatic folds superiorly and the conjunctive area of the anterior and posterior layers of the greater omentum inferiorly.
Communications
The gastrosplenic ligament separates the greater sac from the splenic recess of the lesser peritoneal sac [Figures 26 and 27]. The ligaments of the lesser omentum (GHL and HDL) separate the superior recess of the lesser sac from the greater sac [Figures 8 and 9]. The superior recess is separated from the bare area of the liver and the IVC by a membranous continuation of the inferior coronary ligament [Figure 27]. The inferior recess on the right side communicates with the hepatorenal recess through the foramen of Winslow.
Applied anatomy of the spleen
The ligaments of the spleen
The spleen has five ligaments: one presplenic (the gastrosplenic ligament), three postsplenic (the splenorenal or lienorenal, splenocolic, and pancreaticosplenic ligaments), and one parasplenic (the phrenicosplenic ligament) [Figures 9, 28–31]. The splenocolic, pancreaticosplenic, and phrenicosplenic ligaments are less constant. When present, the phrenicosplenic ligament is identified above the upper pole of the organ, but it does not divide the peritoneal cavity on the left side into two separate subcompartments as does the falciform ligament on the right side. The phrenicocolic ligament, which is not attached to the spleen, is identified near the lower pole and creates a barrier between the perisplenic recess and the left paracolic gutter [Figures 28–30].
The perisplenic spaces (recesses)
The perisplenic spaces (usually described as recesses) are part of the left subphrenic space. The perisplenic recesses are located around the spleen and include three recesses related to the greater sac, namely, the gastrosplenic, splenorenal, and parasplenic recesses, and one recess related to the lesser sac, namely, the splenic recess. The gastrosplenic recess lies between the stomach and spleen [Figure 28 and Video 6]. The splenorenal recess, which is analogous to Morison's pouch, lies between the spleen and left kidney [Figure 30]. The perisplenic recess lies between the diaphragm and spleen [Figure 32]. The lower part of the perisplenic recess is sometimes defined as the splenocolic recess. All three recesses (the gastrosplenic, splenorenal, and perisplenic) arise from the embryologic left peritoneal space and are related to the greater sac. One splenic recess derived from the embryologic right peritoneal space and related to the lesser sac occurs as a fourth recess (splenic recess of the lesser sac) in relation to the spleen [Figures 28, 29 and 31].
Communications
The perisplenic recesses (except for the splenic recess of the lesser sac) are in continuity with each other around the spleen. The gastrosplenic ligament separates the splenic recess of the lesser sac from the gastrosplenic (presplenic) recess, which is a part of the greater sac [Figure 33]. The splenorenal ligament separates the splenic recess of the lesser sac from the splenorenal recess, which is part of the greater sac [Figure 30]. The splenocolic ligament also separates the splenic recess of the lesser sac and the splenocolic recess. The phrenicocolic ligament comes close to the lower pole of the spleen and separates the greater sac from the left paracolic gutter [Figure 33].
The bare areas
The bare area of the liver
The bare area of the liver is a triangular gap located between the superior and inferior layers of the coronary ligament as well as between the anterior and posterior layers of the left triangular ligament. On the left side, the bare area is almost nonexistent. The base of this triangle lies at the IVC while the apex lies at the tip of the right triangular ligament [Figures 34 and 35]. The superior coronary ligament separates it from the right suprahepatic space and the inferior coronary ligament (hepatorenal ligament) separates it from the hepatorenal recess. A short peritoneal reflection between the IVC and the right border of the caudate lobe of the liver separates it from the superior recess of the lesser sac [Figure 36]. The right suprarenal gland is located in this area [Figure 37]. The bare area of the liver is an extraperitoneal space, which communicates with the right anterior pararenal space of the retroperitoneum, and gas and fluid collection within the perirenal space may communicate directly with the bare area of the liver [Figure 38].
The bare area of the stomach
The bare area of the stomach is outlined by the GPL and lies on the posterior surface of the stomach. It has a triangular shape with the bottom facing upward and the tip facing downward. It is located in the upper and lower boundaries of the left and right layers of the GPL. The bare area of the stomach is continuous with the bare area of the esophagus, which lies on the posterior surface of the esophagus close to the gastroesophageal junction [Figure 39]. The phrenic-esophageal ligament, which is in continuity with the GPL, encloses the bare area of the esophagus as a fascial expansion extending in a cone-like manner from the margins of the esophageal hiatus of the diaphragm to the esophageal wall. The GPL separates the superior recess from the bare area of the stomach.
The bare area of the spleen
Traditionally, the spleen is considered one of the intraperitoneal viscera, but the bare areas of the spleen exist between numerous ligamentous attachments. The bare areas can be divided into the splenic hilus and the splenorenal parts. The splenorenal part is located between the renal aspect of the spleen and the splenic aspect of the left kidney. The bare area of the spleen and its permanent relationship to the upper pole of the left kidney is helpful for locating the fluid collection in the left upper quadrant on CT, specifically for differentiating between ascites and pleural fluid [Figure 40].
DISCUSSION
The peritoneal spaces and the separations are summarized in the form of a chart [Figure 41]. The ligaments contain fibers and depending on their thickness, they can be seen either as a hyperechoic line or as alternating stripes of hyperechoic lines. Ligaments inhibit the transmission of sound waves and are best seen when they are surrounded by ascitic fluid, i.e., ligamentum teres or parenchymal tissue on either or both sides, i.e. the GHL ligamentum venosum and ligamentum teres.[14] The identification of each ligament is done in its expected location between the organs and is facilitated by the presence of blood vessels that traverse these ligaments.[14] Metastasis within ligaments is of significant clinical importance as peritoneal surface metastases represent Stage III disease and liver metastases suggest Stage IV disease. A systematic examination of ligaments can be a useful modality for imaging and can provide valuable information to the clinician.[15] EUS of ligaments is also useful for group staging of a luminal malignancy, the sampling of station nodes, and decision-making regarding neoadjuvant therapy without laparoscopy or laparotomy.[15] It has become increasingly essential that clinicians and endosonographers thoroughly understand the peritoneal spaces and the ligaments and mesenteries that form their boundaries to localize disease to a particular peritoneal or subperitoneal space and formulate a differential diagnosis on the basis of that location.[8] In this article, we have attempted to describe the normal EUS anatomy of the peritoneal ligaments, which will enable a greater understanding of the spread of disease processes.
Financial support and sponsorship
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Conflicts of interest
There are no conflicts of interest.
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