The Peritoneal Cavity

Joie Burns

OBJECTIVES

Identify the potential spaces of the peritoneum and the organs and/or ligaments that divide them on diagrams.
Identify the potential spaces of the peritoneum on sonograms.
State the organs located in the peritoneum.
Describe the scanning techniques used to image the potential spaces and diseases of the peritoneum.
Explain the role the greater omentum and mesentery play in limiting the extent of pathology.
Recognize the sonographic appearance of benign and malignant changes seen in the peritoneum.
Analyze sonographic images of the peritoneum for pathology.

GLOSSARY

abscess a pocket of infection typically containing pus, blood, and degenerating tissue

bare area surface area of a peritoneal organ devoid of peritoneum

biloma a collection of extravasated bile that can occur with trauma or rupture of the biliary tract

diverticulum a small pocket communicating with a larger cavity or tube

free fluid fluid outside of vessels, bowel, and organs, seen in the potential spaces

hematoma an extravasated collection of blood localized within a potential space or tissue

hemoperitoneum extravasated blood within the peritoneal cavity

hilum area of the organ where blood vessels, lymph, and nerves enter and exit

iatrogenic treatment induced; may be intentional or unintentional

lymphocele an extravasated collection of lymph

mesentery two layers of fused peritoneum that conduct nerves, lymph, and blood vessels between the small bowel/colon and the posterior peritoneal cavity wall

parietal peritoneum peritoneum lining the walls of the peritoneal cavity

peritoneal organs solid organs and some portions of the bowel within the peritoneal cavity that are covered by visceral peritoneum

potential space an empty fold where the peritoneal layer reflects between two organs or an organ and peritoneal wall, which may contain fluid and other materials when disease is present

retroperitoneal organs organs posterior to the parietal peritoneum that are typically covered on their anterior surface or fatty capsule by parietal peritoneum

seroma fluid collection composed of blood products located adjacent to or surrounding transplanted organs in the early transplantation period

visceral peritoneum peritoneum encasing peritoneal organs

Sonography plays a significant role in the identification of disease processes within the peritoneal cavity; therefore, the peritoneal cavity is an important area of the body for sonographers to be familiar with. There are many disease processes of peritoneal organs that may result in pathology of the peritoneal cavity, including metastasis and a variety of fluid collections. Because of its ability to differentiate between cystic and solid lesions and collections, sonography excels at imaging the potential spaces within the abdominopelvic cavity. Sonography’s real-time capabilities and use of sound waves instead of ionizing radiation make it an excellent technology for imaging as well as biopsy or aspiration guidance. A thorough understanding of the anatomy of the peritoneal cavity, especially its divisions, will assist sonographers in determining the presence and extent of disease processes.

ABDOMINOPELVIC CAVITY

The abdominopelvic cavity can be described by two commonly accepted methods using superficial landmarks. The first, Addison lines, divides the abdominopelvic cavity into nine regions by drawing two parasagittal (vertical) lines and two axial (horizontal) lines. The first of the axial lines is called the transpyloric line and is determined by drawing an imaginary line halfway between the manubrial notch and the superior pubic symphysis. Instead of using the transpyloric line, some choose to use the subcostal line, a line drawn at the inferior border of the last rib, for its ease of visualization. The second of the axial lines is called the transtubercular line and is determined by drawing an imaginary line halfway between the transpyloric line and the superior pubic symphysis. This line also intersects the anterior superior iliac spines of the pelvis. The parasagittal lines are drawn halfway between the manubrial notch and the acromioclavicular joint, called the midclavicular line or mammary line. These lines divide the abdomen into right and left hypochondriac regions; right and left lumbar and iliac regions bilaterally; and epigastric, umbilical, and hypogastric regions centrally¹ (Fig. 5-1).

The abdominopelvic cavity may also be described in quadrants. One imaginary line is drawn vertically from the tip of the xiphoid process to the superior pubic symphysis along the sagittal midline plane, and a horizontal line is drawn at the level of the umbilicus. This divides the abdominopelvic cavity into the right upper quadrant (RUQ), right lower quadrant (RLQ), left upper quadrant (LUQ), and left lower quadrant (LLQ). This simpler method is the one most commonly employed in the clinical setting¹ (Fig. 5-2). The sonographer must be well versed in the anatomy that is found in each of these regions in order to correlate clinical findings with the sonographic examination.

ANATOMY OF THE PERITONEAL CAVITY

A thin sheet of tissues, called the peritoneal membrane, divides the abdominal cavity into peritoneal and retroperitoneal compartments. The largest of the body cavities is the peritoneal cavity, encompassing the abdomen and pelvis.

The peritoneal cavity is formed by the fourth embryonic week and is derived from the mesoderm.² The abdominopelvic cavity is lined with a thin continuous layer of peritoneum. The cavity is completely sealed in males but communicates with the external environment via the fallopian tubes in females. Peritoneum that envelops the organs is referred to as visceral peritoneum, and the peritoneal layer that lines the walls of the abdominopelvic cavity is referred to as parietal peritoneum. This thin layer coating all surfaces of the peritoneal cavity and its organs secretes a small amount of serous fluid, approximately 50 mL, which acts to lubricate visceral surfaces, allowing them to move without friction.¹

As organs develop along the posterior abdominal wall and protrude into the peritoneal cavity, they are covered by visceral peritoneum except at their hilum, where blood vessels, nerves, and lymph enter and exit the organ. The hila of peritoneal organs are considered bare areas because they lack a peritoneal covering. These bare areas are part of the retroperitoneum.

Divisions of the Peritoneal Cavity

The peritoneal cavity is generally divided into two compartments: the greater sac and the lesser sac. The greater sac is the largest, housing the liver, spleen, stomach, first portion of the duodenum, jejunum, ileum, cecum, transverse colon, sigmoid colon, and the upper two-thirds of the rectum.¹ This large sac contains several potential spaces that must be evaluated for free fluid.

The lesser sac may be thought of as a diverticulum of the greater sac and is also referred to as the omental bursa by some. The lesser sac does not contain any organs. This potential space lies immediately posterior to the stomach, extending superiorly to the left suprahepatic recess between the posterior left lobe of the liver and the left hemidiaphragm.

FIGURE 5-1 Addison lines. Nine regions of the abdominopelvic cavity based on Addison lines. The abdominal cavity is divided into nine regions by two sagittal midclavicular lines and two axial lines, the transpyloric line, and the transtubercular line.

FIGURE 5-2 Quadrants of the abdominopelvic cavity. The abdominal cavity can be divided into four quadrants: right upper quadrant, right lower quadrant, left upper quadrant, and left lower quadrant.

The lesser sac extends inferiorly into the fold of the greater omentum. This may also be referred to as the inferior recess of the lesser sac or omental bursa. Note that this fold is patent in infants and small children but generally fuses in adults, thereby significantly limiting the caudal extent of the lesser sac (Fig. 5-3A, B). The lesser sac’s anterior wall is formed by the posterior stomach, whereas superiorly it is enclosed by the lesser omentum, also called hepatogastric ligament. The splenorenal and gastrosplenic ligaments create the left lateral wall of this pocket (Fig. 5-4). The omental foramen, also called the foramen of Winslow, is located at the right lateral aspect of the lesser sac and is the only opening communicating with the greater sac. This opening is found posterior to the hepatoduodenal ligament, the thickened right border of the lesser omentum that guides the portal triad into the liver (Fig. 5-4).

The lesser omentum—also called the small omentum, gastrohepatic omentum, and gastrohepatic ligament—is a fused double layer of peritoneum stretching between the lesser curvature of the stomach and the left sagittal fissure for the ligamentum venosum (transverse fissure). This ligament creates the anterior superior border of the lesser sac, separating it from the supracolic compartment of the greater sac (Fig. 5-5).

Within the greater sac is a large apron-like double-layered sheet of peritoneum called the greater omentum that extends inferiorly from the greater curvature of the stomach and transverse colon. The greater omentum extends inferiorly, anterior to the bowel, folds inward, and travels superiorly to attach on the transverse colon. The anterior and posterior adjacent layers are separate in infants but typically fused
in adults and contain a variable amount of fat³ (Fig. 5-3). The greater omentum functions to prevent the parietal peritoneum of the anterior abdominal wall from adhering to the visceral peritoneum. This mesenteric drape is very mobile and moves to areas of inflammation, surrounding the inflamed area by creating adhesions to wall off infection (Fig. 5-6A, B). It also acts to cushion the abdominal organs to prevent trauma and acts to prevent the loss of body heat from abdominal organs.

FIGURE 5-3 Lesser sac—schematic sagittal sections, lateral view. Note the patent inferior recess of the lesser sac in the infant (A) and the fused nature of the same space in the adult (B). The red arrow indicates the omental foramen.

FIGURE 5-4 Omental foramen. The black arrow extends through the omental foramen through the width of the lesser sac. The opening is posterior to the hepatoduodenal ligament. The lesser space is seen immediately posterior to the stomach. P, peritoneal cavity.

The greater omentum subdivides the greater sac into a supracolic (above the colon) compartment and an infracolic (below the colon) compartment. The supracolic compartment is located anterior to the greater omentum and stomach and inferior to the liver. The infracolic compartment is located posterior to the greater omentum, surrounding the small bowel and colon within the remainder of the greater sac (Fig. 5-7). This division is important because it limits the spread of infected materials, pus, ascitic fluid, and malignant
cells within the peritoneal cavity. Communication between these two compartments is via the paracolic gutters, the lateral borders of the ascending and descending colon.

FIGURE 5-5 Lesser omentum. The lesser omentum is a double layer of peritoneum that stretches between the lesser curvature of the stomach and the left sagittal fissure for the ligamentum venosum.

FIGURE 5-6 Greater omentum. A: Longitudinal image in a patient with appendicitis demonstrates hyperechoic omental fat (arrows) surrounding the inflamed appendix. B: Transverse image again demonstrates the hyperechoic omental fat (arrows) seen surrounding the inflamed appendix. (Images courtesy of Ultrasound-Cases.info, owner SonoSkills.)

Potential Spaces of the Peritoneum

As organs grow into the peritoneal cavity, several pockets and recesses are formed by the organs, their vascular connections, and suspensory ligaments, thereby creating a complex landscape for sonographers to examine when performing abdominal and pelvic examinations. Ligaments divide portions of the peritoneal cavity. Sonographers require a working knowledge of these ligaments to understand where to look for fluid within the peritoneal sac and how to image and describe its location. See Table 5-1 for a description of the ligaments of the peritoneal cavity.

FIGURE 5-7 Divisions of the peritoneal cavity. Green represents the supracolic compartment of the greater sac; pink represents the infracolic compartment of the greater sac; and blue represents the lesser sac.

TABLE 5-1 Ligaments of the Peritoneal Cavity

Gastrohepatic ligament	Also called the lesser omentum, smaller omentum, and gastrohepatic omentum, it connects the lesser curvature of the stomach and the left sagittal fissure for the ligamentum venosum (transverse fissure) of the liver.
Hepatoduodenal ligament	Thickened free edge of the lesser omentum through which courses the portal triad; it connects the liver to the duodenum.
Falciform ligament	Double-layered fold of peritoneum that ascends from the umbilicus to the liver; contained within it is the ligamentum teres. The falciform ligament passes onto the anterior and then the superior surface of the liver before splitting into two layers. The right layer forms the upper layer of the coronary ligament; the left layer forms the upper layer of the left triangular ligament.
Coronary ligament	Bifurcation of the falciform ligament layers that fuse with the parietal peritoneum to form borders of the bare area of the liver, suspending the liver from the diaphragm. The right branch becomes the coronary ligament and the left branch becomes the left triangular ligament, limiting the greater sac at its cephalad extent into anterior and posterior compartments in the right subphrenic area.
Left triangular ligament	Formed by the left branch of the falciform ligament and the parietal peritoneum, it forms the left extremity of the bare area of the liver.
Splenorenal ligament	Also called the lienorenal ligament, it connects the splenic hilum to the posterior abdominal wall, through which the splenic vein and artery travel.
Gastrosplenic ligament	It connects the stomach to the spleen and inferior diaphragm.
Broad ligament	A suspensory ligament that extends from the lateral uterine sidewalls to the pelvic sidewalls, dividing the pelvis into anterior and posterior compartments in the female
Ligamentum teres	Remnant of the fetal umbilical vein, which is contained within the falciform ligament; it passes into a fissure on the visceral liver surface to join the left branch of the portal vein in the porta hepatis.
Ligamentum venosum	It exhibits as a fibrous band (remnant of the ductus venosus) attached to the left branch of the portal vein. It ascends in a fissure on the visceral liver surface to attach above the inferior vena cava. In fetal circulation, oxygenated blood flows to the liver via the umbilical vein (ligamentum teres). Most of the blood bypasses the liver via the ductus venosus (ligamentum venosum) and enters the inferior vena cava.

Potential spaces are areas created by the peritoneal layer, reflecting between two organs or an organ and the peritoneal wall (typically posterior). A potential space is an empty fold; however, when disease is present, fluid or other materials may collect in this space. Because many pathologies present with excretions (ascitic fluid, blood, pus) into the peritoneal cavity, sonographers must examine these potential spaces and characterize the fluid as part of the abdominal and pelvic examinations. The following text includes anatomic descriptions of each major potential space of the peritoneal cavity.

Left Anterior Subphrenic Space

The left anterior subphrenic or suprahepatic space is an extension of the greater sac between the diaphragm and the anterior superior liver leftward of the falciform ligament.

Left Posterior Suprahepatic Space

The left posterior suprahepatic space is also called the superior recess of the lesser sac; this space is an extension of the lesser sac between the diaphragm and the posterior superior liver. See Figures 5-3 and 5-7.

Right Subphrenic Space

The right subphrenic or suprahepatic space is an extension of the greater sac between the right hemidiaphragm and the anterior superior liver rightward of the falciform ligament (Fig. 5-8).

FIGURE 5-8 Subphrenic spaces. A: Right anterior subphrenic space and hepatorenal space. Longitudinal image of the right upper quadrant demonstrates fluid within the right anterior subphrenic space (single arrow); ascites is also seen within the hepatorenal space (double arrows). B: Right anterior subphrenic space and left anterior subphrenic space. Transverse image of the epigastrium demonstrates fluid within the right (*) and left (**) anterior subphrenic spaces separated by the falciform ligament. LLL, left lateral lobe of liver; LML, left medial lobe of liver; P, pancreas; SPL, spleen. (Image A: Courtesy of Philips Medical Systems, Bothel, WA.)

Hepatorenal Space

The hepatorenal space is also referred to as Morrison pouch. This peritoneal potential space is created by the peritoneum, reflecting from the liver over the right kidney and right posterior peritoneal wall. When the patient is in a supine position, this space is the most gravity-dependent potential space of the abdominal cavity, collecting fluid from the supracolic area and the lesser sac. See Figure 5-8.

Omental Bursa

The omental bursa, or lesser sac, is sandwiched between the posterior stomach and parietal peritoneum covering the anterior pancreas (front to back) and the splenorenal and gastrosplenic ligaments and epiploic foramen (side to side). In cases of posterior gastric wall perforation or inflammation or trauma to the pancreas, fluid or a pseudocyst may be identified in this space (Fig. 5-9).

FIGURE 5-9 Lesser sac. A: Transverse image of the epigastrium demonstrates a hematoma (arrows) within the lesser sac in a patient with acute pancreatitis. The posterior wall of the stomach (ST) borders the hematoma anteriorly. The pancreas (PANC) forms the posterior border. B: The computed tomography scan shows the large fluid collection with debris in the omental bursa in a patient with pancreatitis. (Images courtesy of UltrasoundCases.info, owner SonoSkills.)

Right and Left Paracolic Gutters

The right and left paracolic gutters are potential spaces or grooves found along the lateral ascending and descending colons that conduct fluids between the supracolic compartment of the abdomen and the infracolic compartment of the inferior abdomen and pelvis. They are important in determining the extension of disease¹ (Fig. 5-10).

Only gold members can continue reading. Log In or Register to continue