Diagnostic Ultrasound - Abdomen and Pelvis

Peritoneal Spaces and Structures
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Anatomy: Abdomen
TERMINOLOGY
Definitions
• Peritoneal cavity: Potential space in abdomen between
visceral and parietal peritoneum, usually containing only
small amount of peritoneal fluid (for lubrication)
• Abdominal cavity: Not synonymous with peritoneal cavity
○ Contains all of abdominal viscera (intra- and
retroperitoneal)
○ Limited by abdominal wall muscles, diaphragm, and
(arbitrarily) by pelvic brim
GROSS ANATOMY
Divisions
• Greater sac of peritoneal cavity
• Lesser sac (omental bursa)
○ Communicates with greater sac via epiploic foramen (of
Winslow)
○ Bounded anteriorly by caudate lobe, stomach, and
greater omentum; posteriorly by pancreas, left adrenal,
and kidney; on left by splenorenal and gastrosplenic
ligaments; on right by epiploic foramen and lesser
omentum
Compartments
• Supramesocolic space
○ Divided into right and left supramesocolic spaces, which
are separated by falciform ligament
– Right supramesocolic space: Composed of right
subphrenic space, right subhepatic space, and lesser
sac
– Left supramesocolic space: Divided into left
perihepatic spaces (anterior and posterior) and left
subphrenic (anterior perigastric and posterior
perisplenic)
• Inframesocolic compartment
○ Divided into right inframesocolic space, left
inframesocolic space, paracolic gutters, and pelvic cavity
○ Pelvic cavity is most dependent part of peritoneal cavity
in erect and supine positions
Peritoneum
• Thin serous membrane consisting of single layer of
squamous epithelium (mesothelium)
○ Parietal peritoneum lines abdominal wall
○ Visceral peritoneum (serosa) lines abdominal organs
Mesentery
• Double layer of peritoneum that encloses organ and
connects it to abdominal wall
• Covered on both sides by mesothelium and has core of
loose connective tissue containing fat, lymph nodes, blood
vessels, and nerves passing to and from viscera
• Most mobile parts of intestine have mesentery, while
ascending and descending colon are considered
retroperitoneal (covered only by peritoneum on anterior
surface)
• Root of mesentery is its attachment to posterior abdominal
wall
• Root of small bowel mesentery is ~ 15 cm and passes from
left side of L2 vertebra downward and to right; contains
superior mesenteric vessels, nerves, and lymphatics
• Transverse mesocolon crosses almost horizontally in front
of pancreas, duodenum, and right kidney
Omentum
• Multilayered fold of peritoneum that extends from
stomach to adjacent organs
• Lesser omentum joins lesser curve of stomach and proximal
duodenum to liver
○ Hepatogastric and hepatoduodenal ligament
components contain common bile duct, hepatic and
gastric vessels, and portal vein
• Greater omentum
○ 4-layered fold of peritoneum hanging from greater curve
of stomach like an apron, covering transverse colon and
much of small intestine
– Contains variable amounts of fat and abundant lymph
nodes
– Mobile and can fill gaps between viscera
– Acts as barrier to generalized spread of
intraperitoneal infection or tumor
Ligaments
• All double layered folds of peritoneum, other than
mesentery and omentum, are peritoneal ligaments
• Connect 1 viscus to another (e.g., splenorenal ligament) or
viscus to abdominal wall (e.g., falciform ligament)
• Contain blood vessels or remnants of fetal vessels
Folds
• Reflections of peritoneum with defined borders, often
lifting peritoneum off abdominal wall (e.g., median
umbilical fold covers urachus and extends from dome of
urinary bladder to umbilicus)
Peritoneal Recesses
• Dependent pouches formed by peritoneal reflections
• Many have eponyms (e.g., Morison pouch for posterior
subhepatic [hepatorenal] recess; pouch of Douglas for
rectouterine recess)
ANATOMY IMAGING ISSUES
Imaging Recommendations
• Transducer: Typically 2-5 MHz for abdominal survey and
deep recesses, up to 9 MHz for thinner patients
• High frequency linear transducer 8-15 MHz may be used to
evaluate anterior abdominal wall and parietal peritoneum
• Patient examined supine with additional decubitus
positions to determine if fluid collection is free or loculated
• Peritoneal cavity and its various mesenteries and recesses
are usually not apparent on imaging studies unless
distended or outlined by intraperitoneal fluid or air