Download Normal anatomy and pathology of the lesser sac

Normal anatomy and pathology of the lesser sac
Poster No.:
C-2044
Congress:
ECR 2011
Type:
Educational Exhibit
Authors:
M. I. oliveira , B. Viamonte , R. H. Castro , T. C. Fernandes ;
1
1
2
3
2
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4
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Matosinhos, Matosinhos/PT, Porto/PT, Espinho/PT, Vila Praia
de âncora/PT
Keywords:
Trauma, Neoplasia, CT, Anatomy, Abdomen, Inflammation
DOI:
10.1594/ecr2011/C-2044
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Page 1 of 28
Learning objectives
1. Review the normal anatomy and pathology of the lesser sac.
2. Illustrate the imagiologic features of diseases involving the lesser sac on MDCT.
3. Establish the differential diagnosis and the key imagiologic findings.
Background
Peritoneum is the largest and most complex serous membrane in the human body. The
potential peritoneal spaces, such as the lesser sac, peritoneal reflections and the natural
flow of peritoneal fluid determine the route of spread of intraperitoneal fluid serving not
only as boundaries for diseases processes but also conduits for disease spread.
The lesser sac is the cavity formed by the lesser and greater omentum, it is connected
with the peritoneal cavity via Foramen of Winslow.
Conditions involving the lesser sac include infectious, inflammatory, neoplastic and
traumatic processes.
Page 2 of 28
Fig.: Anatomy of the lesser sac in axial (a) and parasagittal (b) drawings of the
abdomen. L- liver, P- pancreas, S- spleen, LS- lesser sac, SR- superior recess, IRinferior recess, SpR- splenic recess, CD- common duct, HA- hepatic artery, PV- portal
vein, GO- greater omentum 1- gastrohepatic ligament, 2- gastro-splenic ligament,
3- splenorenal ligament, 4- gastrocolic ligament, 5- transverse mesocolon. Arrowforamen of Winslow.
References: M. I. oliveira; Matosinhos, PORTUGAL
Images for this section:
Fig. 1: Anatomy of the lesser sac in axial (a) and parasagittal (b) drawings of the
abdomen. L- liver, P- pancreas, S- spleen, LS- lesser sac, SR- superior recess, IR- inferior
recess, SpR- splenic recess, CD- common duct, HA- hepatic artery, PV- portal vein, GOgreater omentum 1- gastrohepatic ligament, 2- gastro-splenic ligament, 3- splenorenal
ligament, 4- gastrocolic ligament, 5- transverse mesocolon. Arrow- foramen of Winslow.
Page 3 of 28
Imaging findings OR Procedure details
LESSER SAC - NORMAL ANATOMY
The lesser sac is a potential peritoneal space localized between the stomach and the
pancreas.
Fig.: Anatomy of the lesser sac in axial (a) and parasagittal (b) drawings of the
abdomen. L- liver, P- pancreas, S- spleen, LS- lesser sac, SR- superior recess, IRinferior recess, SpR- splenic recess, CD- common duct, HA- hepatic artery, PV- portal
vein, GO- greater omentum 1- gastrohepatic ligament, 2- gastro-splenic ligament,
3- splenorenal ligament, 4- gastrocolic ligament, 5- transverse mesocolon. Arrowforamen of Winslow.
References: M. I. oliveira; Matosinhos, PORTUGAL
The lesser sac is a unique remnant of the primitive right peritoneal space, formed due to
the rotation of the viscera in the upper abdomen during fetal development.
Page 4 of 28
Fig.: Embriology of the lesser sac. Cross-sectional drawing of the anatomy of
upper abdomen for a 4-week embryo (a) and 8-week embryo (b). Arrows show the
development of the lesser sac associated with the rotation of the stomach and growth
of the liver. L- liver; S- spleen.
References: M. I. oliveira; Matosinhos, PORTUGAL
BOUNDARIES:
It is bounded by remnants of the dorsal and ventral mesenteries.
Anteriorly, the structure that covers the lesser sac is the lesser omentum, which is a
combination of the gastrohepatic ligament and, to a lesser extent, the hepatoduodenal
ligament (that contains the portal vein, hepatic artery and common bile duct).
The remnants of the dorsal mesentery are also boundaries of the lesser sac, the
gastrosplenic ligament contributes to the lateral border, the splenorenal ligament to the
left lateral and posterior border, and the gastrocolic ligament (forming the superior aspect
of the greater omentum) contribute to portion of the anterior border.
RECESSES:
It is divided in three main recesses:
Page 5 of 28
The superior recess is identified above the pancreas and to the right of the midline on
transverse sections. It extends upwards along the posteromedial face of the liver to the
level of the diaphragm, surrounding the medial aspect of the caudate lobe.
The splenic recess extends across the midline to the splenic hilum and is limited
by the gastrohepatic ligament in the front, the gastrosplenic ligament laterally and the
splenopancreatic ligament behind.
The inferior recess is the larger recess, located to the left of the midline separates the
stomach from the pancreas and transverse mesocolon. An infrapancreatic part may exist
when the transverse mesocolon bows downwards or when an inferior recess persists
within the greater omentum.
FORAMEN OF WINSLOW:
The foramen of Winslow allows communication between the lesser sac and the remainder
peritoneal cavity. It is formed ventrally by the free margin of duodenohepatic ligament,
superiorly by the isthmus of the caudate lobe and posteriorly by the inferior vena cava.
LESSER SAC - PATHOLOGIC PROCESSES
Although the peritoneal reflections forming the boundaries of the lesser sac are
infrequently visualized in the normal patient, lesser sac lesions may be confidently
diagnosed by the characteristic location between the stomach and pancreas.
Fluid within the lesser sac is not a typical manifestation of generalized peritoneal ascites
and its presence should direct a search for pathology in neighboring organs or for
peritoneal malignancy.
INFLAMATORY/INFECTIOUS
The most common type of fluid in the lesser sac is ascitic transudate in patients with
hepatic failure or renal failure. However, ascites only the lesser sac is unusual, and
when an isolated fluid collection is encountered in the lesser sac, pathologic processes
involving the pancreas, stomach or duodenum should be considered. Large amounts of
ascites in the peritoneal cavity flow to the lesser sac through the epiploic foramen.
Page 6 of 28
Inflammatory infiltrates in the lesser sac are commonly secondary to acute pancreatitis.
Because the pancreas does not have a fibrous capsule, the inflammatory process may
spread to the adjacent tissue, and initially accumulates in the lesser sac. A perforated
gastric ulcer or cholecystitis may also cause exudate in the lesser sac.
Fig.: Peritonitis. Axial contrast enhanced CT scan reveals free peritoneal fluid with
fluid accumulation in the lesser sac (*). Also note the parietal peritoneum (arrow) is
thickened and enhances after intravenous contrast administration.
References: M. I. oliveira; Matosinhos, PORTUGAL
Page 7 of 28
Fig.: Acute pancreatitis. Axial and sagittal contrast enhanced CT scans showing fluid
accumulation in the lesser sac (*). Note infiltration of peripancreatic fat and spread of
an inflammatory exudate to the lesser sac (*), findings suggestive of acute pancreatitis.
P- pancreas, S- stomach.
References: M. I. oliveira; Matosinhos, PORTUGAL
Fig.: Acute pancreatitis. Axial contrast enhanced CT scans showing fluid accumulation
in the lesser sac (*). Note pancreas has preserved shape and size, and there is only
slightly reduced uptake of contrast indicating acute pancreatitis. P- pancreas, Sstomach.
References: M. I. oliveira; Matosinhos, PORTUGAL
Page 8 of 28
Fig.: Pancreatic pseudocyst. Developing pseudocyst in a 60-year-old woman with
epigastric pain. (a) Axial contrast enhanced CT scans show a cystic mass in the
pancreatic body and tail (*). (b) On follow-up parasagittal contrast enhanced CT
scans obtained 2 months later, the lesion appears as a unilocular, low-attenuation
fluid collection with a well-defined thin wall (*). This is the typical appearance of a
postinflammatory pseudocyst. P- pancreas, S- stomach.
References: M. I. oliveira; Matosinhos, PORTUGAL
Page 9 of 28
Fig.: Cholecystitis. Axial contrast enhanced CT scans show free peritoneal fluid (**)
with fluid accumulation in the splenic recess of the lesser sac (*) in a patient with acute
cholecystitis who underwent cholecystostomy. P- pancreas, S- stomach
References: M. I. oliveira; Matosinhos, PORTUGAL
Fig.: Duodenal ulcer perforation. Axial contrast enhanced CT scans showing
fluid and free air (* and **) between the stomach (S) and the pancreas (P), in
the lesser sac. Also note a large amount of ascitis and pneumoperitoneum in
midabdomen (red arrows).
References: M. I. oliveira; Matosinhos, PORTUGAL
Page 10 of 28
NEOPLASTIC
Neoplasms invading the lesser sac usually originate from adjacent structures such as
the stomach, liver, or pancreas.
Peritoneal carcinomatosis is associated with generalized peritoneal ascites (within the
lesser and greater sac), peritoneal thickening, seeding nodules, and omental infiltration.
Metastatic peritoneal tumors most often originate from the ovary and stomach.
Fig.: Pancreatic lymphoma. Axial contrast enhanced CT scans showing (a) fluid within
the superior recess of the lesser sac (*), defining its characteristic boomerang shape on
the medial surface of the caudate lobe. (b) Note the pseudocyst in the pancreatic head
(Pq). (c) There is also invasion of pancreatic parenchyma by lymphoma with a nodular
mass (M) in the pancreatic head. Biopsy confirmed Non-Hodgkin lymphoma.
References: M. I. oliveira; Matosinhos, PORTUGAL
Page 11 of 28
Fig.: GIST. Axial contrast enhanced CT scan showing a mass (*) in the lesser sac,
between the stomach (S) and pancreas (P). This mass was proved to be a gastric
GIST.
References: M. I. oliveira; Matosinhos, PORTUGAL
Page 12 of 28
Fig.: Peritoneal carcinomatosis in a 30-year-old woman with ovarian tumor. Axial
(a) and parasagittal (b) CT scans show large amounts of ascites (**), fluid collected
in the lesser sac (*) and diffuse nodular omental infiltration, findings compatible with
carcinomatosis. P- pancreas, S- stomach.
References: M. I. oliveira; Matosinhos, PORTUGAL
TRAUMATIC
Early CT scan evaluation may help to reduce the morbidity resulting from the delay in
diagnosis of injuries to the internal organs.
Patients with an imprint made by a bicycle handlebar edge on the abdominal wall or give
a clear history of abdominal trauma should be treated with great care.
Pancreatic injury is uncommon (less then 5%), either as a result of penetrating or blunt
trauma, but is associated with high morbidity and mortality, particularly if the diagnosis
is delayed.
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Fig.: Pancreatic transection. Axial contrast enhanced CT scan showing fluid
accumulation in the lesser sac (*) due to pancreatic laceration secondary to trauma
from a bicycle handlebar. The patient had an imprint of the handlebar edge on the
hypochondrium. The separation of the pancreatic head and body is clear anteriorly
but posteriorly appears only as a fine linear hypodensity (arrow) that communicates
with the Wirsung, which is not dilated. Also note the pancreatic parenchyma edema
and stranding of peripancreatic fat, due to post-traumatic pancreatitis. P- pancreas, Sstomach, *- collection in the lesser sac, Arrow- pancreatic transection.
References: M. I. oliveira; Matosinhos, PORTUGAL
Page 14 of 28
Fig.: Pancreatic transection. Parasagittal contrast enhanced CT scans revealing
collection in the lesser sac (*) due to pancreatic laceration secondary to trauma from a
bicycle handlebar. P- pancreas, S- stomach, *- collection in the lesser sac.
References: M. I. oliveira; Matosinhos, PORTUGAL
Page 15 of 28
Fig.: Lesser sac hematoma. Contrast enhanced CT scan shows hematoma in the
lesser sac caused by blunt trauma. The patient had a decrease in hemoglobin levels
to 8.3 g / dL (initial Hg 13.3 g / dL), with hemodynamic instability requiring transfusion.
Emergent laparotomy with hematoma evacuation and "bleeder" ligation was performed.
P- pancreas, S- stomach, *- hematoma in the lesser sac.
References: M. I. oliveira; Matosinhos, PORTUGAL
INTERNAL HERNIAS
Lesser sac hernias are rare. The responsible hernial orifice is usually the foramen of
Winslow, but pathologic defects of the transverse mesocolon or omentum, mostly due to
iatrogenic pathology, may also be responsible.
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Lesser sac hernias manifest at CT as a cluster of gas-distended or fluid-filled bowel loops
located between the liver, stomach, and pancreas. The stomach is usually displaced
anteriorly and laterally. Bowel caliber change and unusual course of the herniated smallbowel vessels are helpful in diagnosing lesser sac hernias.
Images for this section:
Fig. 1: Anatomy of the lesser sac in axial (a) and parasagittal (b) drawings of the
abdomen. L- liver, P- pancreas, S- spleen, LS- lesser sac, SR- superior recess, IR- inferior
recess, SpR- splenic recess, CD- common duct, HA- hepatic artery, PV- portal vein, GOgreater omentum 1- gastrohepatic ligament, 2- gastro-splenic ligament, 3- splenorenal
ligament, 4- gastrocolic ligament, 5- transverse mesocolon. Arrow- foramen of Winslow.
Page 17 of 28
Fig. 2: Embriology of the lesser sac. Cross-sectional drawing of the anatomy of upper
abdomen for a 4-week embryo (a) and 8-week embryo (b). Arrows show the development
of the lesser sac associated with the rotation of the stomach and growth of the liver. Lliver; S- spleen.
Page 18 of 28
Fig. 3: Peritonitis. Axial contrast enhanced CT scan reveals free peritoneal fluid with fluid
accumulation in the lesser sac (*). Also note the parietal peritoneum (arrow) is thickened
and enhances after intravenous contrast administration.
Fig. 4: Acute pancreatitis. Axial and sagittal contrast enhanced CT scans showing fluid
accumulation in the lesser sac (*). Note infiltration of peripancreatic fat and spread of an
inflammatory exudate to the lesser sac (*), findings suggestive of acute pancreatitis. Ppancreas, S- stomach.
Fig. 5: Acute pancreatitis. Axial contrast enhanced CT scans showing fluid accumulation
in the lesser sac (*). Note pancreas has preserved shape and size, and there is only
slightly reduced uptake of contrast indicating acute pancreatitis. P- pancreas, S- stomach.
Page 19 of 28
Fig. 6: Pancreatic pseudocyst. Developing pseudocyst in a 60-year-old woman with
epigastric pain. (a) Axial contrast enhanced CT scans show a cystic mass in the
pancreatic body and tail (*). (b) On follow-up parasagittal contrast enhanced CT
scans obtained 2 months later, the lesion appears as a unilocular, low-attenuation
fluid collection with a well-defined thin wall (*). This is the typical appearance of a
postinflammatory pseudocyst. P- pancreas, S- stomach.
Page 20 of 28
Fig. 7: Cholecystitis. Axial contrast enhanced CT scans show free peritoneal fluid (**)
with fluid accumulation in the splenic recess of the lesser sac (*) in a patient with acute
cholecystitis who underwent cholecystostomy. P- pancreas, S- stomach
Fig. 8: Duodenal ulcer perforation. Axial contrast enhanced CT scans showing fluid and
free air (* and **) between the stomach (S) and the pancreas (P), in the lesser sac. Also
note a large amount of ascitis and pneumoperitoneum in midabdomen (red arrows).
Page 21 of 28
Fig. 9: Pancreatic lymphoma. Axial contrast enhanced CT scans showing (a) fluid within
the superior recess of the lesser sac (*), defining its characteristic boomerang shape on
the medial surface of the caudate lobe. (b) Note the pseudocyst in the pancreatic head
(Pq). (c) There is also invasion of pancreatic parenchyma by lymphoma with a nodular
mass (M) in the pancreatic head. Biopsy confirmed Non-Hodgkin lymphoma.
Page 22 of 28
Fig. 10: GIST. Axial contrast enhanced CT scan showing a mass (*) in the lesser sac,
between the stomach (S) and pancreas (P). This mass was proved to be a gastric GIST.
Page 23 of 28
Fig. 11: Peritoneal carcinomatosis in a 30-year-old woman with ovarian tumor. Axial
(a) and parasagittal (b) CT scans show large amounts of ascites (**), fluid collected
in the lesser sac (*) and diffuse nodular omental infiltration, findings compatible with
carcinomatosis. P- pancreas, S- stomach.
Page 24 of 28
Fig. 12: Pancreatic transection. Axial contrast enhanced CT scan showing fluid
accumulation in the lesser sac (*) due to pancreatic laceration secondary to trauma
from a bicycle handlebar. The patient had an imprint of the handlebar edge on the
hypochondrium. The separation of the pancreatic head and body is clear anteriorly but
posteriorly appears only as a fine linear hypodensity (arrow) that communicates with the
Wirsung, which is not dilated. Also note the pancreatic parenchyma edema and stranding
of peripancreatic fat, due to post-traumatic pancreatitis. P- pancreas, S- stomach, *collection in the lesser sac, Arrow- pancreatic transection.
Page 25 of 28
Fig. 13: Pancreatic transection. Parasagittal contrast enhanced CT scans revealing
collection in the lesser sac (*) due to pancreatic laceration secondary to trauma from a
bicycle handlebar. P- pancreas, S- stomach, *- collection in the lesser sac.
Page 26 of 28
Fig. 14: Lesser sac hematoma. Contrast enhanced CT scan shows hematoma in the
lesser sac caused by blunt trauma. The patient had a decrease in hemoglobin levels
to 8.3 g / dL (initial Hg 13.3 g / dL), with hemodynamic instability requiring transfusion.
Emergent laparotomy with hematoma evacuation and "bleeder" ligation was performed.
P- pancreas, S- stomach, *- hematoma in the lesser sac.
Page 27 of 28
Conclusion
Conditions involving the lesser sac may have nonspecific and overlapping features,
making clinical and imaging correlation essential. Familiarity with the lesser sac anatomy,
disease spectrum and characteristics CT appearances allows the radiologist to make the
correct diagnosis for proper management.
Personal Information
References
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3-Yoo E, Kim JH, Kim MJ, Yu JS, Chung JJ, Yoo HS, et al. Greater and lesser omenta:
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