This document summarizes sonographic findings of the abdomen. It describes how ingesting water can improve evaluation of the stomach and small bowel during sonography. The normal bowel wall has five distinct layers that may be visible on ultrasound. Abnormal findings are also described such as bowel obstruction, lymphoma, gastrointestinal stromal tumors, colitis, Crohn's disease, appendicitis, ascites, mesothelioma, splenosis, and hernias. Representative ultrasound images are provided to illustrate normal and abnormal findings.

1. Topic:
General Abdomen
Prepared by:
Safi. Khan

2. Bowel
Sonography can be performed following ingestion of water to
improve evaluation of the stomach and proximal small bowel.
Retrograde infusion of water can also be used to distend the
colon (hydrocolonic sonography) and evaluate colonic
lesions.

4. The normal bowel has five layers that can be seen
sonographically.
The inner hyperechoic layer arises from the interface reflection
between the lumen and the surface of the mucosa.
The second layer is hypoechoic and arises from the combined
mucosa and the muscularis mucosa.
The third layer is hyperechoic and arises from the submucosa.
The fourth layer is hypoechoic and arises from the muscularis
propria. The final outer layer is hyperechoic and arises from
the interface reflection between the muscularis propria and the
serosa or adventitia (plus peri-intestinal fat).
These five layers are routinely seen on endoscopic ultrasound
and are intermittently seen on transcutaneous scans.

7. Normal bowel layers. Long axis views of the stomach with the lumen
filled with water (A) and with the lumen collapsed (B) show the
following: 1, The interface from the mucosal surface is hyperechoic. 2,
The deep mucosa and muscularis mucosa are hypoechoic. 3, The
submucosa is hyperechoic. 4, The muscularis propria is hypoechoic.
5, The interface between the muscularis propria and the serosa is
hyperechoic.
Note that the same layers labeled on one wall of the antrum are repeated
on the opposite wall.

8. On many transabdominal scans when the lumen is collapsed, the
mucosa, the muscularis mucosa, and the submucosa cannot be
distinguished into separate layers. This produces a central
echogenic region that is surrounded by the hypoechoic
muscularis propria, resulting in the typical bull’seye Appearance.
Normal colon. Transverse view of the colon shows the typical
bull’s-eye appearance of collapsed bowel (arrows).

9. In other cases the mucosa and the muscularis mucosa combine to
form a central hypoechoic region, followed by the hyperechoic
submucosa and then the hypoechoic muscularis propria (Fig. 9-3).
The normal intestinal wall should be less than 5 mm in thickness.
Normal stomach. A, Transverse view of the collapsed stomach shows
the combined mucosa and muscularis mucosa as a hypoechoic
central region surrounded by the echogenic submucosa and the
hypoechoic muscularis propria. B, Similar view in the distended
state shows all five layers.

10. Distended, fluid-filled, peristalsing loops are the hallmark of bowel
obstruction scanning in the lateral flanks where dependent fluid-
filled loops are located. When a bowel obstruction is detected, a
search for the cause should be performed. Hernias, intrinsic bowel
wall lesions, abdominal masses, and abdominal fluid collections
can all be detected with sonography.
Small bowel obstruction. Static view of the left upper quadrant shows
a dilated fluid-filled loop of small bowel (cursors) measuring greater
than 3 cm in diameter. An adjacent fluid collection is seen.

12. Small bowel lymphoma in different patients. A, Longitudinal view
shows a focal, hypoechoic, solid mass (cursors) along the
mesenteric wall of the small bowel. Gas in the lumen (arrows)
obscures most of the adjacent mesenteric wall of the bowel. The
antimesenteric wall of the bowel (arrowheads) is thickened, as
are the small bowel folds.
B, Short axis view shows marked concentric thickening of the small
bowel wall (cursors). Gas in the lumen (arrow) produces a dirty
acoustic shadow (S).

14. Gastrointestinal stromal tumors in different patients. A, Transverse
view of the mid abdomen shows a hypoechoic mass (cursors)
with central areas of liquefaction consistent with necrosis.
B, Longitudinal view of the lower abdomen shows a complex mass
(cursors) with a large area of central liquefaction. A small faintly
shadowing calcification (arrow) is also identified. C, View of the
fluid-filled stomach (S) shows a hypoechoic, solid mass (cursors)
arising from the posterior gastric wall.

16. D, Transverse view of the fluid-filled stomach (S) shows a lobulated
solid mass (cursors) with a small intraluminal component and a
larger exophytic component. Longitudinal sonogram (E) and
endoscopic (F) views of the stomach show a solid, hypoechoic
mass (cursors) arising from the collapsed stomach (S). The
retroflexed endoscopic view shows the submucosal portion of the
mass (cursors) adjacent to the endoscope (E).

17. Gastric lipoma. A, Longitudinal sonogram shows a hyperechoic
lesion (arrow) projecting into the lumen of the stomach.

19. Colitis in different patients. Transverse (A) and longitudinal (B)
views of the left colon show diffuse concentric thickening.
Longitudinal sonogram (C) show diffuse thickening of the
transverse colon due to colitis caused by Clostridium difficile.

21. Crohn’s disease in different patients. Transverse sonogram (A)
show concentric thickening of the distal ileum (cursors). Color
Doppler image (B) show diffuse thickening of the distal ileum
(cursors) and increased vascularity and mucosal
enhancement.
(A) (B)

24. Peri-intestinal abscess. A, Short axis view of a small bowel loop
(cursors) shows concentric thickening of the small bowel with an
adjacent irregular fluid collection due to an abscess (A) in a
patient with Crohn’s disease.
B, Short axis view of the sigmoid colon (S) shows concentric colonic
wall thickening with extraluminal inflammatory changes and fluid
(asterisks) in a patient with diverticulitis. The urinary bladder (B) is
seen at the edge of the image.

25. Intussusception in different patients. A, Short axis view of a loop of
the small bowel shows multiple concentric rings of increased and
decreased echogenicity and thickening of the outer small bowel
layer typical of an intussusception.
B, Longitudinal static view shows a focally thickened small bowel
loop (cursors) with multiple layers. The leading edge of the
intussusceptum is seen (arrows).

27. Appendicitis is a common cause of acute abdominal pain and is the
most common condition requiring urgent abdominal surgery. CT is
the primary imaging modality. A high-resolution probe (usually a
linear array or a curved array operating at 5 MHz or higher) should
be used. Patient can point to a specific area of pain and this usually
corresponds closely to the site of the abnormal appendix.
The primary criterion for the diagnosis of appendicitis is an appendiceal
diameter greater than 6 mm. In some patients an intraluminal
appendicolith can be detected.
Appendicitis in different patients. A, Long axis view of the appendix
shows wall thickening with an appendiceal diameter of
9.0 mm. B, Long axis view of the appendix (cursors) shows increased
diameter as well as an echogenic shadowing appendicolith (arrow).

35. Tip appendicitis. A, CT scan shows a normal diameter appendix
with an enhancing wall. B, Long axis view of the base of the
appendix shows a normal diameter of 5.6 mm. A shadowing
appendicolith (arrow) is present. C, Short axis view of the tip of
the appendix shows mild thickening with a diameter of 6.5 mm.

36. the normal appendix can be seen only by experienced
sonographers, and usually only in thin patients (Fig. 9-18). It is
not necessary to see a normal appendix to exclude appendicitis.
Normal appendix. Longitudinal view shows a normal appendix
(cursors) measuring 5 mm arising from the cecum (C).

38. PERITONEUM
The most common abnormality of the peritoneal cavity is Ascites.
Sonography is quite sensitive at detecting ascites as well as
guiding aspiration of ascites. Small amounts of ascites are seen
as anechoic collections most often in the pelvic cul-desac and in
the right upper quadrant between the liver and the abdominal
wall or in the hepatorenal fossa (Morison’s pouch) Ascites. A,
Longitudinal view shows a trace amount of ascites (asterisk) in
the hepatorenal fossa. B, Oblique view shows a trace amount of
ascites (asterisk) between a cirrhotic liver and the abdominal
wall.

41. C, Transverse view shows anechoic ascites (asterisks) floating
around loops of the small bowel (B) and small bowel mesentery
(arrowheads) without compression or distortion of these
structures.
D, Longitudinal view shows complex ascites (asterisks) with diffuse
low-level echoes in the perihepatic space. This is the typical
appearance of hemorrhagic fluid.

42. E, Longitudinal view shows echogenic fluid (asterisk) in the
hepatorenal fossa several minutes following a liver biopsy. This
is typical of acute hemoperitoneum. F, Transverse view of the
right lower quadrant shows a complex multiseptated collection
of ascites (asterisks) between the abdominal wall and
compressed loops of the bowel (B).

43. Mesothelioma, a rare primary malignancy of the peritoneum, can
closely mimic peritoneal carcinomatosis
Mesothelioma in different patients. A, View of the right flank
abdominal wall shows a small, solid peritoneal nodule (cursors).
Larger nodules were seen elsewhere. B, Transverse color Doppler
view shows a large sheet of solid, hypoechoic, hypervascular
tissue (cursors) between the abdominal wall and the liver (L). C,
Transverse view shows a solid, hyperechoic peritoneal mass
(cursors) between the liver (L) and the kidney (K).

48. Splenosis is also a cause of solid peritoneal masses that can
simulate peritoneal metastases. They are more homogeneous
than most metastatic lesions but are otherwise Indistinguishable
Splenosis. Gray-scale (A) and power Doppler (B) views of the right
lower quadrant show a well-defined, hypoechoic, solid nodule
with readily detectable blood flow.

50. Fluid- and fat-containing hernia. Longitudinal view shows a fluid-
filled hernia sac (cursors) communicating with ascites in the
abdominal cavity through a small defect. compression shows
fluid and fat passing in and out of the hernia sac.