layers that we describe from the lumen outward.
IBD:
The classic sonographic feature of
Crohn's disease is the "
target"
sign.
which
means a strong
echogenic center surrounded by a relatively
sonolucent rim of more than
5 mm. This transmural inflammation or fibrosis
can lead to complete circumferential loss of the typical gut
wall layers, which results in a
thick hypoechoic rim on axial
images. Strictures are shown as marked thickening of the gut
wall with a fixed hyperechoic narrowed lumen, dilatation,
and hyperperistalsis of the proximal gut. Peri-intestinal inflammation
leads to the "
creeping fat" sign, which appears as a uniform
hyperechoic mass typically seen around the ileum and cecum.
Mesenteric
lymphadenopathy is seen as multiple oval hypoechoic
masses, usually in the right lower quadrant. In contrast to
other forms of colitis, Crohn's disease is suggested by
skip areas and involvement of the
distal ileum. Possible complications
of Crohn's disease comprise
fistulas,
abscess formation,
mechanical bowel obstruction, and
perforation. Abscesses are seen
as poorly defined, mostly hypoechoic focal masses that can
contain hyperechoic gas. Fistulas are a hallmark
of Crohn's disease and are seen in as many as one third of patients
with advanced disease as hypoechoic tracts with gas inclusions
connecting bowel loops or adjacent structures (bladder, abdominal
wall, vagina, psoas muscle). Detection of gas bubbles
in abnormal locations raises the possibility of
fistulous communication.
Target sign
Circular hypoechoic wall thickening and loss of stratification
"thumbprinting" and narrowing of jejunal lumen in left lower abdomen. Crohn's disease 
Transverse sonogram of ileum (
arrows) shows severe narrowing of small hyperechoic central lumen caused by excessively echolucent wall thickening and loss of stratification, indicating scarring of entire bowel wall.
Large-bowel enema with fine granularity of mucosa reflecting hyperemia and edema confirms suspected sonographic diagnosis of early changes in ulcerative colitis.NON-HODGKIN LYMPHOMA IN THE GIT:
The gut is the most commonly involved extranodal site of lymphoma. The most common sites, in order of descending frequency,
are stomach, small intestine, and colon, especially cecum.
Eighty percent of gastrointestinal lymphomas are of B-cell
origin.
Sonography classically shows
transmural circumferential, profoundly hypoechoic wall thickening
up to 4 cm in diameter, with loss of normal stratification. This pattern, also known as the "pseudokidney" sign
in longitudinal views. The pseudokidney sign is often seen in lymphoma
because of extensive hypoechoic bowel wall thickening, but
it can be seen in any bowel disorder leading to marked bowel
wall thickening. Other findings include nodular
or bulky tumor spread caused by extraluminal involvement. Sonographic
patterns favoring the diagnosis of a non-Hodgkin's lymphoma
over adenocarcinoma are transmural circumferential, profoundly
hypoechoic wall thickening with preserved peristalsis; lack
of intestinal obstruction, because narrowing of the lumen is
uncommon; involvement of a long stretch of the gut; and the
presence of multiple prominent regional lymph nodes.
Other findings include nodular
or bulky tumor spread caused by extraluminal involvement. Mesenteric tumor spread and bulky tumor growth
need biopsy for definite diagnosis because they cannot be reliably
differentiated from other diseases such as primary bowel tumors
or metastases. Isolated mucosal involvement is rare and leads
to hyperechoic thickening of the mucosa. Sonographic
patterns favoring the diagnosis of a non-Hodgkin's lymphoma
over adenocarcinoma are transmural circumferential, profoundly
hypoechoic wall thickening with preserved peristalsis; lack
of intestinal obstruction, because narrowing of the lumen is
uncommon; involvement of a long stretch of the gut; and the
presence of multiple prominent regional lymph nodes.
Profound hypoechoic wall thickening. Non-Hodgkin lymphoma
"Pseudokidney" sign in ileocecal region: marked hypoechoic thickening of bowel wall resembling form of kidney in longitudinal sonogram of cecum. Non-Hodgkin lymphoma
ACUTE TERMINAL ILEITISThe clinical symptoms of acute ileitis are right-sided lower
abdominal pain, diarrhea, and nausea, with an accelerated erythrocyte
sedimentation rate, positive C-reactive protein, and leukocytosis.
Caused by
Yersinia species but
Campylobacter and
Salmonella species may also be cultured. Reported sonographic
features include hypoechogenic mural thickening of the terminal
ileum and cecum between 6 and 10 mm with hypoechoic swollen
ileal folds in the edematous mucosa. Hypoechoic
enlarged mesenteric lymph nodes are frequently seen. Color Doppler sonography
in patients with infectious ileitis shows increased flow centrally
rather than peripherally (as in appendicitis).
Tuberculous enteritis and
Behçet's syndrome also predominantly
affect the ileocecal region
APPENDICITIS
The typical finding of acute appendicitis in transverse sonograms
is the
target sign with a
hypoechoic center, an
inner hyperechoic ring, and an
external thicker hypoechoic ring. In
sagittal images, the inflamed appendix is seen as a
blind-ending noncompressible tubular structure. Focal or circumferential
loss of the inner layer of echoes usually indicates gangrenous
inflammation and ulceration of the submucosa.
The diagnosis can be established with confidence if the appendix is noncompressible, shows no peristalsis, and measures more than 6 mm in diameter on axial images,
and if compression leads to a localized pain response. The surrounding mesentery is often inflamed, which
can be seen as a
hyperechoic diffuse halo sign around the appendix. If an appendicolith is identified in an appendix
of any size, the findings of the examination are always considered
positive. A simple additional color Doppler
examination may be helpful in the diagnosis of early acute appendicitis. The presence of visible
hyperemia or increased flow in the hypoechoic muscular layer of the bowel wall may be a marker
of appendicitis, whereas
increased flow in the mucosal layer most likely represents enteritis. Increased flow
in the fat surrounding the appendix is indicative of transmural extension of the inflammation with mesenteric response. An inflamed appendix
rarely measures more than 15 mm in transverse diameter,
which usually allows differentiation from ileitis. A markedly
enlarged or perforating appendix or dilated fallopian tubes
may lead to interpretive pitfalls.
"
Target" sign (
curved arrows) in acute appendicitis. On transverse image, inflamed appendix is seen with hypoechoic center, inner hyperechoic ring, and outer hypoechoic ring. Note hyperechoic circular area (
straight arrows) of inflamed mesentery ("
halo" sign).
Longitudinal sonogram of inflamed appendix in same patient shows
blind-ending tubular structure (
arrow) of at least 6 mm in diameter.
Longitudinal section of inflamed appendix reveals five round hyperechoic appendicoliths with acoustic shadows.
Complications:
A statistically significant association exists
between
perforation and two sonographic findings:
loculated pericecal fluid and
loss of the echogenic submucosa.
Abscess formation is the major complication of perforating appendicitis.
Abscesses may extend into the pelvis or into the peritoneal
spaces of the upper abdomen. They may be sonolucent or appear
as a complex mass.
SMALL BOWEL DISEASES:
Mesenteric infarction in its late stages leads to small-bowel
wall thickening. In the early stages, however, no
bowel wall thickening may be seen. Doppler sonography can aid
in differentiating ischemic and inflammatory bowel wall thickening.
In approximately
90% of cases, small-bowel infarctions
are due to arterial hypoperfusion; only
10% are caused by mesenteric vein occlusion. Acute intramural intestinal hematoma leads
typically to a homogeneous hypoechoic symmetric thickening
of a long stretch of the affected bowel segment, with reduced
or absent peristalsis and marked luminal narrowing.
In the subacute stage, strong internal echoes caused by
thrombi may mimic an abscess.
OTHER TU'S
Peritoneal carcinomatosis is the most frequent malignant lesion
of the small bowel and may lead to irregular wall thickening
with the typical contraction of several bowel loops to a conglomerate.
Lipomas are the second most common tumors of the small intestine
and occur with greatest frequency in the distal ileum and at
the ileocecal valve. The location of these tumors is submucosal,
or, less frequently, is subserosal. Adenocarcinoma is the second most common
small intestine malignancy and the peak incidence is in the
seventh decade of life.
COLITIS
Striking thickening
of the colonic wall with a wide inner circle of heterogeneous
medium echogenicity surrounded by a narrow hypoechoic muscularis
propria is found in all patients, reflecting the gross submucosal
edema. The lumen of the colon is almost completely effaced
by the mural edema, and 64-77% of the patients have ascites. Pseudomembranous colitis shows typically a strong folding or
gyral pattern of the swollen submucosa.
DIVERTICULITIS
Sonographic features of diverticulitis include visualization
of diverticula,
thickening of the bowel wall,
inflammatory changes in the
pericolic fat (typically on the mesenteric side
of the colonic wall) , intramural or periocolic
abscess , and (usually) severe local
tenderness induced
by graded compression. Diverticula are round or oval echogenic
foci seen in or right next to the gut wall, mostly with internal
acoustic shadowing. Thickening of the bowel wall is usually
considered present when the distance from the echogenic lumen
interface to the hyperechogenic serosa and pericolic fat exceeds
4 mm. Inflammatory changes in the pericolic fat are seen
as ill-defined echogenic areas surrounding the thickened colon
segment.
Pericolic abscesses typically present as hypoechoic
masses adjacent to the inflamed bowel. The major sonographic
finding in patients with uncomplicated acute diverticulitis
of the right colon has been found to be a hypoechoic round
or oval focus protruding from the segmentally thickened colonic
wall and representing small abscesses in the pericolic fat.
Massive hyperechoic inflammatory infiltration seen on mesenteric side of sigmoid colon.
Echolucent fistula is seen in mesentery with small, hyperechoic, gas-containing abscess (arrow).
Diverticulum of sigmoid colon seen as focal hyperechoic intramural structure with acoustic shadow.
COLONIC CARCINOMAS
Colonic carcinomas have two typical
sonographic appearances. The first type is seen as a
localized hypoechoic mass up to 10 cm or more with an irregular shape and a lobulated contour. The intraluminal gas, seen as
a cluster of high amplitude, is usually eccentrically located
around the mass. The second type shows segmental
eccentric or circumferential thickening of the colonic wall.
The mural thickening may be irregular but not as severe as
in the first type. The central echo clusters are
small because the diseased lumen is usually narrow. This type
leads frequently to colonic obstruction. Rectum carcinomas
are seen only when the bladder is well-filled.
Other features: localized irregular
thickening of the colonic wall with heterogeneous low echogenicity;
irregular contour; lack of movement or change in configuration
on real-time scanning; and absence of a layered appearance of
the colonic wall. Other findings include lymphadenopathy in
most patients and abscess formation in 10% of patients.
INTUSSUSCEPTION
Only 5-10% of all intussusceptions occur in adults.
The clinical symptoms may suggest partial obstruction of the
intestine, but diagnosis may be difficult because symptoms
are often nonspecific. The ileocecal region is the most
commonly affected area in children, whereas there is no clearly
preferred anatomic site in adults. Most intussusceptions in
children are idiopathic and are presumed to be the result of
enlarged lymphoid follicles in the terminal ileum. An
organic cause can be shown in as many as 90% of cases in
adults. The leading mass is nearly always a tumor of the intestinal
wall, usually malignant in intussusceptions of the colon and benign in intussusceptions of the small intestine. The sonographic hallmark of intussusception has been
described as the target, "
doughnut," or "
bull's-eye"
sign. Typically, one finds two hypoechoic rings separated
by a hyperechoic ring or crescent on axial images. On longitudinal images, a pseudokidney structure
or layering of hypoechoic lines with hyperechoic areas is observed.
The outer hypoechoic ring is formed by the intussuscipiens
and the everted returning limb of the intussusceptum, with their
mucosal surfaces face to face. The center of the intussusception
varies with the scan level. At the apex, the center is hypoechoic
because of the entering limb of the intussusceptum. At the base,
the entering bowel wall forms a hypoechoic center that is surrounded
by the hyperechoic mesentery. In a case of surgically
proven triple jejunojejunocolonic intussusception, three
hypoechoic rings separated by two hyperechoic rings were found
on sonography.
SOURCE:
http://www.ajronline.org/cgi/content/full/174/1/107?ijkey=803ac7b5dd2197a30a358b5a696cd4e6a2652d4c&keytype2=tf_ipsecsha
