Diagnostic ultrasound ( PDFDrive )

CHAPTER 53 The Pediatric Gastrointestinal Tract 1853
FIG. 53.36 Ascariasis. The long slender parasite is clearly visible
within the bowel on ultrasound (arrows).
sometimes occur in infants and children with inlammatory
conditions such as rotavirus infection or milk allergy. 106 Mycobacterium
tuberculosis, a rare entity in developed countries, can
be transmitted to bowel, with 90% of GI tuberculosis involving
the distal ileum or cecum owing to the abundant lymphoid tissue.
However, GI tuberculosis is an increasingly common disease in
developing countries. 107
On occasion, parasites may be found unexpectedly on ultrasound.
Ascariasis is one of the most common intestinal infestations,
prevalent in areas with poor sanitation. Eggs are passed
with the feces of an infected person and can be transmitted by
the fecal-oral route. Eggs hatch in the small intestine and can
penetrate the intestinal mucosa and travel to the lung. On occasion,
the worms can be identiied in the bowel by their characteristic
slender appearance and thin echogenic line within the
body, representing the alimentary tract 108 (Fig. 53.36).
Enterobius vermicularis organisms, or pinworms, are the
most common helminthic infection in the United States and
Western Europe. Mobile pinworms have been seen within the
appendix during sonographic studies as well as in the surgical
setting. 109
Crohn disease is the most common form of chronic inlammatory
bowel disease in children. Ultrasound can be used as a
screening tool for inlammatory bowel disease and also has value
for assessing success of treatment and potential complications.
Ultrasound sensitivity for the diagnosis of Crohn disease is
comparable to that of other imaging modalities such as magnetic
resonance enterography or CT, 110,111 and ultrasound is probably
more suitable for use in young children. Bowel wall inlammation
in Crohn disease is segmental and transmural and tends to be
asymmetrical, with greater involvement of the mesenteric border
of bowel (Fig. 53.37). A wall thickness of greater than 3 mm is
a sign of active disease on follow-up ultrasound examinations. 112
In early Crohn disease, wall stratiication may be preserved with
thickening of the submucosal layer. 113 With more advanced disease,
actively inlamed bowel wall shows loss of normal stratiication
and is hyperemic with decreased peristalsis. Skip areas and
mesenteric inlammatory changes are characteristic of the disease.
Lymph node hypertrophy and mesenteric ibrofatty proliferation
also favor Crohn disease (Fig. 53.37B). Mesenteric inlammation
that accompanies Crohn disease can be profound and can mimic
other diagnoses in children on initial presentation with the disease.
Contrast-enhanced ultrasound (CEUS) has been shown to
improve identiication of the afected bowel loops in children
with Crohn disease and can also depict the microvasculature of
the bowel wall and surrounding mesentery. 114,115 Some studies
have suggested that CEUS may help to distinguish inlammatory
strictures from ibrotic strictures, which can help solve a common
therapeutic dilemma in resolving Crohn disease. 116 Doppler
measurement of the resistive index in the SMA has been used
to assess progression of disease in patients with active Crohn
disease with only partial correlation. 117 Investigations into use
of ultrasound elastography to detect diminished tissue elasticity
in the afected bowel are in the early stages. Sonography is
indicated in children with suspected complications of regional
enteritis. Ultrasound may identify distal right ureteral involvement
by the inlammatory mass that can result in hydronephrosis.
Although the istulas and sinus tracts that develop in regional
enteritis are usually not discernible sonographically, ultrasound
can be used to identify associated intraabdominal abscesses (see
Fig. 53.37C).
Henoch-Schönlein purpura, a condition caused by an
autoimmune vasculitis involving small vessels in a variety of
body systems, frequently involves the GI tract. Of these patients,
50% to 60% develop abdominal pain from intramural hemorrhage
in the intestines, and this symptom may precede the development
of the more characteristic purpuric skin rash. In such patients,
sonography may detect the involved intestinal loops, which usually
show circumferential, echogenic wall thickening, sometimes
associated with small amounts of free abdominal luid 53 (Fig.
53.38). Sonography also can be used to follow the resolution of
the intestinal hemorrhage. Intussusception is a major complication
of Henoch-Schönlein purpura, and sonography is highly
useful to identify such an intussusception, 118 which usually
involves only the small bowel and does not extend into the colon.
Intestinal hemorrhage may also complicate bleeding diatheses
or blunt abdominal trauma.
A variety of other conditions can result in thickening of the
wall of the small bowel or colon, but few show distinguishing
characteristics at imaging. Hemolytic uremic syndrome is
associated with E. coli 0157:H7 infection, characterized by
hemolytic anemia, thrombocytopenia, and renal failure. Hemolytic
uremic syndrome is usually preceded by a severe hemorrhagic
colitis. Color Doppler imaging reveals that the thickened bowel
segments are hypovascular, 98 probably secondary to ibrin
microthrombi that develop from factors released by the damaged
endothelium (see Fig. 53.32D). Grat-versus-host disease in
bone marrow transplant patients occurs when the transplanted
tissue mounts an attack on host tissues. Skin, liver, and GI
involvement is common. Acute grat-versus-host disease occurs
within 100 days and involves the small intestine in 75% to 100%
of cases. 119 Circumferential bowel wall thickening and mucosal
hyperemia, representing the neovascularization driven by