Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

346 Small Animal Radiolo g y and Ultrasono graphy
linear shadows seen normally. Some masses may become quite large, and it may be difficult
to determine that they are associated with the bowel. The presence of the bowel’s characteristic
bright mucosal-submucosal streak may be the primary clue that the mass originated
in or entraps a loop of intestine. Many masses are eccentric to the bowel lumen, and
careful, thorough examination may be required to confirm or identify the intestinal loops
passing through or adjacent to the mass. The presence of gas within an abdominal mass
should be seen as an indication that the mass is bowel associated (Fig. 3-120). 391 In cats,
intestinal lymphosarcoma produces a transmural hypoechoic lesion that interferes with
normal peristalsis. 338 Lymph node enlargement is seen frequently in association with the
intestinal lesion. 339 Most extramural lesions displace the intestines; therefore there will be
no alteration in intestinal shape nor will there be gas within the mass.
In some cases an intestinal tumor or penetrating foreign body will result in peritonitis
or carcinomatosis. Both processes will cause the mesentery to thicken and shrink, resulting
in bunching of the small intestines, usually into a round ball. It is very difficult to identify
the mass or foreign body in these situations. Also, hydroperitoneum of an echogenic variety
is frequently present. A mass may or may not be identifiable (Fig. 3-121).
In many cases, when observed during real-time ultrasonographic examination, a partially
obstructed bowel segment may appear dilated and contain varying degrees of sloshing liquid
that appears to be going back and forth with the inadequate peristalsis. Even if the specific site
of the partial obstruction is not found, these findings indicate that either laparotomy or possibly
a GI series is indicated, provided survey radiographs have been made. In our experience,
the combination of survey radiographs with either segmental or regional bowel distention, primarily
fluid, combined with the appearance at ultrasonography of ineffective, but active, peristalsis
is adequate to diagnosis partial obstruction and proceed to surgery without a GI series.
Intussusception can be identified using ultrasonography (Fig. 3-122). 336,395-397 In addition
to the dilation of the intestines and lack of peristalsis, the intussusception itself can be
identified as a multilayered lesion, which appears as linear streaks of hyperechoic and hypoechoic
tissue in long section and as a series of concentric rings when viewed in cross-section.
Enteric duplication cysts have been detected using ultrasonography. 399 A cystlike mass
partially encircling and sharing a wall with a segment of small intestines was described. The
wall of the mass had three layers, with a hyperechoic inner and outer layer surrounding a
hypoechoic central layer. The hypoechoic central layer was continuous with the hypoechoic
muscular layer of the adjacent normal intestine. Diffuse mobile echoes were identified
Fig. 3-117 Longitudinal (A and B)
and transverse (C and D) sonograms
of the midabdomen of an 8-year-old
spayed female Silky Terrier with a
history of chronic vomiting and a
palpable midabdominal mass. There
is a hyperechoic curvilinear structure
in the abdomen (arrows). This
structure formed shadows and
appeared to be associated with the
GI tract. This most likely represents a
foreign body but also could represent
mineralization of the bowel
wall. Diagnosis: GI foreign body.
A
B
C
D