Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

C H A P T E R T H R E E
The Abdomen
RADIOLO GY AND ULTRASONO GRAPHY OF THE
ABD OMEN
Abdominal radiography is indicated whenever clinical signs or laboratory findings indicate
the presence of abdominal disease, or whenever a condition is present in which involvement
of, or extension to, the abdomen is possible. These characteristics include (1) gastrointestinal
(GI) signs such as vomiting, diarrhea, tenesmus, anorexia, and unexplained
weight loss, (2) urogenital signs such as polyuria, oliguria, anuria, stranguria, pyuria,
hematuria, polydipsia, and vaginal or preputial discharge or bleeding, and (3) nonspecific
signs such as palpable abdominal masses or organomegaly, suspected hernias or abdominal
wall masses, anemia, and fever of unknown origin. If there is evidence of direct trauma,
it is advisable to obtain radiographs of the abdomen to ensure that there is no internal
damage. When the origin of the medical problem is obscure and other means do not yield
a diagnosis, or when an animal resists or resents abdominal palpation, abdominal radiography
may be indicated as a screening technique.
Abdominal ultrasonography usually is performed in association with abdominal radiography.
In some cases, such as the diagnosis of pregnancy or in the presence of abdominal
fluid, only the ultrasonographic examination will be performed. This decision often is
based on the experience and training of the ultrasonographer. A combined ultrasonographic
and radiographic evaluation usually provides more information than either study
by itself.
TECHNICAL CONSIDERATIONS
Radiography of the abdomen should be performed using a consistent set of technical factors.
A formal technique chart should be used to establish the kilovolt (peak) (kVp) and
milliampere-second (mAs) settings for all exposures. If the animal measures greater than
10 cm at the thickest portion of the abdomen within the field of view, a grid should be used
to reduce the effects of scatter radiation. The grid will prevent a haziness that may be misinterpreted
as intraabdominal loss of detail due to pathologic causes. The exposure time
should be minimized to reduce motion artifact caused by bowel movement. Although in
some animals exposure times as long as 0.1 second will produce satisfactory results, exposure
times of 0.03 second or less are recommended. The radiographs always should be
viewed on a view box with the films consistently oriented. It is customary practice to view
all lateral films with the head facing toward the left, and to view all ventrodorsal or
dorsoventral films with the right side of the patient on the left side of the view box (as if
facing the examiner) and the cranial abdomen in the uppermost position. Consistency in
radiograph orientation facilitates recognition and general familiarity with normal structures
and aids in the interpretation process.
Clipping the hair is essential to achieving a good abdominal ultrasonographic examination.
Limited examination of the abdomen may be possible without doing so in some
animals with a thin hair coat. Wetting the hair coat with alcohol before applying the gel
improves the contact between the skin and transducer. The choice of transducer and gain
settings depends on the patient’s size, organ of interest, and availability of equipment.
Usually the highest-frequency transducer that can penetrate to the depth of the structure
of interest without noise-laden high gain settings is preferred. Although there is ongoing
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