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270 SECTION II III The Mammals

transient, lasting only a day or two, and often refl ect
little more than constipation. Cecal or cecocolic impac-
tion is a concern (Figure 23-5), which can be more
persistent, and may be associated with colic. Alterna-
tively, abdominal distention can be an indicator of
serious underlying disease such as intestinal blockage,
liver disorder, cancer, or ascites.

Abdominal Tumors
Abdominal tumors may affect any organ, solid or
hollow, in addition to the peritoneum. A peripherally
situated abdominal tumor is sometimes visible from
the exterior as a lump or distortion in the abdominal
wall (Figure 23-6), but this is exceptional. Radiographic
detection depends almost entirely on a combination of

organ enlargement and/or disfigurement and to a
lesser extent on displacement. Localized calcifi cation
is present infrequently, and although suggestive of
malignancy, especially of the adrenal gland, offers no
assurance of the existence of such a process (Figure
23-7).
Where a lump or subcutaneous mass is evident, a
lead marker on the overlying skin usually proves
helpful in establishing a radiographic relationship
(Figure 23-8). Likewise, holding or otherwise securing
a palpable mass while ultrasound is performed often

speeds and simplifies the process of sonographic
identifi cation.
Figure 23-4 • Close-up dorsoventral view of the thorax of a
dyspneic rat shows an immense mass filling much of the thorax,

making it appear as if the animal has a pair of hearts (double heart
sign). The lesion proved to be a cancerous tumor that originated
in the cranial mediastinum. With respect to differential diagnosis,
a primary lung tumor would have a similar appearance.

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