Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Three The Abd omen 293
Fig. 3-45, cont’d B, On the ventrodorsal view, the
pylorus (white c) of the stomach is displaced medially.
Diagnosis: Generalized hepatomegaly, in this case
secondary to diabetes mellitus.
B
sally on the lateral view (Fig. 3-47). Enlargement of the caudate lobe may produce a tissue-dense
mass in the dorsal, cranial portion of the abdomen. If the caudate process of
this lobe is affected, the right kidney may be displaced caudally from its normal position
(the thirteenth rib crossing the right kidney at the level of the renal pelvis) (Fig. 3-48).
Pneumoperitoneography may be helpful in outlining the borders of the caudate lobe.
Differential considerations in all of these instances should include primary neoplasia,
such as hepatocellular carcinoma, carcinoid, or bile duct carcinoma; metastatic neoplasia;
torsion; incarceration; or benign lesions, such as hepatic cyst, abscess, or an unusually
large area of nodular hyperplasia.
Occasionally, a liver may appear smaller than normal. Because many animals have livers
that appear small without clinical signs or biochemical abnormalities, it is difficult to
define the exact measurements that should be considered pathologic. The liver often
appears smaller in deep-chested dogs (e.g., Afghan Hounds, Irish Setters) than in dogs with
shorter, squarer thoracic conformation. The position of the stomach close to the
diaphragm is usually a sign of a small liver in this situation. The fundic–pyloric axis is
decreased in that the pylorus is cranially displaced relative to the fundus. Another way of
describing the situation is that the axis is angled toward the thorax. In those cases in which
the liver is quite small, the differential diagnoses should include hypotrophic cirrhosis or
fibrosis (Fig. 3-49). These may be found in association with portosystemic shunts as well as
toxic, metabolic, inflammatory, or idiopathic causes.
Shape Changes. Abnormalities in liver shape are a significant sign of liver disease and
may occur in the absence of hepatomegaly. Only some of the conditions that produce
hepatomegaly will alter the contour of the liver. Irregular, lumpy liver margins may be
caused by neoplasia, abscesses, cysts, cirrhosis, or nodular hyperplasia (Fig. 3-50). Smooth
rounding of the liver edges is a nonspecific finding suggesting hepatic swelling. The radiograph
tends to underestimate alterations in liver shape so that if the liver appears irregular
on a radiograph the degree of change that is present will be marked.