Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

292 Small Animal Radiolo g y and Ultrasono graphy
The most common radiographic change in the liver is an increase in size. Because the
normal appearance varies greatly depending on the animal’s breed and body condition,
recognition of pathology can be difficult. The length of the liver, as measured from the
most cranial point on the diaphragm to the caudal-most point on the ventral liver, has been
correlated with liver volume in normal dogs. 261 Whether this measurement is useful or
practical in patients has not been established. There are several radiographic changes that
indicate hepatomegaly. The greater the number of changes that can be identified, the more
reliable the diagnosis of hepatomegaly becomes. On the lateral view, the radiographic signs
of diffuse hepatomegaly include increased fundic–pyloric axis (defined as a line passing
through the center of the fundic and pyloric regions of the stomach on the lateral view; this
line should be parallel to the twelfth intercostal space), extension of the ventral hepatic border
beyond the thirteenth rib and chondral cartilages, and rounding of the hepatic borders
(Fig. 3-45). On the ventrodorsal view, there may be displacement of the pylorus toward the
midline by the right liver lobes, displacement of the cardia toward the midline by enlarged
left hepatic lobes, and caudal displacement of the stomach, small intestines, and right kidney
by enlarged right hepatic lobes. Although hepatic enlargement will displace the spleen
caudally, the spleen is normally quite moveable. Therefore the position of the spleen is a
poor indicator of hepatomegaly. Generalized hepatomegaly is a nonspecific finding for
which the differential diagnoses include hepatitis; fatty infiltration, either primary or secondary
to diseases such as diabetes mellitus; hyperadrenocorticism, due to hepatic accumulation
of glycogen; passive congestion; hypertrophic nodular cirrhosis; local neoplasia,
such as lymphosarcoma, mast cell tumor, hepatocellular carcinoma, carcinoid, or bile duct
carcinoma; and metastatic neoplasia.
Enlargement of specific hepatic lobes may be more difficult to identify than generalized
hepatomegaly. In some instances, a pneumoperitoneum may be useful in reaching a
definitive diagnosis by clearly outlining the size and shape of a liver lobe. Enlargement or
masses of the left lateral lobe may cause displacement of the cardia of the stomach to the
right on the ventrodorsal view and dorsally on the lateral view (Fig. 3-46). The small intestine
and spleen may be displaced caudally on both views. Enlargement of the right lateral
lobe may cause the duodenum to be displaced medially on the ventrodorsal view and dor-
Fig. 3-45 A 6-year-old female
Poodle with chronic polyuria and
polydipsia. A, On the lateral view
there is extension of the caudal ventral
border of the liver well beyond
the chondral arch (black L) and
increased angulation (i.e., an angle
greater than that of the intercostal
spaces) of the stomach from the fundus
(white f) to the pylorus (black p).
Continued
A