Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

262 Small Animal Radiolo g y and Ultrasono graphy
Fig. 3-14 A 3-year-old male West Highland White Terrier with a 1-
day history of anorexia. The ventrodorsal view revealed that the
spleen lay along the left lateral body wall (white arrows). This is one
of the many positions that the spleen normally assumes. Diagnosis:
Normal abdomen.
of the spleen varies; when it is small it may be difficult to find. This is especially true in cats.
The spleen is hyperechoic when compared with the liver and renal cortex. It has a uniform
homogeneous architecture. The splenic capsule may be evident as a bright marginal line,
although this varies depending on the angle with which the ultrasound beam strikes the
spleen (Fig. 3-15). 11,21 In an animal with peritoneal fluid, the capsule is much more apparent.
The splenic veins can be identified as anechoic structures that enter the spleen along
its medial border. These can be followed as they branch within the splenic parenchyma. In
normal dogs, a hyperechoic area may be identified at the splenic margin adjacent to the
splenic veins. This is the result of mesenteric fat within splenic capsular invaginations.
Splenic arteries are rarely seen, although they may be detected by Doppler ultrasonography.
The shape of the spleen will vary depending on the orientation of the spleen to the
ultrasound beam. It usually is seen as a thin, flat triangle; however, if the beam is oriented
along the long axis of the spleen it can appear as a wider structure. The spleen should be
examined in both longitudinal and transverse planes. The spleen is useful as an acoustic
window for evaluating the left kidney. Imaging the kidney through the spleen provides a
comparison for echogenicity of both structures.
Kidneys. The appearance and location of the kidneys in dogs are affected by the animal’s
age, posture, and general body condition. The kidneys are usually apparent, but the intestines
may be superimposed over them and may obscure some or all of their perimeter. The
right kidney is identified less frequently than the left, because it is less moveable and is normally
in contact with the liver. The kidneys become more moveable and, as the dog ages,
will become more ventrally and caudally located. When positioned in lateral recumbency,
the dependent kidney moves cranially and the nondependent kidney droops, becoming
more visible and more bean shaped. The extent of this movement or drooping is variable.
13,22 The kidneys also move a distance of approximately one vertebral body with respiration.
The right kidney extends from T12 to L1, while the left lies in the area from L1 to