Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Three The Abd omen 263
Fig. 3-15 Transverse sonograms of the spleen of a 5-year-old female
mixed breed dog brought in for abdominal ultrasonographic evaluation
because of a mast cell tumor on the right stifle. The spleen is normal.
The splenic veins can be identified extending to the margin of the
spleen (arrows). Diagnosis: Normal spleen.
L3. On the lateral view, the right kidney is dorsal and cranial to the left kidney and may be
superimposed over the gastric and splenic shadows. Frequently, the cranial pole of the right
kidney is not seen, because it is nestled within the renal fossa of the caudate process of the
caudate lobe of the liver. At this site, there is little or no fat to provide contrast between the
two organs. On the ventrodorsal view, the right thirteenth rib superimposes on the pelvis
of the right kidney. As on the lateral view, it is often difficult to see the cranial pole of the
right kidney on the ventrodorsal view. The left kidney is seen lateral to the spine at the level
of L3 just medial and caudal to the spleen. The normal length of the canine kidney is
approximately 2.5 to 3.5 times the length of the second lumbar vertebral body as measured
on the ventrodorsal view. 23-25 Although the normal width, from the medial to lateral borders,
and depth, from the dorsal to ventral borders, of the kidney are less commonly quantified,
these parameters should be evaluated subjectively. The left kidney, which is
somewhat moveable within the retroperitoneal space, may orient itself on the ventrodorsal
projection at such an angle that its apparent length is shorter than its actual length. In the
average dog, 12 to 20 kg, the kidney measures 6 to 9 cm long, 4 to 5 cm wide, and 3 to 5 cm
thick.
In the cat, both kidneys are located at the level from L1 to L4, with the right kidney usually
slightly cranial to the left. On the lateral view of the cat, the kidney shadows may be
superimposed on each other in the dorsal midabdomen, or the right kidney may be slightly
cranial and dorsal to the left kidney. The area of overlap of renal shadows may be interpreted
incorrectly as a small kidney. On the ventrodorsal view of the cat, it is usually easier
to see the entire perimeter of the kidneys. The right kidney in the cat is located lateral to
the spine and completely caudal to the right thirteenth rib. The left kidney is usually parallel
to the right or just slightly caudal to it. The normal length of the kidney in the cat is
approximately 2.0 to 3.0 times the length of L2. 25-28 In the cat, the average kidney measures
3.8 to 4.4 cm long, 2.7 to 3.1 cm wide, and 2.0 to 3.5 cm thick. Feline kidneys appear
smaller with advancing age, and neutered cats have somewhat smaller kidneys than intact
cats. 27