Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Three The Abd omen 265
Fig. 3-17 Transverse (A) and longitudinal
(B) sonograms of the left
kidney of a 5-year-old castrated male
cat with a history of vomiting and
jaundice of 1-week duration. There
is a thin hyperechoic line visible
within the renal medulla. This is a
normal finding in some cats. It is due
to accumulation of mineral within
the renal medulla. Diagnosis:
Normal kidney.
A
B
may be positioned between the left kidney and the body wall, providing an acoustic
window for examination of the kidney. The right kidney may be examined through the
liver; however, the ribs may cast acoustic shadows that obscure portions of the right
kidney.
Ureters. The ureters in both the dog and cat extend caudally from the kidneys to the bladder,
traversing the retroperitoneal space slightly ventral to the lumbar muscles and slightly
lateral to the vertebral column. Normally, because of their small size the ureters are not visible,
but it is helpful to know their course through the abdomen in order to detect conditions
such as ureteral calculi. The abdominal portion of the ureter is retroperitoneal in
location and lies adjacent to the psoas muscle. Within the pelvic cavity it enters the genital
fold in the male and the broad ligament in the female. The ureters tunnel through the bladder
wall and empty into the bladder at the ureteral orifice onto converging ridges called
urethral columns. These columns continue caudally as ridges called plica urethra and meet
to form the urethral crest, which projects into the urethra. In the male, this terminates at
the colliculus seminalis.
The proximal ureter may be identified during an ultrasonographic examination providing
the patient is cooperative and a high-frequency transducer is used. The proximal
ureter forms the base of the Y pelvis that extends along both sides of the renal crest. With
good resolution, peristalsis may be evident in the proximal ureter just beyond the renal
pelvis; however, the normal ureter cannot be traced beyond the pelvis. Mild to moderate
renal pelvic dilation (pyelectasis) occurs secondary to intravenous fluid administration,
and this dilation can be observed during the ultrasonographic examination in normal
dogs. 38 The ureter must be distinguished from the renal artery and vein. This can be done
using Doppler imaging to determine which is the artery and which is the vein. In addition,
the renal vessels branch and enter the kidney away from the renal crest, more dorsal and
ventral than the ureter in the transverse view, while the ureter branches directly on the
renal crest.
Ovaries. In the female, the ovaries are immediately caudal to the kidneys. They are not
identifiable radiographically.
The ovaries are difficult but not impossible to identify during an ultrasonographic
examination. They can be found adjacent to the caudal pole or just caudal and somewhat
lateral to the ipsilateral kidney. The ovaries are hypoechoic and partially obscured by surrounding
fat. Their round shape and follicular architecture as well as their relationship to
the ipsilateral kidney make their identification possible (Figs. 3-18 and 3-19). Small anechoic
cysts and developing follicles have been identified. A lateral scanning plane, rather
than a ventral approach, may facilitate localization and examination of the canine
ovaries. 39