THE SCIENCE OF SOFT TISSUE SURGERY


Fig. 3. Normal and abnormal transrectal ultrasonographic images of the bladder from 3 horses. A, Normal bladder with layering due to ventral accumulation of mucus and crystals. B, Cystolith located within the dependent portion of the bladder. C, Large cystolith near the trigone region with left ureteral distention due to intermittent obstruction of the left ureter by the bladder stone.


Kidneys should also be evaluated for evidence of chronic renal failure.2,4,6–8 Affected horses may show one or two end-stage kidney(s). End-stage kidneys are small and distorted with near complete loss of renal architecture, making them challenging to recognize by all but expert ultrasonographers (Fig. 2B). In horses with one end-stage kidney, the contralateral kidney is often enlarged but re- tains recognizable renal parenchyma (Fig. 2C). Affected horses may present with obstructive nephrolith(s) in the remaining functioning kidney or an obstructive urolith in the corresponding ure- ter. Evidence of pyelonephritis may also be found in horses with an obstructive ureterolith or cystolith due to ascending infection. Affected kidneys appear enlarged with increased cortical thickening and echogenicity. Concurrent renal abscessation may be apparent due to ascending infection but is relatively unusual.


Transrectal Ultrasound


A rectal or small microconvex transducer is neces- sary for transrectal evaluation of the bladder and ureters. The caudal portion of the left kidney is visible at arms’ length in many horses. If cystos- copy is desired, it should always be performed after ultrasound examination. Gas introduced during endoscopy will obscure ultrasonographic visibility and can mimic the appearance of uroliths in all portions of the urinary tract.


Bladder


The bladder is best evaluated via transrectal ultra- sound, although it may be visible transcutaneously from the inguinal region in some horses, depending on the degree of distention. Transrectally, the bladder is seen ventral to the rectum and is often filled with varying degrees of echogenic urine due to mucus and crystals commonly found in equine urine (Fig. 3A). This appearance is often confused with pyuria by novice and even intermediate ultrasonog- raphers. Cystoliths can be found at the trigone region or in the dependent portion of the bladder (Fig. 3B). They may act as a ball valve by rolling back and forth to cause intermittent obstruction of


404 2019  Vol. 65  AAEP PROCEEDINGS


the urethra and ureters when in the trigone region (Fig. 3C). In such cases, bilateral ureteral disten- tion and wall thickening may be evident on trans- rectal ultrasound that occasionally extends to the renal pelvis which may be visible on transcutaneous imaging. Thickening of the bladder wall may be noted but is not a reliable finding in the authors’ experience. It should also be noted that a recently emptied bladder can appear falsely thickened.


Ureters


The right and left ureters are evaluated separately by beginning at the trigone region of the bladder and following each as far proximally as possible. The small size and maneuverability of a microconvex transducer makes it the probe of choice to obtain transverse views of the ureters along their entire visible lengths (Fig. 4). The use of a rectal trans- ducer to evaluate the caudal ureters has been de- scribed11; however, this transducer is difficult and potentially risky to manipulate within the rectum for evaluation of the proximal and mid-ureteral re- gions. With a microconvex transducer, transverse views of the left ureter can be obtained from the trigone to the left kidney. Due to the right kidney’s cranial location beyond arm’s reach, the right ureter is slightly less visible, with visibility ending caudal to the ureteropelvic junction. The normal ureter is a small (approximately 1 cm) structure that is difficult to identify when collapsed. To begin the exam, ureters are often best identified caudally at the bladder trigone, usually at wrist’s length from the anus. Both ureters are often visi- ble at this location on transverse views. The col- lapsed ureter is often only subtly visible to the right and left of dorsal midline of the bladder. Peristaltic waves will improve ureteral visibility and differen- tiate ureters from blood vessels and the male repro- ductive tract. Ureteral pulses ranged from 1 to 5 pulsations every 2 minutes in one study of normal horses.11 In the authors’ experience, ureteral mo- tility remains detectable with sedation; however, the use of N-butylscopolammonium bromidea typically reduces motility to such an extent that ureters be- come challenging to identify and is therefore avoided


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