Ultrasound
Urinary Tract
Basic Information 
Equipment, Anesthesia
• Transrectal imaging of the urinary bladder and caudal pole of the left kidney is best performed using a 5-MHz linear-array rectal transducer.
• The urethra in male horses can be imaged, depending on the location, either transcutaneously using 7.5- to 10.0-MHz transducer or transrectally using a 5.0- to 7.5-MHz linear-array transducer.
• The right kidney is imaged transabdominally using a 2.5- to 5.0-MHz sector-scanner transducer and the left kidney and urinary bladder using a 2.5- to 3.5-MHz transducer.
Preparation: Important Checkpoints
• Clipping hair over the paralumbar fossa region and cranially to the sixteenth to seventeenth intercostal space on the left and between the fourteenth to seventeenth intercostal spaces on the right is desirable prior to ultrasound evaluation of the kidneys.
• Sedation and restraint in stocks is ideal for transrectal imaging.
• Application of ultrasound gel or isopropyl alcohol will improve image quality.
Procedure
• The urinary bladder may be imaged on the floor of the ventral abdomen just cranial to the pelvic brim.
• The bladder can be examined either transrectally (5.0-MHz linear array transducer) or transabdominally (2.5–5.0 MHz sector-scanner transducer) if the urinary bladder is distended with urine.
• The urinary bladder is best imaged when full of urine.
• The thickness of the wall of the bladder varies with distension but is normally between 3 to 6 mm.
• Equine urine appears as a heterogeneous mixed echogenic fluid due to the presence of mucus and crystals. Crystals can accumulate as sediment in the ventral aspect of the bladder. The sediment can be made to swirl if the bladder is balloted.
• Cystic calculi have an echogenic appearance and produce an acoustic shadow.
• Intramural masses can be imaged in the wall of the urinary bladder.
• Normal ureters and ureteral openings into the urinary bladder can occasionally be imaged transrectally using a high-frequency transducer but become obvious with hydroureter.
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