A thorough examination of the urinary tract is essential in patients presenting with signs of lower urinary tract disease (pollakiuria, dysuria, incontinence). In male dogs, the penile urethra can be palpated through the os penis ventrally. The perineal urethra and the urethra, at the proximal portion of the os penis, should be palpated as stones tend to get lodged as the urethral lumen narrows as it passes through the os. A rectal palpation allows identification of the prostate and prostatic urethra. In female dogs, a vaginal palpation to examine the vestibule, vestibulovaginal junction, urethral papilla and identify a paramesonephric remnant is important. A rectal palpation allows identification of the pelvic urethra. In male and female cats, sedation is usually necessary in order to perform a rectal palpation to examine the urethra.
It is important to evaluate the urethra, especially the pelvic/prostatic urethra in patients presenting with lower urinary tract signs, as standard radiographs and abdominal ultrasound do not allow examination of this portion of the urethra. Soft tissue masses along with stones are commonly missed. An oblique radiographic view of the pelvic urethra with the patient in lateral recumbency helps identify urethral stones that would otherwise be hidden by the pelvis. Transitional cell carcinoma may affect solely the urethra and therefore may only be identified by rectal palpation (missed by ultrasound) and contrast radiography.
Always pre-measure the urinary catheter to avoid knotting/kinking within the bladder.
Female dogs: I recommend doing this blind, guided by digital palpation. With the dog heavily sedated or in ventral recumbency, place a finger at the vestibulovaginal junction, then slide the urinary catheter ventral to your finger. The catheter will not be able to enter the vagina as it is obstructed and will slide into the urethral papilla. If the vestibule is too small to allow digital palpation, place a Foley catheter in the vagina and fill the balloon. While gently pulling the balloon caudally, slide a urinary catheter into the vestibule. Again, as the vagina is occluded, the catheter will enter the bladder.
Hint: if following placement of a Foley catheter, the balloon is unable to be emptied, even if the catheter is cut, it can be punctured with ultrasound guidance.
Male dogs: 5–10 kg, 5 Fr catheter; >10 kg, 8Fr catheter.
Female cats: The urethral papilla is much larger than the opening to the vagina and blind catheterization is usually successful as the catheter enters the urethra easily with the cat in ventral recumbency.
Male cats: If catheterization is difficult, an angled hydrophilic guidewire (0.018 inch) can be used to slide through the urethral lumen and looped in the urinary bladder. An open-ended catheter can then be slid over the guidewire. If the cat cannot be catheterized, antegrade catheterization is recommended. See Lower Urinary Tract Tips: Part 2.
Nonionic iodine water-soluble contrast agent should be used such as iohexol (Hypaque, Omnipaque). Barium should never be used in the urinary tract. Allows evaluation of the urethra for masses, strictures, urethral spasm, stones, etc.). Contrast radiography is indicated in patients with lower urinary tract signs without signs of stones, infection or masses on radiographs and ultrasound. Cats presented with urethral obstruction unable to urinate following removal of a urinary catheter, should be evaluated by contrast radiography. The patient is catheterized and the bladder filled until it is firm with a mixture of 50/50 contrast/sterile saline. The urinary catheter is removed and the bladder is gently expressed and a radiograph is taken (voiding phase). Complete filling of the bladder and urethra are essential in order to obtain a diagnostic exam. This exam can be performed prior to removing a urinary catheter in a cat to ensure the urethra is patent. This exam can also be performed when a urethral or bladder tear is suspected.1-3
1. Weisse C, Berent A, eds. Veterinary Image-Guided Interventions. Wiley-Blackwell; 2015.
2. Dunn M, Berent A. Urologic interventional therapies. In: Ettinger SJ, Feldman EC, Côté E, eds. Textbook of Veterinary Internal Medicine. Chapter 124. 8th ed. Elsevier; 2016:493–511.
3. Butty E, Vachon C, Dunn M. Interventional therapies of the urinary tract. Vet Clin North Am Small Anim Pract. 2019;49:287–309.