Plain Radiography for Diagnosis of Urethral Rupture in Cats

In the Literature

Milne J, Sparks T, Brash R, de Almeida Coelho M, Natsiopoulos T, Holdsworth A. Perineal findings associated with urethral ruptures on plain lateral radiographs in cats. J Feline Med Surg. 2025;27(11):1098612X251379728. doi:10.1177/1098612X251379728

The Research …

Urethral rupture in cats most commonly occurs after a traumatic incident and can lead to significant tissue damage and urethral stricture formation.¹ Urethral rupture can be missed on initial triage because of more time-sensitive injuries or vagueness of clinical signs.² Lower urinary tract studies (eg, positive contrast retrograde urethrography, vaginourethrography) using radiography or fluoroscopy are the preferred diagnostic tests for suspected urethral rupture.¹

This study aimed to determine whether features of urethral rupture in cats could be identified on plain radiographs. The authors hypothesized that a perineal bulge with an irregular soft-tissue opacity would have high sensitivity and low-to-moderate specificity for urethral rupture.

Plain radiographs of cats with confirmed urethral rupture (n = 22) were compared with abdominal/pelvic images obtained from cats without urethral rupture (n = 70). Each image was assessed for a perineal bulge, which was then classified as mild, moderate, or marked in size. Perineal soft tissues were assessed for amount of heterogeneity in opacity. Lastly, the reviewers considered all radiographic findings combined and recorded if urethral rupture was suspected, and if so, whether a lower urinary tract study for further evaluation should be recommended. Radiologists were not provided any clinical information on the patients beyond the radiographs.

Results demonstrated a significant association between urethral ruptures and 3 plain radiographic features: presence of a perineal bulge, a perineal bulge larger in size, and heterogeneous perineal tissue. A significant association was found between presence of urethral rupture and a perineal bulge alone, with high sensitivity (95.5%) and negative predictive value (96.4%-97.1%) but low specificity (38.6%-47.1%) and positive predictive value (32.8%-36.2%). No significant association was found between lack of a visible urinary bladder or the presence of pelvic limb, vertebral, or pelvic fractures and urethral rupture.

… The Takeaways

Key pearls to put into practice:

• Cats presented with blunt force or iatrogenic urinary tract trauma should undergo radiography for assessment for injuries, including perineal bulges. A lower urinary tract study is indicated to confirm urethral rupture in cases in which a perineal bulge, particularly one large in size, and heterogeneous perineal tissue opacity are appreciated.

• Urethral rupture should be suspected in cases in which perineal swelling cannot be explained by the presence or degree of localized trauma.

• Distal urethral rupture may lead to urine leakage in the periurethral tissues, but not the peritoneal space, thus free urine in the abdominal space may not be present.³

• Because of the low specificity and positive predictive value of the presence of a perineal bulge and heterogenous perineal tissue on plain radiographs, whether a lower urinary tract study should be performed should be informed by all relevant information available about the cat, including patient history, physical examination findings, laboratory results, and other imaging results.