MRI Outperforms CT in Diagnosing Canine Urethral and Bladder Tumors

JVIM 2025

Author

Obi Veterinary Education
November 14, 2025

Younjin Kang, Jonghui Baek, Sunghwa Hong, Soyeon Kim, Eunjee Kim, Junghee Yoon, Jihye Choi

Background

Lower urinary tract tumors account for about 2% of canine cancers, with urethral involvement linked to poor prognosis and limited surgical options. Imaging plays a key role in assessing local invasion, yet conventional methods such as retrograde urethrography and ultrasonography provide limited soft‐tissue detail. Computed tomography (CT) offers anatomical precision but insufficient contrast differentiation. In human medicine, magnetic resonance imaging (MRI) has proven superior for soft tissue evaluation of the urethra and bladder. This study aimed to evaluate the feasibility, image quality, and diagnostic utility of MR urethrography in dogs compared with CT, hypothesizing that T2‐weighted (T2W) and contrast‐enhanced T1‐weighted (post‐T1W) MRI sequences would best delineate urethral and bladder wall layers.

Methods

The investigation consisted of two components: (1) a prospective study of five healthy dogs (four Beagles and one Labrador Retriever) and (2) a retrospective evaluation of six dogs with confirmed or suspected uroepithelial tumors. All subjects underwent both MRI and CT under general anesthesia. MRI sequences included T2W, pre‐contrast T1‐weighted (pre‐T1W), and post‐contrast T1‐weighted (post‐T1W) imaging, while CT included pre‐ and post‐contrast scans. Images were assessed for wall layer distinction, urethral conspicuity, and overall quality using a 4‐point scoring system. Interobserver reliability was evaluated using the intraclass correlation coefficient (ICC), and statistical comparisons were made using the Kruskal–Wallis and Mann–Whitney U tests.

Results

In healthy dogs, T2W and post‐T1W sequences provided significantly superior visualization of urethral wall layers compared to CT (p < 0.05). The membranous urethra appeared as a “target‐like” structure on these MRI sequences, comprising three distinct layers: outer and inner hypointense rings separated by a hyperintense middle layer. Post‐T1W images most effectively distinguished bladder wall layers, revealing a highly enhancing inner layer and a hypointense outer layer. CT produced faster acquisitions with fewer motion artifacts but poor soft‐tissue contrast.
In tumor cases, MRI—particularly T2W and post‐T1W—offered superior visualization of lesion margins, urethral wall disruption, and tumor invasion into adjacent tissues compared to CT. Hyperintense urine in T2W images served as a natural contrast medium, enhancing luminal delineation. MRI findings aided differentiation of bladder wall invasion, urethral involvement, and rectal sparing, informing radiotherapy planning.

Limitations

Study limitations included a small sample size, lack of female representation in the normal cohort, and absence of standardized bowel or urethral preparation. Motion artifacts affected some MRI sequences, and small patient size occasionally limited spatial resolution. Additionally, not all clinical cases underwent histopathologic or BRAF confirmation, and the limited number of subjects reduced statistical power.

Conclusions

Magnetic resonance urethrography proved a feasible and effective imaging modality for evaluating canine lower urinary tract anatomy and pathology. T2W sequences optimized anatomical and luminal visualization, while post‐T1W imaging improved tissue boundary definition and detection of tumor invasion. Compared to CT, MRI provided superior soft‐tissue contrast and diagnostic detail, supporting its clinical use for staging and treatment planning of urethral and bladder tumors in dogs. MRI thus represents a noninvasive alternative to retrograde urethrography, minimizing procedural risk while enhancing diagnostic accuracy.

Magnetic resonance imaging and CT images of the prostatic urethra in a normal dog. (A) On the T2-weighted image, the prostatic urethral wall appears as two distinguishable layers: a hyperintense outer layer (arrow) and a hypointense inner layer (arrowhead). The hyperintense outer layer of the prostatic urethra was clearly distinguishable from the hypointense prostatic parenchyma (p). (B) On the pre-contrast T1-weighted image, the prostatic urethra (arrow) appears as a single layer, isointense relative to the prostatic parenchyma (p). (C) On the contrast-enhanced T1-weighted image, the prostatic urethra appears as two blurred layers, with the outer layer (arrow) appearing brighter than the hypointense inner layer (arrowhead). The outer layer enhances more strongly than the surrounding prostatic parenchyma (p). (D) On the contrast-enhanced CT image, the urethral wall appears as a single layer (arrow), slightly more enhanced than the prostatic parenchyma (p).

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