CT Shows Promise for Both Detecting and Typing Uroliths in Dogs and Cats

Computed Tomographic Assessment of Retrograde Urohydropropulsion in Male Dogs and Prediction of Stone Composition Using Hounsfield Unit in Dogs and Cats

Aurélie Bruwier, Benjamin Godart, Laure Gatel, Dimitri Leperlier, Anne-Sophie Bedu

Background:
Urethral and bladder uroliths are a common clinical challenge in veterinary medicine. Retrograde urohydropropulsion is often used to relieve urethral obstruction before cystotomy, but residual calculi are frequently overlooked. This study aimed to assess the success rate of retrograde urohydropropulsion using non-enhanced computed tomography (CT) and to determine if CT-measured mean Hounsfield units (mHU) could predict urolith composition in dogs and cats.

Methods:
This prospective study included 65 animals (55 dogs and 10 cats) with lower urinary tract uroliths who underwent preoperative non-enhanced CT. In 45 male dogs, CT was performed after retrograde urohydropropulsion to assess residual urethral calculi. CT scans were reconstructed using three convolution filters (B30s, B70s, B90s), and mHU values of the uroliths were measured. Stone composition was confirmed by infrared spectrometry. Statistical analyses assessed the association between mHU, convolution filter, and stone type.

Results:
Retrograde urohydropropulsion had a first-attempt success rate of 55.6% and a cumulative success rate of 86.7% after a second attempt. Persistent urethral calculi were most often located in the membranous (42.3%) and penile urethra (38.5%). CT could identify calculi missed on radiographs, including those in the penile and prostatic urethra. mHU values differed significantly by stone type and convolution filter. Calcium oxalate calculi had the highest attenuation (mHU > 1,000 across all kernels), distinguishable from other types. The B30s (smooth) kernel provided the best discrimination. Cystine and struvite stones had overlapping mHU ranges, limiting compositional prediction.

Limitations:
CT mHU values may vary by scanner type and settings. Hand-drawn ROI and variable calculus sizes could affect measurement precision. The sample size for some stone types was small. Urethral stenoses were not detected on CT but required additional imaging (urethrography).

Conclusions:
Non-enhanced CT is a reliable imaging tool to detect persistent urethral calculi following retrograde urohydropropulsion, potentially reducing the rate of incomplete stone removal before surgery. Furthermore, CT attenuation values, especially using a B30s filter, can help predict calcium oxalate composition in vivo, aiding in clinical decision-making and treatment planning. However, precise stone typing still requires laboratory confirmation.

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