Radiology Case

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Radiographic impression: There are multiple marginated radiopaque urethral (penile) calculi measuring between 3 to 5 mm in diameter from the level of the mid os penis to the level of the ischium (proximal penile urethra) (arrows). No cystic calculi are seen.

Radiographic diagnosis: Partial urethral obstruction by a large number of urethral calculi.

Comments: This extreme example of urethral calculi is definitely one for the record books; however most urethral diseases are not this obvious and are often overlooked. Subtle radiopaque urethral calculi can be lodged at the level of the os penis and go unseen due to lack of careful inspection, overexposure, or superimposition of the stifles (particularly superimposition of the fabellae). A lateral projection, with the hind limbs pulled forward, will allow the best evaluation of the entire urethra. The calculi may be non-radiopaque as well. The radiopaque calculi are the calcium oxalate, calcium carbonate, and triple phosphate (small calculi may be nonradiopaque). The nonradiopaque calculi are the urates, and xanthine calculi. The cystine calculi may have a variable radiopacity.

The male patients will typically have more urethral diseases than female patients. The urethral pathologies occur at the various levels. A review of the anatomy of the male urethra may be helpful. The proximal most portion is the prostatic urethra and it, of course, is within the prostate. The next portion is the membranous urethra that resides within the pelvic canal. At the level of the ischium, and as the urethra turns ventrally it becomes the penile or cavernous urethra.

The prostatic urethra may be narrowed by benign prostatic hyperplasia or potentially invaded by neoplasia. The membranous and proximal penile urethra are the most common sites for urethral rupture secondary to catheterization. Calculi are most commonly seen in the penile urethra at the level of the os penis or around the ischial arch. Strictures, polyps, and neoplasia may occur at any level.

Unfortunately standard radiographs cannot image the majority of these disorders and generally ultrasound is of little assistance. Retrograde urethrography is the imaging modality of choice. 1

References

Dr. John Feleciano, DVM, DACVR
Dr. Renee Leveille, DVM, DACVR

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