- Definition
- Pathophysiology
- Systems Affected
- Genetics
- Incidence/Prevalence
- Signalment
- Signs
- Causes
- Risk Factors
BASICS
- Despite the large amount of calcium carbonate crystals in normal equine urine, urolithiasis is rare compared with small animals, possibly because of protective lubricating mucus produced by glands in the renal pelvis and proximal ureter
- The main component of equine uroliths is calcium carbonate along with inorganic elements (magnesium ammonium phosphate, calcium oxalate, or calcium sulfate) and organic matrix (mucoproteins)
- Urolith formation usually requires damage to the renal parenchyma or the uroepithelium of the ureters, bladder, or urethra that allows for adherence of calcium carbonate crystals, which serve as a nidus for stone formation
- Most spontaneously occurring bladder stones are disk-shaped, mildly spiculated, and porous
- Urolithiasis is uncommon (0.11% of equine admissions to 22 teaching hospitals, accounting for ≅8% of all urinary tract disorders)
- In the same study, cystoliths were most common (60% of all urinary stones) followed by urethroliths (24%), nephroliths (12%), and ureteroliths (4%); ≅10% of affected horses had multiple calculi at different sites
Adult horses (mean age ≅10 years) with wide age range with horses <1 year also being possibly affected.
- ≅75% of all reports are in males—stallions and geldings
- A longer and less distensible urethra increases the risk of cystolithiasis and urethrolithiasis in males, but development of calculi at other sites is similar in both sexes
- Nephrolithiasis and ureterolithiasis—weight loss or fever of undetermined origin, with hematuria or pyuria less common. Occasionally, recurrent colic may be reported
- Cystolithiasis—lower urinary tract signs (e.g. pollakiuria, stranguria, hematuria) predominate, and hematuria after exercise is common. Sometimes, behavior changes during exercise
- Sabulous urolithiasis—urinary incontinence
- Urethrolithiasis—may cause severe renal colic signs with partial to complete obstruction (e.g. pollakiuria, stranguria, anuria)
- Nephrolithiasis and ureterolithiasis—lethargy, fever, partial anorexia, intermittent colic, and mild dehydration
- Cystolithiasis—dysuria and possibly urine scalding, but general health usually good
- Urethrolithiasis—a distended, sometimes pulsating urethra may be found below the anus, and careful palpation may allow location of the obstructing urolith. Unlike colic signs arising from the gastrointestinal tract, the penis is often dropped in horses with urethral obstruction
- Rectal examination. Nephroliths—may palpate abnormal-shaped left kidney owing to hydronephrosis. Ureteroliths—enlarged, turgid ureters with focal concretions. Cystoliths—the calculi can be palpable in the neck of the bladder at the level of the pelvic canal if the bladder is not distended. The bladder wall is thickened. Sabulous urolithiasis—unlike cystoliths, this urolith often indents with firm digital pressure. Large atonic bladder with incontinence produced by compressing bladder indicates bladder paresis. Urethrolithiasis—markedly distended bladder when obstructed
- Nephrolithiasis—developmental anomalies, pyelonephritis, acute tubular necrosis, renal medullary necrosis due to NSAID use, and neoplasms can cause parenchymal damage that may serve as a nidus for nephrolithiasis. Ureterolithiasis most commonly is due to passage of small nephroliths into the ureters
- Cystolithiasis—may develop from ascending infections, anatomic or functional causes of abnormal urine flow (or stasis), or with damage to the bladder uroepithelium
- Sabulous urolithiasis—bladder paresis (see chapter Urinary incontinence)
- Urethrolithiasis—may develop at sites of damaged uroepithelium (e.g. site of previous perineal urethrotomy) but more commonly results from passage of small uroliths into the urethra
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS