Recurrent Cystolithiasis with Urethral Obstruction in a Rhesus Macaque (Macaca mulatta) after a Bilateral S1 Ventral Root Avulsion Injury

A series of adult male (n = 6) and female (n = 4) rhesus macaques (Macaca mulatta) underwent a bilateral S1 ventral root avulsion injury for longitudinal lower urinary tract studies in a motor-sparing experimental model of conus medullaris syndrome. The surgeries were well tolerated, and all animals recovered well postoperatively. However, one male animal presented clinically with acute lethargy, poor appetite, and unwillingness to move at 51 days after the bilateral S1 ventral root avulsion injury. Physical examination under sedation detected an enlarged bladder, which was emptied via transurethral bladder catheterization. When the animal re-presented for similar symptoms over the following 2 days, radiographic and ultrasound studies revealed cystolithiasis with urethral obstruction. Repeat transurethral bladder catheterizations reestablished functional patency of the urethra, independent voiding, and full clinical recovery. Two weeks later, the animal presented again with acute lethargy, poor appetite, unwillingness to move, and an enlarged bladder. Cystolithiasis and the recurrence of urethral obstruction were diagnosed by radiographic and sonographic studies. Subsequent transurethral bladder catheterization was unable to dislodge the obstruction, and the animal was euthanized. Necropsy identified 3 bladder stones. Histochemistry of the bladder and urethral walls showed some acute inflammation but absence of chronic changes. Chemical analysis of bladder stone composition showed calcium phosphate (90%) and calcium carbonate (10%). Our case highlights the value of an expedited physical examination and noninvasive imaging to diagnose cystolithiasis complicated by an acute urethral obstruction, a medical emergency, in a rhesus macaque presenting with nonlocalizing symptoms. Although spinal cord injury is an established risk factor for urolithiasis in humans, our case provides the first (to our knowledge) association of a spinal cord injury syndrome with cystolithiasis in a nonhuman primate.