Poster 2: Spontaneous Grade III Pelvic Organ Prolapse (POP) in the Rhesus Macaque

Abstract

OBJECTIVE: We aim to compare the anatomic changes of POP in the rhesus with the clinical condition in women. METHODS: Marked uterovaginal prolapse was identified in a 13.9-year-old (human equivalent age 42) female rhesus macaque 8 months after her fourth vaginal delivery. Uterovaginal position was measured by -POPQ.” T1-weighted and fat-suppressed TSE T2-weighted magnetic resonance images (MRI) were obtained with the pelvis centered in an extremity coil (3 Tesla Siemens Magneton Trio). Perineal descent of the anal verge was measured perpendicularly to a line constructed from the inferior borders of the symphysis and the sacrum. Electromyographic activity (EMG) was evaluated in the anal sphincter, the pubovisceral and pubocaudalis muscles by concentric needle EMG. Muscles were identified during surgical dissection of the ischiorectal fossa with ketamine and opiate anesthesia. Nerve conduction studies were performed on the distal pudendal nerve through the perineal dissection, and on the proximal pudendal nerves and levator ani nerves through an abdominal dissection. The animal was euthanized and immediately perfused with 4% paraformaldehyde to preserve anatomic relationships within the pelvis. RESULTS: Gh is increased, pb is decreased, and perineal descent is increased with prolapse (Table 1). Passive flexion of the tail narrows and extension opens the genital hiatus. The spontaneous firing rates of the motor units were diminished, but motor unit action potentials obtained from the external anal sphincter (EAS) were with large amplitudes and multiphasic, consistent with reinnervation. Direct stimulation of the pudendal nerve proximally and distally elicited a visual twitch and corresponding muscle action potential in the right EAS, but no response could be elicited in the EAS with supramaximal stimulation to the left pudendal nerve. Direct stimulation of the levator ani nerves elicited both a visible twitch and a muscle action potential in the pubocaudalis (PC) and iliocaudalis. At surgical dissection, the uterosacral/cardinal ligament complex, the paravaginal attachment, and the aponeurotic origin of the PC were elongated, but there were no visible tissue breaks.TABLE 1CONCLUSION: This spontaneous case of POP in the rhesus mimics the human condition—with elongation of the genital hiatus, increased perineal descent, connective tissue elongation but not disruption, and evidence of nerve injury. Flexion and extension of the tail closes and opens the genital hiatus similar to contraction and relaxation of the pelvic floor muscles in women.