EXPERIMENTAL STUDIES OF URETHRAL RECONSTRUCTION USING TUNICA VAGINALIS GRAFT

Abstract

As successful results were obtained clinically in human subjects using pedicled tunica vaginalis graft for the replacement of the urethral defect, animal experiments were undertaken to define the role of the graft and histologic findings of the reconstructed urethra. Thirty one male mongrel dogs weighing between 11 and 18kg. were subjected to this study.
After partial excision of perineal urethra 3cm. in length and 80% in circumference, only the outer coverings were sutured leaving the urethral defect open in 10 dogs (Group 1). The same urethral window was patched by a pedicled graft of tunica vaginalis in 13 dogs (Group 2), and by a free graft in 4 dogs (Group 3). Complete urethral defect was created in 4 dogs by excising a 3cm. segment of the urethra and a pedicled tunica vaginalis graft was sutured about a splinting catheter (Group 4).
Observations of postoperative urination and urethrogram were made every week. The animals were sacrificed at intervals varying from 1 to 12 weeks respectively, and the urethra was examined grossly and microscopically.
The results were as follows:
1) In Group 1, the entire length of the urethral defect was lined with uroepithelium, but became moderately narrowed and fibrotic.
2) In Group 2 and 3, both pedicled and free grafts remained viable and the luminal surface of the grafts became lined with uroepithelium regenerated from the remaining urethral strip. The graft was eventually replaced by connective tissue. The lumen retained an adequate diameter in the majority of cases.
3) In Group 4, the urethra was not reformed despite the use of splint and the pedicled tunica vaginalis graft. The lumen was obstructed with marked fibrous tissue.
4) When a urethral strip was preserved, remarkable regeneration of urethral mucosa was noticed, but corpus spongiosum did not regenerate sufficiently in 12 weeks observation.
5) Functional arrangement of connective tissue around the reconstructed urethra seemed to take place by the existence of urine flow.
6) Splinting catheter was valuable to avoid wound infection and urethral narrowing before the canal was re-epithelialized.
7) No pathologic change in the testicle from which the graft was taken was observed.