Anatomical studies of the urethral plate: why preservation of the urethral plate is important in hypospadias repair

Objective To describe the detailed anatomy of the urethral plate in relation to its controversial role in hypospadias surgery. Materials and methods A newborn penis with proximal penile hypospadias and two fetal penises with distal shaft hypospadias were included in the study; 30 normal fetal penises served as the control. Specimens were embedded in paraffin and serially sectioned (6 µm) after formalin fixation. Every 10th section was stained with haematoxylin and eosin. Immunohistochemical staining for nerves (S100), smooth muscles (α-actin), blood vessels (factor VIII) and epithelium (cytokeratins 7, 14 and 18) were used on selected sections, with particular attention to the urethral plate. Masson’s trichrome and Sirius Red stains were used to localize collagen. Results There were extensive blood vessels, glands and smooth muscle under the urethral plate in the hypospadias specimens. These relatively well organized tissues corresponded to an abnormally formed corpus spongiosum. The glands underneath the urethral plate and adjacent to the normal urethra showed positive staining for cytokeratins 7 and 18, respectively (markers of endodermal origin) but were negative for cytokeratin 14 (a marker of ectodermal origin). Penile skin and urethral plate epithelium stained positively for cytokeratin 14 but not for cytokeratin 7 and 18. The urethral plate has a rich nerve supply, as determined by S100 staining. Collagen intensity under the urethral plate was no different from that in normal areas. Tunica albuginea stained intensely for type I and III collagen. Conclusion These results show that the urethral plate is well vascularized, has a rich nerve supply and an extensive muscular and connective tissue backing. These features may explain the lower complication rate with onlay flaps than with tube flaps. Therefore, from these anatomical findings, we continue to advocate preservation of the urethral plate and the onlay island flap for hypospadias reconstruction.