Anatomical evidence redefining the pathogenesis of penoscrotal transposition: It is due to failure of the penis to migrate to the anterior end of the scrotum.

UNLABELLED: The pathogenesis of penoscrotal transposition (PST) was hypothesised by Glenn et al. as failure of caudal migration and fusion of labio-scrotal folds proximal to the genital tubercle ignoring the other possible cause, which was the failure of cephalic migration of the genital tubercle in relation to the labio-scrotal folds. The aims of this study are to describe the anatomic relationship of the phallus and the labioscrotal folds to the unchanging landmarks of the inferior surface of the pubic bones in males and in females and to investigate the causation of penoscrotal transposition. METHOD: The multi-institution study was registered as quality improvement projects. Data were collected prospectively from consecutive males and females undergoing groin surgery from July to November 2023. The diagnosis, penoscrotal appearance, the relationship of the anterior and posterior ends of the labioscrotal folds and the base of the penis (BOP) and clitoris to the anterior and posterior ends of the inferior surface of the pubic bones were recorded independently by two assessors. RESULTS: There were 487 patients: penile shaft hypospadias in 102, proximal hypospadias in 39, no hypospadias in 313 and 33 females. The median age at assessment of males was 1.38 years, females 3.4 years. There was concordance between the two assessors on the positions but there was discordance on diagnosis of PST and bifid scrotum in 7 patients having proximal hypospadias. The anterior end of the scrotum was located at the anterior end of the pubic bones in all patients. BOP was at the anterior end of the pubic bones in penile-shaft hypospadias and in non-hypospadias. BOP was low on the inferior surface of the pubic bones in all 39 patients having proximal hypospadias (p < .00001, Fishers exact test), and majority of them had bifid scrotum and PST. The posterior end of the scrotum was normally located at the posterior end of the pubic bones. In 23 having proximal hypospadias it was located further posteriorly. Labia extended from the anterior end of the pubic bones to the perineal body and base of the clitoris was halfway down the pubic bones. CONCLUSION: In addition to the posterior ends of the labioscrotal folds, the base of phallus also seem to migrate anteriorly with progressive virilisation. The key pathology in bifid scrotum and in penoscrotal transposition is the failure of the base of the penis to migrate anteriorly, rather than the failure of the two halves of the scrotum to migrate caudally.