labioscrotal

Labioscrotal refers to the paired labioscrotal folds (also called labioscrotal swellings) in the developing embryo. These bilateral structures arise from the ventrolateral body wall near the future perineum and are the precursors of external genitalia in both sexes. They are homologous to the male scrotum and the female labia majora.

During early gestation, the labioscrotal folds enlarge as part of genital tubercle and urogenital fold development. In genetic males, androgens (principally testosterone and its metabolite dihydrotestosterone) promote fusion of the folds along the midline, forming the scrotum. The line of fusion becomes the scrotal raphe. In genetic females, the folds do not fuse and instead develop into the labia majora, contributing to the outer female genitalia while the labia minora arise from different urogenital folds.

Clinical relevance is seen in variations of fusion. Incomplete or abnormal fusion of the labioscrotal folds can lead to a bifid or partially formed scrotum, a condition sometimes associated with disorders of sexual development or exposure to altered androgen signaling during development. Conversely, normal development yields the scrotum in males and the labia majora in females, with the surrounding perineal anatomy forming according to typical embryologic patterns.