The ischium as a key anatomical landmark in the classification of persistent urogenital sinus anomalies

BACKGROUND: Congenital adrenal hyperplasia is an endocrine disorder that leads to external virilization in affected females, often accompanied by an abnormal vaginal insertion that joins the urethra, forming a common urogenital sinus. OBJECTIVE: We propose a new anatomical classification for common urogenital sinus anomalies based on the relationship between the distal vagina and the ischial bony landmark on lateral genitography. MATERIALS AND METHODS: The study included girls with virilized external genitalia secondary to congenital adrenal hyperplasia who underwent feminizing genitoplasty between 2016 and 2025. Data maintained by the author were analyzed retrospectively. On lateral genitography, the level of the distal vagina was referenced to the inferior end of the ischium (I-point). A vagina reaching the level of the I-point indicates a low vaginal insertion near the perineum. RESULTS: The study included 21 girls with available preoperative genitograms for comparison with intraoperative findings. Their age at surgery ranged from 9 months to 108 months (mean 47, median 36). In most cases (19 patients; 90%), the distal vagina was low, extending to a level near the "I-point," whether slightly below, at, or just above it. In contrast, two cases (10%) demonstrated a high vaginal position, with the vaginal take-off arising from the posterior urethra opposite the mid-ischium. Imaging-based stratification showed well consistence with operative findings. CONCLUSION: Most cases of congenital adrenal hyperplasia demonstrate a low vaginal insertion near the perineum. The proposed classification provides a useful tool for identifying the uncommon cases with a high vaginal take-off, which is important for preoperative planning and patient counseling.