MALE GENITALIA

• Parenchyma of mesonephric kidney slowly regresses and the mesonephric tubules make contact with testis cords and rete testis.
• Initial portion of mesonephric duct forms the efferent ductules, while the remaining portion forms the vas deferens. An invagination of the inferior portion for the seminal vesicle.
• Paramesonephric duct regresses by week 8.
• Testis descends within the extraperitoneal mesenchyme along the course of the gubernaculum.
• Normal Testicular Descent
• Bilateral descent was present in 91% of cases, whereas unilateral descent was present in 7% of fetuses by 35 weeks (1).

• External genitalia are sonographically similar until about week 12 of gestation (two pairs of genital folds).

• Medial pairs of folds elongate and fuse along the midline enclosing the urethra.
• Lateral folds enlarge, forming the scrotum.
• The urethra may be seen as an echogenic line in the erect penis.

• Penile length has been measured and may be important in cases of bladder outlet obstruction to assist in the differentiation between urethral agenesis and posterior urethral valves (2,3).
• Mean penile length at 14 weeks of gestation is 3.88 mm (90 CI 2.63-5.39) and reaches up to 23.77 mm (90 CI 20.51-27.33) at 38 weeks.

REFERENCES

1. Simindokt Z, Gerrard PS, Wise G. Sonographic assessment of fetal male genitalia. JDMS 1991;7:205-207.
2. Johnson P, Maxwell D. Fetal penile length. Ultrasound Obstet Gynecol 2000;15:308-310.
3. Zalel Y, Pinhas-Hamiel S, Lipitz S et.al. The development of the fetal penis – an in utero sonographic evaluation. Ultrasound Obstet Gynecol 2001;17:129-131.