Hypospadias is a congenital anomaly resulting from incomplete fusion of the urethral (urogenital) folds.
Male and female genitalia arise from common precursor embryonic structures. In males, the urethral folds fuse to form the ventral wall of the penis and the penile raphe. In females, the urethral folds do not fuse, but remain separated forming the labia minora. Similarly, in the male with hypospadias, the urethral folds remain inappropriately separated, leading to the urethral opening on the ventral aspect of the penis. An important high yield association for Step 1/2 is to not circumcise patients with hypospadias as the tissue removed is often used in the reconstruction of the defect.
O'Brien et al. discuss the treatment of hypospadias. They recommend surgical reconstruction early, when the child is between six and nine months old. If cryptorchidism is present in addition to the hypospadias, further investigation is necessary in order to exclude the possibility of an intersex disorder.
van der Zanden et al., in a study of 712 patients with hypospadias, found that hypospadias are caused by interactions between specific genes, estrogen exposure, and maternal hypertension or preeclampsia.
Illustration A shows the fusion of the urethral folds in the normal embryological development of the penis. Illustration B depicts three potential locations of hypospadias.
Image A shows hypospadias in an adult. In this image it is clear that the urethral opening is on the ventral side of the penis.
Answer 1: The urachal duct is a duct extending from the yolk sac to the apex of the bladder during embryonic development. If the urachal duct fails to close, a patent urachus results, and urine leaks from the umbilicus.
Answer 3: The labioscrotal swellings form the scrotum in the male and the labia majora in the female.
Answer 4: The genital tubercle becomes the penis in the male and the clitoris in the female. Incorrect positioning of the genital tubercle during 5th week of gestation results in epispadias, a urethral opening on the dorsal surface of the penis.
Answer 5: The vitelline duct connects the yolk sac to the midgut and closes during the 7th week of embryonic development. Failure of the duct to close results in a vitelline fistula, characterized by meconium discharge from the umbilicus.
O'Brien WM, Gibbons MD. Hypospadias. Am Fam Physician. 1989 Apr;39(4):183-91. Review.
PMID:2650502 (Link to Abstract)
van der Zanden LF, Galesloot TE, Feitz WF, Brouwers MM, Shi M, Knoers NV, Franke B, Roeleveld N, van Rooij IA. Exploration of Gene-Environment Interactions, Maternal Effects and Parent of Origin Effects in the Etiology of Hypospadias. J Urol. 2012 Oct 19. doi:pii: S0022-5347(12)04490-4. 10.1016/j.juro.2012.08.033. [Epub ahead of print]
PMID:23088992 (Link to Abstract)
USMLE World Step 1 QBank Question #1870. Copyright © USMLEWorld, LLC 2012