Pathogenesis of hypospadias--more questions than answers.

Most researchers believe that hypospadias arises from malformation of the penile urethra. However, this concept has been recently rejected, and it has been suggested that the opening of the urethra is "pushed forward" by growth of the perineum. In order to obtain more information on the development of the urethra, late stages of phallic development were studied in 220 rat embryos with scanning electron microscopy (SEM). In our study, signs of rupture of the urogenital membrane or fusion of the urethral folds could not be found. Therefore, we could not confirm the traditional concept for the development of the phallic urethra. A new concept of urethral development is suggested and the pathogenesis of hypospadias is discussed.