Hypospadias is a congenital defect that is thought to occur during the embryologic development of the urethra, between 8 and 20 weeks' gestation. The external genital structures are identical in males and females until 8 weeks, after which time the genital structures develop a masculine phenotype in males, primarily under the influence of testosterone and its byproduct dihydrotestosterone. As the phallus grows, the open urethral groove extends from its base to the level of the corona.

The classic theory is that the urethral folds coalesce in the midline from base to tip, forming a tubularized penile urethra and median scrotal raphe. This accounts for the posterior and middle urethra. The anterior or glanular urethra is thought to develop in a proximal direction, with an ectodermal core forming at the tip of the glans penis, which canalizes to join with the more proximal urethra at the level of the corona. The higher incidence of subcoronal hypospadias supports the vulnerable final step in this theory of development.

In 2000, Baskin proposed a modification of this theory in which the urethral folds fuse to form a seam of epithelium, which is then transformed into mesenchyme and subsequently canalizes by apoptosis or programmed cell resorption. [3] Similarly, this seam theoretically also develops at the glanular level, and the endoderm differentiates to ectoderm with subsequent canalization by apoptosis.

The prepuce normally forms as a ridge of skin from the corona that grows circumferentially, fusing with the glans. Failure of fusion of the urethral folds in hypospadias impedes this process, and a dorsal hooded prepuce results. On rare occasions, a glanular cleft with intact prepuce may occur, which is termed the megameatus intact prepuce (MIP) variant.

Ventral curvature of the penis, termed chordee, is often associated with hypospadias, especially in more severe forms. This is thought to result from a growth disparity between the normal dorsal tissue of the corporal bodies and the attenuated ventral urethra and associated tissues. The abortive spongiosal tissue and fascia distal to the urethral meatus may form a tethering fibrous band that contributes to the ventral curvature. This can range from mild to very severe (90º angle). (See the image below.)

Severe penile chordee. Note extreme ventral curvature of penile shaft. View Media Gallery

The location of the abnormal urethral meatus classifies the hypospadias. Although several different classifications have been described, most physicians use the one proposed by Barcat and modified by Duckett, which describes the location of the meatus after correction of any associated chordee. [4, 5] Descriptive locations in this classification include the following:

Anterior (glanular and subcoronal)

Middle (distal penile, midshaft, and proximal penile)

Posterior (penoscrotal, scrotal, and perineal)

The location is anterior in 50% of cases, middle in 20%, and posterior in 30%; the subcoronal position is the most common overall. (See the images below.)

Proximal shaft hypospadias. Note deficient ventral foreskin, blind urethral pit at glanular level, and lighter pigmented urethral plate extending to true meatus at proximal shaft level. View Media Gallery

Proximal shaft hypospadias. Note typical dorsal hood of foreskin and ventral penile skin deficiency. View Media Gallery