Diphallia

Diphallia
The external male genitalia of a prepubescent male with a form of bifid diphallia

Diphallia, penile duplication (PD), diphallic terata, or diphallasparatus is an extremely rare developmental abnormality in which a male is born with two penises.^[1][2] The first reported case was by Johannes Jacob Wecker in 1609.^[3][4] Its occurrence is 1 in 5.5 million boys in the United States.^[5]

When diphallia is present, it is usually accompanied by renal, vertebral, hindgut, anorectal or other congenital anomalies. There is also a higher risk of spina bifida.^[4] Infants born with diphallia and its related conditions have a higher death rate from various infections associated with their more complex renal or colorectal systems.^{[citation needed]}

It is generally believed diphallia occurs in the fetus between the 23rd and 25th days of gestation when an injury, chemical stress, or malfunctioning homeobox genes hamper proper function of the caudal cell mass of the fetal mesoderm as the urogenital sinus separates from the genital tubercle and rectum to form the penis.^{[citation needed]}

The first case was reported by Wecker in Bologna, Italy, in 1609, and since then, about one hundred cases have been reported.^[1][6] This condition has existed in humans since ancient times.^[7] The two external genitalia may vary in size and shape,^[8] either lying beside each other in a sagittal plane or one above the other in a frontal plane.^[9]

According to Schneider classification in 1928, double penis is classified into three groups: (a) glans diphallia, (b) bifid diphallia and (c) complete diphallia or double penis.^[10] According to Vilanora and Raventos, in 1954, a fourth group called pseudodiphallia was added.^[11]

The current widely accepted classification, introduced by Aleem in 1972, classifies double penis into two groups: true diphallia and bifid phallus.^[8] True diphallia is caused by cleavage of pubic tubercle; bifid phallus is caused by separation of pubic tubercle.^[8][12] Each of these two groups is further subdivided into partial or complete.^[8] True diphallia is where each phallus has two corpora cavernosa and a single corpus spongiosum containing a urethra.^[8][12] True diphallia can be either complete with both penises similar in size, or partial when one of the phallia is smaller in size or immature, though structurally same as the larger phallus.^[8] In bifid phallus, each phallus has only one corpus cavernosum and one corpus spongiosum containing a urethra.^[8][12] Separation of penises down to the base of the penile shaft is complete bifid, whereas to glans is partial bifid.^[8] For complete bifid phallus associated with anomalies, the anterior urethra is absent from each penis and the prostatic urethra is situated in the skin between the two penises.^[13] In partial bifid phallus, the duplication of urethra, corpora cavernosa and corpus spongiosum in one penis is incomplete, and there is only a corpus cavernosum and a spongiosum surrounding the functioning urethra in the other penis.^[14]