Partial bifid diphallia without associated anomalies
A 15-year-old boy, apart from having two penises, had normal external genitalia. His two testicles were within normal scrotum and normally positioned. He had two unequal sized glans at tip of a thick penile shaft, and only urinated through the larger glans. He had a patent anus, one bladder, one normal urethra, normal gastrointestinal and genitourinary systems. Cause
Cause of diphallia is unknown, and also because its associated anomalies vary largely, it is impossible to give a simple, single explanation of its cause. But it is thought to have started from duplication of cloacal membrane in early embryonic development stages in the fetus, between third and sixth week of gestation, because normal development of cloacal folds in the fetus is complete between this time.Normal development of penis occurs with the fusion of cloacal tubercles at anterior end of urogenital sinus. Mesenchyme migrate around cloacal membrane, proliferate and expand around cloacal plate, forming a pair of cloacal folds that fuse to form genital tubercle which develops into penis. If cloacal membrane is doubled, mesenchyme will migrate and surround both cloacal membranes, leading to the formation of two pairs of cloacal folds around two cloacal membranes, resulting in formation of two genital tubercles and thus two penises. The concept of caudal duplication syndrome is used to explain the symptoms of diphallia with associated complex anomalies in lower abdomen and urinary tract.
Further, as mesenchyme migrate from more than one area, failure in migration and in the fusion of mesoderm results in formation of two genital tubercles  and double penises, as well as producing associated anomalies such as double bladders, double urethra, double colons and imperforated anus. Failure in proper fusion of urethral folds results in hypospadias. Failure in mesoderm cell migration results in epispadia.Diphallia is a rare abnormal external genitalia. The cause is uncertain, but most scientists agree that diphallia is a defect of genital tubercle, and occurs at about week three of gestation, when caudal cell mass of mesoderm is affected by various external environmental factors including drugs, infections and malfunctioning homeobox genes. Treatment
Treatment is a case-by-case analysis taking into account considerations for medical and ethical reasons, and involves surgical excision of the non-functioning penis. See also
Bifid penis
Supernumerary body part
Polyorchidism
Penile agenesis
Uterus didelphys
Vaginal septum

References
Notes
A scientific paper of triphallia (three penises) in a marine snail was reported. (Castillo, Viviana M; Brown, Donald I (2012). "One Case of Triphallia in the Marine Snail Echinolittorina peruviana (Caenogastropoda: Littorinidae)". International Journal of Morphology. 30 (3): 791–796. doi:10.4067/S0717-95022012000300003.) In 2021, the first known case of a human with triphallia was recorded in Iraq. ("Triphallia: First Human Case of Baby Born With Three Male Genitalia Reported". 3 April 2021.) Further reading
Chadha R, Bagga D, Gupta S, Mahajan JK. (July 2001). "Complete diphallia associated with features of covered exstrophy." 36 (7): E12, W.B. Saunders Company. National Center for Biotechnology Information, US National Library of Medicine, National Institutes of Health


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