Urethral duplication is rare so far; about 300 cases have been reported in literature; it is expected that many minor incomplete cases may be more common than the reported incidence, but it may escape documentation, this anomaly is most common in males with few cases reported in females [3].

Embryology of urethral duplication is unclear; and there is no single theory explains all of the various types of this anomalies, as a lot of hypotheses have been proposed including; ischemia, abnormal Mullerian duct termination and growth failure of the urogenital sinus [4].

In fact, by the 17 embryonic day, the mesoderm of the tip of the glands has proliferated to form ridges on its caudal paramedian aspect, the medial, bounding the lacunar groove on its medial side, and the lateral lacunar folds, lying on its lateral aspect. During subsequent development these folds increase in prominence, due to proliferation of their mesodermal cores, so the lacunar groove becomes deeper and ectoderm on the latter is continuously proximal with the endoderm of the cleaved urethral plate. In this way, an abnormal lacunar fold duplication can produce a distal urethral duplication, with an accessory blind urethra [5].

At E15, mesodermal growth leading to epithelial compression and fusion occurs and this event might explain a whole series of complex events in the development of the lower urinary tract in the male. A failure of this process is reported to result in epispadias as well as hypospadias might arise later in development if fusion of the urethral folds is arrested [4]. In Arena et al. opinion, an excessive mesodermal growth and a subsequent epithelial over-compression on the urethral plate might lead to urethral and/or bladder sepimentation and be a cause of urethral and/or bladder duplication [6] (Chap. 1).

Duplication of the urethra could be partial or complete and either hypospadiac or epispadiac, depending on the relation of the accessory channel with the orthotopic urethra. Hypospadiac type is extremely rare in comparison to the epispadic one, where there is a dorsal accessory urethral opening and the child is usually incontinent. Some duplication may be associated with an open symphysis pubis or urine dribbling from the epispadiac urethra.

Urethral duplication is classified by Effmann et al. [2] into the following types: (Fig. 27.1)

Mild cases of distal type I duplications (often associated with hypospadias) as well as “Y-type” duplication associated to anorectal malformation were excluded from this classification.

This classification is functional, represents most clinical aspects of UD, however, this classification looks complex, and it does not distinguish sagittal from coronal collateral duplication. In another classification by Woodhouse and Williams sagittal and coronal duplication was included, but this classification does not include many anatomical details that are important for therapeutic decision making [1]^. The Y subtype represents 6–30 % of all urethral duplication. In this subtype, the original urethra is known as “dorsal” urethra and the duplicated one is named as “ventral.” The ventral urethra, originating from the bladder neck or anterior urethra, opens into either the perineum or anus and is the dominant urethra. Usually, the normally located dorsal urethral opening is stenotic, so urine passes through the dominant ventral urethra. Hence, this variety considered as a congenital urethral fistula, and will be discussed in Chap. 28.