Embryology of the distal urethra and external genitals

Dear All,

I am providing a detailed study on ‘Embryology of Distal Urethra and External Genitals’ which is very exhaustive. Every person dealing with Hypospadias should be aware of the embryology of Urethra so as to understand the genesis of this abnormality. In the development of Urethra, there are many concepts aired by various researchers that a proper understanding is difficult.

I am sure our Hypospadiologist; Amilal could throw some informative information on this area that could be beneficial for all of us.

With warm regards,



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  • Amilal Bhat
    Amilal Bhat
    26 Sep 2020 09:23:15 AM

    Embryology of distal urethra  and MIP

    The embryologic basis of MIP variant of hypospadias is obscure. The distal part of the urethra in males is derived from the urethral plate, which grows from the tip of the glans to meet the proximal penile urethra at the coronal sulcus. A cuff of tissue lies at the margin of the sulcus from the prepuce. Failure of fusion of the urethral plate typically results in the arrest of distal urethral & prepucial development; and the formation of a hooded prepuce leading to hypospadias. Duckett & Keating2   postulated that after normal folding of the proximal penile urethra and normal prepucial formation, a misdirected clefting of the glans proceeds down the already fused urethra creating the megameatus. According to their theory prepucial development is apparently independent of that of the glanular urethra. Nonomura et al. 10 proposed a deformation theory in which an ischemic or compressive change occurring after completion of a normal urethra may result in a megameatus and a normally occurring prepuce. Nonomura et al.10 in 1998, postulated that the megameatus intact prepuce (MIP) deformity might occur after completion of penis formation and be due to external compression of the penis in utero. The urethral plate in MIP is always wide and elastic and there is no chordee. Others feel it embryologically related to the Megalo-urethra. But both of these theories does not explain the embryology of megmeatus intact prepuce. Bhat et al. 9 proposed the theory of both canalization and tubularization.  Both canalization as well as closure of glanular plate is needed for the normal glanular urethral development; as opposed to the canalization only. Thus, dorsal canalization is complete, but ventral urethral plate closure remains incomplete (Fig 1A& B).  Overlying the prepucial tubularization is complete that leads to megameatus intact.  But when canalization and tubularization does not meet to complete the normal urethra then it may lead to partial duplication of the urethra with or without hypospadias (Figure 1C).   

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