Pathogenesis of megalourethra.

Idiopathic megalourethra in infants is an enlargement of the pendulous urethra with no evidence of distal obstruction. Two aborted fetuses at 14 and 19 weeks of gestational age exhibited megalourethra with definite complete distal obstruction. The urethras of these 2 fetuses were studied histologically confirming the presence of an uncanalized epithelial core in the glans obstructing the lumen of the patent urethra. Embryologically, this epithelial core is normal but early canalization achieves continuity with the lumen of the penile urethra. In these 2 fetuses canalization was arrested or delayed with complete obstruction of the urethra in the glans and dilatation of the pendulous urethra. In living children with this form of megalourethra the urethra of the glans is patent. Canalization of the epithelial core in the glans of the survivors may have been delayed rather than arrested and may be a cause of megalourethra.