PATHOGENESIS

The embryologic defect underlying the epispadiasexstrophy complex is poorly understood. The most prominent theory argues that the main defect lies in the cloacal membrane, the bilaminar structure consisting of ectoderm and endoderm that is situated anterior to the cloaca (see Plate 2-3). In normal development, the cloacal membrane occupies a large territory on the ventral surface of the embryo just inferior to the body stalk. As development proceeds, however, mesoderm invades the cranial aspect of the cloacal membrane, interposing itself between the ectoderm and endoderm. This mesoderm, which now occupies the infraumbilical space, fuses in the midline and gives rise to the infraumbilical abdominal wall, pubic rami, and anterior surface of the detrusor muscle. In addition, specialized regions of the mesoderm form the paired genital folds, which fuse in the midline to form the genital tubercle (see top left illustration in Plate 2-4). In the meantime, the cloaca undergoes septation into an anterior urogenital sinus and posterior rectum, the orifices of which become exposed following apoptosis of the cloacal membrane.