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Introduction:
Minor minor defects of a spectrum of anomalies are usually more common than the major variants. By contrast, penile epispadias is rare compared with exstrophy-epispadias complex (EEC) and the symphysis pubis is often normal. A review of the literature describing the embryogenesis of the pelvis was undertaken to see whether these two anomalies might have different causes.
Methods:
Descriptions of the normal and abnormal development of the cloaca, external genitalia, pubis and embryonic tail were studied in the literature, including embryological textbooks, many of which were from early 20th century. Special attention was devoted to the rapid lengthening and shortening of the tail, which may compress and deform the genitalia.
Results:
The tail begins to elongate at 21 days of gestation, and lies on the cloacal membrane. It then impacts upon the body stalk and the ventral abdominal wall. By 8 weeks all 10 segments have undergone apoptosis. During its brief presence it may damage the mesodermal components of the developing genitalia by compression and separation of the second sacral pair of mesodermal streams that form the phallus.
Discussion:
Brief compression by the embryonic tail may sever the cloacal-allantoic connection causing the sacral mesoderm to form the phallus behind the allantoic connection, which then lies on the dorsal surface of the developing epispadias penis. This tail compression theory may explain the rarity of epispadias compared with EEC.