Caudal duplication

Caudal duplication, also called caudal duplication syndrome, is a rare birth condition where structures in the lower body—including the tail-end region, the embryonic cloaca, and the neural tube—show a range of duplications and malformations. While the precise cause remains unknown, several theories point to abnormal development during embryogenesis. The condition is typically spotted during second-trimester prenatal ultrasound scans or right after birth, though a few cases have been diagnosed in adulthood.

The term "caudal duplication syndrome" was introduced in 1993 to describe these lower-body abnormalities. More recently, some experts have argued that "caudal split syndrome" might be more accurate, since the defects often involve splitting rather than true duplication.

Signs and symptoms vary widely, encompassing gastrointestinal, urogenital, spinal, and limb anomalies. Common features include anorectal malformations and duplicated external genitalia. Less frequent findings include incomplete duplication of the lower spine and spinal cord (diastematomyelia), as well as partial or complete duplication of the uterus, vagina, colon, and bladder. Spinal malformations can lead to neurological impairment, which ranges from severe to mild or even absent, depending on the specific abnormality. In one reported case, an adult woman with duplication of the colon, rectum, anus, urinary bladder, urethra, uterus, cervix, vagina, and external genitalia had no detrimental symptoms, suggesting that complete urogenital and gastrointestinal duplication can sometimes be asymptomatic. Because each patient presents a unique combination of defects, the impact—whether cosmetic or physiological—varies from person to person.

The cause is unknown, but several theories exist: incomplete separation of monozygotic twins, abnormal adhesion between ectoderm and endoderm during gastrulation, defects in primary developmental fields, mutations in developmental genes (somatic or germ line), and damage to the caudal cell mass or hindgut. The HOX genes, particularly HOX10 and HOX11, are suspected to play a role; misexpression could lead to abnormal growth of caudal mesenchyme. Embryologically, around day 15 after fertilization, the notochord grows from the primitive knot and forms a canal.