Caudal duplication, (or caudal duplication syndrome) is a rare congenital disorder in which various structures of the caudal region, embryonic cloaca, and neural tube exhibit a spectrum of abnormalities such as duplication and malformations. The exact causes of the condition is unknown, though there are several theories implicating abnormal embryological development as a cause for the condition. Diagnosis is often made during prenatal development of the second trimester through anomaly scans or immediately after birth. However, rare cases of adulthood diagnosis has also been observed. Treatment is often required to correct such abnormalities according to the range of symptoms present, whilst treatment options vary from conservative expectant management to resection of caudal tissue to restore normal function or appearance. As a rare congenital disorder, the prevalence at birth is less than 1 per 100,000 with less than 100 cases reported worldwide.
The term "caudal duplication syndrome" has been coined since 1993 to describe caudal abnormalities and conditions. However, there has been recent debate into the appropriateness of the term being "caudal split syndrome" instead of caudal duplication due to the "splitting" nature of the abnormalities, rather than "duplication".
Signs and symptoms
The condition’s symptoms vary greatly due to the diverse spectrum of gastrointestinal (GI), urogenital (genitourinary, GU), spinal, and limb anomalies. Common examples include anorectal malformation, and duplication of the external genitalia, while other symptoms include incomplete duplication of the lower spine, spinal cord, (diastematomyelia) partial fusion of complete duplication of the uterus, vagina, colon, and bladder.
Malformations of the spine have indicated to cause varying levels of neurological impairment. Although the level of neurological impairment is dependent upon the severity and type of spinal abnormality, most reported cases of spinal cord duplication exhibit severe neurological impairment, though cases of mild or absent neurological impairment has also been observed.
Though patients often present a diverse variety of symptoms, a case was observed in which a female adult with duplication of the colon, rectum, anus, urinary bladder, urethra, uterus, cervix, vagina, and external genitalia exhibited no detrimental effects. This suggests that rarely seen cases of complete duplication of the urogenital and gastrointestinal tract are often asymptomatic.
As patients often present a multitude of differing symptoms within the caudal region, each patient exhibits a unique, characterised symptom which may or may not be cosmetically or physiologically detrimental to the individual.
Causes
The exact cause of the condition is unknown. Although various theories indicate incomplete separation of monozygotic twins as an etiological factor, abnormal adherence between the ectoderm and endoderm during gastrulation, polytopic primary developmental field defects, somatic and germ line mutations in developmental genes, and damage to the caudal cell mass and posterior gut have also been linked to cause structural anomalies in the caudal region.
It is speculated that the condition is related to the HOX gene, namely HOX10 and HOX11. Normally coding for the mammalian appendicular and axial skeleton, misexpression of the genetic factors could lead to abnormal proliferation of the caudal mesenchyme.
Embryology is suggested to have an intimate association with the development of caudal duplication syndrome. At day 15 after fertilisation, the notochord grows from the primitive knot, in which it invaginates and forms the notochord canal within. Progressively, on day 20, the ventral wall of the notochord dissolves, while communications are formed between the amniotic and yolk sac. One such connection is the Kovalevsky’s canal. From the 23rd to 25th day of gestation, the spinal cord develops except for its distal-most aspect where the notochord and neural tube are joined to form the caudal cell mass. The canal of Kovalevsky crosses the caudal cell mass, while endoderm located anteriorly to the cell mass develops into the hindgut, various insults towards the cell mass and hindgut during the stage of development may lead to the development of caudal anomalies, one of which is caudal duplication syndrome.