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= Caudal Duplication = 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 surgical excision 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" 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. The level of neurological impairment is dependent upon the severity and type of spinal abnormality. Whilst most reported cases of spinal cord duplication exhibit severe neurological impairment, cases of mild or absent neurological impairment has also been observed.

Though patients are often present with 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.

Causes
The exact causes 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 has 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.

The incomplete regression of Kovalevsky’s canal may lead to formations of fibrous bands joining the hindgut to the spinal canal, possibly leading to the onset of diastemetaomyelia. These bands may divide the notochord, developing into duplications of the lower spine and spinal cord, the adjacent mesoderm is also divided, resulting in duplicates of GI and GU tracts. Overall leading to the presence of a range of anomalies including dorsal enteric fistulas, enteric cysts, spina bifida, malformed or duplicated colon, bladder, sacrum, and lower spinal cord.

Moreover, a midline pelvic mass defect could be an obstacle to caudal migration of paramesonephric structures (eg. Müllerian duct), which could lead to duplication of the genital tract. Whilst failures of migration or fusion of those structures is one of the more prevalent embryological theories for duplication of lower genitourinary organs such as the bladder. Intestinal duplications extending into the rectum or anus is often rare, however, if the caudal cell mass is divided early, duplications of the distal bowel may occur.

In gastrointestinal abnormalities, a mechanism known as “caudal twinning”  is proposed in which during the 23th to 25th day of gestation, the intestinal tract is filled by rapid proliferation of endothelial cells, as the gut increases in size, vacuoles appear within the cell masses to constitute a single lumen. However, in abnormal cases where a vacuole is pinched off, a second lumen is created. The second lumen is then proposed to magnify in size in proportion to the growth of the colon, effectively duplicating all caudal structures distal from the point of separation.

Diagnosis
The condition can often be seen as malformations that can be diagnosed by a prenatal anomaly scan in the second trimester, while progressively detailed examinations can be conducted after the first day of life of the baby. If an abnormality is detected early on, psychological and surgical preparation may be required to resort to a cesarean section to prevent obstructed labour, in which medical pediatric and surgical care soon follows after delivery.

Diagnosis during adulthood is rare in cases where abnormalities are asymptomatic or are not visible upon physical inspection. Similarly to paediatric and prenatal diagnosis, a diagnosis can be made through various imaging modalities such as computed tomography (CT) scans to explicitly define the range of symptoms present in caudal duplication.

Prognosis and Treatment
The rare, complex syndrome includes a wide spectrum of malformations ranging from partial or isolated to complete duplication of caudal organs in GI, GU, and/or neural system. The syndrome may cause some functional impairment such as imperforate anus, but most of them are not life-threatening and can be resolved through surgical treatment. The duplicated organs are in fact functional in many cases. For instance, patients with genital duplication are mostly expected to have normal menstruation, sexual intercourse, and even pregnancy, although their self-esteem and quality of life may be influenced. Since the clinical presentation of each patient and its complexity vary greatly, the management - usually includes surgical intervention - are carefully planned and individualised based on the extent of duplication and functionality of the involved organs.

An extensive work-up is required primarily before prognosis to understand the anatomy of patients and to decide surgical strategy. Imaging modalities such as echocardiography, conventional X-ray, magnetic resonance imaging (MRI), ultrasonography, barium enema, computed tomography (CT) scan, and voiding cystourethrography (VCU) can be used to examine anomalies in detail. Exploratory laparotomy can also be conducted when needed. Based on the work-up results, a multidisciplinary team consisting of pediatric surgeon, pediatric urologist, and a pediatric neurosurgeon plans individualised, staged correction.

In most cases, surgical approach is utilised to excise or fuse the duplicated organs. It is recommended that the medical pediatric and surgery care should be organized soon after delivery. Reconstructive surgeries are performed to resolve the issue of functional impairment such as obstruction of colon, to correct anatomic anomalies that hinder movement or cause infertility, and to improve the cosmetic appearance in the case of genital duplication. The primary goal of the treatment for the syndrome is to relieve symptoms, not to restore normal anatomy, and hence, potentially life-threatening malformations are addressed first and often followed by other anatomic or aesthetic reconstructions in later stages.

Treatments for colonic duplication varies from conservative expectant management for asymptomatic cases to excision of duplicated colon to avoid potential issues such as colon structure and obstruction. Resection is possible when each duplicated colon has a complete blood supply. If duplicated colons share a wall, a septotomy can be performed to create a small hole to connect two colons. In cases where rectum is also duplicated, either the rectums should be converted into one reservoir through septotomy followed by anorectoplasty or the duplicated colon and rectum should be removed and colostomies should be constructed. For patients with poor prognosis for bowel control, a Malone procedure is advised during the colostomy. Alternatively, in cases of renal duplication, the Mitrofanoff procedure can be done.

In cases of malformation of neural cord such as myelomeningocele and tethered cord, preserving neurological function is the utmost importance. Closing myelomeningocele and detethering cord is a highly complex procedure that requires extreme caution not to injure the rectum in which case can cause a cerebrospinal fluid infection.

Epidemiology
Caudal duplication syndrome is a rare condition with only about 40 cases reported in the literature. The prevalence of the syndrome is less than one per 100,000 births. The sex ratio of male to female patients is about 1:2, with no familial or racial predisposition has been found.

History
The first systematic review for caudal duplication symptoms was done and the term "caudal duplication syndrome" was first proposed in 1993. The term was coined to describe rare anomalies associated with complete or partial duplication of caudal structures resulted from insults during embryogenesis to distinguish symptoms of spinal duplication syndrome which only involves spinal duplicity, only when there is associated complete or partial duplicity of vascular structures and/or organs such as bladder and distal gastrointestinal tract the term caudal duplication syndrome can be used.

However, recently in 2013, it was suggested that “duplication” is a misnomer based on an analysis of two cases and literature review in which researchers found “hemi” organs was “split” not duplicated, proposing caudal “split” syndrome may be a more appropriate title.