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siamese twins are joined by a part of their body at birth and the causes of the merger are often unknown .
two cases of siamese twins in connection with taking clomiphene and two with griseofulvin have been reported .
the thoraco - omphalopagus are attached at the chest and abdomen ( 74% of the cases ) , pygopagus are joined at the buttocks ( 18% of cases ) , ischiopagus are attached at ischions ( 6% of the cases ) , and craniopagus at the level of the head ( 2% of cases ) .
the first case reported was that of deslonchamps , in 1851 , cited by taruffi c 1882 and schwalbe in 1907 .
more recently a meta - analysis of 1200 cases of merged twins reported another case .
the other rachipagus ( 21 cases ) of this series of 1200 cases are rather defined as rachipagus parasite .
we present two additional cases of parasite rachipagus on the chest and lumbar levels at the national hospital of niamey , niger .
a three - month - old male infant with a superrnumerary ( extra ) leg attached to the lumbar region was admitted in the neurosurgery services of the niamey national hospital , niger .
this boy was from a consanguineous marriage , after a pregnancy of eight months , and he was delivered per vaginum .
the mother was 17 years old and a history of twin pregnancy was reported in the father 's family .
the infant had a good general condition , and the weight and height were normal .
the back outgrowth looked to be a limb attached to the lower lumbar region with a proximal lipoma .
this limb did not move spontaneously or after stimulation , but the child cried when the parasite was pinched .
there was an appendix located in the upper part of the junction area resembling the male sex organ .
radiographs of the parasite limb and the spine of the child showed the bone structures of the femur , tibia , and fibula , with a junction area at l3-l4 .
the posterior arch was absent from l2 to l5 , with a duplication or agenesis of the posterior articular .
the parasitic limb was excised at the base of which an extradural lipoma and a voluminous meningocele were found .
the intra - dural content included a neural plate and normal roots with a single spinal cord .
excision of the lipoma , repair of the meningocele , and musculofascial reconstruction were easy , and the postoperative follow - up has been uneventful .
autopsy dissection of the parasite showed a dysmorphic ischium merged to the femur by a rudimentary capsule .
lower extremity attached to the lumbar region before surgery lower extremity removed at surgery same patient as figure 1 , immediately after excision this was a male infant born of a consanguineous marriage after eight months of pregnancy .
he presented with a double outline of the upper limb grafted in the inter - scapular region in the midline .
there was no spontaneous motor reflex in the parasite limb , but only a sensation of pain .
these bones were dysmorphic and merged to the dorsal spine , with spina bifida from t5 to t8 .
the bony part of each parasite corresponded , at the spine merger , to the autosite articular bones .
anatomical dissection of the parasite showed structures reminiscent of the scapula bone , humerus , radius , and ulna .
a three - month - old male infant with a superrnumerary ( extra ) leg attached to the lumbar region was admitted in the neurosurgery services of the niamey national hospital , niger .
this boy was from a consanguineous marriage , after a pregnancy of eight months , and he was delivered per vaginum .
the mother was 17 years old and a history of twin pregnancy was reported in the father 's family .
the infant had a good general condition , and the weight and height were normal .
the back outgrowth looked to be a limb attached to the lower lumbar region with a proximal lipoma .
this limb did not move spontaneously or after stimulation , but the child cried when the parasite was pinched .
there was an appendix located in the upper part of the junction area resembling the male sex organ .
radiographs of the parasite limb and the spine of the child showed the bone structures of the femur , tibia , and fibula , with a junction area at l3-l4 .
the posterior arch was absent from l2 to l5 , with a duplication or agenesis of the posterior articular .
the parasitic limb was excised at the base of which an extradural lipoma and a voluminous meningocele were found .
the intra - dural content included a neural plate and normal roots with a single spinal cord .
excision of the lipoma , repair of the meningocele , and musculofascial reconstruction were easy , and the postoperative follow - up has been uneventful .
autopsy dissection of the parasite showed a dysmorphic ischium merged to the femur by a rudimentary capsule .
lower extremity attached to the lumbar region before surgery lower extremity removed at surgery same patient as figure 1 , immediately after excision
this was a male infant born of a consanguineous marriage after eight months of pregnancy .
he presented with a double outline of the upper limb grafted in the inter - scapular region in the midline .
there was no spontaneous motor reflex in the parasite limb , but only a sensation of pain .
these bones were dysmorphic and merged to the dorsal spine , with spina bifida from t5 to t8 .
the bony part of each parasite corresponded , at the spine merger , to the autosite articular bones .
anatomical dissection of the parasite showed structures reminiscent of the scapula bone , humerus , radius , and ulna .
no glandular tissue or other neural tube structures were found at the histological examination . the follow - up ( one year ) was uneventful .
siamese twins occur in cases of twin pregnancies of the mono chorionic , mono amniotic type .
they owe their name to chang and eng bunker ( 1811 - 1874 ) , who were merged twins , from siam .
literature has reported few cases of rachipagus and parasite rachipagus.[36 ] the parasite follows the disappearance of one of the embryos with survival of certain additional structures attached to the normal embryo near or at the junction area .
the two cases in this series are boys from consanguineous marriages with a family history of twin pregnancies .
these cases were rachipagus parasite with the autosite healthy , without associated anomalies or neurological disorders . in one case
the parasite was at the lower lumbar position and in the second case at the upper thoracic position .
it is not uncommon to find sensory or motor innervations of the autosite . in both cases
we report that there was no spontaneous movement of the parasites , but the autosite was sensitive to painful parasite stimulation .
the mechanism that leads to fusion of the twins begins very early in embryonic life , at d6 , post fertilization at the blastocyst stage .
rachipagus merger would ocur at the stage of the neural groove , before the closure of the neural tube , at specific areas called ectodermic depressions .
embryologic events during this period may form a single or double spinal canal with one or two spinal cords . for spencer , fusion alone does not explain the embryogenesis of rachipagus .
this is because during the dissection , the parasite contains abnormal anatomical structures and because neural groove fusion alone will only lead to a union of bones of the vertebral arches of the two embryos , with a unique spinal channel .
it is the mechanism of division - diversion - reunion , which explains the presence of two spinal cords and two vertebral columns in some malformations .
the existence of a single channel containing a single spinal cord in both cases of this study supports the hypothesis of the fusion theory as the mechanism of occurrence of rachipagus .
bones of the limbs are frequently present . more rarely heart and neural tube structures can be found in the parasite . in some lumbar parasites , the glandular tissue , intestine or anal orifice can be observed .
limbs are most frequently found in rachipagus parasites than in teratomas or in the fetus in fetus .
this means that there is a thin line between these pathological entities.[810 ] in some cases a simple surgical resection of the parasite gives satisfactory results for autosites .
rachipagus is a rare embryogenic malformation with a good prognosis on the autosite in the absence of associated congenital anomalies .
we present two cases of rachipagus in two male infants and review the literature on this anomaly . 
 these infants were from consanguineous marriages and cases of twins were reported in their families . in the first case it was a limb attached to the lower lumbar region with a rudimentary posterior arch . at the junction there was a lipomeningocele . 
 anatomical dissection of the limb identified the bones of the lower limb . in the second case , 
 the parasites were joints of the upper limb that were attached to the chest by rudimentary posterior arches . in both cases there was only one spinal canal and a single spinal cord . except the spina bifida in the first case 
 no other malformation was diagnosed . 
 the parasites were successfully excised . 
 the two patients are well at one year of follow - up . 
 rachipagus is a rare embryogenic malformation with a good prognosis in the absence of associated congenital anomalies .