Anencephaly, dorsal hypermelia, and duplication of the vertebral column: A rare type of rachipagus conjoined twins

Abstract

The rare combination of hypermelia with craniorachischisis and duplication of the vertebral column has been found in three cases, two published and one previously unreported. Even though the previous authors had come to other conclusions, careful analysis of the details in these twins leads to the inescapable conclusion that they were all dorsally united parasitic rachipagus twins. The nature of the original union was clearly indicated by (1) the articulation of autositic ribs to two different vertebral columns but to a single ventral sternum, (2) the articulation of parasitic ribs also to the two vertebral columns but fusion of the ribs and clavicles dorsally without an interposed sternum, and (3) the dorsal location of the rudimentary viscera of the parasite. The orientation of notomelic arms was confirmatory but not diagnostic. The proposed embryologic origin of these twins is presented. © 1996 Wiley‐Liss, Inc.

Conjoined twins cephalopagus Janiceps monosymmetros: A case report

“…The specific abnormal embryologic process that results into development of conjoined twins from a single zygote is obviously unknown (Baron et al, 1990; Spencer, 1996; Spencer et al, 1996) although two theories are currently proposed as outlined by Wedberg et al (1979). The collision theory hypothesizes that duplicated embryo axes fuse before tissue differentiation.…”

“…The anatomic features at the site of union of two embryos are not simply buried, instead they are divided vertically, displaced laterally, and reunited to form essentially normal structures with each half of each new structure belonging to a different embryo according to the embryological process of division and diversion of apposing embryological structure. For the same reasons in cephalopagus twins, if the contiguous cerebral hemispheres of the twins do not actually divide, they certainly do separate and divide laterally to form a matched pair (Spencer, 1992, 1995; Spencer et al, 1996). This together with the split facial development from both the embryological axes explains the absence of optic chiasma, pituitary glands, and fusion of sella of both the sides.…”

Heteropagus (parasitic) twins: a review

“…A report by Ozcan et al [58] described another, singularly well-developed epigastric heteropagus with a rudimentary 2-chambered heart with autonomic pulsation independent of the autosite's nervous system. In addition to omphalopagus parasites, primitive heartlike saccules have previously been reported in an ischiopagus parasite and a rachipagus parasite [20,45].…”

“…Proponents of the former suggest that incomplete fission of the blastocyst inner cell mass during the primitive streak stage, 13 to 15 days postfertilization, results in 2 centers of axial growth that retain a connection at some point [8,[39][40][41][42]. "Fusion," in contrast, refers to 2 originally distinct inner cell masses that coalesce secondarily at a later stage [5,[43][44][45][46]. The most commonly advanced theory for the development of asymmetry between autosite and parasite after these events was first postulated by Donitz et al [47].…”

“…Use of tissue flaps, derived either from the autosite or parasite, as well as tissue expanders, have been described [13,28,31,57,63]. Sternal or other bony defects may be present, requiring thoracic reconstruction to prevent mechanical compromise of respiration [40,45,57].…”