Conjoined Twins: Developmental Malformations and ... - SonoWorld

Conjoined Twins: Developmental Malformations and Clinical Implications
somewhat fuzzy. Though it appears impressive, it conceivably could be misleading. "Janiform"
cephalothoracopagus twins, connected ventrally from umbilicus to vertex with two composite faces
oriented in opposite directions, might yield a similar appearance if the orientation of the radiograph was
perpendicular to the midfacial axis, with the two spinal columns partially superimposed, and each pelvis
was rotated approximately 90 degrees to face the same direction as one of the faces.
A few bizarre cases reported in Table 9-1 and in a 1996 article by Spencer et al. [9] are offered as
possible examples of rachipagus twinning, but none provides convincing proof of her interpretation.
Taruffi's monumental review of the world literature up to the early 1880's [10] disclosed no anatomically
confirmed case similar to that depicted in the French radiological paper, and a Medline search reveals no
recent reports of similar cases. Furthermore, I have not found a convincing description of this type of
twinning in another vertebrate species. Before adding the rachipagus pattern to the list of established
patterns of conjoined twins, I would like to see more anatomical evidence than the aforementioned single
radiograph.
The designation of rachipagus is not my only concern about the classification scheme and nomenclature
proposed by Dr. Spencer, which is based primarily upon her embryological theory. It adds new areas of
confusion and controversy without resolving old ones. Simplification is achieved by lumping the most
difficult and controversial patterns of twinning together into a single "atypical" category. Novel words
are introduced and older terms are given new meanings. While insisting upon precision in the application
of some terms, she is imprecise in others. For example, "omphalopagus" has long been used for ventral
supraumbilical conjunction confined to the umbilicus or cord, but Dr. Spencer extends the use of this
term to all cases in the thoracopagus series with separate hearts, regardless of the degree of thoracic
conjunction. Cardiac anatomy is so dominant a consideration in the surgical evaluation of conjoined
twins that there is no obvious need to incorporate it into the name of the twinning pattern at the cost of
anatomical precision.
Creation of the "parapagus" category is, in my view, a particularly unfortunate one. This designation is
proposed for a spectrum of patterns traditionally viewed as axial duplications, most often observed in the
anterior (or rostral) end of the axis. The "parapagus" designation reflects Spencer's fusion theory, which
seems unlikely to achieve wide acceptance. Existing designations for rostral and caudal axial
duplications accurately describe the anatomy of this pattern, and are consistent with the findings of
experimental and descriptive embryology.
Without belaboring all my reservations about this classification scheme, I will simply offer the opinion
that problems involving conjoined twins are not likely to be resolved by new taxonomies. In the
molecular era, new paradigms might lead to entirely different ways of thinking about twinning, but until
then I plan to muddle along with the familiar imperfections of existing terminologies rather than
accepting this new one.
My affection and respect for the author, with whom I have enjoyed a cordial correspondence for many
years, makes it especially painful to express so many negative comments about a book that represents so
http://link.springer-ny.com/link/service/joumals/10024/contents/03/4038/paper/body.html (4 of 5) [9/9/2003 11:23:52 AM]