Department of Imaging, Section Anatomy and Museum for Anatomy and Pathology, Radboud University, Medical Center, Nijmegen, Netherlands.
Pathologisch-anatomische Sammlung im Narrenturm-NHM, Vienna, Austria.
Clin Anat. 2021 Sep;34(6):845-858. doi: 10.1002/ca.23725. Epub 2021 Feb 20.
Shared anomalies, always located close to the area of coalescence and observable in virtually every type of conjoined twinning, are currently seen as separate anomalies caused by mostly unknown and seemingly unrelated pathways rather than being connected to the twinning mechanism itself. Therefore, most (case) reports about conjoined twins are mere descriptions of (external) dysmorphologies lacking reflections on the possible origin of their concomitant anomalies. As we will demonstrate in this article, shared anomalies are influenced, and in some cases solely and sequentially explained, by interaction aplasia and neo-axial orientation; two embryological mechanisms to which each set of conjoined twins is subjected and are responsible for their ultimate phenotypical fate. In this review, we consider how the ventral, lateral and caudal conjunction types and their intermediates determine the phenotypic presentation of the twins, including patterns of shared malformations and anomalies, which in themselves can be indistinguishable from those encountered in singleton cases. Hence, it can be hypothesized that certain anomalies in singletons originate in a fashion similar to that in conjoined twins.
共享异常通常位于融合区域附近，几乎可以在每种联体双胞胎中观察到，目前被认为是由大多数未知且似乎无关的途径引起的单独异常，而不是与孪生机制本身有关。因此，大多数关于联体双胞胎的（病例）报告只是对（外部）畸形的描述，而没有反映其伴随异常的可能起源。正如我们将在本文中展示的那样，共享异常受到相互作用发育不全和新轴向取向的影响，在某些情况下，这两种胚胎发生机制仅单独且顺序地解释了它们，这是每一对联体双胞胎都经历的，也是它们最终表型命运的原因。在这篇综述中，我们考虑了腹侧、侧方和尾侧连接类型及其中间型如何决定双胞胎的表型表现，包括共享畸形和异常的模式，这些模式本身与单胎病例中遇到的模式无法区分。因此，可以假设某些单胎中的异常是类似于联体双胞胎中的异常起源的。
