Microscopic Structure of the Sigmoido-Jugular Junction in the Third-Trimester Fetus

Context and Justification: The sigmoido-jugular junction connects two structures of different compositions and has a complex organization. The sinusoidal portion of its endothelium contains muscle cells in adults. Is this the same presentation observed in fetuses? Objective: To describe the sigmoido-jugular junction in fetuses. Materials and Methods: Over a period of seven months, a histochemical and immunohistochemical study was conducted on 30 sigmoido-jugular junctions taken from 15 fetuses aged at least 32 weeks of gestation. These fetuses were obtained following expulsion due to intrauterine death, after informed consent from the parents. Results: Three portions can be identified: sigmoid, junctional, and jugular. Histochemical preparations revealed the existence of two constant layers and a third layer present only at the jugular level. From the inside out, the layers are as follows: 1) Inner Layer (Endothelium): This layer is clearer from the junction and reveals the presence of smooth muscle cells at the sigmoid level in immunohistochemistry. 2) Outer Layer: At the sigmoid and junctional levels, this layer consists of collagen fibers and becomes median at the jugular level, where it is composed of elastic and muscular collagen fibers. 3) Third Layer: Present only at the jugular level, this layer corresponds to the adventitia. Conclusion: The architecture of the sigmoido-jugular junction in fetuses, which is identical to that in adults, excludes the metaplastic hypothesis regarding endothelial smooth muscle cells in the sigmoid portion. Instead, it favors their role in regulating encephalic venous drainage.