A temporary disc-like structure at the median atlanto-axial joint in human fetuses

Abstract

During observations of mid-term and late-stage fetuses, we found a joint disk-like structure at the anterior component of the median atlanto-axial joint. At mid-term, the disk-like structure was thick (0.1-0.15 mm) relative to the sizes of bones surrounding the joint. However, it did not completely separate the joint cavity, and was absent in the inferior and/or central part of the cavity. This morphology was similar to the so-called fibroadipose meniscoid of the lumbar zygapophysial joint that is usually seen in adults. In mid-term fetuses, there was evidence suggesting that a mesenchymal tissue plate was separated from a roof of the joint cavity. In late-stage fetuses, the thickness (less than 0.15 mm) was usually the same as, or less than that at mid-term, and the disk-like structure was often flexed, folded and fragmented. Therefore, in contrast to the zygapophysial meniscoid as a result of aging, the present disk-like structure was most likely a temporary product during the cavitation process. It seemed to be degenerated in late-stage fetuses and possibly also in newborns. Anomalies at the craniocervical junction such as Chiari malformations might accompany this disk-like structure at the median atlanto-axial joint even in childhood.

Suboccipital myodural bridges revisited: Application to cervicogenic headaches

“…A major proportion of the present specimens had been used for our recent study of a temporarily appearing disk in the median atlanto-axial joint (Sakanaka et al, 2019). The present specimens had been stored in formalin solution for more than 10 years.…”

“…We have also used fetal specimens for investigation of the neurodural junction in the thoracic spinal cord (Cho et al, 2016). Moreover, we have become familiar with the topographical anatomy of the atlanto-occipital region through our recent study of a temporary disk-like structure appearing at the median atlanto-axial joint (Sakanaka et al, 2019). Consequently, using human fetuses near term, the aim of this study was to demonstrate the morphology and individual variations in the suboccipital fascial configuration including the myodural bridge candidate.…”

Regional differences in zygapophysial joint cavities: A histological study of human fetuses

“…The sectional planes were sagittal (24 fetuses) or horizontal (six fetuses from the midterm and near‐term groups). Some of the cervical sagittal sections were used in our previous studies (Kitamura et al, 2019; Sakanaka et al, 2019). Most photographs were taken with a Nikon Eclipse 80.…”

“…Although it was out of the focus, our recent study of the fetal occipitovertebral junction (Ishii et al, 2020; Kitamura et al, 2019; Sakanaka et al, 2019) demonstrated that the morphology of the subaxial cervical ZJ was quite different from that in adults. The cervical joint cavity (JC) is very large because it extends posteromedially along the vertebral lamina far beyond the articular cartilage.…”

Fetal development of the human trapezius and sternocleidomastoid muscles

“…A total of 19 embryos and fetuses at gestational week 6 to 7 (crown-rump length of 15–27 mm) were obtained following miscarriages and ectopic pregnancies managed at the Department of Obstetrics, Complutense University of Madrid (Madrid, Spain). Serial horizontal and sagittal sections of the fetal heads were stained with hematoxylin and eosin, Masson trichrome, or Azan trichrome according to our recent research methods [ 7 - 9 ]. After examination, the stained sections were donated to the collection maintained by the Institute of Embryology, Complutense University of Madrid.…”