Correlations between the Parasternal Neurovascular Bundle and the Chest Skeleton Morphometric Parameters in 4-6-Month-Old Fetuses

The variability of the parasternal neurovascular bundle topography, in particular, of the internal thoracic artery (ITA), requires surgeons to be extremely cautious during surgical interventions on the vessels of the ventral trunk and while performing a puncture of the anterior mediastinum and the heart. However, in literature sources there is no information about correlations between the length of the right and left ITA and some morphometric parameters of the chest skeleton. The purpose of the study was to observe the dynamics of changes in the morphometric parameters of the chest skeleton and establish the correlation between the length of the ITA and the width of the intercostal spaces and the height of the ribs on the right and left of the parasternal line in 4-6-month-old human fetuses. Materials and methods. The anatomical study was conducted on 31 specimens of 4-6-month-old fetuses without external signs of anatomical abnormalities or malformations in the chest skeleton by means of macro- and microscopic preparation, vascular injection, morphometry and the method of variation statistics. Results and discussion. The right and left parasternal neurovascular bundles in 4-6-month-old fetuses are asymmetrical, which means that the length and syntopy of the internal thoracic vessels and the parasternal nerve on the right and left are different. We also detected the variability and asymmetry of the ITA origin to other branches of the subclavian artery. The right ITA is somewhat longer than the left ITA. Two left internal thoracic veins (ITV) – median and lateral ones were found in 22 specimens and two right ITV – only in 17 fetuses; in this case, the ITA is placed between the veins of the same name. In 13 cases there was an arcuate anastomosis in front of the sternum body between the right and left median ITVs. At the beginning of the fetal period of ontogenesis, the intercostal spaces at the level of the costal cartilages are filled with the internal intercostal muscles, whose fibers are directed vertically at the edges of the sternum and obliquely from the place of the connection of the costal cartilage with the sternum. Two fetuses were found to have aplasia and hypoplasia of some structures of the intercostal spaces and constituent structures of the parasternal neurovascular bundle. Conclusions. The topography of the right and left internal thoracic arteries and veins in 4-6-month-old fetuses is asymmetric and so is the location of the nerves accompanying these vessels. From the 4th to the 6th months of fetal development, the length of the right ITA increases from 19.07 ± 3.30 mm to 31.78 ± 2.46 mm, and the that of the left one is from 18.71 ± 2.52 mm to 30, 65 ± 2.58 mm, becoming longer by 1.66 and 1.64 times respectively. The right and left ITAs are usually accompanied by two veins of the same name. The periarterial nerve plexus of the ITA is made up by the branches of the middle and inferior cervical and the first thoracic ganglions as well as by the branches of the 1st -4th intercostal nerves, the phrenic nerve, the cervical and brachial plexus, the vagus and the loop of the hypoglossal nerve, which should be taken into account by surgeons during surgical interventions in the anterior thoracic wall. Three upper intercostal spaces in the examined fetuses were the widest and their width exceeds the height of the corresponding ribs along the parasternal line. The smallest value of the length of the costal cartilage was found in the 1st rib. The bony part of the rib on the parasternal line, beginning with the 2nd rib, gradually becomes longer and the maximum value of the length of the bony part is observed in the 6th rib. Correlations of different strengths were established between the length of the right and left ITAs and the width of the intercostal spaces and the height of the ribs on the parasternal line in 4-6-month-old fetuses