Okajimas Folia Ant. Jpn.. 68(1): 7-14, May, 1991 A macroscopic study of the internal thoracic artery of the rat By Shigeki MIZUKAMI and Shigenori TANAKA School of Nursing, Fukui Prefectural College, Oohatamachi 97-21-3, Fukui 910 Department of Anatomy, School of Medicine, Kanazawa University, Takaramachi 13-1, Kanazawa 920 -Received for Publication, December 11, 1990- Key words: Internal thoracic artery, brachiocephalic vein, gross anatomy, development, rat Summary: The internal thoracic artery (ATI) of rats was macroscopically studied. In this study, the overall features of the artery were virtually elucidated in entirety. The artery was found to arise from the subclavian artery in the thoracic cavity and to immediately break up into the following branches: (1) the pericardiacophrenic artery, (2) the superior epigastric artery, (3) the thymic branch, (4) the comitans branch to the brachiocephalic veins, and finally (5) the bronchoesophageal trunk. As is well known, rats are devoid of the superior caval veins, retaining instead a pair of brachiocephalic veins into adulthood; this is a greatly beneficial condition as it enables us to consider the essential relationships of the ATI to relevant structures which are thought to be directly involved in the development of the ATI. In fact, the rat ATI revealed topographically a remarkable intimacy with the phrenic nerve, the brachiocephalic and inferior caval veins, the heart and lungs and also with the diaphragm; in their development all are in close relationship with the pleuropericardial fold. This fact leads us to the opinion that, for a better understanding of the morphological meanings of the ATI, an understanding of the relationship of this artery to the pleuropericardial fold seems to be a prerequisite. The internal thoracic artery (ATI) of human beings describe how the blood is supplied by this artery to local renders its morphological interpretation not less difficult regions of the thoracic viscera, — e.g., the heart by its extensive and rather complicated distribution. (Halpern, 1957) and thymus gland (Yamasaki, 1990), This artery supplies not only the anterior wall of the the reports dealing with the general morphology of the upper body trunk and the diaphragm, but, after ATI from the standpoint of macroscopic as well as entering the cave of the thorax, also the parietal layer developmental anatomy are very limited. Further of the serosal investments of the thoracic viscera, and studies have been needed to evaluate fully the morpho- the structures located in the mediastina which include logical meanings of this artery in the anatomy of rats. the thymus and lymphatic nodes as well. Furthermore, The present study was therefore undertaken to provide though inconstantly, it gives off branches to the a more detailed description of the overall features of bronchus, esophagus, thyroid gland and also to the the rat ATI in the hopes of obtaining a foothold for upper limbs. a better understanding not only of the rat ATI but of The ATI of rats concerned in this study is distributed the ATI in human beings as well. much more extensively than it is in human beings. In this animal, the bronchus and esophagus, for example, are consistently supplied by branches from the ATI, and Materials and Methods not by those of the intercostal arteries as is usually the case in humans. In addition, the wall of the greatest For the purpose of this investigations, 5 Wistar rats veins such as the brachiocephalic veins of both sides (3 females and 2 males, weighing between 250-300 and the inferior caval vein, are supplied by this artery. gm) were used; the animals were anaesthetised with Furthermore, the wall of the sinus venosus, a part of urethane (sodium ethylcarbamate, 900 mg/kg i.c.), and the right auricle and the right and left atria are perfused through a catheter inserted retrogradely into vascularized by this artery. the abdominal aorta at the level immediately below the While a few detailed reports are available which origin of the renal artery. Outflow of perfusate was Correspondence should be addressed to: Prof. Shigeki Mizukami, School of Nursing, Fukui Prefectural College, Oohatamachi 97-21-3 Fukui 910 7 8 S. Mizukami and S. Tanaka from the cut vena cava inferior below the diaphragm. subclavian vein (Fig. 2), and reached the level of the Perfusion was commenced with 200 ml of normal saline confluence of the brachiocephalic and internal jugular containing heparin (10 IU/ml) and followed by 20 ml vein (i.e., the venous angle). At this point, the ATI of normal saline containing ca. 1 percent of coloring broke up into the following arteries; (1) pericardiaco- matter (Poster color/Sakura), and finally with 400 ml phrenic artery; (2) superior epigastric artery; (3) thymic of a 10 (v/v) percent formalin solution; the animals so branches; (4) comitans branch to the brachiocephalic perfused were postfixed in the same fixative about 2-3 vein; and (5) bronchoesophageal trunk. days prior to dissection. During the dissection the materials were preserved in a 95 percent ethyl alcohol Right pericardiacophrenic artery solution. The dissective procedures and observations of The pericardiacophrenic artery (APP) of rats con- the anatomical details of the ATI were performed by stituted the principal division of the ATI, and continued using fine forceps (Watanabe/Yayoi) under a stereo- the direction of the trunk of this artery (Fig. 2); it was microscope (Zeiss) at a magnification of between 4 and located dorso-lateral to the brachiocephalic vein in 10 times. The working field was illuminated by two contrast to the `comitans branch (of the ATI) to the fiber optical goose neck lamps (Nikon). In the intervals brachiocephalic vein' mentioned below. Coursing between the dissections, the materials, when required, downwards as far as the level of the sinus venosus of were photographed on Neopas (6.2 x 8.8 cm) films with the heart, it gave off cardiac branches of fine caliber Mamiya RB67 camera, and enlarged on projection toward the parietal layer of the pericardium sur- papers (Hishicopy/Mitsubishi; 42.0 x 59.3 cm) to about rounding the sinus venosus (Fig. 2). After quitting the 5-6 times the actual size, where each finding was sinus venosus, the artery accompanied the inferior caval noted. The findings in this study are based on the data vein and the phrenic nerve to reach the foramen venae recorded on a total of 10 photoprojection papers. cavae inferioris of the diaphragm. Passing through this foramen and having appeared in the abdominal cavity, the branch coursed downwards and dorsally along the Findings inferior aspect of the diaphragm to reach its lumbar portion, and was joined by the inferior phrenic artery The morphology of the paired ATI were found in (not depicted). The morphological meanings of the principle to be the same. Therefore, for the sake of course taken by this artery will be considered later in simplicity, the following accounts will be given primarily the text in connection with the pleuropericardial fold for the right side, whilst descriptions of the left ATI (see discussion). will be confined to essential differences from those of the right side. Right superior epigastric artery The right ATI was found to arise from the sub- The superior epigastric artery, after issuing from the clavian artery (Figs. 1 and 2). Not far from the origin ATI, traversed in the superior mediastinum ventrally of this artery, the ATI was found to be crossed by the and slightly caudally around the lateral aspect of the phrenic nerve which coursed down in front of the artery right brachiocephalic vein, and then passing in the from lateral to medial to enter the thorax cavity. The superior mediastinum, reached the ventral wall of the ATI accompanied this nerve, lying on the lateral side thorax (partly depicted in Fig. 1). Here, the artery bent of the latter, and simultaneously behind the right caudally to enter the interval between the transverse Abbreviations A CP deep cervical artery N RC recurrent laryngeal nerve of the vagus nerve A CS superficial cervical artery N PH phrenic nerve A ES superior epigastric artery N X vagus nerve A MPH musculophrenic artery PPF pleuropericardial fold A P pulmonary artery RC VBD comitans branch to the right brachiocephalic vein A PP pericardiacophrenic artery RC VBS comitans branch to the left brachiocephalic vein A RC aortic arch R MDS mediastinal branch A SB subclavian artery R TH thymic branch AS D ascending branch of the bronchoesophageal trunk T BE bronchoesophageal trunk A THI internal thoracic artery V BCS left brachiocephalic vein A THIF inferior thyroid artery V Cl inferior caval vein AU D right auricle V Ji internal jugular vein Cl the first rib V P pulmonary vein D diaphragm V SB subclavian vein DS D descending branch of the bronchoesophageal trunk 3 the 3rd aortic arch E esophagus 4 the 4th aortic arch L lung (bud) 6 the 6th aortic arch Internal Thoracic Artery of the Rat 9 thoracic muscle and the costal cartilages near the was found to emit minute branches to supply the sternum. Coursing down in this interval, the artery thymus glands which were located ventral to the aortic reached the ventral abdominal wall in the epigastric arch (not depicted). fossa as is generally described in the anatomical text- books. En route in the superior mediastinum, the artery Fig. I. Semidiagrarnmatic representation of the internal thoracic artery of rats. 10 S. Mizukami and S. Tanaka Right thymic branches Right comitans branch of the brachiocephalic vein The right thymic branches (R TH), which are well The ATI of rats was found to issue the comitans developed in rats, were found to issue from the ATI branch to the brachiocephalic vein (RC VBD).