AND AZYGOS VEINS by REGINALD J

DEVELOPMENT OF THE INFERIOR VENA CAVA IN THE LIGHT OF RECENT RESEARCH, WITH ESPECIAL REFERENCE TO CERTAIN ABNORMALITIES, AND CUR- RENT DESCRIPTIONS OF THE ASCENDING LUMBAR AND AZYGOS VEINS By REGINALD J. GLADSTONE, M.D., F.R.C.S. University of London, King's College INTRODUCTION SINCE the publication of Rathke's, Kerschner's and Hochstetter's pioneer researches on the development of the venous system, a large amount of ad- mirable work has been carried out on the development of the postrenal part of the inferior vena cava, both in animals and in man. The bulk of this work has been accomplished by American embryologists and more especially by Lewis, Miller, Huntington, McClure, Butler, Sabin and Reagan. The older methods of reconstruction have now been supplemented by the intravascular injection of solutions of Indian ink, nitrate of silver, Prussian blue, and other dyes, into living embryos, the tissues being afterwards fixed, cleared and mounted in celloidin. This method has furnished most beautiful demonstrations of the finer vessels and their anastomoses, even in quite young embryos, e.g. rat embryos having only 2-3 somites (Reagan). But although, under exceptional circumstances, the successful injection of a living human embryo has been accomplished (Broedel), the careful study and reconstruction of serial sections of human embryos is still the most valuable method of research with regard to the development of these blood vessels in man. COMMENTS ON CURRENT DESCRIPTIONS OF THE ASCENDING LUMBAR AND AZYGOS VEINS In three papers written before the publication of the more recent work of the above-mentioned authors, I recorded: (A) two cases of a dorsal position of the ureter relative to the inferior vena cava; (B) one of a postaortic course of the left renal vein; and (C) one of a left postrenal vena cava. In the article dealing with the postcaval position of the ureter, I drew attention to the development of the ascending lumbar vein, by the formation of a longitudinal anastomosis between the lumbar intersegmental veins. This vessel courses vertically in front of the transverse processes of the lumbar vertebrae, and behind the psoas major muscle (fig. 6 of that article). Development of the Vena Cava, etc. 71 The course of an anastomotic vein (text-fig. 1), which commonly arises from the dorsal aspect of the inferior vena cava, and proceeds upwards through the right crus of the diaphragm, or its aortic opening, to join the vena azygos major in front of the body of either the 12th or 11th thoracic vertebra, was also commented on, and figured. A similar anastomotic vein is frequently present on the left side, and passes into the thorax through the left crus of ?>IA. ,.v/s>,, A .~~~ ~ ~~~~~~~~~~~~~~........ Text-fig. 1. Drawing from an adult male subject showing the origin of the vena azygos major and vena azygos minor; and the relation of these vessels to the sympathetic chain, the splanchnic nerves, and the intersegmental arteries. The dotted lines indicate the position of the crura of the diaphragm. ALV. Ascending lumbar vein. NSMi. Lesser splanchnic nerve. IA. Intercostal arteries. RLAzV. Right lumbar azygos vein. HAV. Hemiazygos vein. sa. Sympathetic cord. LLAzV. Left lumbar azygos veinl. Sey. Subcostal vein. NSMa. Greater splanchnic nerve. the diaphragm (text-fig. 1); this vein may arise from a left lumbar vein, the left renal vein or the inferior vena cava, and it usually joins the hemiazygos vein at the level of the body of the 12th thoracic vertebra. The first accurate description of these anastomotic veins in the adult human subject, in this country, was by Robinson(22), who figured five cases, showing the origin of the right anastomotic vein, from the dorsal aspect of the inferior vena cava, at a point below the termination in it of the renal 72 Reginald J. Gladstone veins; and he also drew attention to the frequent termination of the 1st, and sometimes the 2nd lumbar vein in the anastomotic vein of the corre- sponding side. Unfortunately, however, although well aware of the relations, he did not in this paper make any allusion to the termination of the subcostal vein which unites, as is correctly described in the majority of textbooks on human anatomy, with the ascending lumbar vein. This union normally takes place behind the origin of the diaphragm, close to the head of the 12th rib, and by the side of the body of the 12th thoracic vertebra. On the right side the vein which is formed by the union of the subcostal vein with the ascending lumbar vein is regarded as the commencement of the vena azygos major, and the similar vein on the left side as the commencement of the vena azygos minor or hemiazygos vein. The subcostal vein passes into the thorax beneath the lateral lumbocostal arch; the ascending lumbar vein passes upward behind the psoas muscle, and beneath the medial lumbocostal arch. The vena azygos major then ascends in the thoracic cavity for a distance of one or two inches, before it is joined by the slender anastomotic vein (sometimes merely a fibrous cord, text-fig. 3), which ascends in front of the vertebral column either through the right crus of the diaphragm or its aortic opening. The statement therefore that the vena azygos major passes through the aortic opening of the diaphragm does not accord with the description of the origin of the vena azygos major, from the junction of the right subcostal vein, with the right ascending lumbar vein; and since the anastomotic vein in many cases does not pass through the aortic opening, but traverses the right crus of the diaphragm, and is sometimes represented only by an impervious cord, it is obvious that the alternative description of the vena azygos major arising in the abdomen from an "ascending lumbar vein" in front of the vertebral column and psoas muscle and passing through the aortic opening of the diaphragm is inconsistent with the more classical description of its origin in the thorax from the junction of the right subcostal vein with the ascending lumbar vein, namely, that vein which lies behind the psoas major muscle, and in front of the transverse processes of the lumbar vertebrae. The necessity for a more exact description and drawings of the ascending lumbar veins, and of the origin of the vena azygos major, will be apparent on comparing the statements which are quoted below from current textbooks on human anatomy: (1) The vena azygos major or right azygos vein commences in the abdomen, as the right ascending lumbar vein, and enters the thorax through the aortic opening of the diaphragm, lying on the right side of the aorta, the thoracic duct intervening. The ascending lumbar vein is depicted in a figure on the succeeding page as passing upward in front of the psoas muscle, although it is correctly described in the text under the heading of the Lumbar Veins: The vessels of each side are connected by a series of longitudinal anastomosing veins, in front of the lumbar transverse pro- gesses, and the longitudinal vessel thus formed is called the ascending lumbar vein. (2) The azygos vein (O.T. vena azygos major) usually takes origin in the right ascending lumbar vein. It will be found in the interval between the right crus of the diaphragm and the aorta, upon the right side of the cisterna chyli, and it will Development of the Vena Cava, etc. 73 be noticed to enter the thorax by passing through the aortic opening....The vena azygos commences in the abdomen where it anastomoses either with one of the upper lumbar veins or directly with the inferior vena cava. (3) Between the crura and to the right of the aorta lies the right ascending lumbar vein, a longitudinal trunk linking together the transversely coursing lumbar veins, which pass inwards from under cover of the fibrous arches of the psoas to open into the inferior vena cava. This ascending lumbar vein is the beginning of the vena azygos major, but the latter vessel always has a communication with the back of the inferior vena cava as well. In many cases the ascending lumbar vein is hardly visible, and then the vena azygos rises entirely from the inferior vena cava. (4) The larger or right azygos vein commences opposite the first or second lumbar vertebra, by a branch from the right lumbar veins (the ascending lumbar); sometimes by a branch from the right renal vein, or from the inferior vena cava. It enters the thorax through the aortic opening of the diaphragm. (5) The vena azygos major begins in the abdomen, where it may be looked upon as the continuation upwards of the ascending lumbar vein. It passes through the aortic opening of the diaphragm....The trunk lumbar veins are connected beneath the psoas muscle by vertical branches, which cross in front of the transverse processes. I would suggest that the term " ascending lumbar vein" be limited to the vertical precostal anastomosis, which extends between the iliolumbar vein and the termination of the subcostal vein; in other words, the longitudinal vessel behind the psoas major muscle which commences below in the iliolumbar tributary of the common iliac vein, and terminates above by uniting with the subcostal vein, to form on the right side the vena azygos major, and on the left side the vena azygos minor or hemiazygos vein. I would also suggest that the small anastomotic vein which commences on the dorsal aspect of the inferior vena cava or from one of its tributaries near the termination of the right renal vein, and passes upward through the aortic opening of the diaphragm to join the vena azygos major, be called the right lumbar azygos vein; further that the classical description of the origin of the vena azygos major, by the union of the right ascending lumbar vein with the right subcostal vein, be retained, and as a corollary to this, that the description of the vena azygos major commencing in the abdomen as a continuation of the ascending lumbar vein and entering the thorax through the aortic opening of the diaphragm be discarded altogether.

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