- Email: [email protected]
Partial agenesis of the azygos vein: A case report
· ANNALS Of ANATOI¥lY = = = = = = = = = =
Partial agenesis of the azygos vein: A case report Alberto Caggiati and Fabrizio Barberini Department of Anatomy, Faculty of Medicine, University of Rome "La Sapienza", Via A. Borelli 50, 1-00161 Rome, Italy
Summary. In the cadaver of an 86 year old man the inferior segment of the azygos vein could not be found. Furthermore, a normally developed hemiazygos vein drained the right and left intercostal veins from T 10 to T 6. This vessel finally curved towards the right to reach the superior vena cava after having drained the right superior intercostal veins. The left superior intercostal vein ended in a short vessel draining into the left brachiocephalic vein. This condition may be represented in a standard chest radiograph by the socalled "aortic nipple". Agenesis of the azygos vein, suspected because of the presence of this radiological sign, should be confirmed in the living by means of computerized tomography. This can clarify the anatomy of the mediastinal vessels precisely. Embryological pattern of the azygos system accounting for its possible defects is discussed.
minal portion of the right posterior cardinal vein, whereas the lower tract originates from the right supracardinal vein. This embryonic vessel also gives rises to the right ascending lumbar vein. The HV, on the left side of the posterior mediastinum, and the left ascending lumbar vein are derived from the left supracardinal vein. The left superior intercostal vein and the accessory hemiazygos vein originate from the left posterior cardinal vein as does the upper tract of the AV. The HV segment joining the AV is due to the persistence of one of the anastomoses between the right and left posterior cardinal veins (MacLure et al. 1925; Corliss 1981). Studies on this topic which analyze large series of cases statistically never refer to the possible absence of the azygos vein (Rogado 1971).
Key words: Azygos vein - Embryology - Computerized tomography
Case report
Introduction The arrangement of the venous tributaries of the azygos vein (AV) varies considerably (Davis et al. 1958). The pattern commonly described in the anatomical textbooks is present in only about 10 to 15 percent of cases. In about 60-650/0 of the population, minimal changes, mainly involving the collateral vessels, are observed. In the remaining 20 - 25% extensive modifications in the arrangement of the main trunks - i. e. the AV and the hemiazygos vein (HV)are present (Falla et al. 1963). Such a variability is due to the complex embryological origin of this venous system. The AV, as well as the contralateral HV, has a double origin. The first vessel of the upper tract joining the superior vena cava represents the tcrCorrespondence to: A. Caggiati
~;I£ SEMPER
Ann Anat (1996) 178: 273 Gustav Fischer Verlag .lena
.275
During the dissection of an 86 year old man (cause of death unknown) and after opening a window in the posterior parietal pericardium, we noticed that the azygos vein was absent from its typical topographic localization; that is to say, on the right side of the thoracic spine. The pre- and para-vertebral spaces were therefore completely dissected in order to clarify the arrangement of the posterior parietal venous bed in the thorax and in the abdomen. In the posterior mediastinum only one large venous trunk running longitudinally along the left side of the spine was present (Fig. 1 A). This vessel drained the right and left intercostal veins from T 10 to T 6. At the level of the intercostal space between T 6 and T 5, this vessel curved forward and to the right to continue as a short segment reaching the posterior wall of the superior vena cava (Fig. 1 A). The final longitudinal segment of the vessel drained the right superior intercostal veins, but no collector from the left side of the spine reached it (Figs. 1 A, B). The left superior intercostal veins drained into a short vessel reaching the left brachiocephalic vein, after crossing above the descending part of the aortic arch (Fig. 2). The longitudinal vessel
right ascending lumbar vein was not found on the right side of the spine, whereas the right lumbar veins drained directly into the inferior vena cava by means of a short collecting vessel. Apart from those already aforementioned, no other vascular or splanchnic variations were observed. In particular, the arterial system, the portal vessels and the liver were quite normal.
Discussion
Fig. 1. Veins of the posterior thoracic wall. A ) .A her dissection of the mediastinal organs, a single longitudinal vessel is seen to run along the spine, lying on its left side (HV). B) Drawing schematically representing the venous bed described in 1 he tex!.
AA Fig. 2. The left superior intercostal vein (I SIV), after crossing the descending tract of the aortic arch (A.A) anel tht: left sublavian artery (LSA), drains into the left innominate \'l~ il1 IIIV). originated on the left side of the spine from the confluence of the T 10l T 11 left and right intercosta l ve ins . Thi s left root connected the HV to th e left ascendin g lumbar vein . A
In our case the two venous structures derived from the right supracardinal vein were absent (i. e. the lower segment of the AV and the right ascending lumbar vein). Only the upper tract of the AV, representing the terminal portion of the right posterior cardinal vein, was present. The vessels derived from the left supracardinal vein (i. e. the HV and the left lumbar ascending vein) appeared to be well developed . The terminal transverse segment of the HV, resulting from the persistence of one of the intercardinal anastomosis, was also present. Thus it may be postulated that the longitudinal vein, placed on the left side of the spine, and the transverse segment running from the left to the right side of the spine, can be identified as the hemiazygos vein. The last segment of this vessel may represent the upper tract of the AV, resulting from the development of the terminal portion of the right supracardinal vein. Therefore, on the basis of these observations and in the light of existing embryological knowledge, it seems reasonable to conclude that the absence of the lower tract of the AV might be dependent upon the failure of the right supracardinal vein to develop thus causing partial agenesis of the azygos and of the right ascending lumbar veins. Congenital absence of the azygos vein is extremely rare. A wide review of the literature on this topic revealed only 2 cases (Karpowicz 1934; Hatfield et al. 1987). Undoubtedly its rarity is partially due to objective diagnostic difficulties. In fact, such a condition may be diagnosed only during anatomical or surgical dissection of the posterior mediastinum or by computerized radiology (Caggiati et al. 1994). The absence of the azygos vein could also be detected by means of complex radiological techniques (i. e.: azygography, transvertebral phlebography) , seldom employed in the past and to day replaced by computerized radiology (Hatfield et al. 1987). The more frequently employed radiological approach to the thorax - anteroposterior and lateral chest radiography - cannot detect absence of the AV, because it only appears in a very low percentage of normal standard chest radiographs (Galluzzi 1986). Chest stratigraphy is less frequently used, and in most cases other organs than the AV, are the goal of the examination. The left superior intercostal vein appears in about 10% of standard chest radiographs as a protrusion of the first arch of (he left cardiac profile, conventionally known as the
274
"aortic nipple". Enlargement of the left superior intercostal vein is easily recognizable on standard chest radiography. Such an occurrence may be due to one of several pathological conditions, such as congestive hearth failure, portal hypertension, the Budd-Chiari Syndrome, obstruction of the inferior or superior vena cava, and finally, agenesis of the AV (Hatfield et at. 1987). In fact, in cases of agenesis of the AV, the HV plays an important role in the hemodynamic supply, draining almost all the right and left intercostal veins. Consequently, this condition increases the venous flow into the left superior intercostal vein above the normal level. so that it drains preferentially into the left brachiocephalic vell1 under a higher pressure gradient. Based upon these physiopathological data, our suggestion is that Radiologists should request a computerized tomograph of the chest to ascertain the possible congenital absence of the AV, whenever an "aortic nipple" is detected on standard radiography. Thus, the clinician might be provided with morphological support for a differential diagnosis between mediastinal pathological lesions and agenesis of the AV. In this way, a more exac1 value for the real incidence of this variant could be ob1ained
275
References Caggiati A, Barberini F (1994) Congenital absence of the azygos vein. 76th Federative International Congress of Anatomy, Lisboa, abstract book, p 183 Corliss CE (1981) Embriologia umana di Patten. Grasso Ed., Bologna 1981 Davis RA, Milloy FJ, Anson BJ (1958) Lumbar, renal and associated parietal and visceral veins based upon a study of 100 specimens. Surg Gyn Obstet 107: 3 - 18 Falla A, Preston FW, Anson BJ (1963) Classification and calibration of the azygos venous system in 100 specimens. Surg Gyn Obstet 112: 405 -412 Galluzzi S (1986) Telecardiogramma, Siena Hatfield MK, Vyborny CJ, MacMahon H, Chessare JW (1987) Congenital absence of the azygos vein: a cause for "Aortic nipple" enlargement. Am J Radiol 149: 273 - 274 Karpowicz S (1934) Une variation de la veine mediane de dos en coincidence avec Ie defaut de la veine azygos. CR Seances Acad Sci 3: 27 -32 MacLure CFW, Butler EG (1925) The development of the inferior vena cava in man. Am J Anat 35: 331 -383 Rogado LQ (1971) Sistema Azygos - Contribuicao para 0 seu estudo anatomico. Thesis, Lisboa Accepted February 1, 1996
Partial agenesis of the azygos vein: A case report Alberto Caggiati and Fabrizio Barberini Department of Anatomy, Faculty of Medicine, University of Rome "La Sapienza", Via A. Borelli 50, 1-00161 Rome, Italy
Summary. In the cadaver of an 86 year old man the inferior segment of the azygos vein could not be found. Furthermore, a normally developed hemiazygos vein drained the right and left intercostal veins from T 10 to T 6. This vessel finally curved towards the right to reach the superior vena cava after having drained the right superior intercostal veins. The left superior intercostal vein ended in a short vessel draining into the left brachiocephalic vein. This condition may be represented in a standard chest radiograph by the socalled "aortic nipple". Agenesis of the azygos vein, suspected because of the presence of this radiological sign, should be confirmed in the living by means of computerized tomography. This can clarify the anatomy of the mediastinal vessels precisely. Embryological pattern of the azygos system accounting for its possible defects is discussed.
minal portion of the right posterior cardinal vein, whereas the lower tract originates from the right supracardinal vein. This embryonic vessel also gives rises to the right ascending lumbar vein. The HV, on the left side of the posterior mediastinum, and the left ascending lumbar vein are derived from the left supracardinal vein. The left superior intercostal vein and the accessory hemiazygos vein originate from the left posterior cardinal vein as does the upper tract of the AV. The HV segment joining the AV is due to the persistence of one of the anastomoses between the right and left posterior cardinal veins (MacLure et al. 1925; Corliss 1981). Studies on this topic which analyze large series of cases statistically never refer to the possible absence of the azygos vein (Rogado 1971).
Key words: Azygos vein - Embryology - Computerized tomography
Case report
Introduction The arrangement of the venous tributaries of the azygos vein (AV) varies considerably (Davis et al. 1958). The pattern commonly described in the anatomical textbooks is present in only about 10 to 15 percent of cases. In about 60-650/0 of the population, minimal changes, mainly involving the collateral vessels, are observed. In the remaining 20 - 25% extensive modifications in the arrangement of the main trunks - i. e. the AV and the hemiazygos vein (HV)are present (Falla et al. 1963). Such a variability is due to the complex embryological origin of this venous system. The AV, as well as the contralateral HV, has a double origin. The first vessel of the upper tract joining the superior vena cava represents the tcrCorrespondence to: A. Caggiati
~;I£ SEMPER
Ann Anat (1996) 178: 273 Gustav Fischer Verlag .lena
.275
During the dissection of an 86 year old man (cause of death unknown) and after opening a window in the posterior parietal pericardium, we noticed that the azygos vein was absent from its typical topographic localization; that is to say, on the right side of the thoracic spine. The pre- and para-vertebral spaces were therefore completely dissected in order to clarify the arrangement of the posterior parietal venous bed in the thorax and in the abdomen. In the posterior mediastinum only one large venous trunk running longitudinally along the left side of the spine was present (Fig. 1 A). This vessel drained the right and left intercostal veins from T 10 to T 6. At the level of the intercostal space between T 6 and T 5, this vessel curved forward and to the right to continue as a short segment reaching the posterior wall of the superior vena cava (Fig. 1 A). The final longitudinal segment of the vessel drained the right superior intercostal veins, but no collector from the left side of the spine reached it (Figs. 1 A, B). The left superior intercostal veins drained into a short vessel reaching the left brachiocephalic vein, after crossing above the descending part of the aortic arch (Fig. 2). The longitudinal vessel
right ascending lumbar vein was not found on the right side of the spine, whereas the right lumbar veins drained directly into the inferior vena cava by means of a short collecting vessel. Apart from those already aforementioned, no other vascular or splanchnic variations were observed. In particular, the arterial system, the portal vessels and the liver were quite normal.
Discussion
Fig. 1. Veins of the posterior thoracic wall. A ) .A her dissection of the mediastinal organs, a single longitudinal vessel is seen to run along the spine, lying on its left side (HV). B) Drawing schematically representing the venous bed described in 1 he tex!.
AA Fig. 2. The left superior intercostal vein (I SIV), after crossing the descending tract of the aortic arch (A.A) anel tht: left sublavian artery (LSA), drains into the left innominate \'l~ il1 IIIV). originated on the left side of the spine from the confluence of the T 10l T 11 left and right intercosta l ve ins . Thi s left root connected the HV to th e left ascendin g lumbar vein . A
In our case the two venous structures derived from the right supracardinal vein were absent (i. e. the lower segment of the AV and the right ascending lumbar vein). Only the upper tract of the AV, representing the terminal portion of the right posterior cardinal vein, was present. The vessels derived from the left supracardinal vein (i. e. the HV and the left lumbar ascending vein) appeared to be well developed . The terminal transverse segment of the HV, resulting from the persistence of one of the intercardinal anastomosis, was also present. Thus it may be postulated that the longitudinal vein, placed on the left side of the spine, and the transverse segment running from the left to the right side of the spine, can be identified as the hemiazygos vein. The last segment of this vessel may represent the upper tract of the AV, resulting from the development of the terminal portion of the right supracardinal vein. Therefore, on the basis of these observations and in the light of existing embryological knowledge, it seems reasonable to conclude that the absence of the lower tract of the AV might be dependent upon the failure of the right supracardinal vein to develop thus causing partial agenesis of the azygos and of the right ascending lumbar veins. Congenital absence of the azygos vein is extremely rare. A wide review of the literature on this topic revealed only 2 cases (Karpowicz 1934; Hatfield et al. 1987). Undoubtedly its rarity is partially due to objective diagnostic difficulties. In fact, such a condition may be diagnosed only during anatomical or surgical dissection of the posterior mediastinum or by computerized radiology (Caggiati et al. 1994). The absence of the azygos vein could also be detected by means of complex radiological techniques (i. e.: azygography, transvertebral phlebography) , seldom employed in the past and to day replaced by computerized radiology (Hatfield et al. 1987). The more frequently employed radiological approach to the thorax - anteroposterior and lateral chest radiography - cannot detect absence of the AV, because it only appears in a very low percentage of normal standard chest radiographs (Galluzzi 1986). Chest stratigraphy is less frequently used, and in most cases other organs than the AV, are the goal of the examination. The left superior intercostal vein appears in about 10% of standard chest radiographs as a protrusion of the first arch of (he left cardiac profile, conventionally known as the
274
"aortic nipple". Enlargement of the left superior intercostal vein is easily recognizable on standard chest radiography. Such an occurrence may be due to one of several pathological conditions, such as congestive hearth failure, portal hypertension, the Budd-Chiari Syndrome, obstruction of the inferior or superior vena cava, and finally, agenesis of the AV (Hatfield et at. 1987). In fact, in cases of agenesis of the AV, the HV plays an important role in the hemodynamic supply, draining almost all the right and left intercostal veins. Consequently, this condition increases the venous flow into the left superior intercostal vein above the normal level. so that it drains preferentially into the left brachiocephalic vell1 under a higher pressure gradient. Based upon these physiopathological data, our suggestion is that Radiologists should request a computerized tomograph of the chest to ascertain the possible congenital absence of the AV, whenever an "aortic nipple" is detected on standard radiography. Thus, the clinician might be provided with morphological support for a differential diagnosis between mediastinal pathological lesions and agenesis of the AV. In this way, a more exac1 value for the real incidence of this variant could be ob1ained
275
References Caggiati A, Barberini F (1994) Congenital absence of the azygos vein. 76th Federative International Congress of Anatomy, Lisboa, abstract book, p 183 Corliss CE (1981) Embriologia umana di Patten. Grasso Ed., Bologna 1981 Davis RA, Milloy FJ, Anson BJ (1958) Lumbar, renal and associated parietal and visceral veins based upon a study of 100 specimens. Surg Gyn Obstet 107: 3 - 18 Falla A, Preston FW, Anson BJ (1963) Classification and calibration of the azygos venous system in 100 specimens. Surg Gyn Obstet 112: 405 -412 Galluzzi S (1986) Telecardiogramma, Siena Hatfield MK, Vyborny CJ, MacMahon H, Chessare JW (1987) Congenital absence of the azygos vein: a cause for "Aortic nipple" enlargement. Am J Radiol 149: 273 - 274 Karpowicz S (1934) Une variation de la veine mediane de dos en coincidence avec Ie defaut de la veine azygos. CR Seances Acad Sci 3: 27 -32 MacLure CFW, Butler EG (1925) The development of the inferior vena cava in man. Am J Anat 35: 331 -383 Rogado LQ (1971) Sistema Azygos - Contribuicao para 0 seu estudo anatomico. Thesis, Lisboa Accepted February 1, 1996