Azigos ven sistem anomalisi: olgu sunumu

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Introduction
Abnormalities related to the azygos system are not rare (1). In a series
of 200 cases, Bergman et al. have reported the incidence of this anomaly
26% (2). These abnormalities are generally explained by the embryological development. Venous branching of the azygos vein varies (3). There
are two origins of the azygos and hemiazygos veins. By union of these
origins and regression of some parts, azygos system comes into its final
status (4). Different types of structures may occur when these veins
develop. Abnormalities about azygos system and especially the variations
of the hemiazygos veins are not clearly described in the literature. In this
presentation absence of the accessory hemiazygos vein and possible
causes of these types of variations are discussed in view of the embryological development.
Case Report
During the dissection of the posterior mediastinum of a 60-year-old
male cadaver; it was observed that there was no complete accessory
hemiazygos vein in the azygos vein system, and posterior intercostal
veins drained bilaterally to the azygos vein. Right ascending lumbal vein
formed azygos vein and left ascending lumbal vein formed hemiazygos
vein. After left subcostal vein opened to the hemiazygos vein, hemiazygos vein joined to the azygos vein at the level of T10 vertebra. The 10th
posterior intercostals vein joined to the azygos vein by contacting with
hemiazygos vein. Left 7, 8 and 9th posterior intercostals veins conjugated and opened to the azygos vein after forming one single root (Figure
1). Inferior vena cava and superior vena cava were normal and their
courses were usual.
Discussion
The cardinal venous complex that constitutes the main venous
drainage system of the embryo appears in the third week of intrauterine
growth as two big vessels. These vessels, called anterior cardinal vein and
posterior secondary, drain cranial and caudal part of embryo. These two
* GATA Anatomi AD
**Trakya Üniversitesi Týp Fakültesi Anatomi AD
Ayrý basým isteði: Dr. Necdet Kocabýyýk, GATA Anatomi
AD, Etlik-06018, Ankara
E-mail: nkocabiyik@gata.edu.tr
Makalenin geliþ tarihi: 19.09.2005
Kabul tarihi: 15.06.2006
Gülhane Týp Dergisi 2006; 48: 180-182
OLGU SUNUMU
© Gülhane Askeri Týp Akademisi 2006
Summary
Variations seen in the thoracic vein system are
related to the development of these veins.
During the dissection from the posterior mediastinum of the 60-year-old male cadaver, it
was observed that there was no complete
accessory hemiazygos vein, and both posterior
intercostal veins and hemiazygos vein (above
T10 level) drained bilaterally to the azygos
vein. Considering these types of variations is
important during imaging this region and surgical operations.
Key words: Azygos vein, hemiazygos vein,
superior vena cava, venous anomaly
Özet
Azigos ven sistem anomalisi: olgu sunumu
Toraks ven sisteminde görülen varyasyonlar,
embriyolojik olarak bu venlerin geliþimiyle ilgilidir. Altmýþ yaþýndaki erkek kadavranýn posteriyor mediastenindeki diseksiyon sýrasýnda;
v.hemiazygos accessoria'nýn tam olarak oluþ-
madýðý, iki taraflý posteriyor interkostal venlerin ve v.hemiazygos'un (T10 düzeyinde)
v.azygos'a drene olduðu gözlendi. Bölge ile
ilgili görüntüleme ve cerrahi giriþimlerde bu
tür varyasyonlarýn bilinmesi önem arz eder.
Anahtar kelimeler: vena azygos, vena hemiazygos, vena cava superior, venöz anomaliCilt 48 · Sayý 3 · Gülhane TD Azygos vein system abnormality ·181
veins meet both at two sides and constitute common cardinal vein, which
opens to sinus venosus. In the eight
week of embryo an oblique anastomosis occurs between two anterior
cardinal veins. This connection
becomes left brachiocephalic vein
when the caudal part of left anterior
cardinal vein degenerates. Right anterior cardinal vein and right common
cardinal vein constitute superior vena
cava. The left anterior cardinal and
the left common cardinal veins,
which are in the caudal part of left
brachiocephalic vein are mostly
regressed (4). Left common cardinal
vein constitutes left oblique vein of
atrium (5). The beginning part of the
left superior intercostals vein generates from the cranial point of the
postcardinal vein, and drains second,
third and mostly fourth intercostal
veins. In adults both of posterior cardinal veins constitute the root of
azygos vein and common iliac vein.
The cardinal vein and supracardinal
vein gradually take place of posterior
cardinal vein. Both of the supracardinal veins are the last grown vein
packed. The vein, which is at the left
side of these veins degenerates in the
caudal part of kidney and the vein,
which is at the right side constitutes
postrenal part of inferior vena cava
(4).
The azygos and hemiazygos veins
have two origins (1). The first one is
the terminal part of posterior cardinal
vein, which combines with superior
vena cava, and the second one is the
right supracardinal vein. This embryologic vessel gives rise to right
ascending lumbal vein. The left
ascending lumbal vein is composed of
the left supracardinal vein. The left
superior intercostal vein and accessory hemiazygos vein originate from
the left posterior cardinal vein and
this vein simultaneously forms the
upper part of the azygos vein. The
part that connects hemiazygos vein to
azygos vein is actually remainder of
the anastomosis between the left and
the right posterior cardinal veins (6).
Azygos veins embryologically generate from subcardinal veins. The right
subcardinal vein forms azygos vein
and the left subcardinal vein forms
hemiazygos vein.
A transverse anastomosis is
formed between them approximately
at sixth and seventh thoracal vertebrae in adults. At the left side, cranial
part of this anastomosis is partially
atrophied or it remains as accessory
hemiazygos vein. In our case accessory hemiazygos vein did not exist
due to total regression of the left subcardinal vein and atrophy of veins
forming hemiazygos and accessory
hemiazygos veins that were embryologically above anastomosis of right
and left postcardinal veins because of
this, the left posterior intercostal
veins drained into the azygos vein.
Bergman et al. have reported the
incidence of incomplete formation of
hemiazygos and accessory hemiazygos veins as 15% (2). If the hemiazygos is underdeveloped, its branches
open directly into the azygos vein as
observed by Bergman et al. In the
case we reported there were underdeveloped veins, and the posterior
intercostal veins opened into the azygos vein.
In the case reported by Caggiati
and Barberini, two venous structures
that had to be derived from right
supracardinal veins were not seen (6).
Thus in forming venous structure,
there was no main vessel collecting
right intercostals veins, and venous
drainage was collaterally provided by
the only vessel that was longitudinally moving at the left part. That vessel
opens to superior vena cava from left
(6).
In our case, hemiazygos vein
joined azygos vein at the level of T10
vertebra, so that there was one main
vessel. In Mezzogiorno and Passiatore's case there were both of the
vessels and there was a transverse
connection between them (1). In the
case of Özbek et al. hemiazygos vein
was absent (7). Fifth and sixth left
posterior intercostal veins with third
and fourth opened to left superior
intercostals vein. In the case of Özdemir et al., in addition to absence of
hemiazygos vein, there were superior
intercostal veins that drained this
region and the connection vein with
the azygos and accessory hemiazygos
veins (8). In both of the cases azygos
vein opened to superior vena cava.
Cossina et al. have reported two
azygos veins that continue with inferior vena cava (9). This case can be
accounted for by embryological persistence of both supracardinal veins.
Continuing with inferior vena cava of
azygos system is associated with the
anomalies of superior vena cava and
azygos system, congenital heart disease, aspleny and polispleny syndromes, and abdominal situs anomalies (10-12). Congenital heart disease
should be searched in cases with this
kind of anomaly.
Figure 1. Azygos and hemiazygos veins. AV,
azygos vein; SVC, superior vena cava; HV,
hemiazygos vein; (6,7,8,9,10), posterior intercostal veins182 · Eylül 2006 · Gülhane TD Kocabýyýk ve ark.
It is important to determine the
variations of the azygos system especially in the computed tomography
and magnetic resonance imaging of
mediastinum. The anomalous azygos
venous system may easily be confused with aneurysm, lymphadenopathy and other anomalies like tumor
(7,13,14). It is important to keep in
mind this kind of variations in the
mediastinal operations or surgery of
large vessels.