Venous Drainage of the
Abdomen
The main collecting vessels
of the abdomen are the inferior vena cava and the hepatic portal vein. The
hepatic portal vein drains to the liver and it originates from smaller veins
that drain the alimentary tract, its associated glands, and the spleen. Here we
will focus on the inferior vena cava and its tributaries, starting with the
superficial veins that drain the anterolateral abdominal wall. Please note that
these veins accompany the arteries of the same name, mostly in duplicate (venae
comitantes) on both sides of the artery, being enwrapped in the same sheath.
The external pudendal vein, aside from branches originating from
the region above the symphysis pubis, receives the venous blood from the
external genitalia (superficial dorsal vein of the penis or clitoris and
the sub- cutaneous veins of the scrotum or labia majora), and joins, in
many instances, the great saphenous vein or the femoral vein. The
superficial epigastric and superficial circumflex iliac veins, draining
the medial and lateral parts of the lower abdominal wall, respectively, pass
superficial to the inguinal ligament and, piercing the cribriform fascia, enter
the femoral vein (in other instances, the great saphenous vein). In the body’s
midaxillary line the superficial veins of the upper and lower halves of the
trunk communicate through the thoracoepigastric veins, which unite in
the axilla with the lateral thoracic veins, each a branch of an axillary
vein. This system of anastomosis plays an important role in the event of an
obstruction of the superior or inferior vena cava. The thoracoepigastric veins
receive numerous tributaries from the surrounding superficial fascia as well as
veins emerging from the lateral aspect of the mammary gland.
Another collateral venous circulation of clinical significance comes
about through the superficial supraumbilical and infraumbilical veins, which,
by means of five or six paraumbilical veins arising from the integument
and the musculoaponeurotic structures or the abdominal wall, course within the
ligamentum teres and enter the left branch of the portal vein. When portal
venous pressure rises in liver cirrhosis, the paraumbilical veins establish
collaterals with the superior and inferior epigastric and thoracoepigastric
veins, and become enlarged and tortuous, assuming a radial pattern known as the
caput medusae (head of Medusa).
The two deeper veins that drain the anterolateral abdominal wall are the inferior
epigastric and deep circumflex iliac veins, both of which enter the
external iliac vein (the continuation of the femoral vein) after having drained
the same regions supplied by the corresponding arteries. This network of
anastomoses, including the musculophrenic and superior epigastric veins,
likewise conforms to the location of the arteries. The external iliac vein, beginning
posterior to the inguinal ligaments, courses with its homonymous artery
superiorly along the brim of the lesser pelvis to unite with the internal iliac
vein anterior to the sacroiliac joint to form the common iliac vein.
The internal iliac vein collects the blood from all pelvic
structures, except the upper part of the rectum and the sigmoid colon, which
drain to the portal system via the inferior mesenteric vein, and the ovaries
and testes, which reach the inferior vena cava directly via the gonadal veins.
Starting near the superior part of the greater sciatic foramen and ascending
over the piriform and psoas major muscles, the internal iliac vein receives the
superior and inferior gluteal, internal pudendal, obturator, lateral
sacral, middle rectal, and superior vesical veins.
Many of these vessels have their origins in a rich venous plexus, such as
the pudendal, urethrovesical, and uterovaginal plexuses.
The common iliac veins continue along the course of the external
iliac veins in a median direction until the left vein meets the right vein,
marking the starting point of the inferior vena cava. The left common iliac
vein, often somewhat longer than its
right counterpart, receives the middle sacral vein when this unpaired vessel
does not enter (as it does frequently) the angle of the two iliac veins. Both common iliac veins receive the iliolumbar
veins and, in some instances, the lateral sacral veins, if the latter have
not entered the internal iliac vein or have not joined the fifth lumbar vein.
The inferior vena cava commences at the right of L5, ascends along
the aorta anterior to the vertebral column, and continues posterior to the
liver in a groove between the bare area and the caudal lobe. Immediately after
the inferior vena cava receives the three hepatic veins (draining the liver),
the inferior vena cava leaves the abdomen through the diaphragm’s caval
hiatus in the central tendon. Because the caval hiatus lies superior to the
aortic hiatus and the union of the two common iliac veins is inferior to the
aortic bifurcation, the inferior vena cava in the abdomen is about 7 to 8 cm
longer than the abdominal aorta. The first veins to enter the inferior vena
cava are the lumbar veins. The lowest (fifth) lumbar vein empties to the
iliolumbar vein, whereas the upper four lumbar veins, lying on the bodies of
the vertebrae and accompanying the arteries, drain into the posterior wall of
the inferior vena cava but may drain to the azygos or hemiazygos veins. The
connections that the lumbar veins make with the renal, suprarenal, gonadal, deep
circumflex, iliac, and other abdominal veins are manifold. The most important
concerns the longitudinal anastomosis effected through the ascending lumbar
veins. These veins, beginning in the pelvis as a continuation of the
lateral sacral veins, ascend deep in the sulcus between the tendinous origins
of the psoas major muscle and the bodies and transverse processes of
the vertebrae; after
receiving branches from the
lumbar veins, the right ascending lumbar vein drains into the azygos and the
left into the hemiazygos, or sometimes into the left renal vein. Posteriorly,
the ascending lumbar veins make numerous connections with the valveless veins
of the vertebral venous system and thus bring the caval system into
relationship with the veins of the spine, spinal cord, dura mater, vertebrae,
and brain. These relationships provide an explanation for the spread of
infections, tumors, and thrombi from the pelvis, abdomen, or thorax into the
central nervous system, or bones of the skull and spine.
The right gonadal (testicular or ovarian) vein enters the inferior
vena cava superior to the lumbar veins, whereas the left gonadal vein usually
merges with the left renal vein, or possibly the suprarenal vein, or one of the
lumbar veins. The testicular veins, starting from the pampiniform plexus in the
spermatic cord, ascend along the ductus deferens, pass through the inguinal
canal, and, following the artery, course superiorly on the psoas major muscle. The ovarian veins, derived
from the uterovaginal and ovarian plexuses, take a similar course. The large renal
veins lie anterior to the corresponding arteries and show much less
variation than the renal arteries. The right renal vein rarely receives
tributaries, whereas on the left side, supernumerary veins such as the left
gonadal and suprarenal veins typically join the vessel. The right suprarenal
vein usually terminates with a direct connection with the inferior vena
cava and, occasionally, right renal
vein. The left suprarenal vein typically drains into the left renal or inferior
phrenic vein.
Superior to the hepatic veins are the uppermost tributaries of the
inferior vena cava, the inferior phrenic veins, which generally follow
the course of the homonymous arteries. The left one may join the left renal
vein separately or via a common trunk with the left suprarenal vein (5%).
