Venae comitantes of the superior gluteal artery. These veins enter the pelvis through the greater sciatic foramen, above the muscle piriformis, and join the internal iliac vein as a single trunk.

Venae comitantes of the inferior gluteal artery. These veins arise proximal and posteriorly in the thigh and anastomose with the medial circumflex femoral and first perforating veins. They enter low in the greater sciatic foramen, joining the internal iliac vein, and connect with the superficial gluteal veins through the gluteal perforating veins.

Venae comitantes of the internal pudendal artery, commencing in the prostatic venous plexus and ending in the internal iliac vein. These receive veins from the penile bulb and the scrotal (or labial) and inferior rectal veins. The deep dorsal vein of the penis ends in the prostatic plexus, but is connected through that plexus to the internal pudendal veins.

This vein commences in the proximal adductor region and enters the pelvis through the obturator foramen, coursing a retroperitoneal path, passing between the ureter and the internal iliac artery to join the internal iliac vein.

These veins are interconnected by the sacral venous plexus and follow the lateral sacral arteries.

This vein arises from the rectal venous plexus, receiving tributaries from the bladder, prostate, and seminal vesicle.

The rectal venous plexus surrounds the rectum and is connected anteriorly to the vesical plexus in males and to the uterovaginal plexus in females. It has an internal rectal plexus, under the rectal and anal epithelium, and an external rectal plexus outside the muscular layer. In the anal canal, the internal plexus has longitudinal dilations, most prominent in the left lateral, right anterolateral, and right posterolateral sectors. These veins are apt to become varicose and will be known as
internal hemorrhoids. The internal plexus drains mostly to the superior rectal vein but connects extensively with the external rectal plexus. The external rectal plexus drains inferiorly by the inferior rectal veins, a tributary of the internal pudendal vein. The external rectal plexus drains in the middle to a middle rectal vein, a tributary of the internal iliac vein. The superior rectal vein is the beginning of the inferior mesenteric vein and drains the superior part of the external rectal plexus. The veins in the subcutaneous part of the external rectal plexus may thrombose and form the so-called external hemorrhoids.

The wide anastomoses between the rectal venous plexus and the internal iliac vein, as well as with the inferior mesenteric vein, establish communication between the portal and systemic venous systems.

The periprostatic venous plexus is composed of a superficial and a deep plexus. The deep plexus is popularly known as Santorini plexus. The periprostatic plexus is originated from the deep dorsal vein of the penis, when this vessel leaves the penis under the Buck fascia, and penetrates the pelvis passing under the symphysis of the pubis. After penetrating the pelvis, the vein divides into three major branches: the superficial branch and the right and left deep lateral venous plexuses (Figs. 20.6, 20.7). The superficial branch is centrally located and emerges in the retropubic adipose tissue between the pubic–prostatic ligaments, overlying the bladder neck and the prostate (Figs. 20.8, 20.9). This vein often has communicating branches over the bladder and into the endopelvic fascia (Fig. 20.8). Mostly (80% of cases), this vein is really a single midline vessel, presenting early or late bifurcation in 20% of cases. In 10% of cases this superficial vein may be double or may have other anatomic variations. In 10% of cases, the superficial vein is absent.

The lateral venous plexuses (deep plexus, Santorini) pass posterolaterally, beneath the visceral or preprostatic fascia (Figs. 20.10, 20.11, 20.12) and communicate freely with the internal iliac vein (hypogastric vein) through the pudendal, obturator, and vesical venous plexuses. The deep venous plexus (Santorini plexus) can be visualized in dissected specimens only after opening the endopelvic fascia and its right and left condensations, which unite the prostate to the dorsal surface of the pubis (the so-called “pubic–prostatic ligaments”) (Figs. 20.10, 20.11, 20.12).

Because the lateral plexuses (deep plexus) anastomose freely with other pelvic plexuses, any laceration of this structure can lead to considerable blood loss during any kind of retropubic surgery. In addition, although the periprostatic plexus communicates with the paravertebral venous network (Batson plexus), osseous metastases constitute the most common form of hematogenous metastasis of prostatic carcinoma, which occurs through this paravertebral plexus. The most frequent sites involved are the pelvic bone, lumbar spine, femora, thoracic spine, and ribs.

The vesical plexus covers the lower bladder and the prostatic base in males and is connected to the prostatic venous plexus in males and to the vaginal venous plexus in females. It is drained by several vesical veins, tributaries of the internal iliac vein.

There is a superficial and a deep dorsal vein of the penis. The superficial dorsal vein of the penis drains the prepuce and skin, and is positioned longitudinally along the penis, draining to the external pudendal veins. The superficial dorsal vein of the penis receives, along its course, flow from the corpora cavernosa penis through circumflex veins. The deep dorsal vein of the penis runs backward in the midline, under the fibrous penile sheath. It receives blood flow from the glans penis and corpora cavernosa penis, through the circumflex veins. It reaches the prostatic venous plexus after dividing into right and left branches, but has also communications with the internal pudendal veins (Figs. 20.11, 20.18, 20.19, 20.20, 20.21, 20.22, 20.23, 20.24). The deep dorsal vein of the penis has a venous valve beneath the symphysis pubis.

The superficial venous system of the penis including the superficial dorsal vein drains into the superficial femoral vein through the external pudendal vein and the saphenous vein (Figs. 20.25, 20.26, 20.27, 20.28).

The corpora cavernosa penis is formed by sinusoids surrounded by smooth muscle and connective tissues with high wall tonus. The sinusoidal vascular space and arterial inflow are limited in the flaccid state. The venous outflow is unimpeded. During erection, after neurostimulation or intracavernosal papaverine injection, the sinusoidal smooth muscle relaxes, and distended sinusoids compress and obstruct peripheral venules against tunica albuginea. Simultaneously, resistance to arterial flow decreases until cavernosal pressure approaches systolic pressure (Chapter 19, Fig. 19.18).

The crura of the corpora cavernosa penis are drained by crural perforating veins, which are tributaries of the internal pudendal veins (Fig. 20.13).

The uterine venous plexus extends laterally in the broad ligaments, communicating with the ovarian and vaginal plexuses. The uterine plexus is drained by the uterine vein, which is a tributary of the internal iliac vein (Figs. 20.29, 20.30a).

The vaginal plexuses connect with the uterine, vesical, and rectal plexuses and are drained by vaginal veins to the internal iliac veins.

The left common iliac vein may ascend left of the aorta to the level of the left renal vein, where it crosses anterior to the aorta to join the inferior vena cava.

The median sacral veins are companions of the median sacral artery, anterior to the sacrum, joining into a single vein and ending in the left common iliac vein or at the junction of the common iliac veins (Figs. 20.1, 20.4).

A number of anomalies may occur during the development phase of the inferior vena cava in fetal life. The vein may be totally replaced by two or more vessels, with failure of interconnection between the common iliac veins and persistence of a longitudinal channel on the left, supracardinal, or subcardinal veins. It may also undergo a complete transposition to the left of the aorta.

There is a rich collateral venous network bypassing the inferior vena cava in cases of thrombosis or occlusion, either through a superficial or deep venous network. The superficial system includes the epigastric veins, the circumflex iliac, the lateral thoracic veins, the thoracoepigastric, the internal thoracic, the posterior intercostal, the external pudendal, and lumbovertebral anastomotic veins. The deep system includes the azygos vein, the hemiazygos, and the lumbar veins. The vertebral venous plexus, including the Batson venous plexus, is also in the collateral venous circuit (Figs. 20.33, 20.34).

There are four pairs of lumbar veins, draining the lumbar muscles and skin from the abdominal wall. The lumbar veins also drain the vertebral venous plexuses and are connected by the ascending lumbar veins. The left-side lumbar veins are longer and cross behind the abdominal aorta. The first and second lumbar veins may connect to the inferior vena cava, the ascending lumbar veins, or the lumbar azygos vein (Figs. 20.1, 20.33, 20.35).

The ascending lumbar veins originate from the common iliac veins and make connections between the common iliac veins to the iliolumbar and lumbar veins. They ascend behind the psoas major muscles and in front of the vertebral transverse processes. Cranially they join the subcostal veins and turn medially, forming the azygos vein in the right side and the hemiazygos vein on the left (Fig. 20.35).

There is a rich venous network around the kidneys, draining the renal capsule and with anastomoses between the intrarenal venous system and the capsular veins. The perirenal veins drain into the gonadal vein, inferior phrenic vein, and suprarenal veins. There are direct anastomoses directly with the main renal vein and with the ureteric veins (Figs. 20.1, 20.47).

There is only one draining adrenal vein for each adrenal hilum. The right adrenal vein is short and small, and opens directly and horizontally into the lateroposterior aspect of the inferior vena cava, far above the right renal vein (Figs. 20.48, 20.49, 20.50).

The left adrenal vein is longer and larger, and descends from the adrenal gland posteriorly to the body of the pancreas to open into the left renal vein, joined by a branch of the left inferior phrenic vein, about 1 cm from the inferior vena cava (Figs. 20.50, 20.51, 20.52).

Angiographically the hepatic veins of the lower group may be mistakenly identified as the right adrenal vein (Fig. 20.53). Occasionally the right adrenal vein drains into one of the small hepatic veins of the lower group.

The inferior phrenic veins follow the same distribution as that of the companion inferior phrenic arteries on the lower diaphragmatic surface. The right inferior phrenic vein ends in the inferior vena cava, above or together with the right hepatic vein. The left is frequently double and one branch opens in the inferior vena cava or together with the left hepatic vein, whereas the other may join the left adrenal vein or the left renal vein (Fig. 20.54, and Chapter 18, 18.138, 18.139).

The hepatic veins drain the liver parenchyma and start as interlobular veins, draining the sinusoids of the hepatic lobules. According to the classical description, these end at the sublobular veins, which will drain into the hepatic veins? The hepatic veins are valveless and are contiguous with the hepatic tissue.

There are three main hepatic veins emerging from the upper, posterior surface of the liver, opening at the inferior vena cava, and an individual vein from the caudate lobe (Figs. 20.55, 20.56, 20.57). These are called the upper group, which consists of the large, right, middle, and left hepatic veins, and the smaller caudate lobe vein, delineating four well-defined territories of drainage (Figs. 20.55, 20.56, 20.57, 20.58).

The right hepatic veins run at the right hepatic fissure, which divides the right hepatic lobe in the anterior and the posterior sectors. The right hepatic vein drains both the anterior (segments VIII and V) and the posterior (segments VI and VII) sectors of the right hepatic lobe (Fig. 20.55).

In 16 of 25 casts of liver specimens, there was only one right hepatic vein of large diameter receiving several tributaries from the several segments of the right lobe (Figs. 20.59, 20.60

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