Chapter 32: Blood vessels, nerves and lymphatic drainage of the pelvis
Blood vessels
The internal iliac (hypogastric) artery supplies most of the blood to the pelvis (figs. 32-1 and 32-2). It arises from the common iliac artery in front of the sacro-iliac joint. Although the internal iliac artery is often described as ending in anterior and posterior divisions, its various branches arise in a variable manner. They may be divided into parietal and visceral branches.
Parietal branches.
The parietal branches of the internal iliac artery include the iliolumbar, lateral sacral, obturator, superior and inferior gluteal, and internal pudendal arteries. The iliolumbar artery supplies bone and muscle in the iliac fossa. The lateral sacral arteries, which give off spinal branches, supply the sacrum and coccyx. The obturator artery, which is crossed by the ureter, descends and traverses the obturator foramen. It divides into anterior and posterior branches, which encircle the margin of the obturator foramen; an acetabular branch supplies the ligament of the head of the femur. The obturator artery may arise from the inferior epigastric artery (see fig. 25-9) and, if it passes medial to the femoral ring, it is liable to damage during an operation for femoral hernia. The superior and inferior gluteal arteries pass backward between the sacral nerves and leave the pelvis through the greater sciatic foramen, running superior and inferior to the piriformis, respectively.
The internal pudendal artery (fig. 32-3) descends to the greater sciatic foramen, through which it leaves the pelvis. It then crosses the back of the ischial spine and enters the perineum through the lesser sciatic foramen. Next, accompanied by the branches of the pudendal nerve, it traverses the pudendal canal in the lateral wall of the ischiorectal fossa. Finally, it pierces the urogenital diaphragm, traverses the deep perineal pouch, and divides into the deep and dorsal arteries of the penis (or clitoris). The branches of the internal pudendal artery include the inferior rectal artery and vessels that supply the scrotum (or labia), perineum, bulb of the penis (or vestibule), and urethra.
Visceral branches.
These include the umbilical and superior and inferior vesical arteries, the uterine artery (or the artery of the ductus deferens), and the vaginal and middle rectal arteries. The umbilical arteries return deoxygenated blood in the fetus from the aorta to the placenta. The distal part of each umbilical artery becomes the medial umbilical ligament, whereas the proximal part remains patent and gives rise to some of the next branches. The superior and inferior vesical arteries supply the bladder, and the middle rectal artery supplies the rectum.
The uterine artery (see fig. 35-9), comparable to the artery of the ductus deferens, may arise separately or in common with other branches of the internal iliac artery. It descends to the lower part of the broad ligament, where it lies near the lateral fornix of the vagina. It crosses in front of the ureter and ascends along the body of the uterus, between the layers of the broad ligament. Near the uterine tube, it turns laterally and anastomoses with the ovarian artery. Its branches supply the vagina, uterus, and tube. The vaginal artery (see fig. 35-9) arises from the uterine artery or from the internal iliac artery and gives branches to the front and back of the vagina.
The internal iliac (hypogastric) vein lies behind its artery, and its tributaries correspond mostly with the branches of the artery.
Nerves
The pelvis is innervated chiefly by the sacral and coccygeal spinal nerves and by the pelvic part of the autonomic nervous system.
Sacral and Coccygeal Plexuses.
The sacral plexus (fig. 32-4), which lies in front of the piriformis, supplies the buttock and lower limb as well as structures belonging to the pelvis. It is formed by the lumbosacral trunk, the ventral rami of S1 to 3, and the upper division of S4 (see fig. 30-6). The rami are connected to sacral sympathetic ganglia by rami communicantes. The gluteal vessels pass between the rami of the plexus. The largest branch of the plexus is the sciatic nerve.
The pudendal nerve (S2 to 4) supplies most of the perineum
(see figs. 32-2
and 32-3).
It contains motor, sensory (pain and reflex), and postganglionic
sympathetic fibers, and it may be "blocked" medial to the ischial
tuberosity, e.g., during parturition. The pudendal nerve traverses the
greater sciatic foramen below the piriformis, crosses the back of the
ischial spine, and enters the perineum through the lesser sciatic
foramen. It traverses the pudendal canal in the lateral wall of the
ischiorectal fossa, gives off the inferior rectal nerve, and divides
into the perineal nerve and the dorsal nerve of the penis (or
clitoris). The perineal nerve divides into a deep branch to perineal
muscles and a superficial branch to the scrotum (or labium majus).
The coccygeal plexus (S4, 5; Co 1) supplies the skin over the coccyx.
The pelvic splanchnic nerves.
The pelvic splanchnic nerves (S2 to 4) contain parasympathetic preganglionic and sensory fibers. They help to form the inferior hypogastric plexus and thereby supply the sigmoid colon.
Pelvic Part of Autonomic Nervous System.
Sympathetic fibers reach the pelvis by downward continuations of the sympathetic trunks and of the aortic plexus (fig. 32-5).
In front of the sacrum, the sympathetic trunks consist largely of preganglionic fibers and present three or four ganglia each. The two trunks meet in front of the coccyx, where they may form an enlargement termed the ganglion impar. The ganglia on the trunk are connected with the spinal nerves by rami communicantes, which transmit postganglionic fibers chiefly to the lower limbs and perineum.
The aortic plexus is continued as the superior hypogastric plexus (or "presacral nerve"; see figs. 30-4 and 32-6), which divides in front of the sacrum into right and left inferior hypogastric nerves. These descend on the sides of the rectum and vagina and unite with the pelvic splanchnic nerves to form the right and left inferior hypogastric plexuses (fig. 32-6), which give branches to the pelvic viscera (e.g., the rectum, bladder, and uterus). The inferior hypogastric plexuses contain: (1) postganglionic sympathetic fibers; (2) preganglionic parasympathetic fibers, which arise from the sacral part of the spinal cord, travel in the pelvic splanchnic nerves to the inferior hypogastric plexus, and supply the descending and sigmoid colon and the pelvic viscera; and (3) sensory fibers, including pain fibers (many of which travel in the lumbar splanchnic nerves) and reflex fibers from the bladder (which ascend in the pelvic splanchnic nerves).
Lymphatic drainage
Most of the lymphatic vessels from the pelvis drain into groups of nodes associated with the iliac arteries and their branches (see figs. 30-3 and 32-7). External iliac lymph nodes receive vessels from the inguinal nodes, external genitalia, vagina, and cervix; they drain into the common iliac nodes. Internal iliac and sacral lymph nodes receive afferents from all the pelvic viscera (e.g., cervix, prostate, and rectum) and from the perineum, buttock, and thigh; they drain into the common iliac nodes. Common iliac lymph nodes drain the two preceding groups and send their efferents to the lumbar group of aortic nodes, which also receives the afferents of the testis and ovary.
The cervix drains chiefly into the external and internal iliac nodes, the body of the uterus mainly into the external iliac and lumbar nodes. The prostate drains principally into the internal iliac nodes, and the bladder into the external iliac. The upper part of the rectum drains into the inferior mesenteric nodes, the lower part (together with the upper part of the anal canal) into the internal iliac nodes. The lower part of the anal canal, as also the external genitalia, drains into the inguinal nodes.
Questions
32-1 Which artery supplies most of the pelvis?
32-2 What is the course of the umbilical artery?
32-3 Which nerve supplies most of the perineum?
32-4 What are the pelvic splanchnic nerves?
32-5 What is the lymphatic drainage of the colon, rectum, and anal canal?
Figure legends
Figure 32-1 Lumbar aortagram (From Abrams, H.L., ed., Angiography, Little, Brown, Boston, 1961. Courtesy of S.M. Rogoff, M.D.)
Figure 32-2 A, The sacral plexus and branches of the internal iliac artery, medial aspect. B, The most frequent pattern of branches of the internal iliac artery.
Figure 32-3 A, The internal pudendal artery and pudendal nerve. B, An almost sagittal section through the lateral part of the perineum.
Figure 32-4 The sacral plexus and its main branches (after Pitres.)
Figure 32-5 The sympathetic trunks. Preganglionic rami communicantes are shown as interrupted lines, postganglionic rami as solid black lines. (After Pick and Sheehan.)
Figure 32-6 Highly simplified scheme of the sympathetic trunks and ganglia and of the autonomic plexuses in the abdomen and pelvis.
Figure 32-7 Iliac lymphogram, showing inguinal as well as iliac nodes. large efferent vessels are visible. (From Kinmouth, J.B., The Lymphatics, Arnold, London, 1972.)