Posterior Abdominal Wall; Autonomics and Lymphatics of the Abdomen by fdh56iuoui

VIEWS: 28 PAGES: 8

									              Posterior Abdominal Wall; Autonomics and
                      Lymphatics of the Abdomen
                          November 21, 2003

Osteology of the Posterior Abdominal Wall—Dr. Davies did a brief review of the
osteology in the posterior abdominal wall. Specifically, he pointed out the large bodies
of the lumbar vertebrae, the intervertebral discs, the sacral promontory and foramina, the
iliac crest, iliac fossa, sacroiliac joint, and iliopubic eminence. He also noted the greater
and lesser trochanter of the femur. (Netter 240, 152)

He also pointed out the lumbar spinal nerves which pass through the intervertebral
foramina. The dorsal root ganglia are within each intervertebral foramen and the dorsal
and ventral rami protrude outward. If a lumbar disc protrudes outward, it usually affects
the nerve that exits below the disc. For example, the protrusion of the disc between L4-
L5 affects the L5 spinal nerve, not the L4 one (Netter 152, 154).

Muscles of the Posterior Abdominal Wall—The paired muscles of the posterior
abdominal wall are listed in Table 2-12 on p. 300 (Netter 478).

       Psoas major muscle—This is a long, thick fusiform muscle found lateral to the
       lumbar vertebrae. The origin of this muscle is the sides of vertebral bodies,
       intervertebral discs, and transverse processes of L1-L4. It passes inferolaterally
       deep to the inguinal ligament to insert on the lesser trochanter of the femur. This
       muscle is innervated by the lumbar plexus by the ventral branches of L2-L4
       nerves. It is supplied by the subcostal and lumbar arteries. Its actions include:
       works with iliacus to flex the thigh (when standing), flexes trunk (when sitting),
       flexes the vertebral column laterally (by unilateral contraction, assisted by the
       quadratus laborum), and balances the trunk.

       Psoas minor muscle—When present, this muscle is a thin band of muscle fibers
       with a long tendon. The psoas minor originates on the bodies of the T12 and L1
       vertebrae and its tendon inserts on the iliopubic eminence. It is innervated by
       the branches of the ventral primary rami of spinal nerves L1-L2 and is supplied
       by lumbar arteries. The action of psoas minor is to laterally bend and flex the
       lumbar vertebral column.

       Iliacus muscle—The iliacus is a large triangular muscle found lateral to the
       inferior portion of psoas major. It originates on the superior 2/3 of the iliac fossa
       and inserts with psoas major via an iliopsoas tendon on the lesser trochanter of
       the femur. It is innervated by the femoral nerve and supplied by the iliolumbar
       artery. The iliacus muscle acts with the psoas muscles in flexing the thigh. It
       also stabilizes the hip joint.

       Quadratus lumborum—The quadratus lumborum is a thick muscular sheet
       adjacent to the lumbar transverse processes. It originates on the posterior part of
       the iliac crest and inserts on the medial 2/3 of the 12th rib. This muscle is
       innervated by the subcostal nerve and the ventral primary rami of spinal nerves
       L1-L4. It is supplied by the subcostal and lumbar arteries. The quadratus lumbar
       muscle is crossed anteriorly by the lateral arcuate ligament of the diaphragm. Its
       action is to laterally bend the trunk. It also fixes the 12th rib in place.

       Transversus abdominis—The transverses abdominis muscles are continuous
       with the transverses thoracic muscles discussed in a previous lecture.

Nerves of the Posterior Abdominal Wall—The posterior abdominal wall is the site of
many somatic nerves (Netter 478):

       Subcostal nerves are located inferior to the 12th rib and arise from the ventral
       primary rami of T12. These nerves past posterior to the lateral arcuate ligament
       and run inferolaterally on the anterior surface of quadratus laborum. In addition
       to supplying the quadratus lumborum and psoas major muscles, the subcostal
       nerves penetrate the transverses abdominis to supply the skin of the anterolateral
       abdominal wall.

       The lumbar plexus of nerves is located anterior to the transverse processes of the
       lumbar vertebrae and in the posterior aspect of the psoas major muscle. The
       nerve network is composed of the ventral primary rami of L1-L4 spinal nerves.
       The nerves of the lumbar plexus supply the muscles and skin of the lower
       abdominal wall. It has many branches which will be described below (Netter
       479)

       The lateral femoral cutaneous nerve (contributions from L2, L3) crosses
       inferolaterally on the iliacus muscle and enters the thigh posterior to the inguinal
       ligament beside the anterior superior iliac spine.

       The iliohypogastric and ilioingual nerves (from L1) are found between the
       subcostal and lateral femoral cutaneous nerves. The iliohypogastric is the more
       superior nerve and the ilioinguinal nerve is the more inferior one. These can
       come off of a common nerve and both enter the transverses abdominis muscle and
       course anteriorly.

       The genitofemoral nerve (from L1, L2) is found on the anterior surface of the
       psoas major muscle. It runs inferiorly deep to the psoas fascia and divides into
       femoral and genital branches lateral to the external iliac arteries.

       The femoral nerve (from L2-L4) is a large nerve that is located in a fissure
       between the psoas major and iliacus muscles. It passes under the inguinal
       ligament lateral to the femoral artery to supply the flexors of the hip and extensors
       of the knee.

       The obturator nerve (from L2-L4) emerges from the medial border of the psoas
       major and passes through the obturator canal (within the obturator foramen) to the
       medial thigh to supply the adductor muscles. It will come through a groove on
       the deep aspect of the pubic bone on its way to the thigh.

       The lumbosacral trunk comes from part of the ventral primary ramus of L4
       along with the ventral primary ramus of L5. It passes over the wing of the sarum
       and descends into the pelvis to become part of the sacral plexus.

Netter 469 shows the obturator foramen. It is mostly filled in by a strong CT
membrane called the obturator membrane. A small portion of the obturator foramen is
not filled in by the obturator membrane. This is called the obturator canal and through
it passes the obturator nerve and artery. This plate in netter also shows the lesser
trocanter of the femur, which is the insertion site of the psoas major and iliacus muscles.

Respiratory Diaphragm—The diaphragm is a dome shaped partition that separates the
thorax from the abdomen. The diaphragm is a chief muscle of inspiration. During
inspiration, the central portion of the diaphragm descends. The peripheral portions are
fixed to the superior lumbar vertebrae and the inferior margin of the thoracic cavity so
they do not move during inspiration.

The muscle fibers of the diaphragm converge radially to a central aponeurosis called the
central tendon. It is close to the anterior part of the thorax. The terminal part of the
IVC passes through the central tendon to enter the heart. The site where it perforates the
central tendon is called the caval foramen or hiatus. This opening is important because
one would not want there to be muscular contractions around the central hiatus. During
contraction of the diaphragm, the central tendon is pulled away from the IVC. The IVC
passes through at about the T8 vertebral level.

The remaining muscular portion of the diaphragm is a continuous sheet divided into three
regions. The sternal part consists of two muscular slips that attach to the posterior
aspect of the xiphoid process. The costal part consists of muscular slips that attach to
the internal surfaces of the six inferior ribs and their costal cartilages. The left and right
domes of the diaphragm are formed from the costal parts of the diaphragm. The lumbar
part of the diaphragm arises from the medial and lateral arcuate ligaments and the three
superior lumbar vertebrae. The medial arcuate ligament is an arching ligament that
passes/arches over the psoas major muscle. The lateral arcuate ligament is an arching
ligament that passes over the quadratus lumborum muscle. The lumbar part forms the
right and left muscular crura of the diaphragm. The right crus is larger and longer than
the left crus. The right crus arises from L1-L4 while the left crus arises from L1-L3.
The crura are pierced by the greater thoracic splanchnic nerves. The esophagus, its
associated vessels, and the vagal trunks pass through the esophageal hiatus which is
formed in the right crus at the T10 vertebral level. The aorta passes through an aortic
hiatus at the T12 vertebral level. The hiatus is formed by the right and left crura and the
medial arcuate ligament. (Netter 189, 256, 257 and p. 294 COA figure 2.71)

There are several structures which pass posterior to the diaphragm. As mentioned
above, the aorta passes posterior to the diaphragm via the aortic hiatus. The thoracic
duct, psoas major, quadratus lumborum, and azygous veins also pass posterior to the
diaphragm.

Blood supply and Nerves to the Diaphragm—The superior surface of the diaphragm is
supplied by the pericardiophrenic, musculophrenic, and superior phrenic arteries. The
pericardiophrenic and musculophrenic arteries are branches of the internal thoracic
artery. The superior phrenic artery arises from the thoracic aorta. The inferior phrenic
artery arises from the thoracic aorta. The inferior surface of the diaphragm is supplied by
the inferior phrenic artery which usually arises from the aorta, but can sometimes come
from the celiac trunk (Netter 189, 256,257).

The diaphragm is innervated by the phrenic, intercostal, and subcostal nerves. The entire
motor supply for the diaphragm comes from the pair of phrenic nerves. These nerves
descend from C3-C5 (“C3,4, 5 keeps the diaphragm alive”) and spread out along the
inferior aspect of the diaphragm. They also supply sensory fibers to the diaphragm. The
peripheral portions of the diaphragm have afferent fibers of the intercostal nerves and
the subcostal nerve. These afferent fibers carry sensory information from the diaphragm
to the CNS (Netter 189, 190).

Since contraction of the diaphragm is stimulated by the phrenic nerve, transaction of this
nerve can affect contraction. For the example shown on p. 294 in COA, if the right
phrenic nerve is cut, then the right hemidiaphrgam (right half of the diaphragm) will not
be able to contract. As a result, the right hemidiaphragm would remain in a higher
position during respiration than it would if the phrenic nerve were intact. Paralysis of
part of the diaphragm can also occur if there is a spinal cord injury above C3, C4, and C5.

The posterior abdominal wall is supplied by the subcostal and abdominal arteries. It is
drained by the subcostal, lumbar, and ascending lumbar veins.

Lymphatics of the Posterior Abdominal Wall and the Abdomen—Dr. Davies showed
Netter 305, 258, and 306 to demonstrate the different types of lymphatics within the
abdomen and the posterior abdominal wall. All of the body’s lymphatics (except the
right upper body quadrant) drain into the thoracic duct. It is the largest of lymphatic
vessel which originates in an expanded area within the abdomen called the cisterna
chyli. The cisterna chyli is found between the abdominal aorta and the IVC anterior to the
body of L1 or L2 vertebrae. The thoracic duct passes from the cisterna chyli superiorly
and through the aortic hiatus to the right of the aorta. It then crosses over to the left side
of the esophagus at the level of the sternal angle.

The common iliac lymph nodes occur along the iliac vessels and over the sacral
promontory. They drain the lower limb and the lower part of the anterior abdominal
wall. There are usually about six of these. They drain into the lumbar chain of lymph
nodes. The lumbar nodes are found along the IVC and abdominal aorta (from the aortic
bifurcation to the aortic hiatus). These drain the lower limbs, anterior and posterior
abdominal wall, kidneys, suprarenal glands, diaphragm, pelvic organs, and perineum.
The lumbar nodes unite to form the thoracic duct and its inferior swelling, the cisterna
chyli.
The abdomen is drained by parietal and visceral lymph nodes. The visceral lymph
nodes are named according to the vessels that they follow. In the case of the abdomen,
lymph nodes follow arterial flow, not venous flow (ex. celiac nodes, superior mesenteric
nodes, etc.) The parietal lymph nodes include the epigastric and lumbar nodes.

Autonomic Nerves of the Abdomen—The autonomic nerves of the abdomen consist of
a cranial nerve and several splanchnic nerves which carry sympathetic and
parasympathetic fibers (AKA presynatpic) to the nerve plexuses surrounding the
abdominal aorta and to those that travel to the viscera. Dr. Davies used Netter 308, 390
in lecture. Also, there was a handout provided at lecture with a summary of the
autonomics of the thorax and abdomen and their general effects on autonomic
innervation. I am sure that it will be more useful than what I put below, but here it goes:

Sympathetic nerves—The greater thoracic splanchnic presynaptic cell body is located
at SC levels T5-T9. It carries preganglionic fibers into the abdominopelvic cavity by
passing through the crura of the respiratory diaphragm. The greater thoracic splanchnic
presynaptic fibers will synapse at the celiac ganglion. It will then give off postganglionic
sympathetic fibers which distribute with the celiac trunk (as a perivascular plexus) and its
branches to innervate the vascular smooth muscles of the vessels and the viscera they
supply.

The lesser thoracic splanchnic presynaptic cell body is located at spinal cord levels
T10-T11. It carries preganglionic fibers through the crura of the diaphragm to the
aorticorenal ganglion where a synapse occurs. From here, postganglionic sympathetic
fibers distribute with the superior mesenteric artery and its branches to supply the
vascular smooth muscle of the vessels and the kidneys and suprarenal glands.

The least thoracic splanchnic presynatpic cell body is located at T12. It carries
preganglionic fibers through the crura of the diaphragm to the minute ganglia of the renal
plexus where a synapse will occur. The postganglionic sympathetic fibers will then
distribute with the renal artery.

Parasympathetic nerves—The vagus nerves enter the abdominal cavity through the
esophageal hiatus as plexuses that are located on the anterior and posterior aspects of the
esophagus and stomach. The anterior vagal trunk is a continuation of the left vagus
nerve while the posterior vagal trunk is a continuation of the right vagus nerve. The
vagus nerves have their preganglionic cell body located in a nucleus of cranial nerve X.
Their preganglionic fibers are carried by way of cardiac nerves to the heart and lungs,
along the esophagus and stomach, and along the perivascular plexuses to ganglia within
the wall of an organ where the synapse will occur. The postsynaptic fibers are already in
the target organ, so they do not need to be distributed anywhere (like the sympathetics
do). The pelvic splancnic nerves have their presynaptic cell body at spinal cord levels
S2-S4. They distribute their presynaptic fibers along the surface of the rectum, sigmoid
colon, descending colon, and distal 1/3 of the transverse colon (instead of along
perivascular plexuses). The presynaptic fibers synapse in ganglia in the wall of the gut
(the hindgut derivatives) or in the pelvic viscera. There is no need for postsynaptic fiber
distribution b/c they are already in their target organ.

Abdominal Autonomic Nerve Plexuses—These are the nerve networks of the
abdominal area. They consist of both sympathetic and parasympathetic fibers and they
surround the aorta and its major branches. The plexuses along the aorta are all
interconnected.

The celiac plexus surrounds the celiac trunk. It is made up of celiac ganglia that are
unite around the celiac trunk. The parasympathetic portion of the celiac plexus is a
branch of the posterior vagal trunk. The sympathetic portion of the plexus comes from
the greater and lesser splanchnic nerves.

The intermesenteric plexus is the part of the aortic plexus between the superior and
inferior mesenteric arteries. It gives rise to renal, testicular/ovarian, and ureteric
plexuses.

The superior hypogastric plexus is continuous with the intermesenteric and inferior
mesenteric plexus. It lies anterior to the inferior portion of the aorta near its bifurcation..
The superior hypgastric plexus is joined to the inferior hypgastric plexus by the right and
left hypogastric nerves.

The perivascular plexuses include those that are distributed with the arterial supply.
These include the celiac trunk, superior mesenteric artery, renal artery, and inferior
mesenteric artery.

The abdominal part of the sympathetic trunk gives rise to the lumbar splanchnic nerves.
They extend into the abdomen from the thorax, passing posterior to the medial arcuate
ligaments. The abdominal portion of the trunks is composed of four lumbar
sympathetic ganglia that are connected to each other. The trunks receive white rami
communicans from the ventral primary rami of l1 and L2 and send gray rami
communicans back to these levels. The give off the lumbar splanchnic nerves which
pass to the intermesenteric, inferior mesenteric, and superior hypogastric plexuses.

Clinical Correlates—

Hiccups—This is the involuntary, sporadic contraction of the diaphragm which causes
sudden inhalations that are interrupted by the spasmodic closure of the glottis. This
produces a characteristic sound. There are many causes of hiccups including indigestion,
diaphragm irritation, and alcoholism. These are all conditions which disturb the phrenic
nerves. Hiccups are caused by irritation of the afferent or efferent nerve endings or
medullary centers in the brainstem that control the diaphragm, a muscle of respiration.

Referred Pain from the Diaphragm—Pain from the diaphragm can radiate to two
different areas. This is because of the differences in sensory nerve supply for the
diaphragm. The pain caused by irritation of the pleura or peritoneum of the diaphragm is
referred to the area of skin supplied by C3-C5 (the shoulder region). These segments
contribute ventral rami to the phrenic nerves as well as providing innervation to the skin.
Pain caused by irritation in the peripheral region of the diaphragm is referred to the skin
over the costal margins of the anterolateral abdominal wall.

Rupture of the Diaphragm and Herniation of the Viscera—A sudden increase in the
pressure within the thorax or abdomen can cause rupture of the diaphragm or herniation
of the viscera. This is commonly caused by trauma to these areas. Diaphragmatic
ruptures occur mainly on the left side b/c of that side’s congenital weakness. When there
is a traumatic diaphragmatic hernia, the stomach, intestine, mesentery, or spleen can
herniate into the thoracic cavity. A hiatal hernia is the protrusion of some of the stomach
through the esophageal hiatus into the thorax.

Congenital Diaphragmatic Hernia—This is the only relatively common congenital
diaphragm anomaly. This defect is associated with the herniation of the abdominal
contents into the thoracic cavity. This anomaly may cause inhibition in the development
and inflation of the lungs, causing life-threatening difficulties in breathing.

Psoas Abscess—An infection of tuberculosis can spread through the blood to the
vertebrae, especially in children. This abscess/infection can spread to the sheath around
the psoas muscle. This causes the psoas fascia to thicken and form a strong stocking like
tube. The pus from a psoas abscess passes along the psoas within this tube and reaches
the superior part of the thigh.
Posterior Abdominal Pain—The iliopsoas muscle is clinically related to much of the
viscera and nerves of the abdomen. When one of these structures is in a disease state, the
movement of the ileopsoas usually causes pain. If intra-abdominal inflammation is
suspected, the iliopsoas test is performed in which the person is asked to lay on their
unaffected side and to extend their thigh against resistance produced by an examiner’s
hand. If this causes pain, it is known as a positive psoas sign. P. 300 in COA tells some
locations of positive signs associated with various disease states.

Partial Lumbar Sympathectomy—This is the surgical removal of two or more lumbar
sympathetic ganglia by dividing their rami communicantes. When performing such a
surgery (whose details are described on p. 302), one should be careful not to accidentally
remove part of the genitofemoral nerve, lumbar lymphatics, or ureter.

Pulsations of the Aorta and Abdominal Aortic Aneurysm—A tumor within the
pancreas or stomach could transmit pulsations to the aorta b/c of their proximity to each
other. These pulsations could be mistaken for an abdominal aortic aneurysm which is a
localized enlargement of the aorta. An aneurysm usually results from some sort of
weakness in the arterial wall. Pulsations in a large aneurysm can be detected to the left of
the midline and the mass can be moved from side to side. Acute rupture of an abdominal
aortic aneurysm is associated with severe pain in the abdomen or back. Such a rupture
has a high mortality rate b/c blood loss is so heavy. An aneurysm can be repaired by
opening it, inserting a graft, and sewing the wall of the aneurysm over the graft.

Collateral Routes for Abdominopelvic Venous Blood—Three collateral routes are
available for venous blood to return to the heart when the IVC is obstructed or ligated.
The inferior epigastric veins are the first route. These veins anastamose with the superior
gastric veins that ultimately drain into the SVC by way of the internal thoracic vein. The
second route is the superficial epigastric or superficial circumflex iliac veins. These
anastamose with one of the tributaries of the lateral thoracic vein. The 3rd route involves
the epidural venous plexus within the vertebral column. It communicates with the lumbar
veins and the tributaries of the azygyous veins (which drain into the SVC).

								
To top