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).
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