Abdominal nerves & Vessels

• Coeliac Trunk


  • Origin: level of T12 just below aortic hiatus of diaphragm
  • Divides immediately into 3 branches: Left gastric, Common hepatic, Splenic

  
• Coeliac Trunk


  • Relations: Anterior - Omental bursa, Right - Coeliac ganglion, Right crus of diaphragm, Caudate process of liver, Left - Coeliac ganglion, Left crus of diaphragm, Cardia of stomach, Inferior - Upper border of pancreas, Splenic vein
  • Structures supplied: Abdominal oesophagus, Stomach, Duodenum (superior part and descending part until opening of common bile duct), Liver and gallbladder, Part of pancreas, Spleen

  
• Variations of coeliac trunk

  • Textbook case (25%)
  • Trunk with extra branch- Posterior superior pancreaticoduodenal a. (10%)
  • Separate trunk to liver and spleen (5%)
  • Separate trunk to stomach and spleen (3%)
  • 1 trunk to stomach and spleen and another to liver (3%)

  
• Superior Mesenteric Artery


  • Originates 1cm below coeliac trunk at the level of L1
  • Relations: Anterior - Neck of pancreas, Splenic vein, Posterior - Left renal v., Uncinate process of pancreas, 3rd part of duodenum
  • Structures supplied: Duodenum (distal half of descending, inferior and ascending parts), Jejunum and ileum, Caecum and appendix, Ascending colon, Proximal 2/3 of transverse colon

  
• Variations of Superior Mesenteric Artery

  • Textbook case (24%)
  • Common trunk for right colic & ileocolic (20%)
  • Right colic absent (10%)
  • Right colic duplication (6%)

  
• Variations in supply of coeliac trunk and SMA to the liver

  • No supply (textbook case) (50%)
  • SMA supplies right lobe (10%)
  • Common hepatic originates from SMA (3%)
  • Left gastric supplies left lobe (3%)
  • Branch of left gastric to left lobe and left branch of proper hepatic from coeliac plexus (12%)
  • Accessory branch of proper hepatic to lesser curvature of stomach (7%)

  
• Inferior Mesenteric Artery


  • Origin: 4cm above aortic bifurcation at the level of L3
  • Has an oblique course to the left of the pelvic brim
  • Structures supplied: Distal 1/3 of transverse colon, Descending colon, Sigmoid colon, Rectum, Upper 3rd of anal canal

  
• Variations of Inferior Mesenteric Artery

  • Accessory middle colic a. from main trunk
  • Accessory middle colic a. from left colic a.

  
• Gastroduodenal artery


  • Maintains an intermediate position between pancreas & duodenum, a point of surgical significance because of duodenal ulceration

  
• Superior & Inferior pancreaticoduodenal


  • Form anastomosis & vascular arcades

  
• Splenic artery


  • End artery & so obstruction leads to infarction of spleen (segmental)
• Appendicular artery


  • May be thrombosed in appendicitis leading to ischemic necrosis & perhaps rupture of appendix, No collateral circulation because appendicular artery is an end artery
• Pressure of SMA on left renal vein

  May produce left-sided varicocele
• Pressure on duodenum


  May give rise to chronic duodenal ileus- painful obstruction
• Hepatic Portal Vein


  • Forms anterior to IVC and posterior to the neck of the pancreas
  • Union of superior mesenteric and splenic veins
  • In 2/3 of individuals- inferior mesenteric vein joins the confluence of SMV and splenic vein
  • Runs 7-8cm in the hepatoduodenal ligament (of lesser omentum)

  
• Portal-Systemic Anastomoses


  • Submucosa of the inferior oesophagus
  • Peri-umbilical region
  • Bare areas of secondarily retroperitoneal viscera
  • Submucosa of the anal canal
  • Bare area of liver

  
• Portal-Systemic Anastomoses


  • Communication between the portal venous system and the systemic venous system
  • When portal circulation is obstructed, blood from GIT can still reach the right heart through the IVC
  • Hepatic portal vein has no valves, blood can flow in a reverse direction to IVC
• Lymph Drainage of Abdominal Viscera


  • (diagram)

  
• Structures of Posterior Abdominal Wall

  • 5 lumbar vertebrae and their IV discs
  • Ribs 11&12
  • Sacrum and associated ligaments
  • Muscles: Psoas major and minor, Quadratus lumborum, Iliacus, Transversus abdominus, internal oblique and external oblique
  • Diaphragm
  • Fascia
  • Lumbar plexus and sympathetic nerves
  • Fat, vessels and lymph nodes
  • Skin

  
• Endoabdominal (transversalis) fascia


  Lies between the parietal peritoneum and the muscles

  
• Thoracolumbar fascia


  • Posterior layer: Thickest in the lumbar region, Covers the posterior aspect of the vertical deep back muscles, Attachments: Spinous processes of the lumbar and sacral vertebrae and supraspinous ligament
  • Middle layer: Separates the vertical deep back muscles from the quadratus lumborum, Attachments: Tips of the transverse processed of the lumbar vertebrae and intertransverse ligaments, Iliac crest, Lower border of 12th rib
  • Anterior layer (quadratus lumborum fascia): Covers anterior surface of quadratus lumborum, Continuous laterally with aponeurosis of transversus abdominis, Thickens superiorly to form lateral arcuate ligament, Attachments: Anterior surfaces of transverse processes of lumbar vertebrae, Iliac crest, 12th rib

  
• Psoas fascia


  Covers the psoas major muscle, Thickened superiorly to form the medial arcuate ligament, Fuses laterally with the anterior and middle layers of the thoracolumbar fascia, Continuous inferiorly with iliac fascia covering iliacus in the pelvic region, Attachments: lumbar vertebra and pelvic brim, Inflammatory collections track down & appear in groin where it is thinnest

  
• Perirenal fascia


  Multi-laminated fascia covering kidneys, suprarenal gland, upper ureter and p

  
• Thoracolumbar fascia


  • Separates the vertical deep back muscles from the quadratus lumborum
  • Anterior layer (quadratus lumborum fascia) covers anterior surface of quadratus lumborum, continuous laterally with aponeurosis of transversus abdominis, thickens superiorly to form lateral arcuate ligament

  
• Attachments of thoracolumbar fascia


  • Tips of the transverse processed of the lumbar vertebrae and intertransverse ligaments
  • Iliac crest
  • Lower border of 12th rib

  
• Attachments of anterior layer (quadratus lumborum fascia)

  • Anterior surfaces of transverse processes of lumbar vertebrae
  • Iliac crest
  • 12th rib

  
• Perirenal fascia


  • Multi-laminated fascia covering kidneys, suprarenal gland, upper ureter and perirenal fat

  
• Lateroconal fascia


  • Lateral aspect of perirenal fascia that fuses with fascia over transversus abdominis

  
• Muscles


  • Psoas major
  • Psoas minor
  • Iliacus
  • Quadratus lumborum
• Psoas major


  Origin: Lumbar transverse processes, intervertebral discs and adjacent bodies from T12-L5

  Insertion: Lesser trochanter of femur via iliopsoas tendon

  Innervation: Anterior rami of L1-L3

  Main action: Thigh flexion, trunk flexion, lateral flexion

  
• Psoas minor


  Origin: Bodies and transverse processes of T12-L1

  Insertion: Pectineal line

  Innervation: Anterior rami of L1

  Main action: Flexion at lumbar vertebrae

  
• Iliacus


  Origin: Superior ⅔ of iliac fossa, Ala of sacrum, Anterior sacro-iliac ligaments

  Insertion: Lesser trochanter of femur & inferior associated femoral shaft, Psoas major tendon

  Innervation: Femoral n. (L2-L4)

  Main action: Flexes thigh, Stabilizes hip joint, Acts with psoas major
• Quadratus lumborum


  Origin: Medial ½ of inferior border of 12th ribs, Tips of lumbar transverse processes, Iliolumbar ligament

  Insertion: Internal lip of iliac crest

  Innervation: Anterior rami of T12-L4

  Main action: Extends vertebral column, Laterally flexes vertebral column, Fixes 12th rib during inspiration
• Psoas minor lies inferolaterally on sides of T12-L5 bodies anterior to psoas major, absent in 40% of the population
• Iliacus is lateral to inferior part of psoas major, related to the iliac fossa, iliopsoas- conjoined tendon deep to inguinal canal that is the chief flexor of the thigh

  
• Quadratus lumborum lies adjacent to transverse processes of lumber vertebrae, lateral to superior parts of the psoas major

  
• Lumbar plexus


  Originates from the anterior rami of L1-L4, forms deep and within psoas major, branches: Iliohypogastric (L1), Ilioinguinal (L1), Genitofemoral (L1-L2), Lateral femoral cutaneous nerve (L2-L3), Obturator nerve (anterior divisions of L2-L4), Femoral nerve (posterior divisions of L2-L4), Accessory obturator (posterior divisions of L3-L4)

  
• Mnemonic for remembering lumbar plexus branches: Indeed I Get Lazy On Fridays
• Mnemonic for remembering lumbar plexus roots: 2 from 1 root, 2 from 2 roots, 2 from 3 roots
• Autonomic innervation to abdominal viscera

  • Sympathetic trunks pass under medial arcuate ligament, lie in groove between psoas major and vertebral bodies, Coeliac ganglion forms around coeliac trunk, Thoracic splanchnic nerves pass through crura of diaphragm, Coeliac plexus has sympathetic from splanchnic nerves and parasympathetic from vagus trunks, Hypogastric plexus has sympathetic fibres from T10-T12 and parasympathetic fibres from pelvic splanchnic nerves (S2-S4)