Anatomy: Anterior Abdominal Wall April 28 September 2004
Abdomin: defined superiorly by rib cage; anteriorly by inguinal ligament, iliac crest Muscular structure, does not need skeletal support except posteriorly. Slightly more complicated: see lateral view that diaphragm is way up and technically everything below diaphragm is abdominal cavity (see diaphragm up in thorax), have also abdominal cavity down into pelvis. What we see anteriorly is really abdominal wall Organization Anterior abdominal wall divided into quadrants by midline plane and tranverse plane through umbilicus: upper right (UR), upper left (UL), lower right (LR), lower left (LL) Gets more difficult with 9 regions: 1. Umbilical region On sides of umbilical 2. Right lateral (lumbar) 3. Left lateral (lumbar) Towards head: 4. Epigastric: (“around/about stomach”) region 5. Right hypochondriac region (Latin for ribs—chondral) 6. Left hypochondriac region (Hypochondriac: person with ill defined pain in upper rib cage. Right—gallbladder disease, left—gastric problem) 7. Pubic (or hypogastric) region 8. Right iliac 9. Left iliac Important to be able to go between systems: know both! Skin and subdermal connective tissue, which forms Camper’s fascia (fatty layer). Backed up by Scarpa’s fascia (membranous fascia, will hold stitches). Notice that just as fascia layers of thorax come down to abdomen, so do the fascial layers of abdomen extend down over perineum, scrotum, etc. Scarpa’s fascia comes down over perineum; we’ll talk about this more later. Deep fascia is on top of the muscle and cannot be separated from it. Remember orientation of tissue fibers in dermis results in Langer’s lines Notice orientation in abd region tends to be kind of horizontal, kind of anteriorly and inferiorly a little bit. This is important in orienting incisions: vertical incisions in abdomen will not produce nice cosmetic healing. Much more to say about this at end of lecture
Anterior Abdominal Wall
Don’t waste time on layers of skin. Find fascial plane between Scarpa’s fascia and deep fascia. Notice camper’s layer is much thicker in abdominal region; be sure to remove all of it! Muscles of Abdominal Wall A. First layer of muscles: external oblique abdominus, take origin from the ribs, costal margin and inserts into the iliac crest of the pelvic bone. Courses diagonally toward the midline but does not reach it. Just as EIM loses the muscle fibers but the layer continues, the same thing happens here. The muscle of fiber external oblique terminates about in midclavicular line, continues as external oblique aponeurosis (named “neurosis” because ancients thought nerves were some sort of tendon, get flattened tendon, looked like a nerve to them). Is sheath of connective tissue, basically investing fascia, extending anterior and posterior layer of oblique abdominus muscle. This goes toward the linea alba, which is the midline (called linea alba—or “linear alber” If you’re from Boston, apparently—is called that because it is white. alba=albumin; egg white) where the fibers of the right external oblique aponeurosis and the left decussate (weave together) in that line and therefore the external oblique is inserted into the linea alba. Anal region: defect in inferior portion of external oblique aponeurosis, which is the superficial inguinal ring, through this ring testes pass, drag along a lot of tissue which constitute the spermatic cord, so spermatic cord is presenting through the external oblique aponeurosis through this ring. External oblique aponeurosis also forms between the anterior/superior iliac spine and the pubic tubercle the inguinal ligament (of Poupart, see pg 317). Showing diagram: That’s the lower edge of the external oblique aponeurosis. External oblique takes origin from ribs (both costal and chondral portion of ribs, inserting down on iliac crest, becoming aponeurotic and decussating into linear alba. Notice defect in superficial inguinal ring. B. Second layer goes infra laterally to supra medial: internal oblique. Takes origin from iliac crest, inserts into the costal margin. Fibers terminate, layer continues to linear alba and decussate there. Interesting things happen on its way there. Other thing to notice is in external oblique muscle ends at level of ant/sup ileac spine, but internal oblique also takes origin from all along inguinal ligament, almost as far as superficial inguinal ring was in external oblique. Notice fibers are not going upwards here, but are kind of going down because there is no external oblique in this area. C. Third layer: Transverse abdominis. Takes origin from the dense band of fascia (Like the internal oblique did), also takes origin from 10th rib, 11th rib costal margin as well as iliac crest and inguinal ligament. All origins (not insertions) because muscle basically moves horizontally. All are origins in back, insertion is into linea alba. Becomes aponeurotic and fascial couplings continue layer into linea alba.
Anterior Abdominal Wall
Lower free edge, Falx inguinis (sickle shaped) free edge of transverse abdominus, right where spermatic cord starts forming, passes under falx inguinis is the deep inguinal ring. Between deep ring and superficial ring have inguinal canal formed by cremaster muscle of spermatic cord. Cremaster muscle is an extension of the internal oblique muscle which is pulled down on spermatic cord and around testis. (more on this later). No inguinal ring here because of canal in between. Look for this today. . Posterior view: have external oblique (45 degree view) taking origin from 12th rib, 11th rib, costal margins and the costal portions of the ribs. Inserting on ilicac crest. Internal oblique originally from very dense fascia basically at right angles to external oblique. Transverse abd is third layer, proceeding under internal oblique horizontally. Functions of specific muscles. Rotation: external oblique on right is synergistic with internal obl on other side. Strange
Dutch photo of woman shown for this…hmmmm supposedly books are very good.
If you take both sides: muscles are pulling in opposite directions, result is almost like Chinese handcuffs (get fingers stuck). This is the reason for the shape of our waist: cut in. more accentuated in women because women have broader pelvis, making angle sharper. Use of muscles: photo of man sucking it in to show respiratory muscles: contracting in unison, contract very tightly. Antagonistic to diaphragm. D. Rectus abdominus muscles: take originate form sternum, xiphoid and chondral portions of 4th 5th 6th 7th 8th ribs at intercostal margin and insert into pubic bone associated with two pubic crests. Sometimes there are accessory muscles Really sick photo of man sucking in gut, shows how powerful these muscles are flexing out vetebral column—very powerful flexors. Rectus abdominus are very important for Valsalva maneuver. (fixation of thoracoabdominal wall by contraction of abdominal musculature in concert with thoracic musculature with the glottis closed. Resultant increase in thoracoabdominal pressure is used in lifting weights, coughing sneezing, defecation, etc—see pg 318). Generate internal pressure. “turn your head and cough” just before you let your glottis go. Urination, coughing, sneezing, defecation. Basically muscles of abdomen are very important, get pneumatic pillow: gut forced against diaphragm, helps you lift up weight. Rectus abdominus muscles sit in a sheath. Rectus sheath. Diagram displaying posterior aspect, anterior is reflected. Has interesting relationships. Notice that the fascia (aponeuroses) coming from internal and external oblique muscles has relationship with sheath. The EO gets aponeurosis, courses anterior to rectus abdominus muscle and fuses to a portion of the aponeurosis of internal oblique, and half goes anterior and half goes posterior. Transverse abdominus aponeurosis passes posterior to rectus abdominus muscle and fuses with aponeurosis of internal oblique and that becomes the posterior leaf of rectal leaf. Is that clear? Ha.
Anterior Abdominal Wall
Above umbilicus, have complete rectus sheath. Anterior leaflet formed by aponeurosis of external oblique fusing with one half of the aponeurosis of internal oblique. The posterior leaflet of rectus sheath is formed by the other half of the internal oblique aponeurosis and rectus abdominus fusing together. Sheath is smooth and goes down holds rectus abdominus. Rectus abdominus is attached above umbilicus by tendinous inscriptions which are remnants of segmentation. These adhere to rectus sheath anteriorly but not posteriorly. As you run your finger down the posterior leaflet you will find an arc that will catch your finger (possibly two arcs) this is the semicircular line of Douglas (arcuate line) something has happened with arrangement of the aponeuroses that are forming the rectus sheath. At arcuate line, all aponeuroses go anterior to rectus sheath. No posterior rectus sheath. Get arcuate line representing end of rectal sheath. Possibility of more than one. If internal oblique goes anterior completely before the transverse abdominus aponeurosis then there will be two: one representing internal oblique layer and one representing the transverse abdominus layer. Probably more common to have more than one than to have just one. Important landmark: below this, where posterior rectus sheath should be have transversalis fascia and the other side of that is peritoneum. This can be a potential space for herniation. Spigelian hernias. Used to be difficult to diagnose (now use ultrasound), easy to fix. Also important due to blood vessel coming in behind anterior arcuate line. Importance of directionally of muscles: gridiron incision (McBurney). Professor of surgery at Columbia, developed incision for appendectomy making incision along Langer’s lines, then cut through each of layers separately. Otherwise suturing doesn’t work too well: “trying to sew two paintbrushes together end to end” if patients sneeze after surgery muscle layers open No strength in muscles. Iatrogenic hernia. (IT’S YOUR FAULT!!!) If cut along fibers, the muscle fibers come together and no problem! Also allows you to avoid nerves: De-innervated muscles atrophy. Blood supply to abdominal wall intercostal arteries (9th, 8th, 7th, 6th) along wall, sometimes anastomosis occurs. Orientation might not be quite as distinct as nerves. Also have lumbar arteries (supplying external obliques, internal obliques, IO, TA) Rectus abdominus gets supply from different source (two sources): Internal thoracic artery comes down along sternum, branches into musculophrenic artery which comes along costal margin and supplies diaphram and gives off anterior intercostal arteries. The second branch is superior epigastric, which passes adjacent to costal margin and xiphoid process (other reason not to extend incision—get major bleeding). Supplies rectus abdominals Get anastomoses of inferior epigastric, which is a branch of the femoral artery (sometimes external inguinal artery) comes out anterior of rectus sheath. How does it get there? Arcuate line. In addition to problem of transverse incision of rectus abdominals will cut off blood supply (have enough collateral circulation).
Anterior Abdominal Wall
Arterial anastomoses: really nasty photo of poor guy. Hypertrophy all over the place, skin looks bubbly….stenosis of aorta. Veins basically follow the arteries. Only thing of importance (other than that there’s more variability) and theres a lot of anastomosis. One problem is around area of umbillucus. Varices can develop in paraumbilical veins which connect with portal vein (portal hypertension) from GI tract to liver, varices occur there. If anyone has stenosis of the liver, get these. When extreme get caput medusae. Even if modest can see veins radiate on infrared film. Do not want to make incision on person with ETOH problem without knowing….get massive bleeding! Nerves: Sixth-12th intercostal nerves (12th is subcostal). Coming down into suprapubic region. T12 is right above pubis. T10 goes to umbilicus. These are lateral cutaneous branches. Cutaneous nerves of the abdomen (have lateral posterior and anterior branches), will see these nerves poke through muscles. These are superficial. Deep branches: 6-12. Deep branches innervate abdominal muscles (internal, external, transverse) and also coming across to innervate rectus muscles, muscles of abdominal wall. This presents problems because a vertical incision which is lateral to rectus muscle will incise innervation of rectus muscle—iatrogenic hernia! How to go into abdominal wall? Two ways: drop incision from xyphoid on linea alba (“white line” -- bloodless). BUT need blood to heal, so it will not heal very well. Use very large steel sutures and roll fascial layer together. Will itch, poke out through skin. =Breeding ground for iatrogenic hernia. Best way is paramedial incision down through anterior rectal sheath and retract rectus abdominus laterally (sheath allows it to move)…can retract massively! Make incision through posterior sheath. Haven’t cut muscle, vessel, have extensive access. Come out, suture up with small sutures the post leaf of rectal sheath, let muscle slide back. Just have layer of sutures on anterior rectal sheath. Paramedial incision is best access. Netter diagram of hernias: Hernia in linea alba Umbilical hernia (can be congenital) Incisional hernia (nerves were cut) Hernia at linea semilunaris (Spigelian hernia, usually don’t see because pulled under sheath). Veil of perineum: between last layer of muscle and perineum is transversalis fascia, gain access to perineum.