ABDOMINAL WALL
I. GENERALITIES - ABDOMEN
A. Abdominal boundaries
1. Superior - diaphragm
2. Inferior - pelvic inlet (pubic symphysis, iliopectineal line, sacral promontory)
B. Boundaries - abdominal wall
1. Superior - cartilages and ribs 7-12, xiphoid process
2. Inferior - pelvic bones, inguinal ligament
a. Landmarks
i. anterior superior iliac spine
ii. pubic symphysis
iii. pubic crests
iv. pubic tubercle
v. inguinal ligament
C. Layers - anterolateral wall
1. Skin
2. Superficial fascia
3. 3 layers of enclosing muscles plus one anterior midline vertical muscle
4. Transversalis fascia (endoabdominal fascia)
5. Extraperitoneal fatty layer
6. Peritoneum
D. Posterior abdominal wall - has other muscles and special features which will be discussed after the abdominal contents are understood
II. SKIN – typically fairly thin. Langer’s lines almost horizontal - inferiorly sloped at medial end
III. SUPERFICIAL FASCIA
A. Thick, fatty superficial layer (Camper’s fascia)
1. Continuous with fatty subcutaneous tissue in adjacent areas
2. Into scrotum as dartos f. and continued into lower limb
B. Thin membranous deep layer (Scarpa’s fascia)
1. Attached inferiorly to iliac crest, fascia lata, and urogenital diaphragm
2. Specialized near midline to form suspensory (fundiform) ligament of the penis or clitoris
C. Subcutaneous tissue in the scrotum forms a specialized layer called Dartos fascia which contains smooth muscle. It is continuous with the subcutaneous tissue of the abdominal wall as is the subcutanea of the labia majora in the female. NOTE: there is NO Dartos fascia in female.
D. Cutaneous nerves - ventral primary rami
1. Intercostal nerves T7-11 (Thoracoabdominal)
a. Anterior and lateral cutaneous branches distribute segmentally
b. T7 - just inferior to xiphoid process
c. T10 - at level of umbilicus in anterior midline
2. Subcostal nerve (T12)
a. Anterior terminal segmentally distributes like T7-11
b. Lateral terminal turns inferiorly across iliac crest to upper hip
3. Iliohypogastric nerve (L1)
a. Anterior terminal distributes to suprapubic region
b. Lateral terminal crosses iliac crest to upper hip
4. Ilioinguinal nerve (L1)
a. Supplies anterior scrotal/labial regions
E. Cutaneous vessels - veins accompany arteries of same name
1. Superior epigastic a. - supraumbilical region near midline anastomose with inf. epigastric a.
2. Musculophrenic a. - area below costal arch - anastomose with deep circumflex iliac a.
3. Intercostal (T10-11) and subcostal aa. - distribute like nerves of same name
4. Inferior epigastric a. - supplies infraumbilical region near midline - most branches are muscular - from external iliac a.
5. Superficial epigastric a. - Infraumbilical region - from femoral a.
6. Superficial circumflex iliac a. - near inguinal region and iliac crest from femoral
7. Veins can provide collateral routes between inferior and superior caval systems. Also near umbilicus - portal-caval anastomoses - superficial epigastric and lateral thoracic vv.
8. Lymphatics - above umbilicus > axillary nodes - below umbilicus > superficial inguinal nodes
IV. MUSCLES OF ANTERIOR - LATERAL ABDOMINAL WALL
A. Rectus abdominus
1. Origin - pubic crest and symphysis
2. Insertion - anterior xiphoid process and cartilages of ribs 5-7
3. Rectus sheath - dense C T covering of the muscle
a. formed by the aponeurotic insertions of the 3 anterolateral muscles
b. tendinous intersections - lines where rectus fibers attach to the rectus sheath
c. linea alba - midline fusion of the rectus sheaths of both sides
d. linea semilunares - lateral boundary of the rectus sheath
4. Action - raises the thorax toward the thigh
5. Innervation - intercostal nn. (Thoracoabdominal nn 7-12)
B. Pyramidalis
1. Minor muscle, often missing
2. Anterior to the most inferior portion of rectus abdominus
3. Arises from pubis, inserts in the linea alba
C. External abdominal oblique
1. Origin - lower 8 ribs
2. Insertions - iliac crest, pubic tubercle, linea alba. Free border between ilium and pubis forms inguinal ligament
3. Action - shared with the internal oblique and transversus. Flexes and rotates vertebral column and compresses abdominal contents. Can rotate trunk toward opposite side.
4. Fiber direction - origin to insertion, anteriorly and inferiorly
5. Innervation - intercostal nn.(Thoracoabdominal nn)
D. Internal abdominal oblique
1. Origin - thoracolumbar fascia, iliac crest, lateral inguinal ligament
2. Insertion - lower -3-4 ribs, linea alba, pubic bone (crest and pectineal line)
3. Fiber direction - superiorly and anteriorly (right angles to external oblique)
4. Actions - similar to external oblique but rotates to same side
5. Innervation - intercostal nn.
E. Transversus abdominus
1. Origin - thoracolumbar fascia, lower costal cartilages, iliac crest, inguinal ligament
2. Insertion - linea alba, pubic bone (crest and pectineal line)
3. Fiber direction - transverse
4. Action - shares with external and internal obliques
5. Innervation - intercostal nn.
F. Rectus sheath formation
1. Superior 2/3 (above arcuate line)
a. Anterior layer
i. external oblique aponeurosis
ii. part (anterior lamina) of internal oblique aponeurosis
b. Posterior layer
i. part (posterior lamina) of internal oblique aponeurosis
ii. internal oblique aponeurosis
iii. transversalis fascia
2. Inferior 1/3 - below point 1/2 way between the pubis and umbilicus
a. Anterior layer
i. external oblique aponeurosis
ii. internal oblique aponeurosis
iii. transversus aponeurosis
b. Posterior - transversalis fascia
3. Arcuate line
a. line of transition between the superior and inferior regions of the rectus sheath
V. TRANSVERSALIS FASCIA (ENDOABDOMINAL FASCIA)
A. Located deep to transversus abdominus
B. Part of continuous layer just inside the muscle layers of the abdominopelvic cavity
C. Same layer has other names in other locations (diaphragmatic fascia, pelvic fascia)
VI. EXTRAPERITONEAL FATTY LAYER
A. Located between transversalis fascia and parietal peritoneum
B. Most extraperitoneal contents located in this layer
VII. PARIETAL PERITONEUM
A. Serous lining of peritoneal cavity
VIII. BLOOD SUPPLY, INNERVATION AND LYMPHATICS OF ABDOMINAL WALL
A. Innervation by ventral primary rami of segmental nerves T7-L2
1. Thoracoabdominal intercostal nn. (T7-11)
a. passes from ICS, posterior to costal cartilage - between internal oblique and transversus mm.
b. enters back of rectus sheath - ends as anterior cutaneous branches
c. T7 end just below xiphisternal junction
d. T10 at umbilicus
2. Subcostal nn. (T12)
3. Iliohypogastric n (T12-L1)
a. runs in expected intermuscular plane
b. pierces internal oblique near anterior superior spine
c. runs between internal and external oblique
d. anterior cutaneous br. superior and lateral to pubic symphysis
4. Ilioinguinal n. (L1)
a. enters inguinal canal
b. becomes cutaneous at superficial inguinal ring
c. same course as iliohypogastric n. through body wall
B. Arteries to muscular wall
1. Superior epigastric a. - br. to superior, medial portion of wall
2. Musculophrenic a. - area near costal margin
3. Posterior intercostal aa. (T10-11) and subcostal a.(T12)
4. Lumbar segmental aa. (L1-4) - mostly to posterior wall
5. Inferior epigastric a.
a. br. of external iliac a. just above inguinal ring
b. ascends in extraperitoneal fat to enters rectus sheath at the arcuate line
c. branches
i. muscular
ii. subcutaneous
iii. cremasteric - supplies spermatic cord/round ligament
iv. pubic branch - may form accessory obturator a.
6. Deep circumflex iliac a.
a. br. of external iliac a.
b. courses toward anterior superior iliac spine
c. branches to adjacent structures
7. Subcutaneous aa. - may supply muscular wall - described previously
a. superficial epigastric
b. superficial circumflex iliac
c. superficial external pudendal
C. Veins - similar to aa.