5.1: Abdominal Wall, Inguinal Area & Scrotum

Anterior Abdominal Wall

Nine regions delineated by midclavicular lines (reach midinguinal point) and intertubercular plane (across iliac crest tubercles) and transpyloric plane (between jugular notch and top of pubic symphysis)

-           hypochondrial and epigastric regions superior

-           umbilical and lumbar regions middle

-           hypogastric and iliac areas inferiorly.

Abdominal Muscles & Incisions (231-4)

Separate in flanks, fused ventrally into the rectus.

External Oblique (232)

Arises lower 8 ribs/costal cartÕs.  Upper 4 slips interdigitate with serratus anterior, lower 4 with lat dorsi.  Slips are directed downwards and ventrally.

Inserts Posterior fibres insert into anterior half of outer lip of iliac crest, rest into wide insertion of EO aponeurosis which runs anterior to rectus to insert into linea alba (the two sides interdigitate).

-           Inferior border forms inguinal ligament (of Poupart), where its inferior edge rolls inwards ¨ origins to IO and transversus; fascia lata begins below this.

Free margins: are posterior & upper borders.

-           upper border is only content of rectus sheath above the costal margin.

-           Posterior free border forms anterior boundary of Lumbar triangle of Petit = EO anteriorly, lat dorsi posteriorly and iliac crest inferiorly) (Pl 237)

Nerve: lower 6 intercostal nerves.

Internal Oblique (233)

Arises: thoracolumbar fascia (see Pl 161), anterior 2/3 of iliac crest and lateral 2/3 of inguinal ligament. 

-           fibres run upwards and ventrally, attaching to the base of the costal cartilages superiorly

Insertion: costal cartilages (noted), becomes aponeurotic at tip of ninth costal cartilage and mostly inserts into rectus sheath:

-           split around the sheath below the costal margin, but wholly passes in front of rectus below the arcuate line (Pl 235)

Lowest fibres ¨ form post wall of inguinal canal. 

Nerve: lower 6 intercostals & 1st lumbar. 

Transversus (234)

Similar to IO; arises from:

-           (1) from lateral third of inguinal ligament (more lateral than IO)

-           (2) anterior 2/3 of inner lip of iliac crest

-           (3) lumbar fascia

-           (4) from inner aspects of lower 6 costal cartilages interdigitating with diaphragm. 

-           (5) 12th rib.

Inserts aponeurotically behind rectus, except below arcuate line ¨ in front of it.

Rectus (234)

Arises from pubic crest & tubercle ¨ Insert at 5th - 7th CCÕs, xiphoid process.

-           close together initially, broaden out above separated by linea alba

Tendinous intersections x3, at umbilicus, at xiphisternum, and between these two.

-           these are superficial and blend with anterior layer of the rectus sheath.

Nerves: lower 6 intercostals (entering posterolateral aspect)

Blood: Superior and inferior epigastrics and intercostal vessels

Pyramidalis: front of pubis & symphysis ¨ linea alba.  Nerve supply = 12th IC nerve.

-           lies anterior to rectus 

Rectus Sheath (235)

EO aponeurosis + anterior lamina of IO aponeurosis anteriorly, post lamina of IO aponeurosis + transversus aponeurosis posteriorly.  All aponeuroses pass anteriorly below level of arcuate line of Douglas. 

-           actually the EO apone=urosis only fuses with the medial aspect of the sheath

-           the semilunar line is the graceful curve of the lateral rectus edge where IO is splitting

Contents of the sheath:

Rectus, pyramidalis, ends of T7-T12 intercostal nerves, ?accompanying posterior intercostal vessels, and superior and inferior epigastrics.

-           the nerves run between transversus and IO (same pattern as in ribs).   Note on Plate 240 that they dip into the posterior rectus sheath, then pierce the muscle medially (supply it) and emerge as the anterior cutaneous branches.

-           Note also lateral cutaneous branches: pierce IO and EO to reach skin.

Superior epigastric: continuation of internal thoracic; passes through diaphragm fibres to reach sheath. Generally runs 4-8 cm off midline.

-           anastomosis inside it with inferior epigastric: (from external iliac at inguinal ligament) (Pl 234) Ð passes behind conjoint tendon, then over arcuate line to enter sheath.

Blood to abdominal wall

Intercostal and epigastric vessels and:

-           lumbar arteries (end anterolaterally, see back section)

-           deep circumflex from external iliac behind inguinal ligament (Pl236); this runs towards ASIS, then may give an ascending branch at risk in the gridion incision.  Then anastomoses with iliolumbar and superior gluteal arteries.

Lymphatic drainage of abdominal wall

Superficial

Above umbilicus ¨ pectoral group of axillary nodes

Below ¨ inguinal nodes. 

Deep

Above umbilicus ¨ mediastinal nodes

Below ¨ external iliac & para-aortic nodes

Actions of abdominal wall:

i)                       move trunk: flex vertebral column (mainly rectus); IO and EO also abduct and rotate

ii)                     depress ribs: powerful expiration (while erector spinae prevents flexion)

iii)                   compresses abdomen: EO, IO, transversus; evacuates pelvic contents or expires by pushing diaphragm (depending on contraction of other groups)

iv)                   supports/protects viscera: including reflex contraction

Test: Lie on back, lift head (tests rectus only)

Abdominal Incisions

Midline: Standard: skin, subcut tissue, linea alba, transveralis fascia, extraperitoneal fat, peritoneum.

-           beware bladder in pubic region.

For laparoscopic port incision at umbilicus, angle to pelvis to avoid aorta damage.

-           and avoid the inferior epigastrics when inserting other ports

-           going to the left of midline above umbilicus avoids the falciform ligament

Paramedian incision: incise anterior wall of rectus sheath vertically 2cm from midline, retract rectus muscle (dissect off the tendinous intersections)

Rectus split incision: through vertical incision 3cm from midline (may devascularise some muscle, but usually of no concern).  If below umbilicus, anterior sheath closure relied on for strength.

KocherÕs right subcostal incision: parallel to and 3cm below R costal margin, from midline to beyond the rectus sheath.  Avoid cutting both 8th and 9th intercostal nerves & ligate superior epigastric artery.

Curved rooftop (double Kocher): under both costal margins ¨ good access

Gridiron (McBurneyÕs): oblique muscle-splitting for appendicectomy. Spit mÕs in line of their fibres.

-           do not damage Ilioinguinal and Iliohypogastric nerves between IO and EO.

-           Ascending branch of deep circumflex iliac artery may come near to incision.

Transverse muscle-splitting incision is better: same but incise transversely ¨ cosmetically better.

Transverse muscle-cutting incision: ~umbilical level, cut all abdo muscles; usually can retract the rectus medially, one intercostal may be cut by this incision.

PfannenstielÕs lower abdo transverse incision: to pelvic organs, cut above symphysis.

Lumbar incision: for extraperitoneal approach to kidney. Below rib 12, incise lat dorsi and EO.

-           avoid the subcostal nerve deep to internal oblique but ligate vessels.  Peritoneum not entered.