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MBBS program in Anatomy, Jos, 2003
 
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Anterior abdominal wall

 

This is the gateway to the abdominal cavity anteriorly. It exposes the true intraperitoneal structures such as the small intestine, stomach, distal duodenum, transverse colon and sigmoid colon

It is provided with the following layers

1. Skin

2. Superficial fascia

3. THERE IS NO DEEP FASCIA

4. Layer of muscles which are arranged in three strata

a.  External oblique muscle of abdomen

b.  Internal oblique muscle of abdomen

c.  Transversus abdominis

The three layers correspond to the three layers of muscles in the intercostal spaces which are the external intercostal, internal intercostals and innermost intercostals muscles

5. Transversalis fascia

6. Parietal peritoneum

The layers of muscles are separated by a rectus sheath which contains the rectus abdominis. The sheath is made up of the aponeurosis of the abdominal muscles. Hence we have the aponeuroses of external oblique muscle of abdomen, internal oblique muscle of abdomen and transverses abdominis.

External oblique muscle of abdomen

This muscle has an extensive origin from the external surfaces of the lower 8 ribs as digitations. It then runs downwards and forwards like the external intercostals muscles to reach the insertion at the linea alba. The linea alba is the white line which separates the two sides of the abdominal musculature and provides the insertion of all the aponeurosis of the abdominal muscles.

The external oblique has three free borders. |

Superior free border is formed at the anterior aspects of the 5th 6th and 7th costal cartilages.

Lumbar free border which forms part of the boundaries of the lumbar triangle.

Inferior free border is formed by the inguinal ligament which is just the inward rolling of the external oblique aponeurosis. This aponeurosis is formed at the lateral border of the rectus sheath at a point called the linea semilunaris.

The following are also points of insertion of the external oblique muscle and aponeurosis

1. Anterior superior iliac spine

2. Pubic tubercle

The above two will form the attachments of the inguinal ligament

IT is also attached to the anterior 2/3 of the outer lip of the iliac crest.

Internal oblique muscle of abdomen

This muscle takes its origin from the following parts

1. Anterior 2/3 of the intermediate lip of iliac crest

2. Lateral 2/3 of the inguinal ligament

3. Conjoint lamellae of thoracolumbar fascia.

It then runs upwards and forwards as the internal intercostals muscle. It then gains its attachment (insertion) to the linea alba by its aponeurosis and also to the costal margin.

Its lower fibers also gain insertion together with the transversus abdominis, to the conjoint tendon

Transversus abdominis

 This is the innermost layer. It runs from the following parts

1. From costal margin

2. From the innermost lip of the iliac crest at its anterior ½

3. From the lateral 1/2 of inguinal ligament

4. Fascia covering the iliacus muscle

5.  Conjoint lamellae of the thoracolumbar fascia

From these extensive origin, the fibers run into the linea alba after helping to form the posterior wall of the rectus sheath.

Some fibers gain attachment to the conjoint tendon with the internal oblique.

Rectus abdominis

The rectus abdominis takes its origin from the front of the body of the body of pubis. It then runs a straight course to reach the anterior surfaces of the 5th, 6th and 7th costal cartilages where it is attached.

It has tendinous intersections which are prominent in the muscular individual

Pyramidalis

This muscle takes origin form the superior aspect of symphysis pubis and is inserted into the linea alba. It is small pyramidal shaped muscles and is not present in all individuals.

 

Nerve supply to muscles

T7-T12 spinal nerves and L1 nerve

But the pyramidalis has a special supply from T12 nerve- subcostal nerve.

Blood supply from lumbar arteries and anterior intercostal arteries

Venous drainage is also from the lumbar veins and special veins which form caput medusae pattern around the umbilicus. A prominent vein is the thoraco-epigastric vein. Anterior abdominal wall veins distend in portal hypertension forming the characteristic caput medusae.

Rectus sheath

This is the collection of the aponeurosis of the anterior abdominal wall muscle

  • The anterior wall is formed by the external oblique aponeurosis and also
  • The anterior lamella of the internal oblique aponeurosis
  • Posterior wall of the sheath is formed by the transversus abdominis aponeurosis and the posterior lamella of eh internal oblique aponeurosis. The posterior wall of the rectus sheath disappears at the midpoint between the umbilicus and symphysis pubis so that all aponeurosis below this point run anteriorly to form the anterior wall of rectus sheath. The point of departure of rectus sheath posteriorly is called the arcuate line of Douglas. Below this point there is no posterior wall of rectus. The rectus abdominis muscles lie directly on the transversalis fascia. Hence we have the various walls of the rectus sheath as follows

1. Above the costal margin- we have the posterior wall formed by the 5-7th costal cartilages, anterior surfaces. It has only external oblique aponeurosis as its anterior wall

2. Below the costal margin, we have the regular sheath with the external oblique aponeurosis and internal oblique anterior lamella. The posterior wall is formed by  the transversus abdominis and the posterior lamella of the internal oblique.

3. Below the arcuate line- there is no posterior wall of rectus sheath.

Inguinal canal

This canal is small one running for about 4cm from the superficial (external) inguinal ring to the deep inguinal ring

It has the following boundaries.

Floor- this is made up of the inguinal ligament. This ligament is the inward rolling externally of the aponeurosis of the external oblique muscle.

Anterior wall. This is made up of the skin, superifical fasciae of Campers and Scarpas. Then the external oblique aponeurosis and finally the internal oblique at its lateral 1/3.

Roof is formed by the conjoint muscle of the internal oblque and transversus abdominis muscles. They run form their attachments to the inguinal ligament (lat 1/3 for transversus abdominis, lat ½ for internal oblique muscle).

Posterior wall is formed medially by the conjoint tendon of the internal oblique and transversus abdominis as they run from the roof to the posterior wall. They form an arch which interconnects the anterior to the roof and to the posterior walls. Laterally the posterior wall is formed by the transversalis fascia.

Medial wall is formed by lacunar ligament

Content. For the ease of description we say the content is mainly spermatic and ilioguinal nerve in the male and round ligament of uterus and ilioinguinal nerve in the female.

If we however follow the rule of three we come up witht eh following

Content is the spermatic cord.It has 3 coverings, 3 arteries, 3 nerves and 3 others

Covering: 1. External spermatic fascia . This is derived from the external or superficial inguinal ring.

2. Internal spermatic fascia. This is derived from transversalis fascia. It is the most internal of the coverings.

3. Cremasteric muscle and fascia, which are derived from the internal oblique muscle in the inguinal canal. It is the intermediate covering.

3 arteries

1. Testicular artery

2. Cremasteric artery

3. Artery of vas deferens

 

Nerves

1. Genital branch of genitofemoral nerve

2. Ilioinguinal nerve

3. Autonomic nerves (Sympathetic fibers)

 

3 others

1.Pampiniform plexus of veins which become the testicular vein or ovarian vein at the external inguinal ring

2. Lymphatic

3. Fat and ductus (vas) deferens

Hernia

A hernia is an abnormal protrusion through a normal or abnormal space or opening. In the case of the inguinal hernia, it is an abnormal protrusion through the normal inguinal canal opening. It may be congenital and if so , it may extend through th e embryological processus vaginalis into the scrotal sac forming the so called congenital inguino-scrotal hernia.

The inguinal canal is formed as  an oblique opening through the muscles of the anterior abdominal wall. It extends from the superficial inguinal ring (external oblique aponeurosis) to the deep inguinal ring (transversalis fascia). It is about 4cm long.  The hernia is usually a viscus, such as small or large intestine, urinary bladder, appendix, omentum etc. It passes through  the deep inguinal ring acquiring the similar covering of internal spermatic fascia. It also acquires the covering of cremasteric fascia in the inguinal canal. In order to separate it therefore from the  spermatic cord, the line of cleavage with  the above fasciae must be sought for. It may extend from the deep inguinal ring to the superficial inguinal ring, in which case it is called the indirect or oblique hernia. If it enters through the posterior wall made up of conjoint tendon (medially) and transversalis fascia (laterally), it is called a direct hernia.

A hernia is repaired by removing the hernial sac after the reduction of the hernia and then reconstructing the inguinal canal using stitches that reduce its size.

Other types of hernia exist in the anterior abdominal wall. All anterior abdominal wall hernias are said to be external hernias as opposed to the internal hernias which occur in the peritoneal and other cavities of the body.

Other external hernia includes

  • Femoral hernia

  • Interstitial hernia (passes through the muscle fibers

  • Epigastric hernias – through linea alba above the umbilicus

  • Paraumbical hernia

  • Umbilical hernia

  • Lumbar hernia (found a the lumbar triangle)

.Blood supply to the anterior abdominal wall

  • Intercostal vessels

  • Internal thoracic artery

  • Musculophrenic artery

  • Lumbar arteries

 

Applied anatomy

Ritzk observation

Ritzk in 1980 observed that the traditional description of the attachments of the anterior abdominal wall muscles need some measure of modification. Thus  he observed that the aponeurotic fibers of the external oblique run in two layers as they approach the linea alba. The superficial layer move across the linea alba and becomes continuous with fibers of the internal oblque aponeurosis on the opposite side. Hence the traditional description that the fibers of the external oblique pass to the linea alba may not be entirely correct. The advantage of this type of architectural arrangement is not clearly understood but may be related to the need for increased contractile function of these oblique muscles of the anterior abdominal wall.

2. Anatomy of anterior abdominal wall incisions.

Surgical incisions are made into the anterior abdominal wall primarily in order to gain access into the peritoneal cavity. Sometimes this situation is reversed to that the incision is made into the posterior abdominal wall in order to reach the retroperitoneal structures. These retroperitoneal structures like the kidneys, suprarenal glands, ascending and descending colon, duodenum and pancreas are best approached from the posterior abdominal wall incisions while intraperitoneal structures such as the intestines (small), sigmoid and transverse colon etc (stomach, liver, spleen) can be reached via the anterior abdominal wall incisons. There are several incisions which can be made into the anterior abdominal wall as follows

a. Gridiron incision- this incision is made into the anterior abdominal wall without cutting through their muscles. It is therefore called the split-muscle incision. This incision, takes into consideration, the path or course of the fibers of the muscles of the anterior abdominal wall. Hence it is noted that the external muscle/ aponeurosis runs downwards and forwards just like the external intercostal muscle. This is followed by the internal oblique muscle and aponeurosis which runs upwards and forwards and then by the transverses abdominis which runs transversely. A good example of the gridiron incison is that made for appendicectomy in order to expose the caecum and the appendix which the caecum carries. In this incision the knife is passed through the so called McBurney’s point, which is a point placed at the junction between the lateral and intermediate 1/3 of the line joining the umbilicus with the anterior superior iliac spine on the right. This incision runs downwards and forwards along the McBurney’s point and pases throught the following layers

1. Skin

2. Campers fascia

3. Scarpa’s fascia

The next layer is the layer of external oblique apneurosis and muscle

 

 

The fibers of this layer are split to make room for the incision rather than using a knife.

The next layer is the layer of the internal oblique and again the fibres of this muscle/aponeurosis are split along their course, which means the split runs upwards and forwards.

Finally the split in the fibers of the transversus abdominis runs transversely.

After the layers of the muscles, we then reach the parietal peritoneum. This peritoneum is divided using a knife  longitudinally or transversely in order to expose the peritoneal cavity. The appendix may lie behind the caecum and this is the position preferred in 75% of cases- i.e. it is retrocecal or retroileal.

It also can lie in front of the cecum, Ie pre-ileal or it may be pelvic in position thereby lying in the abdominopelvic corridor or within the greater pelvis. It may be long or short and it may have various types of curvature. The cecum itself may be retroperitoneal which then renders the operation more delicate. But in most cases it is intraperitoneal and it can then be easily delivered through the incision to the outside where operation on its contained appendix takes.

After the procedure, the surgeon does not bother to stitch back the muscular layers. But he stitches the skin, superficial fasciae and parietal peritoneum. It is believed that the muscle fibers will realign once the operation is finished and therofre this method obviates the need for incision, or stitches into the muscles which normally will cause scar formation.

Midline incisions

These are incisions given to the linea alba either superior or inferior, i.e. below or above the umbilicus. They are very simple since they simply pass through the fibrous conglomeration which forms the linea alba. The incision only passes trough skin, superficial fascia, before reaching the linea alba. After the linea alba, the incision is made longitudinally into the parietal peritoneum. Its main advantage is speed. Hence it is favoured in Caesarean section, where speed is required in order to deliver the baby speedily. It has a major disadvantage which is that it heals with ugly scars and takes a long time to heal because of its relative avascularity.

Also the linea alba incisions are very simple to make and even to stitch back.

Paramedian incision

This type of incision passes throough the anterior abdominal wall and its various layers but avoids the midline or the linea laba. Examples include subcostal incision for splenectomy or other operations on the spleen. Another important incision is the transverse incision which is used for cosmetic reasons- called in gynaecology Pfannenstiel incision. This incision is placed in the hypogastrium and is used to access the pelvic organs such as uterus, fallopian tubes, ovaries, and male reproductive organs.

The incision passes through the skin, then superficial fasciae- Campers and Scarpa. Then it reaches the anterior wall of rectus sheath. The recti are then pushed laterally in order to expose the posterior sheath. This sheath is now divided in continuity with the parietal peritoneum and transversalis fascia. Below the arcuate line of Douglas there is no posterior wall of the rectus. The incision into the posterior structures now changes to a longitudinal one in order to adequately expose the peritoneal cavity. After the operation, the layers are closed up one by one until it reaches the skin

Another type of non midline incision is the common hernial incision. This incision is made with its inferior edge running from the external inguinal ring, backwards and upwards.

 

 

 

Oluwole Ogunranti

Professor of Anatomy and Director Human Anatomy Lecture Series.

7 January 2003 

University of Jos Human Anatomy Lecture Series http://jogunranti.tripod.com

 


 
 

 

 

 
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