Anterior Abdominal Wall and Hernias

The abdominal cavity is beneath (inferior to) the diaphragm, above (superior to) the pelvic cavity and walled by muscle on its lateral and anterior faces. Since the anterior and lateral sides are only muscle, tone is important to avoid herniation of the abdominal contents.

The pelvis is separated from the abdomen by an imaginary line running through the sacral promontory to the symphysis pubis.

Surface Anatomy

4 quadrant system – Upper Right Quadrant (URQ), Lower Left Quadrant (LLQ), etc. divide the abdomen into four parts via a midsagital line (xyphoid to pubis) and a transumbilical line (side to side through the belly button).

9 regions system:

superior to costal cartilage: right hypochondriac, epigastric, left hypochondriac
between costal cartilage and transtubercular plane (through ASIS): right lumbar, umbilical, left lumbar
below transtubercular plane: right inguinal, hypogastric, left inguinal

Anterior Superior Iliac spine – the part of the pelvis that is prominent of the anterior, superior and lateral to the pubis.

Costal margins- the edge of the costal cartilage from the rib 10. The Xyphoid process is in the middle.

Inguinal Ligament- formed by the Exterior Oblique which extends between the Ant. Sup. Iliac spine and the pubic tubercle

Linea semilunaris – the lateral border of the Rectus Abdominus

Pubic tubercles- prominences on the pubic bone, found lateral to the midsagital line.

Umbilicus – belly button (located at L3-L4 on thin people but its position varies with age and obesity)

Layers of the Anterio-lateral Abdominal Wall

(1) Skin

(2) Superficial fascia (outer "fatty" Camper’s // inner "fibrous" Scarpa’s)

(3) External Oblique muscle

(4) Internal Oblique muscle

(5) Transverse Abdominus muscle

(6) Transversalias fascia – continuous layer between abdominal wall muscles and the extraperitoneal fat

(7) Peritoneum (with extraperitoneal fat)

(8) Abdominal viscera

Muscles

External Oblique – forms inguinal ligament

Origin: Costal surfaces of ribs 5-12

Insertion: Linea alba, Pubic tubercles, iliac crest (anterior ½)

Innervation: Inferior 6 thoracic nerves, subcostal nerve

Internal Oblique

Origin: Thoracolumnar fascia, iliac crest, inguinal ligament

Insertion: Inferior borders of ribs 10-12, Linea alba, pubis

Innervation: Ventral rami of inferior 6 thoracic nerves, 1^st lumbar nerve

Transversus abdominis

Origin: Costal cartilages 7-12, thoracolumnar fascia, iliac crest, inguinal ligament

Insertion: Linea alba, pubic crest, pectin pubis via conjoint tendon

Innervation: Ventral rami of inferior 6 thoracic nerves, 1^st lumbar nerve

Rectus Abdominus – within rectus sheet

Origin: Pubic symphysis, pubic crest

Insertion: Xyphoid process, costal cartilages 5-7

Innervation: Ventral rami of inferior 6 thoracic nerves
tendinous intersections interrupt the rectus abdominus

The function of these muscles is to maintain the structural integrity of the abdomen, to compress and support the viscera, trunk stabilization, flexion, and rotation. When they contract they increase abdominal pressure; this provides the force needed for defecation, micturition (urination), and parturition (childbirth).

Common Aponeurosis – are tendinous endings to the first 3 muscles that completely encase the Rectus Abdominus.

Linea Alba is the midline tendinous raphe of the common aponeurosis.

Arcuate line is the inferior margin of the posterior wall of the rectus sheath.
Inferior to the Arcuate line the aporneurosis of the Transversus Abdominus joins the other aponeuroses anterior (in front of) the Rectus Abdominus. This occurs midway between the umbilicus and the pubic crest.

Nerves

have a segmental positioning. Dermatomes can be mapped to nerves (e.g. T10 is nerve for the umbilicus) a Dermatome is an area of skin innervated by a single spinal nerve. "Referred Pain" is when pain is felt in a region of the abdomen because part of the viscera is hurt (e.g. kidney infections present as lower back pain)

Blood Vessels – the anterior-lateral abdomen gets its blood from

From the top middle (deep superior) – the internal thoracic artery becomes the superior epigastric artery

From lower (deep inferior) – the external iliac artery gives rise to the superficial epigastric (in the midline), the inferior epigastric (in the deep middle) and both of the circumflex illiacs (superficial and deep).
Veins and lymph both drain either to the axilla (if above the umbilicus) or towards the inguinal canal (below umbilicus)

Peritoneal folds – an elevation of peritoneum with a free edge, some are old fetal circulation structures.

Lateral peritoneal folds: raised by the inferior epigastric vessels.(indirect hernias are lateral to the inf. epigastric)
Medial peritoneal folds: remnants of umbilical arteries
Median peritoneal fold: remnant of the fetal urachus.

Ligamentum Teres: the free edge of the Falciform Ligament (a remnant of the left umbilical vein) goes to liver

- fundiform ligament holds up the penis

Inguinal Region

Inguinal Ligament: is formed by the External Oblique reflecting back upon itself. It extends between the anterior superior iliac spine and the pubic tubercle. The fibers that cross the midline are known as the reflex inguinal ligament.

Inguinal Canal: is an oblique passage superior and parallel the Inguinal Ligament that is about 4 cm long. In males the spermatic cord goes through this canal, in females, the round ligament. (remnant Gubernaculum, see below)

Superficial inguinal ring- triangular opening of the canal. Formed by the external oblique. (medial to deep)
Deep inguinal ring- not really a ring, more like a hole in the transversus abdominus. (lateral to superficial)

Development- the canal forms between the 5^th and 32^nd week of gestation. The gonads begin forming during the 5^th week in the posterior abdomen. A fibrous cord, the Gubernaculum connects the gonad with the future scrotum (or labia majorum in females) and passes through what will be the inguinal canal. The testes migrate due to differential growth and pulling by the gubernaculum to eventually descend through the inguinal canal to the scrotum. This pulls down a portion of the peritoneum that becomes disconnected and later known as tunica vaginalis.

Male Genitalia – scrotum, spermatic cord, and testis

Scrotum – consists of two layers, skin and superficial fascia. Dartos muscle wrinkles them. The superficial fascia of the scrotum is continuous anteriorly with the superficial fascia of the anterior abdominal wall. Blood supply is via perineal branches of the internal pudendal, external branches of femoral artery, and cremasteric artery. Drainage is accomplished via the scrotal vein. Innervation is from the genital branch of the genitalfemoral nerve, the scrotal branch of the ilioinguinal nerve, and the perineal branch of the posterior femoral cutaneous nerve.

Spermatic Cord – travels through the inguinal canal to link the testis with the abdomen. It contains the Ductus Deferens (carries sperm), Arteries (testicular artery), Veins (pampiniform plexus – cools blood), and Lymph vessels.

Testis – covered by (in order from out Þ in) the skin and superficial fascia of the scrotum, Dartos muscle, Scarpa’s fascia, Colle’s fascia, exterior spermatic fascia (from external oblique), Cremasteric muscle (from internal oblique), deep internal spermatic fascia (from transversalias fascia), and tunica vaginalis (from peritoneum, see above). The testis are the male reproductive organ and produce male germ cells (sperm) and androgens (male sex hormones). The epididymus is a comma shaped structure above the testis where sperm undergo their final maturation.

Anatomy Structures

Skeletal/Surface Landmarks:

Xiphisternal Junction- where the xyphoid process connects to the sternal body, at the 7^th costal notch
Costal Margin- the lowest edge of the costal cartilage that connects the ribs to the sternum
Pubic Crest- the thicken superior border of the pubic bone
Pubic Tubercle- ~2.5 cm from the median plane, an important bony landmark when inguinal hernia is present
Anterior Superior Iliac Spine- the bony part of the pelvis that juts out anteriorly, where the inguinal ligament starts
Iliac Crest- when you put your hands on your hips, they rest on the iliac crest (the superior margin of the ileum)

Superficial Fascia:

Camper's (fatty) Fascia- the fatty layer of the superficial fascia
Scarpa's (fibrous) Fascia- the shiny, fibrous layer just under the fatty layer

Nerves:

Anterior Cutaneous Nerves-pierce the rectus sheath a short distance from the median plane. T10 innervates the umbilicus
Iliohypogastric Nerve- supplies the skin over the inguinal region
Ilioinguinal Nerve- runs just superior to the iliac crest, supplies the skin of the inner thigh, when stroked will raise testis

Muscles and Associated Structures:

External Abdominal Oblique Muscle and its aponeurosis-from the 5^th-12^th ribs to the iliac crest, linea alba, and pubic tubercle
Linea Alba- the white line down the center of the anterior abdomen,
Superficial Inguinal Ring (Medial and Lateral Crura)- a triangular aperture in the aponeurosis of the external oblique
Inguinal Ligament- from the external oblique, runs between the anterior superior iliac spine and the pubic tubercle
Internal Oblique Muscle and its aponeurosis- from the iliac crest and inguinal ligament to the ribs, linea alba, and pubis
Transversalis Fascia (often fused with Peritoneum)- lines most of the abdominal wall
Rectus Abdominis Muscle – "six pack" muscle running vertically along the ventral abdomen
Rectus Sheath (Anterior and Posterior Layers)- made of the aponeurosis of the obliques and transversus abdominus
Tendinous Intersections- where the rectus sheath is firmly attached to the Rectus abdominus
Arcuate Line- below this line the tranversus abdominus’s aponeurosis is located anteriorly to the rectus muscle

Vessels:

Inferior Epigastric Vessels- from the external iliac arteries, runs superiorly to the tranversalis fascia until the arcuate line
Superior Epigastric Vessels- from the internal thoracic arteries, anastomose with the inferior epigastric arteries
Deep Circumflex Iliac- runs on the deep aspect of the anterior abdominal wall parallel to the inguinal ligament.

Male Reproductive Anatomy:

Scrotum- consists of two layers, skin and superficial fascia. Superficial fascia contains the Dartos muscle
Spermatic Cord- from the deep inguinal ring, to the posterior border of the testis, contains the Ductus Deferens and Vessels
Testis- the main male reproductive organ. Where sperm and androgens are made
Gubernaculum-a ligament during development that extends from the testis (internal) to the future scrotum (external)
Dartos (Tunica Dartos)- in the superficial fascia of the scrotum, "wrinkles" scrotum
External Spermatic Fascia- continuous with the aporneurosis of the external oblique
Cremasteric Fascia and Muscle- "pulls testis up", from the internal oblique
Ductus Deferens- about 45 cm long, carries sperm form the epididymus to the ejaculatory duct through the inguinal canal
Deferential Artery- artery of the ductus deferens from the inferior vessicular artery and anastomoses with the testicular artery
Testicular Artery- the artery that supplies the testis, arises from the aorta at L2
Pampiniform Plexus of Veins-large vine-like venous plexus, located within the internal spermatic fascia
Tunica Vaginalis- the remnant of the peritoneum that exists in the testis
Epididymis (Head, Body, and Tail)- comma shaped structure above and behind the testis, where sperm mature
Efferent Ductules- these ductules transmit sperm from the testis to the epididymus
Seminiferous Tubules- where sperm are formed in the testis

Hernias

a hernia is a protrusion of a structure of organ through the tissues normally containing it
hernias are the most common cause of small bowel obstruction

Inguinal Hernia – two varieties:

(1) Direct – herniation passes directly through the posterior wall of the inguinal canal – passes medial to inferior epigastric vessels, through Hesselbach’s triangle (made up of lateral edge of the Rectus abdominus, the inguinal ligament, and the inferior epigastric vessels)

does not go through the inguinal canal or descend into the scrotum

Acquired, associated with weakness in the posterior wall of the inguinal canal.

(2) Indirect – herniation occurs through the Inguinal canal, through the deep inguinal ring (passes lateral to the inferior epigastric vessels)

does extend into scrotum

Congenital, associated with the persistence of the processus vaginalis.

Umbilical hernias – protrusion of viscera or omentum through the abdominal wall at the umbilicus (usually congenital)

Femoral hernias – passage of viscera through the femoral ring into the femoral canal (below the line of the inguinal ligament)

Diaphragmatic hernias – abdominal viscera passing via congenital opening of the diaphragm into the thoracic cavity and displacing thoracic contents (mediastinum) to the right. Two varieties:

(1) Paraesophageal hernias (rolling) – the gastric fundus passes into the thoracic cavity via a weakness or widening in the diaphragm adjacent to the opening for the esophagus.

can lead to incarceration and strangulation of the stomach

(2) Hiatus (sliding) – herniation of the gastroesophageal junction upward into the mediastinum. ("sliding" or "fixed")

Can be fixed with a Nissen Fundulplication – surgery in which fundus is wrapped around the esophagus, creating a new sphincter.
causes reflux (not incarceration of the stomach)

Frequency of Abdominal Wall Hernias:

Inguinal: male 97%, female 50%
Femoral: male 2%, female 34%
Umbilical: male 1%, female 16%

Treatment: all these hernias have to be fixed surgically or incarceration can occur, leading to strangulation (cuts off blood supply) and death of the bowel.

Exception to this rule: Umbilical Hernia does not have to be fixed right away, it sometimes resolves by itself because as the baby grows the bowel can get ‘sucked’ back into the abdomen – therefore fix at 3 years if not corrected

Review

muscular layers that contribute to the rectus sheath:

the exterior oblique, the internal oblique, and the transversus abdominus.

vessels on the deep surface of the rectus abdominis muscle:

The superior and inferior epigastric vessels can be found on the deep surface of the rectus abdominus

The superior epigastric is from the internal thoracic artery (which is off the subclavian artery)
The inferior epigastric is off the external iliac artery.

abdominal wall layers that form the margins of the external and internal inguinal opening

The superficial inguinal ring is made from the external oblique, the deep inguinal ring is made from a hole in the transversalias fascia

continuity from male genitalia to the abdomen

Cremaster Þ internal oblique, Dartos muscle Þ membranous deep layer of the superficial fascia of the anterior abdominal wall, Tunica Vaginalis Þ a sac derived from the peritoneum.

herniations

A indirect hernia passes laterally, direct passes medially to epigastric vessels

umbilicus

The umbilicus is normally found a L3-L4 but its position varies due to age and obesity.