Anterior Abdominal Wall and Inguinal Region

• This lecture goes over the anterior abdominal wall and the inguinal region

Clinical Anatomy

• Abdomen x-rays show the liver, right kidney, right transverse process of L1, ascending colon, right psoas major, small bowel, pelvic bone, right femur, splenic flexure, transverse colon, left kidney, left 11th rib, descending colon, left pedicle of L3, spinous process of L4, left sacroiliac joint, and bladder
• A Barium Meal, viewed via x-ray, shows the duodenum (first and second parts), fundus of the stomach, body, pylorus, angular notch, and pyloric antrum
• A Barium Enema, viewed via x-ray, shows the jejunum
• Locations of hernias include umbilical, incisional, epigastric, spigelian, inguinal, and femoral

Objectives

• Demonstrate landmarks of the anterior abdominal wall: costal margin, xiphoid process, umbilicus, transpyloric plane (L1), subcostal plane, anterior superior iliac spine, iliac tubercle, pubic tubercle, and pubic symphysis
• Explain the use of these landmarks to divide the anterior abdominal wall into descriptive regions
• Outline the arrangement of the external oblique, internal oblique, transversus abdominis and rectus abdominis muscle layers, rectus sheath, transversalis fascia, and parietal peritoneum
• Describe the rectus sheath and its contents
• Define the linea alba and the linea semilunaris
• Define the sources and distribution of the motor and sensory nerves to the abdominal wall and diaphragm
• Describe the blood supply of the abdominal wall
• Explain the nature and course of the inguinal canal making correct use of the following terms: superficial and deep inguinal rings, pubic tubercle, pubic symphysis, scrotum, testis, spermatic cord (testicular vessels and ductus deferens) and round ligament of the uterus
• Distinguish between mid-inguinal point and midpoint of inguinal ligament
• Distinguish between direct and indirect inguinal hernias
• Summarize the anatomical basis for femoral hernia
• Understand the basis of the abdominal region/quadrant in clinical examination, imaging and surgical procedures

Class Content

• Skeletal framework of abdomen
• Abdominal regions and cavity
• General arrangement of the abdominal wall muscles
• Abdominal wall blood supply and nerve supply
• Inguinal region and inguinal canal
• Inguinal hernias (direct and indirect)
• Femoral hernia

Abdomen Boundaries

• The abdomen is the part of the trunk between the thorax and the pelvis
• Superior boundary is the diaphragm
• Inferior boundary is the pelvic inlet

Skeletal Framework

• The skeletal framework of the abdomen is the bony landmarks of the sternum and xiphoid process, costal margin cartilages, iliac crest and fossa and anterior superior iliac spine (ASIS), pubic tubercle, pubic symphysis, and thoracic and lumbar vertebrae and sacrum
• The gallbladder area is palpable around the tip of the right 9th costal cartilage

Abdomen Quadrants

• Superiorly bounded by cartilages of 7th to 10th ribs
• Inferiorly bounded by the inguinal ligament and pelvis
• For general clinical descriptions, it is divided into 4 quadrants by a transumbilical plane and median plane

Nine Regions

• Abdomen has 9 regions delineated by the subcostal plane, intertubercular plane, and 2 midclavicular planes
• Subcostal plane cuts through the inferior border of the 10th costal cartilage and body of the L3 vertebra
• Intertubercular plane lies between iliac tubercles and L5 vertebra
• 2 Midclavicular planes pass from the midpoint of the clavicles to mid-inguinal points
• The transpyloric plane in most cases cuts through the pylorus of the stomach, the tips of the 9th costal cartilages, and the lower border of the L1 vertebra

Abdominal Lines

• Linea alba passes in the median line to the symphysis pubis and is formed by the fusion of the rectus sheath
• Linea semilunaris passes along the lateral border of the rectus abdominis and crosses the costal margin at the tip of the 9th costal cartilage

Abdominal Wall Fascia

• Skin
• Subcutaneous tissue comprised of the superficial fatty layer and the deep membranous layer
• The investing (deep) fascia
• Muscles and their aponeurosis
• Deep fascia
• Extraperitoneal fat
• Parietal peritoneum
• Superficial fatty layer of Camper is continuous with the superficial fat of other body regions
• Deep membranous layer of Scarpa blends with the deep fascia of the upper thigh, the penis and scrotum, or labia majora, and into perineum as Colles' fascia

Abdominopelvic Cavity

• Abdominal and pelvic cavities is a continuous structure
• The diaphragm separates the thoracic and abdominal cavities
• Upper part of the abdominal cavity extends beneath the thoracic cage
• The pelvic inlet (pelvic brim) arbitrarily separates the abdominal from the pelvic cavity

Visceral Structures

• Stomach, duodenum, small and large intestines
• Liver, pancreas, and spleen
• Kidneys, ureters, and urinary bladder
• Reproductive organs
• Abdominal vessels
• The anterior abdominal wall is often used for clinical examination and surgical access to various intra-abdominal organs
• The choice of incisions in surgery aims at minimizing damage to nerves and muscles in order to preserve functional integrity of the abdominal wall and prevent hernia

Abdominal Surgical Incisions

• Surgeons use various incisions to gain access to the abdominal cavity, choosing the incision that allows adequate exposure and has the best cosmetic effect
• Common incisions include: median or midline, left paramedian incision, Gridiron (muscle-splitting) incision, transverse (abdominal) incision, suprapubic (Pfannenstiel) incision, and subcostal incision

Surgical Incisions Continued

• Median midline incisions cut through the linea alba, superior or inferior to the umbilicus; provide minimal blood loss, avoids major nerves and easy access for exploration
• Paramedian incisions cut to the right or left of the midline; avoid nerves, frees the rectus abdominal muscle which decreases tension to the muscle, gives access to the peritoneal cavity.
• Gridiron (muscle splitting)/McBurney incisions are an incision of the external oblique aponeurosis in the direction of its fibers; the internal oblique and transversus abdominis are then incised and split in the direction of their fibers which are then retracted; provides good access with almost no muscle damage and avoids damage to local nerves
• Transverse incisions cut through the anterior rectus sheath and the rectus abdominis; cause the least amount of nerve damage and the muscular segments can be rejoined, they are incredibly useful for dissection above the level of the umbilicus
• Pfannenstiel (suprapubic incision): This transverse, slightly convex cut transects the linea alba and anterior layer of the rectus sheath at the pubic hairline; Separates the underlying rectus muscles via the tendons (to allow better reattachment) and identify the surrounding nerves; used for most gynecologic surgeries

Abdominal Wall Muscles

• The anterior wall contains paired vertical rectus abdominis muscles within the rectus sheath
• The lateral wall contains 3 flat sheet muscles: external oblique, internal oblique, and transversus abdominis
• The posterior wall contains the post vertebral muscles eerector spinae group, psoas major, quadratus lumborum and iliacus muscles
• The three flat muscles are separate in the flanks and their fibres continue anteriorly as aponeurotic sheets that connect the muscles to bones and cartilage and contribute to the rectus sheath

Muscle Attachments

• The external oblique muscle laterally has an external surface on the lower 8 ribs and medially fans out to attach to the xiphoid process, linea alba, pubic crest and tubercle, and anterior half of iliac crest; the muscle fibres are directed downward and forward (inferomedially); the inferior margin curls under to form the inguinal ligament
• The internal oblique muscle laterally has thoracolumbar fascia, the iliac crest (anterior 2/3rd), and the inguinal ligament (lateral half); medially has lower 3 ribs and costal cartilages, linea alba (rectus sheath), xiphoid process, and pubic crest; its muscle fibres are directed downward and backward; the lowest fibres of internal oblique and transverse abdominis join to form the conjoint tendon
• The transversus abdominis muscle laterally has the lower 6 costal cartilages, thoracolumbar fascia, iliac crest (anterior 2/3rd), and inguinal ligament (lateral 1/3rd); medially has the xiphoid process, linea alba (rectus sheath), symphysis pubis, and conjoint tendon; the muscle fibres are directed horizontally; the neurovascular plane lies between this and the internal oblique

External Oblique and Inguinal Ligament

• The aponeurosis fuses medially with the rectus sheath
• Forms superficial inguinal ring in the aponeurosis (a hole in EOA)
• Lower aponeurotic edge is rolled inwards and forms the inguinal ligament; stretches between the ASIS to pubic tubercle

Rectus Abdominis

• Long strap muscle of the anterior abdominal wall enclosed in the rectus sheath and has two heads
• Superior attachment to 5-7 costal cartilages and the xiphoid process
• Inferior attachment to the Symphysis pubis and pubic crest
• Divided into segments by tendinous intersections which are attached to the anterior wall of the rectus sheath
• Segmental nerve (T7 to T12) supply provided
• This may be of surgical importance if there is a hematoma of rectus muscle is localised, or in paramedian incision, to displace muscle laterally (nerve supply comes from lateral)

Rectus Sheath

Anterior Walls

• Formed by aponeuroses of the external, internal and transverse abdominis muscles

Above Umbilicus

• The internal oblique aponeurosis splits and encloses the rectus abdominis
• The aponeuroses of external oblique remains in front and the transversus abdominis aponeurosis remains behind the muscle

Below Umbilicus

• All 3 aponeurotic layers are anterior to the rectus muscle

Posterior Wall

• The posterior wall of the sheath is incomplete and stops short below the umbilicus at the arcuate line
• Below the arcuate line, the rectus abdominis muscle is in contact with the transversalis fascia
• An arcuate line often demarcates the transition between the posterior rectus sheath covering the superior three quarters of the rectus abdominis and the transversalis fascia covering the inferior quarter

Transversalis Fascia

• Forms the Deep Inguinal Ring in the fascia (a hole in transversalis fascia), about 1.5 cm above the midpoint of the inguinal ligament

Arteries

• Neurovascular plane is between internal Inguinal oblique and transversus abdominis
• Blood supply of the rectus muscle: superior epigastric artery (terminal branch of internal thoracic (mammary) artery) and inferior epigastric artery (branch of external iliac artery)
• Vessels enters the rectus sheath and anastomose forming a potential by-pass to abdominal aorta
• Blood supply of the flank muscles: intercostal arteries 7-11, subcostal artery, lumbar arteries and deep circumflex iliac arteries
• Venous drainage: Deep veins bearing the same names accompany the arteries

Nerve Supply of Abdominal Wall

• External oblique supplied by anterior rami of T7-T11 spinal nerves
• Internal oblique supplied by anterior rami of T7-T12 and L1 spinal nerves
• Rectus abdominis supplied by anterior rami of T7-T12 spinal nerves (no L1)
• All terminate by supplying the skin
• Parietal peritoneum has same segmental nerves of the body wall to provide somatic sensory supply
• Visceral peritoneum has NO somatic sensory innervation

Dermatomes

• T7-T9 correlates to epigastrium sensation
• T10 correlates to umbilicus sensation
• T11-12 correlates to inferior to the umbilicus sensation
• L1 (IHN and IIN) correlates to inguinal and pubis sensation

Abdominal Wall Functions

• Compresses the abdominal content and increase the intra-abdominal pressure to aid expiration, evacuation of urine, faeces, parturition, heavy lifting
• Helps to maintain posture
• Supports viscera (mainly the intestines)
• Flexes and rotates the trunk
• The rectus abdominis is the most powerful flexor of the vertebral column (lower thoracic and lumbar)
• External and internal obliques of both sides are important partners in this action

Inguinal Region

• Inguinal region is also called groin
• Between ASIS and pubic tubercle [PT]
• Weakness of this region causes hernia; hernias occur in both sexes with Males greater than Females which is clinically important

Inguinal Canal Structure

• Oblique passageway in the lower part of the anterior abdominal wall
• Present in both males and females, 4 cm long in adults
• Lays above the medial half of the inguinal ligament
• Extends from deep inguinal ring (a hole in transversalis facia) to superficial inguinal ring (a hole in external oblique aponeurosis)
• Contains spermatic cord and ilioinguinal nerve, blood and lymphatic vessels in males
• Contains round ligament and ilioinguinal nerve, blood and lymphatic vessels in females

Walls

• The anterior wall contains the external oblique aponeurosis along the whole length, and the internal oblique muscle reinforcing lateral to the 1/3 area
• The floor has a rolled inferior edge of external oblique aponeurosis forming the inguinal ligament
• The roof has arching fibres of internal oblique and transverse abdominis
• The posterior wall contains the transversalis fascia and medially the conjoint tendon

Inguinal Hernia

• Inguinal hernia may be indirect when it occurs through the deep inguinal ring (often in young males) or direct (in older people often with conditions that predispose to increased intra-abdominal pressure, e.g. cough, constipation) when it occurs through the posterior wall
• Repair of a hernia often requires the walls to be strengthened to prevent recurrence

Hernias

• A hernia is an abnormal protrusion of an organ through the structure that usually contains the organ
• What makes up a hernia: sac (eg peritoneum), defect (the hole through which the hernia has occurred), and contents of the sac (eg bowel)

Hernia Terminology

• Reducible: sac returns to containing cavity
• Irreducible: sac cannot be returned to containing cavity
• Obstructed: sac contains blocked bowel
• Strangulated: sac has contents with a compromised blood supply

Clinical Features

• Lump in the groin
• May come and go
• There are different kinds of pain
• Vomiting and constipation may results
• Look for associated conditions

Factors That Prevent Hernias

• Oblique passage
• Posterior wall (immediately behind the superficial inguinal ring) is reinforced by the conjoint tendon
• When intra-abdominal pressure is increased on coughing and straining, the roof compresses the contents of the canal against the floor, so that the canal is completely closed

Common Inguinal Region Hernias

• To understand hernias you must know the anatomy of the inguinal canal and the femoral canal
• Inguinal hernia can manifest as indirect or direct inguinal hernia
• Femoral hernia

Comparison of Inguinal Points

• Mid-inguinal point is half way between ASIS and pubis; landmark for femoral artery in groin
• Midpoint of inguinal ligament between ASIS and pubic tubercle, a landmark for deep inguinal ring and indirect inguinal hernia; medial to this for direct inguinal hernia

Comparison of Inguinal Hernias

• Bulge through weakened fascia of abdominal wall
• Directly behind the superficial inguinal ring
• Medial to the inferior epigastric vessels.

Indirect

• Traverses inguinal canal;
• Same course as spermatic cord
• Enters inguinal canal at the deep inguinal ring; lateral to the inferior epigastric vessels
• Can pass into the scrotum or labia majora
• Has Male > female
• Congenital, injuries
• A direct hernia defect lies MEDIAL to the inferior epigastric vessels and directly behind the superficial inguinal ring but it DOES NOT enter the scrotum
• An indirect hernia defect lies LATERAL to the inferior epigastric vessels and can PASS into the scrotum or labia majora

Direct

• Older age group
• Acquired defect in posterior wall of the inguinal canal
• Associated with chronic straining
• Associated with weak musculature
• Path is straight through the posterior wall of the inguinal canal but doesn't enter the scrotum
• Defect is in the posterior wall of the inguinal canal medial to the inferior epigastric vessels

Indirect

-Most common type

• Tend to be in younger adults and children
• The hernia takes an indirect path through the abdominal wall
• The defect is a dilated deep ring
• Passes through the inguinal canal and into the scrotum
• Superficial inguinal ring is palpable above and lateral to the pubic tubercle by invaginating the scrotal skin with the finger; follow the spermatic cord to the superficial ring, and if the ring is dilated, it may admit the finger without causing pain
• A hernia produces an impulse against the finger when the patient coughs, yet one cannot distinguish as to whether it is direct or indirect

Femoral Hernias

• A femoral hernia occurs through the femoral canal (in the femoral triangle)
• Not as common as inguinal hernias
• Commonly seen in elderly and female as the femoral or pubic regions are wider in female when compared to male
• Have a high incidence of obstruction and strangulation
• On examination femoral hernias tend to be irreducible, and hot and painful if they are strangulated
• They can be distinguished from inguinal hernias because they appear below and lateral to the pubic tubercle
• Inguinal hernias are above and medial to the pubic tubercle

Course Summary

• The lecturer covered the skeletal framework, abdominal regions, abdominal wall structure, inguinal region and inguinal canal, and both inguinal and femoral hernias