Diagnostic Ultrasound - Abdomen and Pelvis

Abdominal Wall
Anatomy: Abdomen
TERMINOLOGY
Definitions
• Abdomen is the region between diaphragm and pelvis
GROSS ANATOMY
Anatomic Boundaries
• Anterior abdominal wall bounded superiorly by xiphoid
process and costal cartilages of 7th-10th ribs
• Anterior wall bounded inferiorly by iliac crest, iliac spine,
inguinal ligament, and pubis
• Inguinal ligament is inferior edge of aponeurosis of external
oblique muscle
Muscles of Anterior Abdominal Wall
• Consist of 3 flat muscles (external oblique, internal oblique,
and transverse abdominal), and 1 strap-like muscle (rectus)
• Combination of muscles and aponeuroses (sheet-like
tendons) act as a corset to confine and protect abdominal
viscera
• Linea alba is a fibrous raphe stretching from xiphoid to
pubis
○ Forms central anterior attachment for abdominal wall
muscles
○ Formed by interlacing fibers of aponeuroses of the
oblique and transverse abdominal muscles
○ Rectus sheath is also formed by these aponeuroses as
they surround rectus muscle
• Linea semilunaris is a vertical fibrous band at lateral edge of
rectus sheath bilaterally
○ Aponeuroses of internal and transversus abdominis join
in linea semilunaris before forming rectus sheath
• External oblique muscle
○ Largest and most superficial of 3 flat abdominal muscles
○ Origin: External surfaces of ribs 5-12
○ Insertion: Linea alba, iliac crest, pubis via broad
aponeurosis
• Internal oblique muscle
○ Middle of 3 flat abdominal muscles
○ Runs at right angles to external oblique
○ Origin: Posterior layer of thoracolumbar fascia, iliac crest,
and inguinal ligament
○ Insertion: Ribs 10-12 posteriorly, linea alba via broad
aponeurosis, pubis
• Transversus abdominis (transversalis) muscle
○ Innermost of 3 flat abdominal muscles
○ Origin: Lowest 6 costal cartilages, thoracolumbar fascia,
iliac crest, inguinal ligament
○ Insertion: Linea alba via broad aponeurosis, pubis
• Rectus abdominis muscle
○ Origin: Pubic symphysis and pubic crest
○ Insertion: Xiphoid process and costal cartilages 5-7
○ Rectus sheath: Strong fibrous compartment that
envelops each rectus muscle
– Contains superior and inferior epigastric vessels
• Actions of anterior abdominal wall muscles
○ Support and protect abdominal viscera
○ Help flex and twist trunk, maintain posture
○ Increase intra-abdominal pressure for defecation,
micturition, and childbirth
○ Stabilize pelvis during walking, sitting up
• Transversalis fascia
○ Lies deep to abdominal wall muscles and lines entire
abdominal wall
○ Separated from parietal peritoneum by layer of
extraperitoneal fat
Muscles of Posterior Abdominal Wall
• Consist of psoas (major and minor), iliacus, and quadratus
lumborum
• Psoas: Long thick, fusiform muscle lying lateral to vertebral
column
○ Origin: Transverse processes and bodies of vertebrae
T12-L5
○ Insertion: Lesser trochanter of femur (passing behind
inguinal ligament)
○ Action: Flexes thigh at hip joint; bends vertebral column
laterally
• Iliacus: Large triangular sheet of muscle lying along lateral
side of psoas
○ Origin: Superior part of iliac fossa
○ Insertion: Lesser trochanter of femur (after joining with
psoas tendon)
○ Action: "Iliopsoas muscle" flexes thigh
• Quadratus lumborum: Thick sheet of muscle lying adjacent
to transverse processes of lumbar vertebrae
○ Invested by lumbodorsal fascia
○ Origin: Iliac crest and transverse processes of lumbar
vertebrae
○ Insertion: 12th rib
○ Actions: Stabilizes position of thorax and pelvis during
respiration, walking, bends trunk to side
Paraspinal Muscles
• Also called erector spinae muscles
○ Invested by lumbodorsal fascia
• Composed of 3 columns: Iliocostalis: Lateral; longissimus:
Intermediate; spinalis: Medial
• Origins: Sacrum, ilium, and spines of lumbar and 11th-12th
thoracic vertebrae
• Insertions: Ribs and vertebrae with additional muscle slips
joining columns at successively higher levels
• Action: Extends vertebral column
ANATOMY IMAGING ISSUES
Imaging Recommendations
• High-frequency (5-12 MHz) linear transducer for anterior
abdominal wall and paraspinal muscles
• 3-5 MHz for posterior abdominal wall muscles
• Supine position for examination of anterior and lateral
abdominal wall
○ Image during Valsalva maneuver and in standing position
to increase abdominal pressure and elicit hernias
○ Prone position for ultrasound of paraspinal muscles
• Compare with contralateral side to check for symmetry
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