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Abdominal wall and para-spinal structures anatomy


Abdomen: Region between diaphragm and pelvis


Anatomic Boundaries
Anterior abdominal wall is bounded superiorly by xiphoid process and costal cartilages of 7th-10th ribs
Anterior wall is 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 oblique and transverse abdominal muscles
Rectus sheath is also formed by these aponeuroses as they surround rectus muscle

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 a 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 a broad aponeurosis, pubis

Transverse abdominal 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
3 tendinous intersections divide rectus sheath into distinct muscle bellies
This gives rise to '6-pack' appearance of well developed rectus abdominus musculature
Arcuate line lies about midway between umbilicus and pubic crest
Above arcuate line, internal oblique aponeurosis splits to enclose rectus muscle
Below arcuate line, internal oblique passes wholly in front of rectus muscle so that rectus muscle lies directly on transversalis fascia
Actions of anterior abdominal wall muscles
Support and protect abdominal viscera
Help flex and twist trunk, maintain posture
Increase intraabdominal 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

Imaging Recommendations
High-frequency (7-10 MHz) linear transducer for anterior abdominal wall and paraspinal muscles
3-5 MHz for posterior abdominal wall muscles

Patient may be asked to perform Valsalva maneuver to increase abdominal pressure and exaggerate abdominal wall hernia for better visualization
Comparison with contralateral side to check for Symmetry

Gallery and Imaging

Graphic shows the aponeuroses of the internal and external oblique and transverse abdominal muscles are 2-layered and interweave with each other, covering the rectus muscle and constituting the rectus sheath and linea alba. About midway between the umbilicus and symphysis, at the arcuate line, the posterior rectus sheath ends. The transversalis fascia is the only structure between the rectus muscle and parietal peritoneum below the arcuate line. The arcuate line is also the location where the inferior epigastric artery enters the rectus sheath.


Graphic shows the lumbar vertebrae are covered and attached by the anterior longitudinal ligament, and the diaphragmatic crura are closely attached to it, as are the origins of the psoas muscles which also arise from the transverse processes. The iliacus muscle arises from the iliac fossa of the pelvis and inserts into the tendon of the psoas major, constituting the iliopsoas tendon, which inserts into the lesser trochanter. The quadratus lumborum arises from the iliac crest and inserts into the 12th rib and transverse processes of the lumbar vertebrae. Diaphragmatic and transverse abdominal fibers interlace. The psoas and quadratus lumborum pass behind the diaphragm under the medial and lateral arcuate ligaments.
Graphic shows the paraspinal muscles and muscles of the back. The latissimus dorsi muscles are not included. The erector spinae have thick tendinous origins from the sacral and iliac crests and the lumbar and 11th-12th thoracic spinous processes. Superiorly, the muscle becomes fleshy and subdivides in the upper lumbar region to become the iliocostalis, longissimus, and spinalis muscles (from lateral to medial), tapering as they insert into the vertebrae and ribs. The erector muscles flank the spinous processes and span the length of the posterior thorax and abdomen. They are responsible for extension of the vertebral column.

Transverse extended field of viegrayscale ultrasound of the midline anterior abdominal wall shows the paired rectus abdominis muscles separated bthe linea alba. The rectus abdominis muscles arcomparable in echogenicitand thickness. The surrounding rectus sheath is seen as a fine, thin, echogenic structuraround the muscles.

Transverse color Doppler ultrasound of a rectus abdominis muscle shows arteries within the muscle. At the upper abdomen, these arbranches of the superior epigastric artery, and at the lower abdomen comprise branches of the inferior epigastric arteries. These anastomose at the umbilicus.

Longitudinal extended field of vie(EFOV) grayscale ultrasound shows the distal rectus abdominis muscle and its tendinous insertion into the symphysis pubis. Note hothe rectus abdominis muscle tapers distally.


Transverse extended field of viegrayscale ultrasound shows the relationship of the medially located rectus abdominis and the laterally located oblique and transverse abdominal muscles. Mediallythe external and internal oblique and transversus abdominal muscles form aponeuroses that compose the rectus sheath.

Transverse grayscale ultrasound at the right anterolateral abdominal wall shows the relationship of the lateral abdominal wall muscles in better detail. Note the oblique and transverse abdominal muscles taper medially as they become aponeuroses.

correlative axial contrast-enhanced CT illustrates the muscles of the abdominal wall. The rectus abdominis muscle in the anterior abdominal wall and the oblique and transverse abdominal muscles in the anterolateral abdominal wall and their aponeuroses arshown.

Coronal oblique grayscale ultrasound using the liver and right kidneas acoustic windows shows the right psoas muscle that originates from the lumbar spine and inserts into the proximal femur.

Transverse grayscale ultrasound shows the right upper abdomen using the liver and kidneas acoustic windows. The kidneis identified lateral to the psoas and anterior to the quadratus lumborum. The psoas is identified along the paravertebral region in its entirabdominal course. The quadratus lumborum originates from the iliolumbar ligament and iliac crest to inserinto the last rib and lumbar transverse processes. It is easily identified as the muscle on which the kidnerests.

Transverse grayscale ultrasound shows the right upper abdomen. Continuing the scan inferiorlythe relationship of the posterior abdominal wall musculature would be maintained.

Correlative coronal CECT shows the paralumbar location of the psoas muscles and their medial location relative to the kidneys. The psoas muscles originate from the lumbar and 12th thoracic vertebral bodies and their transverse processes, running past the pelvic brim wherthey course inferolaterally to be joined bthe iliacus muscle.

Correlative axial CECT better illustrates the anatomic relationships of the kidney with the posterior abdominal wall muscles. The kidneis lateral to the psoas muscle and rests upon the quadratus lumborum muscle. The erector spinae muscles arimmediately posterior to the quadratus lumborum, and the 2 muscles arinvested blumbodorsal fascia.

Correlative axial CECT shows the level of the inferior pole of the right kidney. The psoas muscle and quadratus lumborum muscles, seen in their midsections, arnothicker.

Transverse grayscale ultrasound in the lower abdominal region shows the right psoas muscle, composed of the psoas minor resting upon the psoas major muscle. The 2 muscles cannot be separated clearly on ultrasound. Owing to their depth, the paraspinal muscles cannot be demonstrated in detail.

Transverse grayscale ultrasound of the same patient shows the right lower abdomen. The distal psoas muscle has diminished in size. It rests on the medial portion of the iliacus muscle. The iliacus muscle is a flat muscle that fills the iliac fossa. Both the psoas and iliacus muscles continue inferiorly together.

Distally, the fibers from the iliacus muscle converge and inserinto the lateral side of the psoas muscle to form the iliopsoas muscle.


Correlative axial CECT shows the level of the inferior pole of the kidney. The quadratus lumborum muscle is morlaterally located, and the psoas muscle is directly anterior to the erector spinae muscle.

Correlative axial CECT shows that the psoas muscle has begun its dorsolateral course and is noanterior to the iliacus muscle. The iliacus muscle is easily identified as a flat muscle filling the iliac fossa, arising from the upper 2/3 of the iliac fossa, inner lip of the iliac crest, anterior sacroiliac and the iliolumbar ligaments, and base of the sacrum.

Axial correlative CECT shows the psoas and iliacus muscles have converged and arnoindistinguishable. The resultant iliopsoas muscle passes beneath the inguinal ligament and becomes tendinous as it inserts into the lesser trochanter of the femur.


Transverse extended field of viegrayscale US of the back (with patient prone) shows the erector spinae muscles flanking the spinous process. Thearinvested blumbodorsal fascia, which also invests the anteriorly located quadratus lumborum muscle. The kidneys are partially demonstrated.

Transverse EFOgrayscale US shows the right erector spinae muscle (with patient prone). The 3 columns (iliocostalis, longissimus, and spinalis muscles, from lateral to medial) composing the erector spinae arnot clearly separated on ultrasound. They aridentified collectively as a thick fleshmuscle lateral to the spinous process.

Correlative axial CECT shows the paraspinal muscles at the level of the kidneys. The erector spinae muscles originate from a broad and thick tendon that is attached to the sacrum and iliac crest distally as well as the lumbar and lower 2 thoracic spinous processes morproximally.


Transverse grayscale ultrasound shows a small hyperechoic nodule in the subcutaneous fat of the anterior abdominal wall. Mild intrinsic vascularity on color Doppler imaging was present (not shown). Histology following surgical excision revealed an angiolipoma. No deep extension is present.

Transverse grayscale ultrasound shows a well-defined hypoechoic mass in the anterior abdominal wall. Theris small fascial defect of the linea alba.

Transverse ultrasound of the same patient as the previous image shows widening of the fascial defect and increased herniation of omental fat with Valsalva maneuver. The intraperitoneal communication is much morconspicuous with Valsalva maneuver. Fatty hernias of the linea alba usually occur in the epigastrium and artypically small and painful. The predilection for the epigastrium mabe related to extra tension on the linea alba at this location due to pull from the diaphragm


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