Abdominal Wall (12)

SAIT DMST 254: Abdomen & Superficial Structures 1

Course Introduction

Title: Abdominal Wall
Discipline: Diagnostic Medical Sonography
Term: Winter 2026
Institution: Southern Alberta Institute of Technology (SAIT)
Department: School of Health and Public Safety

Course Learning Outcome

Objective: Assess abdominal wall structures on sonographic images.
Supplementary Materials: Students are encouraged to read the assigned pages in the following textbooks for enhanced understanding:
  - Kawamura (3rd ed.): Chapter 2, pages 14-23
  - Kawamura (4th ed.): Chapter 2, pages 14-23
  - Kawamura (5th ed.): Chapter 4, pages 39-50
  - Curry Prince: Chapter 6, pages 78, 85-88

Indications for Abdominal Wall Sonography

Palpable mass: Distinguishing between wall and abdominal cavity.
Surgical Wound Assessment: Evaluating healing and complications.
Trauma: Assessing injuries to the abdominal wall.
Findings on Other Imaging Modalities: Providing further investigation where needed.

Scanning Technique

Transducer: Use of a high frequency linear transducer.
Pressure: Minimal pressure should be applied; a standoff pad may be required.
Patient Preparation: None needed prior to examination.

Abdominal Wall Layers

Epidermis
- Thickness: 1 to 4 mm.
- Sonographic Appearance: Highly reflective layer, appears echogenic.
Subcutaneous Tissue
- Composition: Mostly fat.
- Thickness and Echogenicity: Variable; influenced by water content, typically less echogenic compared to muscle.
Muscle Layer (Anterior and Lateral)
   - Rectus Abdominis:
     - Paired muscle in the midline of the anterior abdominal wall.
     - Origin: Symphysis pubis and pubic crest.
     - Insertion: Xiphoid process and costal cartilage.
     - Contains tendinous insertions that attach to the rectus sheath anteriorly, aiding in hematoma localization.
   - Linea Alba:
     - Fibrous band extending from xiphoid to symphysis pubis, formed by fusion of aponeuroses of the three anterolateral abdominal muscles.
     - Appears sonographically as echogenic, wider above umbilicus, may cause refractive duplication artifact (e.g., “double aorta”).
   - Arcuate Line:
     - Notable anatomical point located between the umbilicus and symphysis where the posterior portion of the rectus sheath passes in front of the rectus muscle.
   - External Oblique:
     - Originates from the outer surface of the lower 8 ribs.
     - Inserts into xiphoid, linea alba, pubic bones, and anterior iliac crest.
   - Internal Oblique:
     - Lies deep to external oblique, with origins from lumbar fascia, anterior iliac crest, and inguinal ligament.
   - Transversus Abdominis:
     - Deep to internal oblique, fibers run horizontally originating from lower 6 ribs, lumbar fascia, iliac crest, and inguinal ligament, inserting into the xiphoid, linea alba, and symphysis pubis.
   - Sonographic Appearance of Muscle:
     - Hypoechoic to sonolucent, featuring specular reflectors, giving it a striated look.

Abdominal Wall Muscle Layer (Posterior)

Psoas Major:
- Shape: Fan-shaped muscle, originating from the sides of the vertebral column and inserting into the lesser trochanters of the femurs.
- Appearance: Sonographically, appears hypoechoic and lateral to the spine.
Quadratus Lumborum:
- Shape: Flat muscle, found posterolateral to the psoas muscle.
- Origin: Iliac crest and inserts into the 12th rib and upper four lumbar vertebrae.
Iliacus:
- Origin: Iliac fossa, sacrum, and SI joints.
- Inserts into the psoas major and lesser trochanters.

The Inguinal Canal

Description:
  - Obliquely oriented tunnel, runs inferior and medial, characterized as slit-like with openings at each end.
  - Deep Inguinal Ring:
    - Opening at the superior end, located midway between the anterior superior iliac spine (ASIS) and symphysis pubis, feature a defect in transversalis fascia.
  - Superficial Inguinal Ring:
    - Opening at the inferior end, through external oblique aponeurosis, containing spermatic cord (males) and round ligament of uterus (females).

Diaphragm

Overview:
  - Dome-shaped muscle separating thorax from abdominal cavity, plays a crucial role in respiration.
  - Origin:
    - Peripheral thoracic cage with fibers originating from three areas: lumbar spine (crura), lower sternum, and lower six ribs.
  - Muscle Fiber Arrangement: Convergence into a central tendon.
  - Sonographic Appearance:
    - Diaphragm shows as a highly echogenic arc; crura appear as thin hypoechoic bands positioned relative to major abdominal structures (e.g., aorta, IVC).

Pleural Space Scanning Approaches

Approaches:
- Abdominal/Subcostal approach.
- Intercostal approach.
Sonographic Windows:
- Utilizing liver (right) or spleen (left) for visualization.
Diaphragm Thickness:
- Normal thickness is approximately 5 mm.
Mirror Image Artifact:
- Indicative of absence of pleural fluid.
Distance from Rib Interface:
- When scanning intercostally, pleural space is within 1 cm from rib interface.
Echogenic Appearance of Pleura:
- Visceral Pleura: Bright linear interface that moves with respiration (gliding sign).
- Parietal Pleura: Weak echogenic line, may be obscured, can show hypoechoic separation from visceral pleura.
Gliding Sign:
- Refers to the movement of the visceral pleura back and forth during a live sonography assessment.

References

Curry, R. A., & Prince, M. (2021). Sonography: Introduction to normal structure and function (5th ed.). St. Louis, MO: Elsevier Saunders.
Kawamura, D., & Nolan, T. (2023). Diagnostic medical sonography abdomen & superficial structures (5th ed.). Baltimore, MD: Lippincott Williams & Wilkins.

Copyright

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