What are the layers of the abdomen?

Layers of the Abdomen

The abdomen consists of multiple distinct layers from superficial to deep: skin, subcutaneous tissue (comprising superficial adipose layer, membranous layer, and deep adipose layer), muscles and aponeuroses (external oblique, internal oblique, and transversus abdominis), transversalis fascia, preperitoneal fat, and parietal peritoneum.

Detailed Anatomy of Abdominal Wall Layers

Superficial Layers

1. Skin
2. Subcutaneous Tissue - Consists of three distinct layers 1:
   • Superficial adipose layer (SAT) - Contains fibrous septa forming polygonal-oval fat lobes
   • Membranous layer (Scarpa's fascia) - Continuous fibrous membrane rich in elastic fibers (average thickness ~847 μm)
   • Deep adipose layer (DAT) - Contains predominantly oblique-horizontal fibrous septa forming large, flat polygonal lobes

Muscular Layers

1. Muscles and Aponeuroses - Three paired muscles:

   • External oblique muscle and aponeurosis (most superficial)
   • Internal oblique muscle and aponeurosis (middle layer)
   • Transversus abdominis muscle and aponeurosis (deepest muscle layer)

   These muscles form complex aponeurotic structures that cross the midline. The aponeuroses create a "plywood-like" structure with multiple layers crossing in different directions 2.

2. Rectus Sheath - Houses the rectus abdominis muscles:

   • Anterior layer - formed by external oblique aponeurosis and anterior lamina of internal oblique aponeurosis
   • Posterior layer - formed by posterior lamina of internal oblique aponeurosis and transversus abdominis aponeurosis
   • Below the arcuate line, all aponeuroses pass anterior to rectus abdominis

3. Linea Alba - Midline fibrous structure formed by the decussation (crossing) of aponeurotic fibers from both sides of the abdomen 2

Deep Layers

1. Transversalis Fascia - The innermost layer of the endoabdominal fascia, representing the inner epimysium of the transversus abdominis muscle 3
2. Preperitoneal Fat
3. Parietal Peritoneum - The innermost layer lining the abdominal cavity

Clinical Significance

Surgical Considerations

• Understanding these layers is crucial for proper surgical technique during abdominal wall closure and reconstruction 4
• In midline laparotomy closure, the World Society of Emergency Surgery recommends:
  • Mass closure technique (including all layers except skin) is preferred over layered closure as it's faster with similar outcomes 4
  • Separate closure of the peritoneum is NOT recommended 4
  • A suture-to-wound length ratio of at least 4:1 is recommended for continuous closure 4

Abdominal Wall Reconstruction

• For complex abdominal wall reconstruction, techniques like transversus abdominis muscle release (TAR) may be used 5
• When definitive fascial closure cannot be achieved, a skin-only closure is viable with delayed synthetic mesh repair 4
• Component separation technique is an option for large midline abdominal wall hernias 4

Diagnostic Imaging

• Ultrasound is the first-choice imaging modality for assessing abdominal wall disorders 6
• CT and MRI provide comprehensive assessment of all abdominal wall layers

Common Pitfalls and Considerations

• Failure to properly identify and close fascial layers can lead to incisional hernia formation
• Terminology confusion: "superficial fascia" should only refer to the membranous layer (Scarpa's fascia) of the subcutaneous tissue 1
• When using negative pressure wound therapy for open abdomen management, an interface layer must be used to protect exposed organs and prevent adhesions between bowel and abdominal wall 4
• The transversalis fascia is often confused with the entire endoabdominal fascia, but it's actually just the innermost component 3

Understanding these anatomical layers is essential for proper surgical technique, diagnostic interpretation, and effective management of abdominal wall pathologies.