What are the layers of the abdomen from superficial to deep?

Layers of the Abdomen from Superficial to Deep

The abdominal wall consists of multiple distinct layers from superficial to deep: skin, superficial fascia (with superficial and deep adipose layers separated by a membranous layer), external oblique muscle/aponeurosis, internal oblique muscle/aponeurosis, transversus abdominis muscle/aponeurosis, transversalis fascia, preperitoneal fat, and parietal peritoneum.

Detailed Layered Structure

Superficial Layers

1. Skin
2. Superficial Fascia - composed of:
   • Superficial adipose layer (SAT) - characterized by fibrous septa forming polygonal-oval fat lobes 1
   • Membranous layer (Scarpa's fascia) - continuous fibrous membrane rich in elastic fibers with average thickness of 847.4 ± 295 μm 1
   • Deep adipose layer (DAT) - contains fibrous septa oriented obliquely-horizontally, defining large, flat polygonal fat lobes 1

Muscular Layers

1. External oblique muscle/aponeurosis
2. Internal oblique muscle/aponeurosis
3. Transversus abdominis muscle/aponeurosis

Deep Layers

1. Transversalis fascia
2. Preperitoneal fat
3. Parietal peritoneum

Regional Variations

The arrangement of these layers varies by region:

Anterior Rectus Sheath

• Above the arcuate line: formed by external oblique aponeurosis and anterior lamina of internal oblique aponeurosis
• Below the arcuate line: formed by all three aponeuroses (external oblique, internal oblique, and transversus abdominis)

Posterior Rectus Sheath

• Above the arcuate line: formed by posterior lamina of internal oblique aponeurosis and transversus abdominis aponeurosis
• Below the arcuate line: absent (only transversalis fascia)

Clinical Significance

Understanding these layers is crucial for:

1. Surgical Approaches: The membranous layer of the superficial fascia serves as an important dissection plane 1

2. Hernia Repair: Proper identification of fascial layers is essential for successful repair

3. Imaging Interpretation: CT and ultrasound can visualize these layers with varying thickness depending on body region and individual factors 2

4. Wound Closure: Current guidelines suggest mass closure (including all layers except skin) is preferred over layered closure in emergency surgery due to its speed and similar outcomes 3

5. Peritoneal Closure: Evidence indicates that separate closure of the peritoneum during abdominal wall closure is unnecessary and may increase operating time 3

Anatomical Relationships

The abdominal wall layers form a complex structure with:

• Bilaminar aponeuroses that cross the midline
• Trilaminar walls of the rectus sheath (plywood-like structure)
• Decussation of aponeurotic fibers at the linea alba 4

Understanding these layers helps surgeons identify proper tissue planes during procedures and allows for appropriate imaging interpretation in the diagnosis of abdominal wall pathologies.