Linea semilunaris

The linea semilunaris (also semilunar line or Spigelian line) is described by Adriaan van den Spiegel (°1578 †1625) described the Linea Semilunaris as the line forming and marking the transition from muscle to aponeurosis in the transversus abdominis muscle of the abdomen. It needs to be distinguished from the lateral border of the rectus abdominis muscle sheath which is often wrongly described as semilunar line. The lateral border of the rectus sheath is part of the recently described EIT ambivium to more precisely describe this important part of the anterior abdominal wall. The EIT ambivium is formed by the Musculus Obliquus Externus (MOE), the Musculus Obliquus Internus (MOI) and the Musculus Transversus Abdominis (TA). Understanding the interrelationship between the lateral muscles and the medial compartment is of paramount importance for surgeons to understand the surgical anatomy.

Clinical significance
Several surgical techniques such as posterior component separation and eTEP(enhanced Totally Extra Peritoneal) techniques rely on a thorough understanding of the anatomy of the EIT ambivium to be performed safely and avoid complications.