Linea semilunaris

The linea semilunaris was first described by Adriaan van den Spiegel.^[1][2][3]

There are two commonly used definitions identifying the linea semilunaris.^[4][1][5] The first is defined as corresponding with the lateral border of the rectus sheath.^{[1][6][7][8][9]} In this definition, it is formed by the aponeurosis of the internal oblique at its line of division to enclose the rectus.^[9][10] This is reinforced anteriorly by the external oblique, and posteriorly by the transversus abdominis above the arcuate line.^[11][10][9] The second definition identifies it as the line forming and marking the transition from muscle to aponeurosis in the transversus abdominis muscle, known as the spigelian aponeurosis.^{[1][12][13][14]} In both definitions, it extends from the cartilage of the ninth rib to the pubic tubercle.^[4][6][7] The terms spigelian fascia and spigelian aponeurosis have also been used to define the linea semulunaris.^[5] In this definition it refers to the aponeuroses of the lateral abdominal muscles lateral to the rectus muscle.^[5] In other definitions the spigelian aponeurosis/spigelian fascia is the aponeurosis of the transverse abdominal muscle medial to the linea semilunaris and lateral to the rectus muscle.^[15][14]

A hernia through the linea semilunaris is called a Spigelian hernia.^[16][17] This usually occurs at the meeting point of the linea semilunaris with the arcuate line and the lateral border of the rectus abdominis muscle.^[16]