A Spigelian hernia (or lateral ventral hernia) is a hernia through the spigelian fascia, which is the aponeurotic layer between the rectus abominis muscle medially, and the semilunar line laterally. These hernias almost always develop at or below the linea arcuata, probably because of the lack of posterior rectus sheath. These are generally interparietal hernias, meaning that they do not lie below the subcutaneous fat but penetrate between the muscles of the abdominal wall; therefore, there is often no notable swelling.