Spigelian hernia: surgical anatomy, embryology, and technique of repair.

Spigelian hernia (1-2% of all hernias) is the protrusion of preperitoneal fat, peritoneal sac, or organ(s) through a congenital or acquired defect in the spigelian aponeurosis (i.e., the aponeurosis of the transverse abdominal muscle limited by the linea semilunaris laterally and the lateral edge of the rectus muscle medially). Mostly, these hernias lie in the "spigelian hernia belt," a transverse 6-cm-wide zone above the interspinal plane; lower hernias are rare and should be differentiated from direct inguinal or supravescical hernias. Although named after Adriaan van der Spieghel, he only described the semilunar line (linea Spigeli) in 1645. Josef Klinkosch in 1764 first defined the spigelian hernia as a defect in the semilunar line. Defects in the aponeurosis of transverse abdominal muscle (mainly under the arcuate line and more often in obese individuals) have been considered as the principal etiologic factor. Pediatric cases, especially neonates and infants, are mostly congenital. Embryologically, spigelian hernias may represent the clinical outcome of weak areas in the continuation of aponeuroses of layered abdominal muscles as they develop separately in the mesenchyme of the somatopleura, originating from the invading and fusing myotomes. Traditionally, repair consists of open anterior herniorraphy, using direct muscle approximation, mesh, and prostheses. Laparoscopy, preferably a totally extraperitoneal procedure, or intraperitoneal when other surgical repairs are planned within the same procedure, is currently employed as an adjunct to diagnosis and treatment of spigelian hernias. Care must be taken not to create iatrogenic spigelian hernias when using laparoscopy trocars or classic drains in the spigelian aponeurosis.