A Concealed "Natural Orifice": Umbilicus Anatomy for Minimally Invasive Surgery.

INTRODUCTION: A recent development in minimally invasive surgery (MIS) is single-port surgery, where a single large multiport trocar is placed in the umbilicus. All medical schools require that students complete an anatomy course as part of the medical curriculum. However, there is limited instruction regarding the detailed parts of the "umbilicus." In several famous anatomy atlases, the umbilicus is not dissected at all and is merely represented as a button. Until now, the true nature of the umbilicus has not been anatomically demonstrated. METHODS: Five cadavers were obtained from the Osaka Medical College medical student anatomy class. The umbilicus was dissected in the anatomy laboratory, to demonstrate all the layers. A detailed dissection was performed, focusing on the exact center of the umbilicus, in order to ascertain whether there exists a "natural orifice" or a fascial defect. RESULTS: In all cadavers, a small defect of fascia was identified just below the center of the umbilicus. Yellow fatty tissue was present just below the skin in the exact center of the umbilicus. A probe placed exactly in the middle of this defect passes easily through into the abdominal cavity. CONCLUSIONS: With the widespread use of MIS, umbilical incision is commonly used to reduce pain and improve cosmetic results. This study consistently revealed a natural defect of fascia in the center of the umbilicus. Therefore, the umbilicus can be called a concealed "natural orifice." It is important to recognize and utilize this defect effectively to minimize unnecessary tissue trauma during MIS.