In diagnostic laparotomy (most often referred to as an exploratory laparotomy and abbreviated ex-lap), the nature of the disease is unknown, and laparotomy is deemed the best way to identify the cause.he most common incision for laparotomy is the midline incision, a vertical incision which follows the linea alba. 1  The upper midline incision usually extends from the xiphoid process to the umbilicus. 2  A typical lower midline incision is limited by the umbilicus superiorly and by the pubic symphysis inferiorly.