Potential foramen to allow communication between the pleural cavity and retroperitoneal space during laparoscopic surgery: a cadaver study of Bochdalek's triangle.

The indications for laparoscopic retroperitoneal surgery have recently been greatly extended and the technique has become popular, but concomitant pleural injury or pneumothorax has been reported from numerous hospitals in Japan. Which anatomical information is useful to avoid surgical injury of the suggested weak portion of the diaphragm? We identified a diaphragm-free triangular area or Bochdalek's triangle in 90.1% of elderly Japanese cadavers (100/111 cadavers), comprising about 622.8 mm(2) in area (height 47.9 mm, base 25.0 mm). In most cases (80.1%; 129/161), the entire triangle was restricted to the superior side of the 12th rib in addition to the medial side of the distal end of the rib. A "potential foramen" (PF) was defined as the diaphragm-free triangle >100 mm(2) in area on the parietal pleura. Most triangles (77.6%, 125/161) met this criterion. The PF was often covered by the kidney (93.3%), and had a mean area of 318.9 mm(2). The PF was located 42.3 mm from the distal end of the 12th rib, while the inferior pleural margin was 27.8 mm superior to the rib end. When the triangle was large, the PF was also large, with the PF often occupying >50% of the triangle area (62/125; 49.6%). To avoid the distal end of the 12th rib, in laparoscopic retroperitoneal surgery, we recommend making a transverse skin incision at the midpoint between the end of the 12th rib and the iliac crest.