An investigation of the embryologic development of the fascia used as the basis for pancreaticoduodenal mobilization.

BACKGROUND: The retropancreatic fusion fascia, or fascia of Treitz, is a critical anatomical landmark during retropancreatic mobilization of the pancreatic head and duodenum (the Kocher maneuver).
METHODS: Using semiserial sections from 24 human fetuses of 9-30 weeks gestation, we examined the development of this fascia.
RESULTS: Retroperitoneal fixation of the pancreas occurred at around 10 weeks. Up to 20 weeks, an apparent remnant of the mesoduodenum was attached to the now-distinct renal fascia. Lymphatic vessels and follicles congregated along the ventral aspect of the fusion plane during early development. In 20- to 30-week fetuses, the duodenum began to occupy a definite position and, at the same stage, a candidate for the fascia of Treitz was seen; it was separated from the thick renal fascia by loose connective tissue.
CONCLUSIONS: We hypothesize that mechanical stress during the development and growth of the duodenum causes the transformation of an indistinct remnant of the peritoneum into a distinct fascia. This mechanism is similar to that seen during the development of the renal fascia, in which the developing adrenal cortex and migrating kidney generate stress on a bundle of thin collagen fibers. Therefore, the fascia of Treitz is unlikely to be a simple remnant of the peritoneum. The fascia, if evident during surgery, should be attached to the pancreatic parenchymal side.