The mesocolon - A histological and electron microscopic characterisation of the mesenteric attachment of the colon prior to and after surgical mobilisation

Aims: Colonic mobilisation requires separation of mesocolon from underlying fascia. Despite the surgical importance of planes formed by these structures, no study has formally characterised their microscopic features. The aim of this study was to determine the histological and electron microscopic appearance of mesocolon, fascia and retroperitoneum, prior to and after colonic mobilisation. Methods: In 24 cadavers, samples were taken from right, transverse, descending and sigmoid mesocolon. In twelve cadavers specimens were stained with haematoxylin and eosin (3 sections), or Masson's trichrome (3 sections). In the second twelve cadavers, lymphatic channels were identified by staining immunohistochemically for podoplanin. The ascending mesocolon was assessed with scanning electron microscopy. The above process was firstly conducted with the mesocolon in-situ. The mesocolon was then surgically mobilised and the process repeated on remaining structures. Results: The microscopic structure of mesocolon and associated fascia was consistent from ileocaecal to mesorectal level. A surface mesothelium and underlying connective tissue were evident throughout. Fibrous septae separated adipocyte lobules. Where apposed to retroperitoneum, two mesothelial layers separated mesocolon and underlying retroperitoneum. A connective tissue layer occurred between these (i.e. Toldt's fascia). Lymphatic channels were evident both in mesocolic connective tissue and Toldt's fascia. Following surgical separation of mesocolon and fascia both remained contiguous, the fascia remained in-situ and the retroperitoneum undisturbed. Conclusions: The findings demonstrate that the contiguous mesocolon and retroperitoneum are separated by mesothelial and connective tissue layers. These properties generate the surgical planes (i.e. meso and retro-fascial planes) exploited in colonic and mesocolic mobilisation.