# Thin‐Adipose Compartment at the Colonic Mesentery–Perirenal Fat Interface: Histological and Three‐Dimensional Morphological Studies

## TL;DR

This study identifies a thin layer of fat between the colonic mesentery and perirenal fat, revealing its structured and continuous nature in human anatomy.

## Contribution

The discovery of a previously unrecognized thin-adipose compartment and its three-dimensional continuity in the abdominal region.

## Key findings

- A distinct thin-adipose compartment was consistently observed between the colonic mesentery and perirenal fat.
- The compartment is enclosed by dense connective tissue and contains small vessels.
- The compartment extends in three directions and demonstrates craniocaudal and lateral continuity.

## Abstract

To elucidate the anatomical characteristics and three‐dimensional continuity of a previously unrecognized thin‐adipose compartment between the colonic mesentery and retroperitoneum, using correlative microscopy and block‐face imaging.

In this study, which was conducted at the anatomical laboratory of the Institute of Science Tokyo (formerly Tokyo Medical and Dental University), seven adult cadavers were examined. Histological analysis was conducted on six specimens using paraffin sections stained with Elastica van Gieson and Masson's trichrome. One cadaver underwent three‐dimensional morphological analysis using correlative microscopy and block‐face imaging. Serial block‐face images of the perirenal region were captured at 100‐μm intervals, and three‐dimensional reconstruction segmentation was performed.

A distinct thin‐adipose compartment was consistently observed between the colonic mesentery and perirenal fat, enclosed by dense connective tissue and containing small vessels. Similar compartments were also found between the perirenal fat and pararenal fat, and beneath the peritoneum along the abdominal wall. These compartments extended in three directions from the peritoneal reflection and demonstrated craniocaudal continuity; laterally, these compartments converged to form a triad‐like junction.

The thin‐adipose compartment represents a structurally organized anatomical unit rather than amorphous filler. Its consistent continuity and integration with adjacent structures support a compartment‐based framework of intra‐abdominal anatomy, which has potential relevance for understanding surgical anatomy.