Endopelvic fascia in rectal cancer surgery: cadaveric anatomy and histological continuity between the obturator fascia and the rectum

Purpose In rectal cancer surgery, dissection on either side of the endopelvic fascia (EPF) determines whether this layer remains on the pelvic wall or is included with the specimen. However, its continuity with adjacent pelvic wall and rectal supporting tissues, and the anatomical meaning of these local dissection planes, remain unclear. This cadaveric study aimed to clarify the macroscopic and histological characteristics of the EPF in relation to the obturator fascia, rectal wall, and hiatal ligament. Methods Macroscopic examination of three formalin-fixed cadavers assessed fascial architecture around the levator ani, obturator internus, and rectum. Histological analysis of eight formalin-fixed cadavers used Masson’s trichrome staining and α-smooth muscle actin immunohistochemistry. EPF thickness was measured in six specimens at defined distances from the obturator fascia and rectal wall. Results The EPF formed a dense connective tissue layer on the superior surface of the levator ani and continued laterally into the obturator fascia without a distinct boundary. Medially, it transitioned into interfascicular connective tissue between rectal longitudinal muscle bundles and the smooth muscle-rich hiatal ligament. In four obturator-side specimens, thickness ranged from 0.03 to 0.65 mm. In two rectal side specimens, thickness at the rectal interface was 1.69 and 2.82 mm; these limited descriptive observations do not establish a regional difference. Conclusion The EPF is continuous with pelvic wall and rectal supporting tissues rather than a discrete membrane. These cadaveric findings define its local morphology but do not establish implications for surgical dissection planes, circumferential resection margin status, operative or oncological outcomes, or pelvic function.