Objective The purpose of this study was to examine the membranous layers of the human pituitary gland and their relationships with invasive adenomas. Method Histological and microdissection techniques were used to study 8 fetal and 10 adult human cadavers, respectively. The distribution of the membranous layers was observed, and their thickness was measured Results In all specimens, the pituitary glands were found to be coated by 2 membranous layers, the inner layer being referred to here as the lamina propria and the outer as the pituitary capsule. In all specimens, the 2 membranes were intact with no histological defects. An interstice or cavity between the 2 layers was found on the surface of the adenohypophysis. However,as these 2 layers got closer and closer to each other, they began to adhere on the surface of the neurohypophysis.The thickness of the pituitary capsule was not constant like that of the lamina propria: the inferolateral part of the capsule was thicker than the other parts. The medial wall of the cavernous sinus (CS) was also a bilayered membrane just like the other CS walls: the 2 layers of the medial CS wall were composed of the lateral part of the pituitary capsule and the fibrous layer. Many fibrous trabeculae arising from this fibrous layer divided the CS into several small venous spaces and connected the internal carotid arteries with the medial wall. Conclusions The lateral part of the capsule (dura mater) and the fibrous layer constituted the medial wall of the CS, which has a superior part that is weaker than the thicker inferior part. Invasive adenomas might be a radiological misunderstanding of the extremely displacement of the CS medial wall by the tumor's pushing. While between the tumor and the pituitary capsule, a .safety surgical interface still exists.