Coccygeal body revisited: An immunohistochemical study using donated elderly cadavers

Abstract

To describe the normal anatomy and histology of the adult coccygeal body (CB) and to discuss about the origin and function, using immunohistochemistry, we examined 29 CBs found in 32 elderly donated cadavers without macroscopic pathology in the pelvis. The CB was usually located in or near the anococcygeal ligaments. It was almost always composed of multiple masses or nodules of round glomus cells (smooth muscle actin or SMA++). However, the CB sometimes contained abundant dilated veins with scattered glomus cells. Thus, the CBs varied from the glomus cell nodule-dominant type, through an intermediate morphology with a mixture of nodules and veins, to the vein-dominant type. Each glomus cell mass was surrounded by abundant sympathetic nerves. In all specimens, we found multiple abnormal arteries, each of which carried a glomus-like cell layer around the almost -obliterated vascular lumen; as well as an SMA-negative thick arterial wall containing abundant sympathetic nerves. The ligaments around the CB are known to be under strong mechanical stress from the pelvic floor. We considered abnormal arteries containing the unique internal layer as an intermediate between a normal muscular artery and a glomus cell mass of CB. Under long-termed mechanical stress, a muscular artery seems to lose smooth muscles with increased sympathetic nerve fibers, to compensate for the lack of muscle function. Taken together with fetal morphology (our recent report), some or most of the CBs might not be an arteriovenous shunt but a result of stress-induced acquired transformation of pericytes. Anat Rec, 2017.