Muscle spindle and Pacinian corpuscle: conceptions, misconceptions, and the far-fetched hypothesis of an experienced...

The muscle or neuromuscular spindle is a proprioceptive microanatomic structure, which together with the Golgi tendon organ, is responsible for the reflex are that determines the tonic state of muscle. The Pacinian corpuscle (or corpuscle of Vater-Pacini) is a pure mechanoreceptor, sensitive to pressure, typically found in the skin, subcutis and superficial soft tissues. Generally, both the muscle spindle and Pacinian corpuscle are microanatomical findings that are too unremarkable to focus on during the course of routine work in surgical pathology. We recently encountered such a structure, which required full attention to be correctly identified: the incidental finding was a curious muscle spindle, the "fibrous capsule" of which mimicked the "lamellar body" of Pacinian corpuscle. This report accurately mirrors the manner in which the events occurred and emphasizes the fundamental anatomical notions that were ignored, and is also an opportunity to mention some of the pathological conditions affecting the aforementioned often-neglected receptors.