Incidence and ultrastructure of rudimentary cilia in benign and malignant peripheral nerve tumors

The incidence and ultrastructure of cilia were examined in 26 peripheral nerve tumors. The cilia had the common features of elongated shafts and basal structures consisting of two basal bodies. The basal body contained two basal feet and some long striated rootlets. The cilia lacked central tubules and two dynein arms of subfiber A, suggesting that they were nonmotile and rudimentary. The quantitative results showed that the incidence of cilia was low in Schwann cells and fibroblasts of the 20 benign tumors and slightly higher in perineurial cells of the 12 neurofibromas. Conversely, the incidence was high in most of the 6 malignant tumors. Only one perineurial cell from normal mature nerve examined carried a cilium, although no cilia were seen in the other perineurial cells, Schwann cells, and fibroblasts observed. The results showed that ciliary formation was more marked in the more actively proliferating tissues such as malignant tumors, and less so in the less actively proliferating tissues such as benign tumors. Ciliary formation may be one of the ultrastructural features commonly observed in proliferative tissues.