Multifunctional mesenchymal cells resembling smooth muscle cells in ganglia of the wrist.

The term ganglion was coined by Hippocrates to designate a knot of tissue containing mucinous fluid (Soren, 1966). The aetiology and pathogenesis of these cystic swellings which occur in the region of joints and tendon sheaths is as yet unresolved. On the basis of light microscope studies (Carp and Stout, 1928; De Orsay, Mecray, and Ferguson, 1937; King, 1932; Soren, 1966), ganglia have come to be regarded as degenerative lesions occurring in or adjacent to the joint capsule, and older theories that they represent herniations of synovia, or neoplasms, have been more or less discarded. The wall of this cystic lesion appears to be composed of fibrous tissue, and two recent electron microscope studies, one in the Japanese (Arai, 1967) and the other in the German (Cotta and Becker, 1969) literature, support the idea that this lesion is composed of mesenchymal cells showing fibroblastic and synoviaI type of differentiation. However, we have recently studied five examples of ganglia arising in the region of the wrist joint and have found that the predominant cell resembles smooth muscle cells, and not fibroblasts or synovial cells as suggested by other authors. A point unresolved by light microscopy is whether ganglion cavities have a cellular lining. The mucinous content and the glistening appearance of the cavity wall certainly suggest that the cavity may be lined by cells, and some authors have stated that the cavities are in fact so lined. Thus Soren (1966) states, 'Fibrocytes also lie along the inner walls of the cavities and form an incomplete lining which resembles the synovium of a joint capsule'. Contrary to this is the widely held view eloquently epitomized by Carp and Stout (1928) who state, 'There is often a dense, smooth, shiny, white membrane lining the lumen. This is simply a condensation of the fibrous tissue of the wall and has no special lining cells'. Recently published studies on the ultrastructure of ganglia (Arai, 1967; Cotta and Becker, 1969) have again reiterated the idea that a synovial type of differentiation occurs in ganglia and that in parts at least the cavity is lined by such cells. As will be shown later, our findings and interpretations are different from this. In this paper we wish to record the structure of the ganglion wall, lining, and contents as revealed by the electron microscope. The ganglion contents have not been hitherto examined in this fashion but it seemed to us that by examining the contents one might be able to distinguish between material produced as a result of tissue necrosis from a secretion produced by lining cells.