Tissue differentiation in malignant synovial tumours.

Tumours composed of different kinds of tissue show different characteristics in rate of growth, infiltration of surrounding structures, frequency of complications such as necrosis and haemorrhage, and development of metastases. Thus the prognosis, either natural or following treatment, of various neoplasms, differs. This applies obviously to tumours of different organs or structures, but is true also of tumours of related tissues. It is desirable, therefore, that we should clearly differentiate tumours which, though different, are apparently similar in kind or origin. The recognition of the nature and, by inference, the origin of a tumour depends in ideal circumstances on a number of observations-the site of the primary growth, its relation to surrounding tissues, the gross features of the tumour mass and its histological characters. The last two go hand in hand but histological features provide the more important criteria. The differences in normal tissues (for example, in a limb) are due to’ differences in the direction and degree of differentiation of their original cells, which may have given rise to fibrous tissue, bone, cartilage or synovial tissue amongst others. In the same way tumour cells may differentiate in different directions, and according to which preponderates so the tumour is named. A most important point here is that any conclusion as to the origin of a tumour is merely assumption, and that, though it is commonly stated in the literature that tumours have arisen from synovial membrane, it will be shown that such statements are unjustified and are liable to give rise to confusion. Synovial tumours are now easily recognised and their principal clinical and pathological features are known. They constitute a group different and distinct, both clinically and pathologically, from other connective tissue tumours. This paper is intended to be a general review of them and also to emphasise one particular topographical sub-group which has been given inadequate attention.