Skin tumours are usually divided into melanoma and non-melanoma types. Malignancies of the adnexal structures, of which sweat gland tumours are an example, are characterized under the non-melanoma types. Sweat gland malignancies are rare tumours that are usually associated with a poor prognosis. Given the rarity of these tumours, MRI findings of such tumours have not been described previously in the literature. We present a case report of an unusual malignant tumour of sweat gland origin known as a malignant chondroid syringoma of the skin with described MRI features. The MRI features are non-specific depicting intermediate signal intensity, changes on the proton density sequence and increased signal on the T2 and STIR-weighted sequences. Although these imaging features are characteristic of most soft tissue masses MRI can, in most cases, accurately depict the anatomic extent and identify tissue of origin, depth of invasion and relation to adjacent structures, such as muscles and bones. Thus high-resolution MRI of the skin in the future can be extremely helpful in characterizing and staging dermal neoplasms.

Pigmented villonodular synovitis is an uncommon proliferative disease of the synovium, which is usually monoarticular, presenting as chronic monoarthritis of the knee. To our knowledge, the case under discussion is only the second report in the English language medical literature of isolated involvement of the proximal tibiofibular joint.