CASE STUDIES IN DIAGNOSTIC IMAGING Series editor

A 46 year old man presented with a growing mass over his wrist. Erosions of the triquetrum and hamate were present radiographically. Magnetic resonance imaging (MRI) showed a solid mass arising from the extensor carpi ulnaris tendon, which was T1 hypointense and isointense, T2 hypointense, and bloomed on gradient echo images. The preoperative diagnosis of giant cell tumour of the tendon sheath was confirmed on histopathological examination of the excised specimen. The clinical, pathological, and imaging features, with emphasis on MRI findings, of this condition are reviewed. (Ann Rheum Dis 2001;60:550–553) Clinical history A 46 year old man presented with a one year history of a growing mass in his left wrist. He stated that the mass developed soon after minor contusion to the wrist. On examination, the mass was located over the ulnar aspect of the wrist. It measured about 2 cm in diameter and was mildly tender. It was fixed in the longitudinal plane to the deep structures but was mobile in the transverse plane. The mass was not attached to the overlying skin, which had a normal appearance. Hand and wrist movements were normal, and sensation was intact. There was no other systemic abnormality. Imaging findings A radiograph of the left wrist showed osteolytic involvement of the ulnar aspects of the triquetrum and hamate. Both these bones had well defined “punched-out” erosions with sclerotic margins. The joints were normal and bone density was preserved (fig 1). Magnetic resonance imaging (MRI) demonstrated a well defined, lobulated soft tissue mass eroding the ulnar aspect of the triquetrum and hamate. The base of the fifth metacarpal, pisiform, and ulnar styloid were in close proximity to the mass but were unaVected. The mass arose from the extensor carpi ulnaris tendon, and involved the proximal abductor and flexor digiti minimi muscles. The mass was isointense on T1 weighted and proton density weighted images with small areas of hypointensity within, becoming generally more hypointense on T2 weighted images. On gradient echo images the lesion appeared more prominent with a further increase in hypointense signal, confirming the magnetic susceptibility eVect due to the presence of haemosiderin deposits. There was moderate heterogeneous contrast enhancement, sparing the areas of haemosiderin deposition (figs 2 and 3). DiVerential diagnosis On radiographs, the finding of well defined sclerotic-marginated bony erosions is consistent with a longstanding non-aggressive process. When the joint space is preserved and two adjacent carpal bones are aVected, the main diVerential diagnosis will include intraarticular synovial disease, extra-articular synovial disease arising from the tendon sheath, and extra-articular non-synovial disease. MRI is the imaging method of choice for evaluating the presence and extent of soft tissue masses of the musculoskeletal system. It is particularly useful for assessing masses in the hand and wrist, where benign lesions predominate. 2 A specific diagnosis may be made, or strongly suspected, from the characteristic MRI features of certain lesions, such as ganglion, haemangioma, arteriovenous malformation, lipoma, and giant cell tumour of the tendon sheath. Lesions with predominant T2 shortening will appear largely hypointense on T2 weighted images. T2 shortening may be due to low cellularity, high collagen content, fibrotic scar tissue, Figure 1 Anteroposterior radiograph of the left wrist showing erosions of the ulnar aspects of the triquetrum and hamate. The margins of the erosions are well defined with a sclerotic rim. Ann Rheum Dis 2001;60:550–553 550 Department of Diagnostic Radiology, Singapore General Hospital, Singapore