A 39-year-old Caucasian man complained of a firm, discrete lump on his left wrist. A skeletal survey was negative. What possibilities can be suggested and what is the most likely diagnosis? Radiographic Findings Figure 1 demonstrates sharply marginated radiolucent defects in the fourth and fifth metacarpals, the os hamatum, the os triquetrum, and the os capitatum. There is no expansion of any of the involved bones, but the cortical outlines are absent over small portions of the dorso-ulnar aspects of the os triquetrum and the fifth metacarpal. A soft-tissue mass is known to be present because of information supplied previously, but it is not demonstrated well in the radiograph. There is no periosteal reaction or osteoporosis. Differential Discussion Although many entities may cause lucent defects in bones, the differential possibilities in this case are quite limited for several reasons. One important factor is the distribution: multiple bones are involved across joints in a limited area. Fibrous dysplasia and multiple enchondromata occasionally involve adjacent bones and might be considered briefly for that reason, but there are some important objections to these two diagnoses. Fibrous dysplasia may expand and attenuate the cortex, but small-bone involvement, cortical destruction, and soft-tissue masses are not generally present. Multiple enchondromata frequently do involve small bones of the hand, but involvement of the tubular bones is more common. The cortex is frequently thinned and may be expanded but remains intact unless there is extreme expansion. Angiomas of osseous origin may occur in several adjacent bones and thus be seen on both sides of joints, but they are rarely associated with soft-tissue masses and their intraosseous margins are not usually as sharply demarcated as those of the lesions in this case. Hemangiomas arising in soft tissue may secondarily affect the underlying bony structures, but in this situation one usually finds only superficial erosion of the surface of the bone. The external surface of the cortex may show concavity and thinning but not complete disruption, and an intraosseous component of the lesion is not seen. Calcified phleboliths are often present in such lesions. One might wish to consider metastatic disease as a cause of multiple lytic lesions, but it would be rare for metastases to produce both bone and soft tissue lesions around a joint. Furthermore, because metastatic lesions tend to be rapidly destructive, the individual osteolytic areas tend not to have the clearly defined, smooth margins seen here. The involvement of a cluster of adjacent bones in one small area on one side of the body would not be expected with metastases.