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Background
In the hand, surface-based bone tumors can present as palpable subcutaneous mass lesions that may need to be differentiated from tumors of subcutaneous tissue or the skin. Juxtacortical chondroma (JCC) or parosteal chondroma is a benign cartilaginous neoplasm of the bone surface, originating from the periosteum, that accounts for less than 2% of the chondromas. In the small tubular bones of the hand, JCC is more common than enchondroma occasionally assuming the histopathological features of chondrosarcoma. On radiographs, JCC is small, well-circumscribed, and cortically based, with no involvement of the underlying bone, but cortical scalloping, saucerization, sclerosis, and overhanging edges may also occur in some larger tumors. CT may show subtle matrix calcification. On MR images, JCC appears as a juxtacortical lesion of intermediate signal on T1- and T2-weighted images, respectively, that shows peripheral enhancement following gadolinium administration. Soft tissue edema may be present in adjacent soft tissue. Differential diagnosis of JCC includes soft tissue chondroma (STC). This benign cartilage-forming tumor typically occurs in extra-articular soft tissue locations. Radiographically, STC is well defined, with no involvement of the underlying bone, although some tumors may exercise compression on adjacent bone causing cortical erosion. STC has a lobular appearance on MR images, with low to intermediate signal on T1- and T2-weighted images, and peripheral or septal contrast enhancement. Matrix calcification or ossification may be seen. The osteochondroma (OC) is a benign, juxtacortical cartilage-capped bony protuberance on a sessile or pedunculated base. Typically, the cortex and spongy bone of OC flare into the host bone. Both CT and MR images exhibit cortical and marrow continuity of the OC with the host bone and a cartilaginous cap. Bizarre parosteal osteochondromatous proliferation (BPOP; Nora's lesion) is a rare, benign proliferative osteocartilaginous process. This surface bone lesion lacks continuity with the parent cancellous bone and may mimic other bone neoplasms, or cause mass effects with neurologic, vascular, or tendon complications. Radiography reveals proliferations and both CT and MRI allow assessment of the integrity of underlying cortical bone.

Educational Goals / Teaching Points
We describe the classical imaging-histological presentations of benign cartilaginous lesions in the hand.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Cartilage tumors of bone and soft tissue are a heterogenous group of lesions showing considerable differentiation. We illustrate the MRI features with pathologic correlation of some benign cartilage lesions of bone and soft tissue, in the hand.

Conclusion
Because of tight anatomic compartments and a superficial location, bone and soft tissue lesions in the hand can be painful and are usually palpable. Knowledge of the MRI pathologic features of these lesions may help radiologists, pathologists, and orthopedic oncologists reach the correct diagnosis.