Differential Diagnosis based on radiographic appearance include juxtacortical chondroma and bizarre parosteal osteochondromatous proliferation (BPOP).

Pathology: Bone, cartilage and soft tissue were noted in left index finger excision specimen.  Pathologic specimen of the lesion was initially erroneously diagnosed as osteochondroma but subsequent review of and correlation with plain radiographs determined the correct diagnosis to be a juxtacortical chondroma.

Final Diagnosis: Juxtacortical chondroma

Discussion: Juxtacortical chondroma (or periosteal chondroma) is a benign cartilaginous lesion with epicenter at the surface or just underneath the periosteum. It most commonly occurs in the metaphyseal region of long tubular bones, frequently at sites of tendon or ligament insertions. Characteristic findings include erosion of the cortex with sclerotic inner border. Calcifications are common and a solid “buttress” of periosteal new bone may be seen. On CT the lesion can be demonstrated to be separate from the medullary cavity, which distinguishes juxtacortical chondroma from osteochondroma. MRI demonstrates cartilaginous tissue in a well-defined lobular lesion best appreciated on T2 weighted sequence.
      Juxtacortical chondromas are relatively rare and account for approximately 2.2% of benign bone tumors. They may occur at any age but have a peak occurrence in the second through fourth decades. There is slight predilection for males. Clinical presentations may vary. The lesions are generally painless although as the lesion enlarges pain may occur.