This type has been called periosteal chondroma
Periosteal chondroma is a benign hyaline cartilage neoplasm of the bone surface that arises from the periosteum  and has the potential to grow .
Additionally, if the mass is in the early stages of periosteum chondroma formation, the cortex may not yet be eroded, making it nearly impossible for a CT scan to distinguish between CC and periosteal chondroma based on this characteristic.
Differential diagnosis of bone tumors Bone Tumor Age Common Location Periosteal chondroma
Children and Adults Proximal humerus, M>F 2:1 proximal and distal femur, and the phalanges of the hands and feet.
They may occur in a medullary location (Enchondroma) or on the surface of the bone (Periosteal chondroma) (1)
(10) It is often associated with tendons, tendon sheath or joint capsule (11); unlike periosteal chondroma, it is located outside the periosteum.
Considering the radiologic and histopathologic features, the location and the age of the patient, this lesion was most consistent with the diagnosis of a juxtacortical chondroma (periosteal chondroma).
Histologically, these tumors usually demonstrate definitive anaplasia, although sometimes the distinction between a periosteal chondroma and low-grade chondrosarcoma is difficult or indeterminate.
The proximal humerus and adjacent soft tissues are the second most likely region in the extremities to contain a neoplastic lesion; the proximal humerus is the third most common long bone (after distal femur and proximal tibia) affected by bone tumor.(3) Sixty percent to 70% of all shoulder tumors occur in the humerus.(5) Cartilaginous lesions of all types (chondroblastoma, enchondroma, periosteal chondroma
, chondrosarcoma) have a predilection for the proximal humerus; marrow cell lesions and metastatic carcinoma are the common malignant lesions.(1) Ten percent to 15% of osseous metastases are in the upper extremity,(4) and of these, 50% will occur in the proximal humerus.(2)
The radiological differential diagnosis includes periosteal chondroma
, and if any intra-lesional calcification calcific tendinitis and synovial chondromatosis also kept in mind.