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.
Rib cage periosteal chondroma on pediatrics, a case report
Periosteal chondroma; a distinctive benign cartilage tumor.
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.