Benign Osteochondroma: This diagnosis is most likely due to the presence of multiple similar rib lesions, the appearance of the lesions on imaging (cortically based soft tissue component, peripheral calcification), and the mention of osteochondromatosis as a possible diagnosis. The fact that Dr. Gitelis initially stated it was benign and the surgeon's team wasn't "overly concerned" about malignancy also supports this diagnosis.

Osteochondromatosis: Given the presence of multiple rib lesions, osteochondromatosis is a possible diagnosis. This condition is characterized by the presence of multiple osteochondromas, which are benign cartilage-capped bone tumors.
Fibrous Dysplasia: Although less likely, fibrous dysplasia is a consideration due to the presence of multiple bone lesions. However, the imaging characteristics and clinical presentation are not as strongly suggestive of this diagnosis as they are for osteochondroma.
Enchondromas: These are benign cartilage tumors that can occur in the bones of the hands, feet, and long bones, but can also be found in the ribs. The imaging findings could be consistent with enchondromas, but the presence of multiple lesions and the specific characteristics of the lesions make osteochondroma more likely.

Malignant Chondrosarcoma: Although the clinical presentation and imaging findings suggest a benign process, it is crucial not to miss the possibility of a malignant chondrosarcoma. The fact that the lesion is growing and has a heterogeneous appearance on MRI raises some concern for malignancy. Chondrosarcomas can arise from pre-existing benign cartilaginous lesions, making it essential to consider this diagnosis, especially given the patient's history of possible hereditary multiple exostoses (HME).
Other Malignant Bone Tumors: Other malignant bone tumors, such as osteosarcoma or Ewing's sarcoma, are less likely given the imaging characteristics and clinical presentation but should not be entirely ruled out without thorough evaluation, including pathology.

Hereditary Multiple Exostoses (HME) with Malignant Transformation: If the patient indeed has HME, there is a small risk of malignant transformation of one of the osteochondromas into a chondrosarcoma. This diagnosis is rare but important to consider given the patient's possible history of HME.
Other Rare Bone Tumors: Other rare bone tumors, such as chondroblastoma or giant cell tumor, could be considered but are less likely given the clinical presentation and imaging findings.